well drove the Yukon today still sometimes has a flare on the 2-3 shift the transmission guy told me that he replaced everything in the trans and it must be electrical he thinks the pcm. any way to test the pcm? he also said one thing he could try was to install a kit that converts the trans pressure form electronic to vacuum anyone done this?
transmission nightmare
- Thread starter l306x
- Start date
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Vacuum modulator is not recommended for a street vehicle. Stay with the EPC.
Not knowing the builder or his work, like I said earlier the harness or a ground may have been damaged. If not immediately after the accident, then maybe a wire was moved during repair into interference with something and over time the shielding got scuffed off creating a short circuit. Seen this quite a few times. Again, if you have or know someone with a Fluke 88 meter, check all the circuits for continuity.
If the 2-3 is the only thing that flairs, and everything else is good, then really the only build-related things are:
1) Seals around direct clutch apply piston are not sealing or the piston is cracked. Must tear down to inspect. I'll give the benefit of a doubt to the builder that he air-checked ALL the hydraulic circuits during reassembly. Believe it or not, many shops out there neglect this.
2) Direct clutch clearance set too high. Factory recommends .060" max... I set mine to no more than .030". On the factory setup, 0.080" or more can cause a flair on the 2-3. This can happen if you put in the narrow width steels (meant for the 9 and 10 friction packs, which I do not like due to the thin steels) in a factory 6-friction pack. You could try installing a corvette servo... the back side of the servo acts as the 2-3 accumulator... if the 3-4 clearance is a little loose the vette servo could tighten up the timing enough to overcome the flair. Not a permanent fix, but will work as long as you don't beat on it regularly.
3) Checkball capsule behind the servo leaks. It is common for many rebuild shops to neglect this check ball capsule. If it leaks, it will cause a 2-3 flair and will eventually burn up the direct clutch (aka 3-4 clutch). While you can see it in the servo bore (in the case housing) with both servos removed, the valvebody and separator plate must come down to replace this... an "easy out" bit makes a great tool for removing the capsule from the case. By hand, contact the capsule with the bit, turn until you feel it grab, then pull it out. Install the new capsule in the same orientation.
There may be a few things I'm forgetting right now. Transmissions can be hard to diagnose over the internet, especially if repeat rebuilds are occurring (which red flags to me the builder isn't experienced with the 4L60E).
Not knowing the builder or his work, like I said earlier the harness or a ground may have been damaged. If not immediately after the accident, then maybe a wire was moved during repair into interference with something and over time the shielding got scuffed off creating a short circuit. Seen this quite a few times. Again, if you have or know someone with a Fluke 88 meter, check all the circuits for continuity.
If the 2-3 is the only thing that flairs, and everything else is good, then really the only build-related things are:
1) Seals around direct clutch apply piston are not sealing or the piston is cracked. Must tear down to inspect. I'll give the benefit of a doubt to the builder that he air-checked ALL the hydraulic circuits during reassembly. Believe it or not, many shops out there neglect this.
2) Direct clutch clearance set too high. Factory recommends .060" max... I set mine to no more than .030". On the factory setup, 0.080" or more can cause a flair on the 2-3. This can happen if you put in the narrow width steels (meant for the 9 and 10 friction packs, which I do not like due to the thin steels) in a factory 6-friction pack. You could try installing a corvette servo... the back side of the servo acts as the 2-3 accumulator... if the 3-4 clearance is a little loose the vette servo could tighten up the timing enough to overcome the flair. Not a permanent fix, but will work as long as you don't beat on it regularly.
3) Checkball capsule behind the servo leaks. It is common for many rebuild shops to neglect this check ball capsule. If it leaks, it will cause a 2-3 flair and will eventually burn up the direct clutch (aka 3-4 clutch). While you can see it in the servo bore (in the case housing) with both servos removed, the valvebody and separator plate must come down to replace this... an "easy out" bit makes a great tool for removing the capsule from the case. By hand, contact the capsule with the bit, turn until you feel it grab, then pull it out. Install the new capsule in the same orientation.
