transmission

[Devil Pup]

I have a TH350 behind a 5.7 350 right now with 4/10 in the rear i think. when I'm on the freeway or even on the roads "live in AZ the speed limits are about freeway every where you go." it seems my truck is whining out the 3rd gear that the TH350 has to offer. i was curious if i put a 700R4 in it would this help a lot? I seem to have a lot of motor problems and I'm wondering if it could be due to all the high RPM's all the time. . . Thanks guys

[TheSeeker]

Dont drive so fast.

[cdowns]

yes the overdrive tranny will make a world of difference// but you need a solid base engine in proper tune

[LMN8UR]

Wouldn't it be cheaper to ditch the 4.10:1 for a 3.43:1?

With 255-70-R15 and the 4.10 the 60 mph rpm should be 2847. and with 3.43 that would drop to 2382.

Popular rears (RPM at 60) (255/70-15) ==>

With 1:1 top gear
Ratio - RPM
2.76 - 1916
3.08 - 2139
3.43 - 2382
3.73 - 2590
4.10 - 2847

With 0.7:1 overdrive
Ratio - RPM
2.76 - 1341
3.08 - 1497
3.43 - 1667
3.73 - 1813
4.10 - 1993

Dropping engine RPM will extend engine life and increase MPG (As a rule).

[71meangreenc10]

Just coming from AZ I loved the highway speeds of 75+ (miss it here in 55 land)....... I would can the 4.10's and go with either 3.08's or 3.54's. You may not have to change the carrier from 4.10 to 3.54 but I am not sure about the 3.08's if it will fit. That would be a cheaper option than the trans swap, just make sure to fix the speedo drive if you do it.


Smitty

[Devil Pup]

ok. first off. how can i not drive so fast if the traffic is goin that fast? lol

how hard is it to change the gears in the rear? how long does it take and any idea on how much that runs?

[Wrenchbender Ret]

There are plenty of salvage rear ends for these trucks & many of them are 3.08 gears. I would find a used rear end & change the whole thing. I run 3.08 gears in mine with a 700R4 trans. You cruise along & don't hear the engine at all.

[Devil Pup]

thats exactly what i want. but do you still have the git up and go at the start?

[Wrenchbender Ret]

The 700r4 has a low first gear. It will jump right out. If I get on a real long hill on the interstate with a head wind & the A/C on I have to down shift to third but it still is not winding too high.

[Longhorn Man]

is your truck a 10 or 20 series?

[Devil Pup]

its a C20

[Bullfloat]

Originally Posted by Wrenchbender Ret

There are plenty of salvage rear ends for these trucks & many of them are 3.08 gears. I would find a used rear end & change the whole thing. I run 3.08 gears in mine with a 700R4 trans. You cruise along & don't hear the engine at all.

Thank you, thank you, thank you. I have spent the better part of 2 hours trying to find out this type of information.

I have a 68 c-10 with a 3-on-the-tree saginaw with a rebuilt 350 from a 78 Chevy. I assume that I have the 4.11 rear diff or higher. (can't read the ratio code on the housing). I would like to keep the 3 speed, and switch to a floor shift (still researching what part I need to buy), but didn't know what gear ratio to use. Are there any problems I should be aware of when converting to a 3.08 rear diff? besides the fact I will have to switch to a 5 lug rim? Are there connection issues (emergency/parking brake) ?
I don't plan on doing any hauling or towing with the 68.

Thank you again.

p.s. sorry if I have hijack this thread, just got really excited when I seen this info.

[Longhorn Man]

on a c/20, gears are limited without some seriouse work.
Assuming coils since they were standard, you can get a 4.57 or a 4.10 gear. You can get a 5.13... but that's in the wrong direction.
You can try and locate a dana rear out of a big block truck. It would have a 3.54 gear unless optioned otherwise.
That is it for easy work.
Anything else, and you'll need to get a rear end (14 bolt is easy to locate and has many ratios avalible both stock and aftermarket) and then weld on the correct mounts for coils.

If you have leafs, then it's a little easier, but mods are still needed for 99% of the rears you will find.