TH 400 differences between sbc and bb

[Steven B.]

What are the specific differences between the TH400 behind a small block and a big block?

[Joe L.]

Re: TH 400 differences between sbc and bb

What are the specific differences between the TH400 behind a small block and a big block?

Steve------


1) torque converter

2) governor assembly

3) control valve assembly (in some cases, the valve is the same between big block and small block)

[Terry M.]

Re: TH 400 differences between sbc and bb

What are the specific differences between the TH400 behind a small block and a big block?

Be careful. There was a BB 400 and the REALLY BIG, BIG BLOCK (CY) TH 400. The CY has other differences than those noted above. I don't think you were referring to the CY trans in your question, but I just wanted to point out there is more to the story.

[Joe L.]

Re: TH 400 differences between sbc and bb

Be careful. There was a BB 400 and the REALLY BIG, BIG BLOCK (CY) TH 400. The CY has other differences than those noted above. I don't think you were referring to the CY trans in your question, but I just wanted to point out there is more to the story.

Terry------


The differences for the "CY" THM-400 involved exactly the same components I described above. Basically, there were three sets of these components----one set for THM with small block, one set for THM with big block except SHP or HD and one set for big block with SHP or HD (i.e. "CY" coded trans).

[Michael H.]

Re: TH 400 differences between sbc and bb

Be careful. There was a BB 400 and the REALLY BIG, BIG BLOCK (CY) TH 400. The CY has other differences than those noted above. I don't think you were referring to the CY trans in your question, but I just wanted to point out there is more to the story.

Terry

In addition to the items mentioned above, there are also quite a few differences in clutch plate/wave plate/release spring count and clutch drum pistons for various transmission/engine applications.

Some have wave steel clutch plates while others have flat plates for a firmer shift. The count also increases for some with larger engines or more perf. For example, a standard small block may have four or five steel wave plates while others, like the CY units, have six flat steel plates. (and composition plates)
There's an almost endless variety of combinations of wave/flat plates for all the transmission codes/applications.

Some units have a different clutch release spring count too. Some have three springs and others have twelve.

There may be a different accumulator spring also. A stiffer spring for HD units results in a firmer shift.

I have the charts here somewhere that show the correct combination of steel/friction plates, with part numbers, for all TH400 units from 1964 through about 1973.

[Terry M.]

Re: TH 400 differences between sbc and bb

I know Mike. Back when I was going to school we had the books for rebuilding the TH400 that listed the proper springs (by number and color) and plates. It also had nice colored fold out oil flow diagrams. I wish I had the eyes roll emoticon now for those diagrams. Like you I think I still have one of those books someplace, but I haven't had to deal with a TH400 since I sold the Orange Suburban. Now days it is only us gray haired guys who know about them.

BTW: I remember a story about the CY transmission in The Restorer some time ago. It illustrated a number of the unique features of that example. It was the automatic equivalent of the M22.

[Michael H.]

Re: TH 400 differences between sbc and bb

I know Mike. Back when I was going to school we had the books for rebuilding the TH400 that listed the proper springs (by number and color) and plates. It also had nice colored fold out oil flow diagrams. I wish I had the eyes roll emoticon now for those diagrams. Like you I think I still have one of those books someplace, but I haven't had to deal with a TH400 since I sold the Orange Suburban. Now days it is only us gray haired guys who know about them.

BTW: I remember a story about the CY transmission in The Restorer some time ago. It illustrated a number of the unique features of that example. It was the automatic equivalent of the M22.

Terry

I just found the GM book from the Hydra-Matic div. on the TH400. Lot of good info that I forgot was in there.

There are three pages on the various clutch disc count for all transmissions from 64-73. All are listed by transmission code.

I can scan and post if anyone is interested.

I've forgotten the application for the CY unit. Was that used with L88 in 69?

[Ray K.]

Re: TH 400 differences between sbc and bb

Michael,

Yes, the "CY" transmission was used with '69 L-88, L-89, L-71, and the Camaro / Chevelle / Nova 396 /375 HP .

[Terry M.]

Re: TH 400 differences between sbc and bb

Michael,

Yes, the "CY" transmission was used with '69 L-88, L-89, L-71, and the Camaro / Chevelle / Nova 396 /375 HP .

Also used with the 1971 Corvette LS6.

[Terry M.]

Re: TH 400 differences between sbc and bb

Is that the green covered book Mike?

[Michael H.]

Re: TH 400 differences between sbc and bb

Is that the green covered book Mike?

Terry

Yes, called "Systematic Trouble Shooting". Distributed by "Service Department, Hydra-matic Div., General Motors".

It has a cutaway drawing of a TH400 on the cover.

[Terry M.]

Re: TH 400 differences between sbc and bb

Terry

Yes, called "Systematic Trouble Shooting". Distributed by "Service Department, Hydra-matic Div., General Motors".

It has a cutaway drawing of a TH400 on the cover.

Yes that is what we used in school. I have it around here someplace.

[Steven B.]

Re: TH 400 differences between sbc and bb

Terry

I just found the GM book from the Hydra-Matic div. on the TH400. Lot of good info that I forgot was in there.

There are three pages on the various clutch disc count for all transmissions from 64-73. All are listed by transmission code.

I can scan and post if anyone is interested.

I've forgotten the application for the CY unit. Was that used with L88 in 69?

Michael, very interested. Thanks! Steve

[Mike E.]

Re: TH 400 differences between sbc and bb

Corvette Mike in CA has had a 69 L88 automatic for sale for some time. I don't know if its real or not...I think it's priced at over half million dollars.

http://corvettemike.com/used-corvettes-for-sale/1969-Corvette-L88-Convertible-1875

Mike

[Gary R.]

Re: TH 400 differences between sbc and bb

$500,000 sounds like a deal. I took my 72's original TH400 and installed a earlier drum and higher element sprag, made the mods to the pump, valve body along with the full street/strip tricks and put in a mild 2000 stall convertor and run it all the time. It is overkill for the hp level of the car but it will hold up to a lot of abuse if I ever choose to drop in another engine with 500-600hp, I doubt it though. I would certainly consider $500,000 for it and will throw in the complete car, heck for a fellow vette owner I'll build a 12 bolt diff conversion for it just case you want to drop in that 600hp engine.