There may be a few things I'm forgetting right now. Transmissions can be hard to diagnose over the internet, especially if repeat rebuilds are occurring (which red flags to me the builder isn't experienced with the 4L60E).
thanks jay,
from what I can tell the builder knows what he is doing. he dose "bench rebuilds " for a lot of local repair shops. I called him after I installed the trans and it still flared he told me to drop it off at his shop. he took the trans out to look everything over again put it back in still flared. he took it out again looked it over put a different valve body in it still has a flare (from what I recall it is not as bad as it was) so he told me he has double checked everything and he is sure it is not in the trans.. thinks it is electrical. under light throttle is seems fine. I would say over 1/2 throttle you can notice the flare. he thinks it is a shift timing issue
I purchased the car damaged so I am not sure if it had the flare before the crash or not ..I e-mail the past owner and she never wrote back .... I will try again
I put a vette servo in it before the rebuild it did not help so I took it out....maybe I should try it again? I also have a .50 boost valve worth a try?
I will look over all the wires again....I do not have a fluke 88 meter but I can try to get one. thanks again for the help!
from what I can tell the builder knows what he is doing. he dose "bench rebuilds " for a lot of local repair shops. I called him after I installed the trans and it still flared he told me to drop it off at his shop. he took the trans out to look everything over again put it back in still flared. he took it out again looked it over put a different valve body in it still has a flare (from what I recall it is not as bad as it was) so he told me he has double checked everything and he is sure it is not in the trans.. thinks it is electrical. under light throttle is seems fine. I would say over 1/2 throttle you can notice the flare. he thinks it is a shift timing issue
I purchased the car damaged so I am not sure if it had the flare before the crash or not ..I e-mail the past owner and she never wrote back .... I will try again
I put a vette servo in it before the rebuild it did not help so I took it out....maybe I should try it again? I also have a .50 boost valve worth a try?
I will look over all the wires again....I do not have a fluke 88 meter but I can try to get one. thanks again for the help!
The PCM has no effect on shift timing. The 4L60/65E is still a hydraulic transmission... the electronics just initiate the shift. The speed and firmness of the shift is still dictated by hydraulic operation (accumulator settings, line pressure, separator plate hole sizes, clutch clearances, servo size, etc).
Without driving your truck I can't nail down the true cause... normally a flair is a build related issue, not electrical. If you have 1st and 2nd gear, there is no electrical reason why 3rd and/or 4th won't engage correctly. Only way I see this happening is if there is a bad ground or short in the power supply to the trans giving intermittent power surges during shift commands, causing erratic solenoid/valvetrain movement. But that should also happen in 1st and 2nd gear.
For a 2-3 flair, basically what's happening is the band is releasing before the 3-4 clutch can apply. Or, the band is releasing too fast, and the 3-4 is coming on when it's supposed to. You MUST understand that the for the 3-4 clutch to engage, oil is directed to the back side of the 2nd servo (to push off the band) before the hydraulic circuit is completed by pressurizing the 3-4 apply piston. The 3-4 clutch clearance and the servo pin travel are the non-hydraulic elements of this shift timing equation and are equally as important. This is what makes this transmission so hard to build right.
Ask the builder what clearance he set the 3-4 clutch pack at. This is the most critical clearance in the transmission (next to the end clearance) and should be no more than 0.060" (preferably 0.040"-0.050" for a stock transmission, and 0.030" with modified shift holes in the separator plate). Then ask what the servo pin clearance is, along with what separator plate and if/what mods he may have done to it. With this information i should be able to help you find the problem if it's build-related. You have to build a lot of these things under high-power situations to learn the balance and range of things that will work.
Without driving your truck I can't nail down the true cause... normally a flair is a build related issue, not electrical. If you have 1st and 2nd gear, there is no electrical reason why 3rd and/or 4th won't engage correctly. Only way I see this happening is if there is a bad ground or short in the power supply to the trans giving intermittent power surges during shift commands, causing erratic solenoid/valvetrain movement. But that should also happen in 1st and 2nd gear.
For a 2-3 flair, basically what's happening is the band is releasing before the 3-4 clutch can apply. Or, the band is releasing too fast, and the 3-4 is coming on when it's supposed to. You MUST understand that the for the 3-4 clutch to engage, oil is directed to the back side of the 2nd servo (to push off the band) before the hydraulic circuit is completed by pressurizing the 3-4 apply piston. The 3-4 clutch clearance and the servo pin travel are the non-hydraulic elements of this shift timing equation and are equally as important. This is what makes this transmission so hard to build right.
