I have a 25' 1985 Regal with a GM 454. I assume I have the Turbo 400 transmission. Can someone confirm this for me or tell me how I can identify the transmission? Thanks for your help.

It is almost certainly a TH400 variant. Actually, many motorhomes have the 475 version which is identical externally but has stronger straight cut gears rather than the standard angular gears in the TH400.

You can tell by the shape of the oil pan. Here's a posting on that.

https://www.barthmobile.com/eve...1087061/m/5943946077

here some info on turbo hydromatic

Steve, I read your post with pics about the installation of the new oil temp sending unit. Are you saying that if my oil pan looks like yours, its a 475? I'll take pics and post
Jim

The shape of the oil pan will show if it is a TH350 or 400. (I don't think they put 350s in motorhomes but maybe in the class C ones...)

Unfortunately, it is impossible to tell from the outside if the TH400 has the straight cut planetary gears. If they were installed in the heavy duty TH400 transmissions they are sometimes referred to as the 475 model (or 3L80HD)

You might be able confirm this with a serial# and the right wizard at Hydramatic, otherwise a teardown is the only way. Chances are, the Pee chassis had the 475 from the factory, if you have the original tranny.

At rebuild time any good trans shop can put in the HD gears into any TH400 to beef it up.

quote:

Originally posted by Steve VW:

Unfortunately, it is impossible to tell from the outside if the TH400 has the straight cut planetary gears. If they were installed in the heavy duty TH400 transmissions they are sometimes referred to as the 475 model (or 3L80HD)

You might be able confirm this with a serial# and the right wizard at Hydramatic, otherwise a teardown is the only way. Chances are, the Pee chassis had the 475 from the factory, if you have the original tranny.

At rebuild time any good trans shop can put in the HD gears into any TH400 to beef it up.

I believe the brake on the tailshaft indicates straight cut gears. The few I have broken down were that way. I have not broken down a P30 tranny without the drum brake, so not sure on that.

You can hear them, too.

My understanding is that the straight cut gears were to address an end thrust issue, not a strength issue. Many, many beefed-up TH400s use the helical gears with no problems. They use a roller bearing to take the hi torque end thrust.

Jake's Performance, for example, uses billet input shaft, forward hub, intermediate shaft, 36 element sprag super drum, Griner transbrake, deep pan, 6 clutch direct, 5 clutch forward, 4 clutch intermediate, rollerized, but still uses helical gears.

Jake says straight cut gears are in fact weaker than helical and don't lubricate as well. They use them only in very heavy applications where we want to eliminate thrust loading from the helical gears.

His opinion is shared by many other builders, including my guy.

posted this on another question~~~~

http://www.4btswaps.com/forum/...nd-swap-guide-thread

read down---it gets into some depth