4L60e issues after rebuild

[Tataocb]

I have rebuilt about 10 of these transmissions this year as a "side hustle" of which 8 have worked successfully after rebuild. There are two that I am working on right now that I need some assistance with. When I rebuilt the first 4-5 transmissions I used the Transmission Bench rebuild tutorial as well as Nick Transmissions videos on YouTube to learn how to rebuild them. Both of these transmissions were not originally in the car they ended up in. They were cores left from the other rebuilds. For both rebuilds I used a gasket/seals kit, replaced frictions and steels, molded pistons, aluminum accumulator pistons, new solenoids, band, filter and reused the wiring harness. In both cases I checked the input drum for leaks around the shaft and both were good. I also checked the separator plate and repaired any check ball areas where the hole had been enlarged. All clearances were checked. The 3-4 clutch pack was at 0.060. Now for the issues.

Transmission A - original issue was loss of 3-4 gear

After installing it had two issues:

A. Reverse felt like it was difficult to engage, like the calipers were stuck or the vehicle brakes were applied when trying to use reverse.
B. 2-3 flare shift.

I replaced the servo with another one I had and took it for a drive but the 2-3 flare shift was still there.

After that I decided to remove the transmission and open it back up. I tested the drum assembly through the pump (feeding compressed air through the pump holes) and found that reverse was not engaging. I then found one of the sealing rings on the pump was flattened so I replaced all sealing rings on the pump and the input shaft. I tested the drum assembly with the pump again and reverse was now engaging.

I put the drum assembly back in the transmission and checked to make sure it would spin with the band in place (to check clearance) and it did. I reassembled the transmission and bought a test plate to check through the valve body and all the clutch packs applied correctly. I could also feel the band engaging and disengaging when air was applied and removed through those circuits.

Is there anything else I can check for the flare shift? Should I perhaps go with a corvette servo?

Transmission B - original issue was loss of 3-4 gear

After installing the transmission it worked well for 2 weeks and then it lost 3rd and 4th. The transmission was removed. I checked for leaks around the input shaft again and did not find any. I checked the drum assembly through the pump and everything engaged correctly. I replaced the 3-4 clutch pack and reassembled. I did an air check through the pump and then again using the test plate after reassembly and everything engaged fine. I finished reassembling the transmission, installed it, took it for a drive and still no 3rd or 4th gear.

This was not the transmission that was originally in this car. The one it had before had a rattling noise, but shifted through all gears so I do not think the issue is in the vehicle's electrical system. I am wondering if the issue might be with the harness that goes inside the transmission? Both shift solenoids were replaced with new ones. Otherwise, if the transmission air checked fine, why would it lose 3rd and 4th once installed?

Any help would be greatly appreciated.

 

[NickTransmissions]

I have rebuilt about 10 of these transmissions this year as a "side hustle" of which 8 have worked successfully after rebuild. There are two that I am working on right now that I need some assistance with. When I rebuilt the first 4-5 transmissions I used the Transmission Bench rebuild tutorial as well as Nick Transmissions videos on YouTube to learn how to rebuild them. Both of these transmissions were not originally in the car they ended up in. They were cores left from the other rebuilds. For both rebuilds I used a gasket/seals kit, replaced frictions and steels, molded pistons, aluminum accumulator pistons, new solenoids, band, filter and reused the wiring harness. In both cases I checked the input drum for leaks around the shaft and both were good. I also checked the separator plate and repaired any check ball areas where the hole had been enlarged. All clearances were checked. The 3-4 clutch pack was at 0.060. Now for the issues.

Transmission A - original issue was loss of 3-4 gear

After installing it had two issues:

A. Reverse felt like it was difficult to engage, like the calipers were stuck or the vehicle brakes were applied when trying to use reverse.
B. 2-3 flare shift.

I replaced the servo with another one I had and took it for a drive but the 2-3 flare shift was still there.

After that I decided to remove the transmission and open it back up. I tested the drum assembly through the pump (feeding compressed air through the pump holes) and found that reverse was not engaging. I then found one of the sealing rings on the pump was flattened so I replaced all sealing rings on the pump and the input shaft. I tested the drum assembly with the pump again and reverse was now engaging.

I put the drum assembly back in the transmission and checked to make sure it would spin with the band in place (to check clearance) and it did. I reassembled the transmission and bought a test plate to check through the valve body and all the clutch packs applied correctly. I could also feel the band engaging and disengaging when air was applied and removed through those circuits.