Ask the builder what clearance he set the 3-4 clutch pack at. This is the most critical clearance in the transmission (next to the end clearance) and should be no more than 0.060" (preferably 0.040"-0.050" for a stock transmission, and 0.030" with modified shift holes in the separator plate). Then ask what the servo pin clearance is, along with what separator plate and if/what mods he may have done to it. With this information i should be able to help you find the problem if it's build-related. You have to build a lot of these things under high-power situations to learn the balance and range of things that will work.
thanks for the great info jay,
I just got a e-mail from the last ower and she said that they never had any transmission problems before the crash. The truck was crashed on the RH front I have looked it all over a few times but I will do it again.
I just got a e-mail from the last ower and she said that they never had any transmission problems before the crash. The truck was crashed on the RH front I have looked it all over a few times but I will do it again.
looked all the grounds over all look OK...the only wires by the crash are the MAF wires and the headlights they all are fine..I did run across a sonnax article about 2-3 flare it talks about the pcm not turning the B solenoid off cleanly so the trans will flare the shift . they amp tested the trans fuse on a 98 chevy truck to see how long it took for the solenoid to turn off.
I don't see a trans fuse on my fuse box anyone know what fuse you would amp test on a 03 Yukon?
thanks
I don't see a trans fuse on my fuse box anyone know what fuse you would amp test on a 03 Yukon?
thanks
Since this is a rebuilt transmission, we're probably just chasing the rabbit into the hole. The builder needs to figure out what's wrong.
The solenoids should have been replaced during rebuild. The trans is connected directly to the PCM via the harness, no individual fuse that I'm aware of other than the main PCM fuse (the truck will not run if this is blown). The trans harness faces up towards the belly of the truck so you will have to squeeze under there. The harness should have 12-13 pins, the B solenoid should be the 2nd from the left in the row of 4 pins (row of 4 pointed up). If you drop the pan and unplug the solenoid (A is nearest the 1-2 accumulator, B the other one), you should read 20-40 ohms across the terminals. It's a simple on/off solenoid so there's little to go wrong. The speed of the electrical signal coming from the PCM is MANY orders of magnitude faster than the speed of the solenoid. I don't see this being the problem here.
If you clean the case and harness connectors good and it still does it, your last bet is to unhook the harness at the PCM and carefully clean all the pins.
There's not much else it can be other than build related.
---------- Post added at 10:02 AM ---------- Previous post was at 09:54 AM ----------
Just as one last check, we can override the solenoids altogether.
Take the truck out for a spin and shift manually using the column shifter. Start from a stop, and at consistent throttle (say 1/4-1/2) shift 1-2-3 at around 3000 rpm in each gear. Let me know if it still flares on the 2-3 when you move the shifter from D2 to D3. Depending on the result this may be as far as i can help you on here.
The solenoids should have been replaced during rebuild. The trans is connected directly to the PCM via the harness, no individual fuse that I'm aware of other than the main PCM fuse (the truck will not run if this is blown). The trans harness faces up towards the belly of the truck so you will have to squeeze under there. The harness should have 12-13 pins, the B solenoid should be the 2nd from the left in the row of 4 pins (row of 4 pointed up). If you drop the pan and unplug the solenoid (A is nearest the 1-2 accumulator, B the other one), you should read 20-40 ohms across the terminals. It's a simple on/off solenoid so there's little to go wrong. The speed of the electrical signal coming from the PCM is MANY orders of magnitude faster than the speed of the solenoid. I don't see this being the problem here.
If you clean the case and harness connectors good and it still does it, your last bet is to unhook the harness at the PCM and carefully clean all the pins.
There's not much else it can be other than build related.
---------- Post added at 10:02 AM ---------- Previous post was at 09:54 AM ----------
Just as one last check, we can override the solenoids altogether.
Take the truck out for a spin and shift manually using the column shifter. Start from a stop, and at consistent throttle (say 1/4-1/2) shift 1-2-3 at around 3000 rpm in each gear. Let me know if it still flares on the 2-3 when you move the shifter from D2 to D3. Depending on the result this may be as far as i can help you on here.
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ugh!!! This guy just does not have a good track record at this point 
He may need to head back to Wyotech 
He may need to head back to Wyotech 
