HamadUP

I have that question in mind for a while, does the L88s that came with the M40 option have a different TH400 trans? .. I know for the 4 speeds it has to be M22 to withstand the extra HP and TQ, but what about the TH400? or did GM make a higher rated one for the 88s?

Ironcross

The T400 automatic was used in the first Chevy powered Funny cars with some slight tweaking modifying the shift patterns and a special converter....so there strong enough even supercharged and Nitro....I used a L88 with a T400 in a new 68 El Camino and currently have a LS7 454 in a 68 Camaro with its T 400 automatic and coupled with a good converter.... The engine nor trans know where there being used but are both very compatible together wherever you find them.....Vettes or whatever and basically stock,

Corey_68

Th400s are damn near bulletproof stock, no worries running a stock one for most builds.

HamadUP

Thats interesting, I should be really proud of my original '71 TH400 then!

bkvette3

As corey68 said - "BULLETPROOF". When I was looking for a big block '68 Vette, it had to have the TH400. No manual - tired of rowing gears all the time.

...Roger...

I agree they were very tough , I tortured one in my Suburban towing everything for 10 years.
They were a little too tough on the u-joints in early C3s.

Solid LT1

To answer your question YES the L-88 had a special THM400 transmission and the torque convertor had six bolts holding it to the flexplate compared to the normal 4 bolts used on most Chevrolets. The high HP 396 used the same transmission and 2nd generation Z28's also had a simular THM400. Full throttle shift points were reworked to happen over 6000PRM and there should be a tag on the side of the transmission with the correct code for it.

Never work on a L-88 auto but a good friend of mine used to own a L-89 aluminum head 69 Nova ss396 that was one SCARY FAST RIDE!

Here is a quick rundown stolen from the Chevelle forum:
1965-1975 Chevrolet Turbo 400 Identification Codes ......
Chevrolet)
transmission)
codes)-- engine sizes....(horsepower).....Chevrolet factory useage.......

CA)- 350,396,400,402...(145hp--325hp)...Chevrolet, Monte Carlo...
CB)-396,400,427,454....(180hp-345hp-390hp)....Chevrolet...police...
CC)-327,396................(xxxhp-325hp)........Chevelle, Camaro...police...
CD)-327,350,400,402,454...(215hp--330hp)...Chevrolet, Chevelle, Monte Carlo...
CE)-396......................(350hp)...Cheve lle, Camaro, Nova...
CF)-402,427,454..........(215hp-335hp-350hp)...Chevrolet, Chevelle, Monte Carlo...
CG)-396,454................(265hp--390hp)...Chevrolet, police...
CH)-396,427................(390hp)...Chevrol et...
CJ)-396,402.................(xxxhp--240hp)...Chevy Truck 10,20,30 series...
CK)-350......................(165hp--300hp)...Corvette...
CL)-427......................(400hp)...Corve tte...
CM)-307.....................(xxxhp)...Chevro let...
CP)-xxx......................(xxxhp)...Chevy Truck C-30 series...(no info)...
CQ)-427.....................(335hp)...Chevro let...
CR)-400,402,454.........(170hp--390hp)...Chevrolet, Monte Carlo, Chevelle, police...
CS)-454......................(245hp-360hp-365hp)...Corvette, Chevelle, Monte Carlo...
CT)-xxx.......................(xxxhp)...Chev y Truck C10 & C20 series...(no info)...
CW)-402.....................(375hp)...Chevel le, Camaro, Nova...
CX*)-396,427..............(375hp-425hp-430hp-435hp)...COPO...
......Chevrolet, Chevelle, Camaro, Corvette, Nova........... *high shift point...
CY*)-350,396,427,454...(245hp-375hp-425hp-430hp-435hp-450hp)...
......Chevrolet, Corvette, Chevelle, Camaro, Nova........... *high shift point...
CZ)-350......................(205hp--255hp)...Corvette...

LS7Vette

TH400 = Great Trans !!!!!!!

Peterbuilt

My tag was gone when I got it, where on the trany are these codes?

gbvette62

The 69 L-88 used a special TH400, that had a different shift points. This trans was also used was with the 69 435's, and the 71 LS-6. I don't know enough about 396/375's or Z28's, to say if they shared this particular trans.

For 1968, L-88s used the same TH400, as any other 68 427 engine.

The trans identification code is located on a plate on the right side of the trans case, just above the rear corner of the trans pan. This would be the only external identification of on the trans.

Rowdy Rat

The THM400 used behind the Corvette solid lifter engines in 1969 used a special "CY" code transmission. Word is that only 255 (I have a copy of the letter from GM) of these were installed in special high performance applications in 1969 (L-71/L-89/L-88).

Some good information in this thread:

http://www.yenko.net/ubbthreads/ubbt...599#Post102599

During 1969, the "CX" transmission was the special unit for the Camaros, Chevelles, etc. while the "CY" trans was the special unit for Corvettes.

Regards,

Stan Falenski

7T1vette

Certainly, the torque converter was much different than a stock unit. I'm betting that the bearings/bushings in that unit were significantly stronger than basic units and they had to be balanced much better in order to handle the increased RPM without vibrating or shaking apart.

If you have a THM-400 and want to run it behind a high powered engine, it should get a new torque converter that is designed to handle that load and also is well matched for the engine's peak RPM and torque.

Ironcross

This is exactly what GM used on the solid lifter engines {a special non stock converter} providing good idling characteristics when in gear and making it much easier on U-joints and the driver/owner

jr9170

Paul Borowski

...on the 1973 & up "broadcast sheet" or "tank sticker", it is noted right after the engine suffix, top line.

...the chart above is correct for my 1974's L-48 application, which is "CK", 165hp-300hp Corvette.

Tom73

Okay, we have two point of view.

So was it a different trans? To me haveing reprogramed shift points does not make for a different transmission. Was the gear sets, bearings, valves, etc the same or not?

The torque converter is a different issue.

tom...

7T1vette

Well, from an engineering point of view, there is no way you could just stick an internal component that rotates at engine rpm [or higher]...and designed for turning less than 6000 rpm...into a tranny behind an engine that could turn 7000 rpm and expect some of them not to blow apart. Surely some of the internal components (along with the torque converter) had to be balanced better--if not made of different materials.

That question is a good one, however, and it would be interesting to know the specifics of what was 'different'.

earthquake68

Same trans with slightly different stuff inside.

They had hardened steel input shafts and different spragues. The truck trans only had a 9 element sprague and the hotrod trans had, I think, 15 element sprague. They make 32 element spragues for racing purposes. Another difference was a case saver for the direct clutch assembly. That's a thin metal band that goes between the last steel and the aluminum case. This was a popular spot to break the case. (which I've done even with the case saver) I've built more than a few Th400's. I've also broke more than my share. Not bullet proof, but close. You really have to try to break a Th400. If you manage to do that with some regularity, then you need a Dedenbaer 'glide. They truly ARE bulletproof. I've seen a Th400 hold on to 1,200+ hp. and the aftermarket 'glide put down 2,500+ hp. Anything after that you need a direct drive pneumatic clutch.

So the 'Vette trans is the same only different. The biggest difference being the forward clutch assembly drum. (has the input shaft pressed into it and also it's where the sprague slips onto the back.) and the case was machined a little deeper so they could put a case saver in it.

A non-hotrod Th400 could easily be made into a hotrod version. I usually spend around $1,200 just for the parts to bulletproof a Th400. Not including the original cost of the trans. Then you have to buy a converter and a bellhousing so it's NHRA legal. Yes, in drag racing, we cut the bellhousing off and replace it with a 1" thick SFI approved unit.

TWINRAY