OK, first I have already done several searches here and elsewhere with no luck. I have a TH400-NP205 stock setup that came out of an 83 1 ton w/ 454 4x after buying the whole truck and gutting it I am now aware that the original TH400 case's top mount bolt hole on the bell housing is missing. I had planned on going through this tranny for my buggy build anyhow. So here's the question does anyone make a stronger aftermarket case housing? I have the HD case now and was wanting to know if there is a better unit available seeing how I really need to change cases anyhow. Thanks for any info. Shawn

The HD case is a little thicker around the bellhousing area and usually has a bolt on aluminum flexplate cover. There is also a possibility that is also has the straight cut planetaries in 1st gear (th475). Everything else is identical.

Yes, I realize I have an HD case. I want to know if there is any other cases made aftermarket that may be stronger yet than an HD case. Thanks Shawn

The HD/K case is not thicker in the bell housing itself. The only diff is in the inspection cover mounting flange where it is thicker and mounts the cover with 6 3/8 bolts instead of 4 sheet screws. I could find NO other differences, and I cut up the front of a "K" case th350 taking measurements along the way. I suppose it could be different for th400s, but I doubt it.

No, AFAIK, there is nothing stronger unless it's some obscure racing case, but I doubt it.

The only thing you can do is use a racing "blow proof" bell housing like the "Ultra Bell". I fooled around with one of those for a while and it was just too much trouble. It mounts with the pump bolts and the way it is supposed to seal seems basically impossible. Mine leaked no matter what I did. They are also made for the considerably smaller high-stall high rpm converters used in drag racing, so a typical converter will not fit. The propaganda said it should, but I wound up having to counter sink the mounting holes (for pump bolts) AND build an 0.93 shim to go between the bell housing and the engine. Now it sits on a shelf...

Sounds like a major pain in the a** but maybe I willl do some more research on this. I thought about cutting a mid plate (steeel 1/2" thick to mount on the outside of the case bolt holes and trying to tig an alum chunk back in place for the original hole. Thought maybe this would be a more inexpensive route than a new case. Any website links for the blow proof housing? Thanks Shawn

nevermind I found it http://www.racewithjw.com/index.html

I know nothing of a TH475 but if you know anything of how an automatic transmission actually works, the idea that "1st gear gets straight cut planetary gears" is mildy retarded. All gears go through the same planetary set...

Not sure why he replied as it had nothing to do with what I was asking about?


I know nothing of a TH475 but if you know anything of how an automatic transmission actually works, the idea that "1st gear gets straight cut planetary gears" is mildy retarded. All gears go through the same planetary set...

The tie in is that the t475 is the strongest of the factory hydramatics. The reason is that the gearsets are straight cut as opposed the typical helical cut. This elimates or reduces load on the thrust washers and decreasing chances of failure I will infer that he telling you to find one of these as it may have a stronger case. (false) This transmission seems to be fairly rare and was offered primarily in the p30 chassis. Apparently they were put into alot of buses, as well and there may be some Caddys with them but I suspect people are confusing this with the th425 from front drive Toranados, Eldarados and its ilk. These would be step vans and motor homes. An identification point would be the drum e-brake on the tail.

Thanks for the clarification, Shawn


The tie in is that the t475 is the strongest of the factory hydramatics. The reason is that the gearsets are straight cut as opposed the typical helical cut. This elimates or reduces load on the thrust washers and decreasing chances of failure I will infer that he telling you to find one of these as it may have a stronger case. (false) This transmission seems to be fairly rare and was offered primarily in the p30 chassis. Apparently they were put into alot of buses, as well and there may be some Caddys with them but I suspect people are confusing this with the th425 from front drive Toranados, Eldarados and its ilk. These would be step vans and motor homes. An identification point would be the drum e-brake on the tail.

I am going to recommend the "Ultrabell"
But, after reading the thread,I now remember the problems that BadDog mentioned. I got mine to seal up without problems, and now remember having to re-counterbore a few (all?) holes, and something about shim distance. :confused: sorry, its been too long ago when I did mine.

Bottom line.... you'd think/expect it to go right together for the $ you pay. it does not.BUT for the beef and strength, and the ability to buy ANY TH400 and use them, I still recommend it. (just don't plan on tossing it together in an afternoon)

*I run across BOP TH400's 10 to 1 on the overpriced chevy patterned ones,

Using the little pump bolts going into tapped aluminum to hold the case together as the Ultrabell does just never sounded like a good idea to me - though I am surprised I haven't busted a T400 case yet.

Back the the P-30 chassis TH-400's with the integrated cast aluminum inspection cover/oil pan. When I purchased my 4BT's they had these TH-400's with an adjustable bolt in place of the vacuum modulator. It looked pretty beefy to me but I am not sure on the helical/straight cut gears or first gear ratio's either. I think that the fellow at the yard mentioned they had different bellhousings available, Chevy, BOP, and another one which I forgot...

I think that the fellow at the yard mentioned they had different bellhousings available, Chevy, BOP, and another one which I forgot...



Jeep/AMC