vetternr

Does anyone have any good information on what to upgrade a stock 1972 Corvette B.B. from a Turbo Hydramatic 400 auto trans to something newer like a 700R4 or newer ? Also, is there any market to sell used ( good ) Turbo 400 trans ?

Al

Douglas Mariani

There's plenty of information out there for the 700R4 conversion. Mine was done 25 years ago on my 80. And yes there is a market for a Turbo 400 transmission

ajrothm

A 200R4 will bolt right in place of the T400. Just need a different slip yoke. Look at Bowtie Over Drives for the conversion stuff.. If its a basically stock 454, a mildly built 200R4 will work fine. The car will be quicker, more efficient and more pleasurable to drive. If you plan on serious power mods down the road, then the trans situation will get real expensive, real quick.

DC3

Check out SST's A41 kit with a 4L60E. Comes with everything you need for the conversion including new shorter driveshaft, new cross member, shifter conversion parts, electronic controller, ATF, etc.

Here's the link: https://shiftsst.com/blog/post/1968-...ctfit-kit.html

I just received my kit to replace my TH400.

DC

7T1vette

200-4R is easier to swap into a 68-74 car than the 700-R4. But the latter one is more available. If you have a GOOD transmission rebuild/repair show in your area, they might give you some decent credit on a swap for a rebuilt unit that you want. You'll just have to check on that. The 400 is pretty 'bullet-proof'; if you unit isn't damaged, it would have some trade value, I would think.

The 200 will fit right into the existing space envelope using the stock cross-member and driveshaft. If you go with the 700, you will have to modify your D/S or purchase another one and replace [or modify] the cross-member. Your shift and lockout cables will work with the new unit, but you will need to modify the brackets for them to compensate for the different mounting bolt locations on the 'new' pan bolts. Or you can purchase the correct brackets for that trans.

Either unit uses a TV cable for modulating the shift firmness (instead of a vacuum modulator like the 400). It would be BEST to have that local tranny shop do the hookup and adjustment on this, rather than DIY....but you CAN do it, if you are 'savvy' and can follow directions.

To get the advantage of locking in all 4 forward ranges, you need to modify the little shift detent plate (on the side of the shifter in trans. tunnel). Not a tough job, but a bit challenging. Or you can leave things as they are in your car and just put it in Drive and have at it. You can still lock it in gear for 2nd, 3rd, and Drive...but not in 1st, without modifying that shift detent plate.

It is important {IMO} that you purchase and install a lockup clutch controller for that function in the 'new' trans. Lockup is where you save a LOT of fuel and make the trans a much more efficient system. If you don't have a controller unit, you can EASILY screw up the converter by MIS-using / abusing it. The L/U clutch is not meant to absorb much loading...only used in low torque, steady-state operation. Stock systems automatically drop out of L/U when the throttle is increased significantly.

Hope this helps you with your planning. Doing this is a GREAT improvement: lots quieter in the cabin on highway runs, MUCH better fuel mileage (20% +/-), MUCH easier on the engine, etc.

caskiguy

I asked myself and some professionals the same question. I have a 1970 Coupe and after much deliberation I chose to rebuild & beef up my TH400 (which I own) rather than go with the expense of an Overdrive unit. A lot of arguments each way but I'm happy with my choice as the TH400 is a very strong transmission and it will perform just fine.
Money saved vs miles driven and such ? Meh.

7T1vette

Unless you have BRUTUS under the hood, the stock THM-400 doesn't need to be "upgraded". It may need a rebuild because of wear/tear and/or age....and a different torque converter to better match engine/drivetrain and converter stall choice, but they were VERY stout as they came from Hydra-Matic when new.

LenWoodruff

I would like to update to and overdrive trans. I have cruise so I what to keep the speedometer cable so that will still function.

DC3

The SST kit I linked above comes standard with a custom tail shaft set up to drive a mechanical speedometer cable. I saved a few bucks by going with the standard electronic tail shaft since I've converted my speedometer to an Autometer electronic option.


DC

LenWoodruff

I thought the SST kit was a manual not an automatic?

DC3

They offer two manual options and one automatic option. Go to the link and click on the A41 tab.

DC

LenWoodruff

Thanks for the clarification.