Is there anything else I can check for the flare shift? Should I perhaps go with a corvette servo?

Transmission B - original issue was loss of 3-4 gear

After installing the transmission it worked well for 2 weeks and then it lost 3rd and 4th. The transmission was removed. I checked for leaks around the input shaft again and did not find any. I checked the drum assembly through the pump and everything engaged correctly. I replaced the 3-4 clutch pack and reassembled. I did an air check through the pump and then again using the test plate after reassembly and everything engaged fine. I finished reassembling the transmission, installed it, took it for a drive and still no 3rd or 4th gear.

This was not the transmission that was originally in this car. The one it had before had a rattling noise, but shifted through all gears so I do not think the issue is in the vehicle's electrical system. I am wondering if the issue might be with the harness that goes inside the transmission? Both shift solenoids were replaced with new ones. Otherwise, if the transmission air checked fine, why would it lose 3rd and 4th once installed?

Any help would be greatly appreciated.

A few things:
1. ALWAYS replace ALL Electrical/Electronic parts on these transmissions - NOTHING should be reused!
2. ALWAYS install a 093/Corvette Servo! Never re-use the preexisting 2nd gear servo, inner diameter is usually worn out and makes no sense to buy a new 553 servo
3. ALWAYS drill your 2-3 feed and 2-3 accumulator (aka band release) .093" for factory rebuilds, larger for higher stall applications
4. Set band clearance to 1/8" of inch travel on the reverse input drum and/or .050-.090 on the servo travel
5. Run your 3-4 clutch pack clearance to between .035-.050 - NO LOAD RELEASE SPRINGS unless you're doing something really high performance/high RPM then install Transgo's high rate return springs (their bleeder orifice can be omitted for applications under 5500 RPM)
6. Convert the TCC regulator/isolator valves to an-on off configuration by installing a Fitzall valve that's made for that transmission's vintage - you will re-use the isolator valve, which is the valve that is most inboard
7. Tip - Find something to block the 3-2 downshift valve inboard and then put the factory 3-2 downshift valve spring inside the AFL spring to increase AFL pressure to your solenoids - gives the apply circuits a bit more hydraulic pressure / strength to keep clutch packs applied at WOT, especially if engine power is significantly increased over stock

> Did you replace all of the forward drum pistons with new bonded steel/rubber pistons?
> Do you closely inspect the crown of the drum for micro fractures/very small cracks (I had a couple come apart on me after installation and found they had latent defects that were creating leakage into the case but wasn't presenting on an air check or fluid pressure test)

For trans B, I'd replace the forward drum and do the necessary checks on the replacement as well as drill the plate per #3 above...Install new Corvette servos in all 700R4s and 4L60Es; always install all new electronics/electrical parts for any electro-hydraulically controlled transmissions. Guidance for Trans A is largely the same as trans B; replace the forward drum if you have any doubts.

Quote my post or mention me if you have any questions or need more assistance.

 

[lyncht1967]

A few things:
1. ALWAYS replace ALL Electrical/Electronic parts on these transmissions - NOTHING should be reused!
2. ALWAYS install a 093/Corvette Servo! Never re-use the preexisting 2nd gear servo, inner diameter is usually worn out and makes no sense to buy a new 553 servo
3. ALWAYS drill your 2-3 feed and 2-3 accumulator (aka band release) .093" for factory rebuilds, larger for higher stall applications
4. Set band clearance to 1/8" of inch travel on the reverse input drum and/or .050-.090 on the servo travel
5. Run your 3-4 clutch pack clearance to between .035-.050 - NO LOAD RELEASE SPRINGS unless you're doing something really high performance/high RPM then install Transgo's high rate return springs (their bleeder orifice can be omitted for applications under 5500 RPM)
6. Convert the TCC regulator/isolator valves to an-on off configuration by installing a Fitzall valve that's made for that transmission's vintage - you will re-use the isolator valve, which is the valve that is most inboard
7. Tip - Find something to block the 3-2 downshift valve inboard and then put the factory 3-2 downshift valve spring inside the AFL spring to increase AFL pressure to your solenoids - gives the apply circuits a bit more hydraulic pressure / strength to keep clutch packs applied at WOT, especially if engine power is significantly increased over stock

> Did you replace all of the forward drum pistons with new bonded steel/rubber pistons?
> Do you closely inspect the crown of the drum for micro fractures/very small cracks (I had a couple come apart on me after installation and found they had latent defects that were creating leakage into the case but wasn't presenting on an air check or fluid pressure test)

For trans B, I'd replace the forward drum and do the necessary checks on the replacement as well as drill the plate per #3 above...Install new Corvette servos in all 700R4s and 4L60Es; always install all new electronics/electrical parts for any electro-hydraulically controlled transmissions. Guidance for Trans A is largely the same as trans B; replace the forward drum if you have any doubts.

