4:56…. Or … 4:88? That’s the Question

[swathdiver]

I used to have a '76 K5 blazer w/373 gears, TH350 and 35" tires and it was an absolute dog. Zero acceleration, took forever to get moving (had a 350 engine). I installed 4.56 gears in the rear (removed the front drive shaft prior to) as I wanted to see what sort of difference it would make before doing the front diff. It made a subtle difference, acceleration improved but not dramatically. I then installed 4.88s and it made a much more notable difference, woke that little 350 up and it made for a much more enjoyable driving experience, especially on the trails. I then put 4.88s in the front diff. I sold that thing as fuel mileage wasn't measured in miles per gallon, it was measured in gallons per mile and was a rust bucket. But the gears made a big difference.

As long as the vehicle is in the 'green' with the selected gear ratio per those gear ratio charts, it will be fine but for 35s in a 5-6k lb vehicle, I'd go 4.56 at minimum.

I hear ya but there's a huge difference with 4.88s in a 4L60 and a 6L80.



In this example the stock NHT with 3.73 gears smokes the 4-speed truck with 4.88s ratio wise.

My 2012 came with 3.73 gears and has been running 35s for over ten years. About 2 years ago we had to do a reman transmission at about 130K. Right now the tires make the final drive ratios equivalent to 3.42s which we have in our other 6-speed trucks. 4.10s would bring the 2012 back to 3.73 rpms. Would you still counsel steeper gears?

 

[NickTransmissions]

I hear ya but there's a huge difference with 4.88s in a 4L60 and a 6L80.

View attachment 404653

In this example the stock NHT with 3.73 gears smokes the 4-speed truck with 4.88s ratio wise.

My 2012 came with 3.73 gears and has been running 35s for over ten years. About 2 years ago we had to do a reman transmission at about 130K. Right now the tires make the final drive ratios equivalent to 3.42s which we have in our other 6-speed trucks. 4.10s would bring the 2012 back to 3.73 rpms. Would you still counsel steeper gears?

If that's the case, then use the ratio that best corresponds w/the vehicle's intent use and performance requirements. Sorry, was thinking of TH350/700R4 ratios not the 6L80E with its much deeper deeper 1st gear. The overarching point is that the final drives must be updated considered based on application, use case and transmission gearing when you put significantly bigger tires on the vehicle.

 

[NickTransmissions]

I hear ya but there's a huge difference with 4.88s in a 4L60 and a 6L80.



In this example the stock NHT with 3.73 gears smokes the 4-speed truck with 4.88s ratio wise.

My 2012 came with 3.73 gears and has been running 35s for over ten years. About 2 years ago we had to do a reman transmission at about 130K. Right now the tires make the final drive ratios equivalent to 3.42s which we have in our other 6-speed trucks. 4.10s would bring the 2012 back to 3.73 rpms. Would you still counsel steeper gears?

I was thinking 4-speed 4L60E as this thread is in the 2000-2006 section and it's not specified that the trans is a 6L80E, sorry for any confusion. In real life ill obviously already know what trans is in the vehicle...Should have asked first...

 

[NickTransmissions]

So the build is coming along nicely. Lots of hard honest work and lessons learned along the way. Exactly what I’d hoped for when I took this 4x4 project on. Thanks to this forum and other resources, I’ve had allot of support along the way. That said, I’m to the crossroads of re-gearing the rear differential. Currently running 35x12.5x20 wheels on a 6” lift. I’ve read all kinds of threads and heard the arguments from all sides and points of view. Kind of goes back to the main question, what is the purpose of the vehicle and what am I doing with it? Mostly will just be a fun rig for my son and I drive drive around town, run up to the lake etc. I may pull a small trailer or boat now and again. We live in the hills of Northern California, so not flat land by any means.

So the question is, what gears? Right now running stock G80 3.73’s. And honestly, it doesn’t lag all that bad. Not as much as I thought it would. Now I’m leaning towards 4:56 gears because I’d like to drive it down to work now and again, freeway miles about 50 each way. Maybe an occasional hunt trip down in the valley. I’ve heard some say go 4:88 while others say that is overkill.

Welcoming your thoughts and much appreciated!!

Dan

Dan, do you have a 4L60E or 6L80?

 

[Dantheman-2003]

All- thanks for the input. I should have added I am running a stock 4L60 transmission. Recently serviced the transmission fluid and filter, which was a pain in the *SS. Getting ready to install the Trucool upgrade cooler.

