Rebuild Transmission?

[ChrisT2006]

Ok, so here’s the deal. I’ve got a ‘89 RCLB running 285/70/R17 tires, 3.42 gears, and a 700R4. I’ve been having issues with the transmission slipping, particularly on hills, where it downshifts 1-2 gears to get up even the slightest of grades. It will also try to “hunt” for the right gear when cruising at 45-65 mph, constantly changing gears. Occasionally the truck is slow to even engage reverse and drive. So my question is, should i rebuild my transmission? Would that even fix the problem? I read somewhere that 3.42 gears coupled with 33” inch tires is a death wish, so would regearing to something like 4.10’s fix the issue?
Thanks in advance

 

[NickTransmissions]

Ok, so here’s the deal. I’ve got a ‘89 RCLB running 285/70/R17 tires, 3.42 gears, and a 700R4. I’ve been having issues with the transmission slipping, particularly on hills, where it downshifts 1-2 gears to get up even the slightest of grades. It will also try to “hunt” for the right gear when cruising at 45-65 mph, constantly changing gears. Occasionally the truck is slow to even engage reverse and drive. So my question is, should i rebuild my transmission? Would that even fix the problem? I read somewhere that 3.42 gears coupled with 33” inch tires is a death wish, so would regearing to something like 4.10’s fix the issue?
Thanks in advance

Install 4.10s then rebuild the transmission. Check out my 700R4 Information thread for tips, pointers, instruction and additional resources. (link is in my signature line)

 

[ChrisT2006]

Install 4.10s then rebuild the transmission. Check out my 700R4 Information thread for tips, pointers, instruction and additional resources. (link is in my signature line)

Okay, so the 3.42 gears are helping to cause the problem?

 

[NickTransmissions]

Okay, so the 3.42 gears are helping to cause the problem?

Yes...in overdrive, you do not have enough mechanical leverage to build RPM fast enough so that you can build 3-4 clutch apply pressure fast enough to meet input torque demand when you go to accelerate while in 4th. So for now, I'd drive it in 4th gear only when on a level grade but as soon as you have to accelerate for any reason, manually down shift into third. Example would be having to climb a grade or pass someone on the freeway.

Anytime you put large tires without also changing the gear ratio in your axle(s), you change the effective final drive ratio, making it taller. That leads to reduced mechanical leverage at all speeds and RPM, stressing the engine and transmission.

 

[GrimsterGMC]

When I got my truck it had the factory 3.42 ratio and 33 inch tires so the same basically as yours. I did exactly what Nick said and changed to 4.1 ratio diffs and that made a world of difference to the driving experience. Previously it would constantly switch the TCC on and off as cruising at 60 mph was right on the tipping point, but now it requires more throttle to disengage it. It basically took the rpms vs mph back to where the factory had it with the factory tire size. Just remember to change the speedo calibration to suit the new ratio so the ECU knows what speed you are doing.

 

[ChrisT2006]

When I got my truck it had the factory 3.42 ratio and 33 inch tires so the same basically as yours. I did exactly what Nick said and changed to 4.1 ratio diffs and that made a world of difference to the driving experience. Previously it would constantly switch the TCC on and off as cruising at 60 mph was right on the tipping point, but now it requires more throttle to disengage it. It basically took the rpms vs mph back to where the factory had it with the factory tire size. Just remember to change the speedo calibration to suit the new ratio so the ECU knows what speed you are doing.

Alright, thank you for the info. All the info on this site is incredible