Quote my post or mention me if you have any questions or need more assistance.

Wow! what a thorough response Nick, thanks for taking the time. This forum member appreciates you being a pro and sharing and I'm sure others do as well. BTW, what brand of Corvette servo do you recommend?? Terry

 

[Tataocb]

A few things:
1. ALWAYS replace ALL Electrical/Electronic parts on these transmissions - NOTHING should be reused!
2. ALWAYS install a 093/Corvette Servo! Never re-use the preexisting 2nd gear servo, inner diameter is usually worn out and makes no sense to buy a new 553 servo
3. ALWAYS drill your 2-3 feed and 2-3 accumulator (aka band release) .093" for factory rebuilds, larger for higher stall applications
4. Set band clearance to 1/8" of inch travel on the reverse input drum and/or .050-.090 on the servo travel
5. Run your 3-4 clutch pack clearance to between .035-.050 - NO LOAD RELEASE SPRINGS unless you're doing something really high performance/high RPM then install Transgo's high rate return springs (their bleeder orifice can be omitted for applications under 5500 RPM)
6. Convert the TCC regulator/isolator valves to an-on off configuration by installing a Fitzall valve that's made for that transmission's vintage - you will re-use the isolator valve, which is the valve that is most inboard
7. Tip - Find something to block the 3-2 downshift valve inboard and then put the factory 3-2 downshift valve spring inside the AFL spring to increase AFL pressure to your solenoids - gives the apply circuits a bit more hydraulic pressure / strength to keep clutch packs applied at WOT, especially if engine power is significantly increased over stock

> Did you replace all of the forward drum pistons with new bonded steel/rubber pistons?
> Do you closely inspect the crown of the drum for micro fractures/very small cracks (I had a couple come apart on me after installation and found they had latent defects that were creating leakage into the case but wasn't presenting on an air check or fluid pressure test)

For trans B, I'd replace the forward drum and do the necessary checks on the replacement as well as drill the plate per #3 above...Install new Corvette servos in all 700R4s and 4L60Es; always install all new electronics/electrical parts for any electro-hydraulically controlled transmissions. Guidance for Trans A is largely the same as trans B; replace the forward drum if you have any doubts.

Quote my post or mention me if you have any questions or need more assistance.

Thanks for taking the time to send the thorough explanation.

I did replace the forward drum pistons with new bonded steel/rubber pistons. I will have to check the crown of the drums for cracks.

How do you accomplish the tighter than stock clearance on the 3-4 clutch pack? Do you use thicker steels, frictions or end plates? Or do you use a different combination of steels and frictions than stock?

 

[NickTransmissions]

Thanks for taking the time to send the thorough explanation.

I did replace the forward drum pistons with new bonded steel/rubber pistons. I will have to check the crown of the drums for cracks.

How do you accomplish the tighter than stock clearance on the 3-4 clutch pack? Do you use thicker steels, frictions or end plates? Or do you use a different combination of steels and frictions than stock?

You're welcome and good move replacing those stupid aluminum apply pistons with the late model bonded rubber/steel versions as the earlier, aluminum ones will crack on you.

You may not know but there's at least three different thicknesses of 3-4 flat steel available from the factory, including .105" (4L60E), .085" (4L65E) and 700R4 early and late (the thicknesses escapes me atm but are easily googled). So I have an entire drawer full of these different thicknesses plus some steels available in the aftermarket that have varying thickness. You can also mix/match 3-4 apply rings...for example a late 700R4 #4 apply ring will be about .015" taller than the standard #7 apply ring that went into all 4L60/65/70Es so you can shrink you clearance that way. The really old 700R4s (pre-1988) use an unmarked apply ring that's taller still, so less clearance than the other two.