Dan, do you have a 4L60E or 6L80?

Stock 4L60

 

[NickTransmissions]

Super, thanks Dan and you're welcome.

@swathdiver - For this particular case, my original guidance stands with the caveat that 4.11 gears would work as well given the 4L60Es deeper first gear ratio (3:08 to 1) to get it off the line compared to the TH350's / TH400's gear ratios of 2.50 to 1 and that 4.88 may be a bit overkill for regular street/highway driving.

The 6L80, as you pointed out, can accommodate 3.73s w/35s (33" rolling dia) owing to it's much deeper 1st gear ratio to get it moving; .67-1 ratio in sixth w/3.73 gears and 35"s still somewhat stress the 2-6 and 4-5-6 clutch but not dangerously where as 4.10/4.11 would be ideal for 6L80E equipped vehicles where as something like 4.30-4.56 would be a good combo to pair w/a 4L60E equipped vehicle if low RPM acceleration/power was more of a priority (like something intended for a lot of off-road/trail use). I did not consider the OPs truck had a 6L80 when initially responding and as mentioned, should have asked first.

So the takeaway is to consider the transmission and it's ratios relative to engine, final drive and intended application when deciding on gear sets. All things equal, as long as the actual final drive is in the green (appropriate range) of gear ratios, everything should be fine.

Hopefully this clears up any confusion and closes the loop.

 

[swathdiver]

Super, thanks Dan and you're welcome.

@swathdiver - For this particular case, my original guidance stands with the caveat that 4.11 gears would work as well given the 4L60Es deeper first gear ratio (3:08 to 1) to get it off the line compared to the TH350's / TH400's gear ratios of 2.50 to 1 and that 4.88 may be a bit overkill for regular street/highway driving.

The 6L80, as you pointed out, can accommodate 3.73s w/35s (33" rolling dia) owing to it's much deeper 1st gear ratio to get it moving; .67-1 ratio in sixth w/3.73 gears and 35"s still somewhat stress the 2-6 and 4-5-6 clutch but not dangerously where as 4.10/4.11 would be ideal for 6L80E equipped vehicles where as something like 4.30-4.56 would be a good combo to pair w/a 4L60E equipped vehicle if low RPM acceleration/power was more of a priority (like something intended for a lot of off-road/trail use). I did not consider the OPs truck had a 6L80 when initially responding and as mentioned, should have asked first.

So the takeaway is to consider the transmission and it's ratios relative to engine, final drive and intended application when deciding on gear sets. All things equal, as long as the actual final drive is in the green (appropriate range) of gear ratios, everything should be fine.

Hopefully this clears up any confusion and closes the loop.

Awesome Nick. I did not mean to imply that you didn't know which transmission we were working with. I wanted to know if... I'm sure this could be stated more clearly... that it is really the final drive ratios that matters based on different transmission ratios, gears and engine power when selecting the axle ratio. And you have answered that as yes, with several examples.

I agree, 4.10s in the NHT truck would be better for the transmission.

All good stuff.

I reckon that the OP will be well served by upgrading the original transmission to the 4L65 standard and run at least a 4.56 gear.

My children are learning that running a truck with 35s is enormously expensive.

 

[drakon543]

i went 33s and kept the stock gearing but that was a manual trans on that and i still had plenty of cases i wish i had done 4.11. totally different truck than what we are talking about but bigger tires and regearing should always be considered regardless of the truck.

 

[NickTransmissions]

Awesome Nick. I did not mean to imply that you didn't know which transmission we were working with. I wanted to know if... I'm sure this could be stated more clearly... that it is really the final drive ratios that matters based on different transmission ratios, gears and engine power when selecting the axle ratio. And you have answered that as yes, with several examples.

I agree, 4.10s in the NHT truck would be better for the transmission.

All good stuff.

Thanks, @swathdiver ...

My children are learning that running a truck with 35s is enormously expensive.

Yep, wallet size should be, at minimum, equivalent in proportion to tire size and 35s require a big wallet...but they sure are fun!

 

[Dantheman-2003]

@NickTransmissions- 1 other question I had, was about re-gearing the front diff. I read somewhere that if your re-gear to 4:56 then you can’t utilize the 4wd option until you re-gear the front. Does that sound right?