TH400

[MudSlinger79]

I was wondering how well will a th400 stand up to a cummins?

[pulltilbroke]

Better than a 727

[Richie O]

My uncle has a hot rod p/u with a big block chevy that has run 158 mph in the 1/4. It has a built 400 turbo. I think they are a strong tranny. I know the Big block does not have the torque that the diesels can have but 158 mph in the 1/4 is a strong truck and the power and torque must be pretty high. I know I have a 90 3/4 ton chevy with the 3 speed 400 and it has over 200,000 miles. It has survived my abuse as well as a teenage boy that owned it before me. Wide open nuetral drops, 50 mph then dropped into reverse.

[Raymo]

I have a 400 from my mud truck that had 220,000 on it, I put a manual valve body on it and a 3200 stall converter and it held strong for 4 more years with my 39.5's and temps in the 260 range lmao, still works, just leaks a bit...

[MMiller]

Do you believe anybody makes a tough enough convertor with a low stall to go behind the cummins? I know there is tons of 2000-to probably 8000 rpm stall convertors for gas applications, but does anybody make a 1400-1500 rpm stall convertor that will take the 4-5-600 ft lbs of torque at that rpm for a th400?

Then, if they do, are the shafts tough enough to take that abuse? I know that there is support for the 727/518/47rh, for this application.

I guess these are the questions in my mind, the cummins grunt will show weak links much quicker then any big block chevy will.

Michael

[SChandler]

I agree with MMiller. The thing with a TH400 is that they were never set up internally to operate at the rpm's that a Cummins operates at. When I looked into what it would take to swap a Cummins into my dad's 93 Chevy, the amount of work required to make the 4L80E trans (essentially a TH400 with overdrive and electronic controls) live behind the Cummins made the prospect of an A518 swap at the same time much more manageable. And that was with a diesel application 4L80E. A diesel application 727 is only going to need a good converter and maybe a shift kit to survive. The TH400 will need a complete overhaul and a custom converter before it will be happy behind a Cummins. There is a guy on Comp Diesel using a TH400 in his drag truck (mid 80's Chevy short bed), but that is in a high rpm, P7100 motor in a relatively light weight truck.

[pulltilbroke]

What about a TH400 that was behind a 4bt in bread trucks

[BobS]

What about a TH400 that was behind a 4bt in bread trucks

Those were TH475's. They were not equipped with a vacuum modulator. If you ever looked through the Dovebid website during an auction you will find a very high percentage of vans listed with bad transmissions. The 4BT that came in these 6700 pound vans (with 32" tires & 4.10 axles) usually had engines rated in the 275 - 300 ft/bt ranges at 1800 RPM's. They used a "wavy ring spacer" that bolted between the flexplate and the torque converter. This spacer seems to have two problems; it cracks and in doing so it causes the front seal to fail. The TH400 is a good transmission but the major obstacle to overcome is getting it to handle the high torque that the Cummins starts to produce around 1200 RPM's. There are some folks who are running them but the dollars to build one might be better spent on rebuilding a 47RH. The newer stepvans with the intercooled 4BT had Allison non overdrive transmissions which was how they eliminated the TH475 problem.