Lastly, you can use different combinations of apply and backing plates from 700R4s to adjust clearance or machine your 4L60E backing and apply plates to fit more frictions and steels...You can also use 4L65/70E apply and backing plates to do the same.

Check out my 700R4 and 4L60E forward drum changes and interchange video where I cover all possible forward drum set ups that went into 700R4s and 4L60Es over the years..It's a good overview of everything that was produced and out there for those transmissions.

 

[Tataocb]

This is how I ended up resolving the issues:

Transmission A - The stator shaft was worn out on the inside where the reverse drum goes. I replaced the pump and used a corvette servo (as well as new 3-4 clutch pack), and that took care of the issue.

Transmission B - I ended up replacing the input drum and installing a corvette servo as well, and that took care of the issue. I assume the drum had a leak once the fluid warmed up that I could not detect while I had it outside of the transmission.

I have a different question now, @NickTransmissions. I got an exchange that is from a 2008, but the case is no good. It is missing a piece where the pan bolts onto so it is not possible to install the pan. I have another core that I took apart and used the components for parts and the case is good. I believe it is off a 2001 transmission based on the tag. So my question is, would it be possible to transfer all the components from the 2008 transmission into the case from the 2001 transmission, and successfully be able to use it after a rebuild in a 2007 and up vehicle? Or would the case need to be from a 2004 and up that use the pump to case molded seal ring instead of the o ring that goes on the groove of the pump?

Thanks,

 

[NickTransmissions]

This is how I ended up resolving the issues:

Transmission A - The stator shaft was worn out on the inside where the reverse drum goes. I replaced the pump and used a corvette servo (as well as new 3-4 clutch pack), and that took care of the issue.

Transmission B - I ended up replacing the input drum and installing a corvette servo as well, and that took care of the issue. I assume the drum had a leak once the fluid warmed up that I could not detect while I had it outside of the transmission.

I have a different question now, @NickTransmissions. I got an exchange that is from a 2008, but the case is no good. It is missing a piece where the pan bolts onto so it is not possible to install the pan. I have another core that I took apart and used the components for parts and the case is good. I believe it is off a 2001 transmission based on the tag. So my question is, would it be possible to transfer all the components from the 2008 transmission into the case from the 2001 transmission, and successfully be able to use it after a rebuild in a 2007 and up vehicle? Or would the case need to be from a 2004 and up that use the pump to case molded seal ring instead of the o ring that goes on the groove of the pump?

Thanks,

Confirm the 2008 case isn't a late year case for the 09 model year, which saw a slew of changes that would make it completely incompatible for any pre-2009 application (if you haven't already done so). If it's otherwise not a 2009 model year case, you can swap everything over, except the pump body - that has to be replaced with one that take an O-ring. So grab a 1996-2003 pump body (last four digits of the casting number are 1073) and mate it to your existing stator/stator support assembly (machine the pump body if necessary). Air check all the clutch packs in the two drums through the pump to confirm proper function. Put a new o-ring seal on before final installation and you're good. Obviously replace all gaskets, seals, sealing rings, etc (common sense stuff).

I'd also have some different thickness selective spacers and Sonnax .015 shims at the ready as you'll likely need a couple iterations of front end play adjustment before it's within spec (.015-.030) when doing a case swap.

 

[Tataocb]

@NickTransmissions - I come to you again hoping you can share your knowledge with another issue.

I rebuilt a transmission (new clutches, steels, seals, bonded pistons, corvette servo, etc) and everything checked out during the air check with the test plate. I sold it to a guy who installed it on a 2007 GMC Sierra Classic (it looks like a 2006 and he says all the parts he buys are using an 06 as his vehicle when searching). He got a new torque converter and installed it. He added close to 3 gallons of Dex/Merc fluid and is having issues with it shifting into 3rd gear. I asked him to try shifting manually and when he moves the shifter into 3rd gear it slips and the revs just go up. I also asked him to unplug the harness (to get it in limp mode, which from what I understand is 3rd gear) and it moves, but when it gets to around 35, the RPMs are around 3500 and does not seem to want to go any faster. He lives about 20 min from me so I went to take a look today. We unplugged the harness from the transmission and went for a drive and experienced what I just described.

