THM375 info and opinions wanted

[delta881972]

so i fanally jacked up my 72 delta and verified that the trans is in fact a thm375.(375-THM in 1"tall letters on bottom face of tailhousing)
i would like to bounce the idea of keeping the th375 instead of upping to the th400 when i swap in the 455 in place of the stock 350 now in the car. its my understanding that other than being generally "beefier" the th400 has a steel support inside that the th350 doesnt? has anybody been inside the th375 and have any thoughts on its quality or durability and if it has this support inside?
also if anybody has any good links to 455 rebuild documents/sites and thm transmission rebuild sites PLEASE let me know as this project will be my first time inside olds running gear. good rebuild manual titles and authors for both the 455 and thm transmissions info would be fantastic.
my plans for the 455 ill be installing: EDL intake/carb, MSD ignition, cam, pistons, light work on my "J" heads, and headers and of course all the little upgrades to waterpump, oil pump, fuel pump, oil filter relocation, etc.
any other info needed to give me good advice just let me know! thanks everybody.

[jaysun]

The the 375 is basicly a th400 with a couple of differences.

First, externaly the th375 uses the smaller th350 sized output shaft, yoke and tailshaft

Second. Internaly the th375 has one less friction in the forward clutch pack and one less friction in the direct clutch pack. (4 each instead of 5) and the matching thicker apply pistons. It also has the late weaker roller ramp style direct drum (as do most 71 and latter 400s). instead of a sprag clutch. Depending on application the valve bodies and modulators will be sightly different.

The 375 and 400 center supports are identical, depending on year. However the later (68 i believe) supports are slightly thinner for a support to case snap ring to prevent beating up the spines in the case.

How to work with and modify the turbo hydramatic 400 transmission by ron sessions is an excellent book. the performance mods chapter is a little thin IMO.

This is good: http://www.hotrodders.com/forum/th40...cs-145318.html

I know hardly anything bout the internal workings of a th350 sorry.

Not a tranny expert, just know a few things. Im doing my first 400 build this spring

Jason

[delta881972]

thanks jason, some great info there the link to the th400 rebiuld info with pictures is awesome. i was hoping that a bunch of motorheads on here would chime in with all kinds of useful tidbits about the th375 but apparently there arent many here familiar with it

[jaysun]

I reread my post and realized i really didn't give any recommendations. i'd swap out the forward and direct pistons with the thinner 5 clutch pistons. I'd also get the smooth sprag direct drum and a 34 element sprag. A couple words of warning here. first either the piston or the direct drum needs to have a checkball to vent tranny fluid out. if not the directs will stal applied for some time. Second the sprag race does wear, so, buy one from a builder that can verify that it is good. I have no idea on the strengh of the output shaft or yoke. But the yoke looks to be the weak point. *might* be a good idea to get upgraded. From what i understand the stock tan bw clutches will handle up to 500 hp. Upgrade as needed after that. I can't give recommadations on brands, as i'm not a builder.

Keep in mind that your building for a heavy car.

/I'm not a tranny expert. just know a few things.

Jason

[delta881972]

if anybody else has any relevent info for me that would be great! this post has sat idle for a while now so....