Building a TH350 automatic for rockcrawling

[Greg]

I just thought I'd document my build of a TH350 that's going to be used for wheelin. I'm going to be running a 2003 GM 5.3l V8, TH350 and a 4.3 Atlas in a TJ Wrangler. I have never had good luck with auto trannys from the muscle car days and have been reluctant to wheel anything with an auto, but I'm determined to give them a try due to how much more enjoyable an auto seems to make off-roading.

I found a local guy that had been rebuilding TH350 for longer than I've been around, he knows how to build them right & has a ton of experience building GM autos for racing applications. He told me which rebuild kit he liked, so I picked up that one. I added a Manual Valve body with engine braking in 1st & 2nd gear. This will be very helpful on the steep descents.

Here's a list of the parts & (part #'s) I've compiled, places you can get them and approx. price. Keep in mind these part#'s and prices are for a TH350 & will be different for a TH400 or other auto.



TCI Manual Valve Body with Engine Braking
From - Summit Racing
Part# - 321001
Price - $195

High Performance Rebuild Kit
From - Northern Auto Parts
Part# - TH350HP
Price - $109

TH350 Aluminum Deep Tranny Pan, 2 quarts extra
From - Summit Racing
Part# - SME-1000R
Price - $103

Summit Racing brand Torque Converter, TH350, 12", 2000 RPM Stall
From - Summit Racing
Part# - SUM-G2702
Price - $119.95



I plan to run an aftermarket torque converter with a stall range of around 1800-2000 RPM. I've done a lot of reading & it seems that the jury is still out regarding how a deep crawl ratio is affected by the stall speed of a torque converter and tire size. I don't want to be driving thru the brakes, but I also don't want the engine screaming when I'm driving in high range. I'll be running 5.13 gears with 40" tires and the 4.3 reduction of the Atlas. That's going to be a pretty steep crawl ratio, but we'll see how it all works out once it's together. If 1st gear is too low for certain obstacles, the full manual valve body will allow me to start out in 2nd gear for a higher ratio, allowing a good bump & wheel spin if needed.

Additionally, I'm going to run some kind of external oil cooler to further reduce the temp of the tranny fluid. I do want to run the fluid thru the cooler in the radiator too, which between that, the external cooler & the deep transmission pan I doubt I'll have heating trouble from the transmission.

I wanted to be there during the transmission rebuild so I could document the process, but I'm going to be working out of town during that time. So the next pics may just be a shiny rebuilt transmission. I'll add more as the build progresses.

Here's some pics of the components going into the TH350.-

 

[spaggyroe]

Awesome Greg!

I'll be keeping an eye on this thread, as I need a similarly built TH400 for my project.


Thanks. :greg:

 

[Meat_]

Ask Timp what stall he has in his TH400, he drives through the brakes just a tiny bit while in low low in his 4spd Atlas but he has plenty of brakes for the other gears. He has a 5.3 vortec, 39.5's and IIRC he has 5.13's

 

[Jinx]

Greg,
Something to think about: Some guys like the reverse manual valve body. It makes that quick shift from first to reverse really easy in case you need to save a roll.

I am a big believer in the remote cooler thing, cooked atf leaves you sitting on the trail... plus more fluid capacity...

Good luck on your build,

PS if this thing going to see much road time? vs road time, that might determine some things also...

 

[Greg]

Greg,
Something to think about: Some guys like the reverse manual valve body. It makes that quick shift from first to reverse really easy in case you need to save a roll.

I am a big believer in the remote cooler thing, cooked atf leaves you sitting on the trail... plus more fluid capacity...

Good luck on your build,

PS if this thing going to see much road time? vs road time, that might determine some things also...

I decided against the reverse manual VB because I'll probably be in Drive most of the time anyhow. Reverse isn't far! I think the only time I'll be shifting out of Drive will be to bump up something in 2nd gear, perhaps 1st for the really deep gearing.

It'll see very little road time, I do want to take it to the mountains above Ouray & Silverton and driving to the trail head of 21 Road is always fun. I went with a TH350 over a transmission w/ overdrive because I doubt I'll be running highway speeds often with 40" tires, 5.13 gears & full hyd steering. Less parts to break too.

 

[yellowbronco]

I love how thorough you are Greg, all the part #'s, pics of them too. Could you build up a C6 so I can ride on your coat tails?

 

[Greg]

I love how thorough you are Greg, all the part #'s, pics of them too. Could you build up a C6 so I can ride on your coat tails?

Nah, you can follow my lead for your C6 build.

 

[Greg]

Well, not much tech to add at this point. The transmission was assembled while I was away working, but my builder said everything went well. He also mentioned that with the manual valve body & the instructions that guided him in the rebuild, this transmission was going to be fully manual, which is just what I wanted. He also removed a O-ring in the transmission which will speed up the 2-3 shift.

Here's the rebuilt transmission-