I made this manual shift solenoid activation device by using two toggle switches going to ground and the shift solenoids and taking a 4L60e pigtail and using only 3 wires (shift solenoid A, B and 12v) and wrapping the rest up without hooking them up to anything. The 12v feed wire goes to the driver side fuse box using a 20 amp fuse. I then have two switches, both going out to ground on one end and the other end of one going to shift solenoid A on the pigtail and the other switch going to shift solenoid B. So we plugged that in and went for a test drive. With both solenoids ON it drove in first, then turned off solenoid A and it shifted to second and held it until around 45 mph. I then turned solenoid B off (so they were both off) and the transmission slipped, but would jerk and kind of engage if revved up to around 4500 RPMs. I then turned solenoid A back on (so A was ON and B was OFF) to get 4th gear and it shifted and 4th gear worked fine. I was able to get it up to 60 mph before we ran out of road (country backroads).

That confused me as I was expecting 4th gear NOT to work since 3rd gear was slipping. From what I understand, the only difference is the band engages de input drum. So I assumed that if 3rd gear was out, it was because the input drum was not holding pressure and maybe leaking fluid, but if that were the case, then shouldn't 4th gear be out as well? Is there anything else I should test before dropping the transmission and taking it apart again? I replaced both shift solenoids, and left the ones it had for the rest. Could one of the other solenoids be bad causing 3rd gear to slip, but not 4th? I checked the one way clutches and they were fine. The guy says he is not in a hurry to get the truck going so I can have a couple days to try to diagnose without having to take it apart. The only other thing I noticed is that it had to be revved a bit to get reverse to engage. The stator shaft sealing rings were replaced and they checked out fine during the air check with the test plate. Is there anything else I can check? Is it normal for 3rd gear to be out, but 4th gear works fine? I know that most people say 3rd and 4th are out, and that is most likely because they do not have the manual solenoid control to test 4th gear and cannot get to higher speeds with 3rd gear being out.

Any insight you can provide would be greatly appreciated. Thanks.

 

[NickTransmissions]

@NickTransmissions - I come to you again hoping you can share your knowledge with another issue.

I rebuilt a transmission (new clutches, steels, seals, bonded pistons, corvette servo, etc) and everything checked out during the air check with the test plate. I sold it to a guy who installed it on a 2007 GMC Sierra Classic (it looks like a 2006 and he says all the parts he buys are using an 06 as his vehicle when searching). He got a new torque converter and installed it. He added close to 3 gallons of Dex/Merc fluid and is having issues with it shifting into 3rd gear. I asked him to try shifting manually and when he moves the shifter into 3rd gear it slips and the revs just go up. I also asked him to unplug the harness (to get it in limp mode, which from what I understand is 3rd gear) and it moves, but when it gets to around 35, the RPMs are around 3500 and does not seem to want to go any faster. He lives about 20 min from me so I went to take a look today. We unplugged the harness from the transmission and went for a drive and experienced what I just described.

I made this manual shift solenoid activation device by using two toggle switches going to ground and the shift solenoids and taking a 4L60e pigtail and using only 3 wires (shift solenoid A, B and 12v) and wrapping the rest up without hooking them up to anything. The 12v feed wire goes to the driver side fuse box using a 20 amp fuse. I then have two switches, both going out to ground on one end and the other end of one going to shift solenoid A on the pigtail and the other switch going to shift solenoid B. So we plugged that in and went for a test drive. With both solenoids ON it drove in first, then turned off solenoid A and it shifted to second and held it until around 45 mph. I then turned solenoid B off (so they were both off) and the transmission slipped, but would jerk and kind of engage if revved up to around 4500 RPMs. I then turned solenoid A back on (so A was ON and B was OFF) to get 4th gear and it shifted and 4th gear worked fine. I was able to get it up to 60 mph before we ran out of road (country backroads).

That confused me as I was expecting 4th gear NOT to work since 3rd gear was slipping. From what I understand, the only difference is the band engages de input drum. So I assumed that if 3rd gear was out, it was because the input drum was not holding pressure and maybe leaking fluid, but if that were the case, then shouldn't 4th gear be out as well? Is there anything else I should test before dropping the transmission and taking it apart again? I replaced both shift solenoids, and left the ones it had for the rest. Could one of the other solenoids be bad causing 3rd gear to slip, but not 4th? I checked the one way clutches and they were fine. The guy says he is not in a hurry to get the truck going so I can have a couple days to try to diagnose without having to take it apart. The only other thing I noticed is that it had to be revved a bit to get reverse to engage. The stator shaft sealing rings were replaced and they checked out fine during the air check with the test plate. Is there anything else I can check? Is it normal for 3rd gear to be out, but 4th gear works fine? I know that most people say 3rd and 4th are out, and that is most likely because they do not have the manual solenoid control to test 4th gear and cannot get to higher speeds with 3rd gear being out.

