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th400 for offroad racing

4K views 13 replies 6 participants last post by  6T6mustang 
#1 ·
so, lately I have been doing a few ultra 4 ls engines for some friends and customers and was approached about building a th400. my background is in c4/c6 trans and have only done a few th350's,e40d, 4r100, a4ld's etc...
these are 5-6k lb. tube buggies racing on 40" tires with 500-700 hp in 4x4 under fairly brutal conditions. he has been killing a trans about every other race so far. the last unit had some oversize sprags and I believe a 4l straight gearset with a pressed input and was doing better, about 3 races till failure, he says it has a tad of bronze in the pan.
I would like to help him out but need to do some research on what it takes to make one live in the desert before I feel right about selling someone one. pretty sure I can make one live more than a race but if you guys have any thoughts about parts selection or lube mods, tricks, etc.
I still need to get the trans to my shop and see what is causing his failures, but want to feel like I can actually do more than toss some clutches in it... thanx
 
#3 ·
He has been told by many people that no one can build a th400 to live over a thousand hp. I said shit, c4's can handle it for a couple passes but the desert is a different animal. There are some stupid expensive setups out there but these guys aren't gonna buy a 18k culhane trans. Most run a th400 or a 4l60/80, trans temps regularly run 250+ degrees, sometimes 300+. My initial thoughts are backlash/jarring and fluid temp may be the areas of concern..
 
#6 ·
I have found that Engine Braking in 2nd and stabilising the Direct Drum on the Sun Gear Shaft helps the Intermediate Sprag survive.
The energy stored in the Drive Train tends to hammer the Intermediate Sprag around during de- acceleration, landing after jumps etc.
Obviously Oil Cooling is important along with correct Cooler Flow/ Pressure.
Also don't overlook the Installation.
Ideally the Transmission should attach to the Engine Mid Plate and be soft mounted at the rear.
Transmissions are designed to twist not bend.
 
#7 ·
I have been building Offroad transmissions and converters for more than 15 years. Ultra4 is a little different only in the sense that the trucks are relatively short wheel base. The components needed to successfully build these transmissions do exist and they must be correctly sourced. Gear ratio plays into the setup big time. The converter is also an area of major concern. Feel free to call anytime for help, recommendations or advice. There are so many things that must be considered, space and time does not allow, nor does a keyboard give us the correct communication format...
 
#8 ·
I highly recommend you get a hold of Gordon Stoney at Stoney Automotive. Ex Hydramatic lead engineer. He has been involved in the off road racing trans game for a long time. Great guy to deal with.
 
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