[jfranco]

Hi,

This is the transmission tag I was sent that is connected to a 454 from an 1980s RV.
Anyone able to tell me what this is, or do I need to have him look for something stamped on the case?

Thanks!

 

[Paulz]

Big block Chev in the 1980s, it's more than likely a TH400. Got a picture of the trans pan?

 

[jfranco]

Was able to get a picture of the pan, looks to be a Th400.

 

[stuarta]

Could have straight cut planetary gears.

 

[jfranco]

Could have straight cut planetary gears.

Is that a good thing or a bad thing? Anyway to tell without opening it up?

 

[ericnova72]

Is that a good thing or a bad thing? Anyway to tell without opening it up?

Good thing if you are after ultimate strength and durability.....bad thing if you want it quiet, straight cut gears tend to whine or howl/whistle.....sounds like a school bus in low gear. (LOL).

Other than finding someone who has a code list for the side tag I think the only way to know the innards is disassembly.

Does it have a deep pan on it?

 

[jfranco]

Good thing if you are after ultimate strength and durability.....bad thing if you want it quiet, straight cut gears tend to whine or howl/whistle.....sounds like a school bus in low gear. (LOL).

Other than finding someone who has a code list for the side tag I think the only way to know the innards is disassembly.

Does it have a deep pan on it?

Thanks. No, pan looks shallow.

 

[KirkM!chapman]

If the out put shaft is the same as a turb 350 it is a 375 which is turbo 400 with small out put shaft, is no doubt that it is a turbo 400, the other question is if it has the staright gears if it does then it was built for RV, buses, and so on ,

 

[smokeyfan1000]

If it's GM factory trans behind a 454 it should be/I would believe it'd be... a Turbo Hydro 425. Was only used with 454s The 396/402s got the TH 400 And the 425 will have extra clutch plate (/s?) than a TH400. But that was 1970s. ?

 

[KirkM!chapman]

Smokey you are correct 💯 my opinion was based on 1980 RV but this day in time who knows😅Ihave 425 in 1990 service truck

 

[Crosley]

Smokey you are correct 💯 my opinion was based on 1980 RV but this day in time who knows😅Ihave 425 in 1990 service truck

The T-425 is a FWD transaxle... You may be thinking about a T-475 transmission which was used in many motorhome applications.

 

[KirkM!chapman]

Lol 🤣 your right 475 I should have been watching what my fingers were doing, thinking one thing in typed another.

 

[smokeyfan1000]

Smokey you are correct 💯 my opinion was based on 1980 RV but this day in time who knows😅Ihave 425 in 1990 service truck

I once worked for athe city I lived in. They had a large truck ('brick truck") we used to build manholes with. It was new and this was in late 70s to early 80s IIRC That truck had a 4 spd (or was it a 5 spd? can't remember) automatic trans but I never knew what GM named it. It was a heavy duty auto trans too. Maybe this guy's trans is one of those??

 

[farna]

Probably an Allison auto in a heavy truck. Allison is owned by GM.

 

[predator carb guru]

I once worked for athe city I lived in. They had a large truck ('brick truck") we used to build manholes with. It was new and this was in late 70s to early 80s IIRC That truck had a 4 spd (or was it a 5 spd? can't remember) automatic trans but I never knew what GM named it. It was a heavy duty auto trans too. Maybe this guy's trans is one of those??

TH400's are three speeds only. As stated, likely an Allison.

 

[jfranco]

Thanks guys.
I have the transmission now, here are a few other pictures if it helps any.

 

[ericnova72]

That should be the TH-475, with the straight-cut planetary gearset.
It has the big chassis truck driveline brake assembly provision at the output end of the trans....that 4 bolt pattern matches a brake backing plate and there was a special yoke with a brake drum on it to lock the driveshaft as a parking brake.

You'll have to do some changing of the tailshaft housing and yoke, seal, etc for regular car or truck use. I've done it once, many years ago. Worst part of the whole deal is you have to completely disassemble the trans to do it, since you have the swap the output shaft so it will accept a slip yoke. The output shaft is last part coming out, first part going back in during a rebuild.. LOL

Might be a damn good transmission needing nothing more than a re-seal and soft parts kit along with a shift kit.

 

[Crosley]

Open the trans up... See what planet design is in it. If it was rebuilt over the decades and the planets may have been replaced? I like a set of helical cut gear planets with a torrington bearing between them for a HD or High HP application.