Any insight you can provide would be greatly appreciated. Thanks.

Sounds as though there's either a line pressure issue or loss of pressure/pressure deficiency in the 3-4 clutch hydraulic circuit...Do a line pressure test, first at idle then take it for a drive with the vehicle-to-transmission harness connector plugged in - observe line pressure at the 2-3 shift and beyond...One thing that could cause this problem on a freshly built transmission is debris getting into the 3rd accumulator check ball capsule and preventing it from seating completely, thus creating a leak in the 3rd apply circuit...If this occurs, you'll have the symptoms you are seeing at normal line pressure conditions but under max pressure, the issue can be masked. If it is the 3rd acc check ball capsule, you'd need to pull it out and put in a new one...To be clear, I have seen one bonafide check ball capsule failure in all my 4L60Es and 700R4s tested over the years...It almost never actually breaks but crud gets in and cause 3rd apply issues.

When you unplug the case connector and put the transmission in limp mode, line pressure is maxed out and all adapts are frozen...Since you manually overrode the system via your test device, you were able to command shift solenoid A back on without the computer's 'knowledge' which gave you max line pressure conditions while in 4th, which appear to have been sufficient to keep the 3-4 pack compressed and band applied, sustaining 4th gear.

Start with the idle and driving pressure test and go from there.

 

[Tataocb]

Sounds as though there's either a line pressure issue or loss of pressure/pressure deficiency in the 3-4 clutch hydraulic circuit...Do a line pressure test, first at idle then take it for a drive with the vehicle-to-transmission harness connector plugged in - observe line pressure at the 2-3 shift and beyond...One thing that could cause this problem on a freshly built transmission is debris getting into the 3rd accumulator check ball capsule and preventing it from seating completely, thus creating a leak in the 3rd apply circuit...If this occurs, you'll have the symptoms you are seeing at normal line pressure conditions but under max pressure, the issue can be masked. If it is the 3rd acc check ball capsule, you'd need to pull it out and put in a new one...To be clear, I have seen one bonafide check ball capsule failure in all my 4L60Es and 700R4s tested over the years...It almost never actually breaks but crud gets in and cause 3rd apply issues.

When you unplug the case connector and put the transmission in limp mode, line pressure is maxed out and all adapts are frozen...Since you manually overrode the system via your test device, you were able to command shift solenoid A back on without the computer's 'knowledge' which gave you max line pressure conditions while in 4th, which appear to have been sufficient to keep the 3-4 pack compressed and band applied, sustaining 4th gear.

Start with the idle and driving pressure test and go from there.

@NickTransmissions - Thanks for such a prompt reply! You are beyond awesome, hats off to you!

Back to the issue, I always set the case valve body side up (with the valve body removed) and level out the back, put a few drops of transmission fluid where the check ball goes and check to see if any of it comes out inside the case or if it all comes out through the servo bore. Then I start with the assembly process. This has always tested out fine in the transmissions I have rebuilt. However, since I test it at the beginning, there is a chance that debris could get in there during the reassembly process. With the transmission in the vehicle, I cannot think of a way to test it properly, perhaps only drop the pan and valve body, remove the servo and blow some compressed air to see if that will clean it up.

Assuming there is no leak in the check ball capsule, could it be there is a leak in the drum that under normal 3rd gear pressure leaks enough fluid that the clutch pack is not able to stay properly compressed, but when it goes to 4th gear, the max line pressure is high enough to where the amount being leaked does not drop the pressure low enough to cause the clutch pack to not stay compressed?

Regarding the line pressure test, what readings should I expect to see while in 1st, 2nd and then finally when it shifts into 3rd? With the vehicle-to-transmission harness plugged in, I will not be able to get it to shift into 4th gear so I will not be able to get a reading for that gear. Should I instead try it with my testing device to get it to shift into 4th gear, or maybe run a separate test? From what I understand, the reading in Reverse is the max pressure, correct?