Is There Any Problems With Swapping A Th350 With An Th400 On A79 Vette Frameing .if Anybody Could Let Me Know It Would Be Appreciated Before I Dismantle Every Thing .im A New Member And I Restored My 79 And My Friend Gave Me A Redone Th400 After The Fact As Per Usual . Too Ge My Highway R.p.m. Down

 

Both the 350 and the 400 have 1:1 drive ratio, so changing to the 400 will do nothing to drop the engine RPM on the highway.

 

Ya gotta move to a 200 4R or a 700 R4 if you want an automatic with overdrive to reduce the RPM's.

 

2004R is the way to go, gets a better over all gear ratio and it has overdrive.

 

THANKS TO ALL / SOUNDS GOOD

 

The THM400 tranny is a much stronger trans than the 350 unit...but I don't know that you need more strength than the 350 [for the stock engine]. But the 400 also is a HP 'waster'...not very efficient. An overdrive tranny is a much better replacement for your 350..but it will cost a good piece of change. If your 350 is well worn and the 400 is fresh (and not much money), the 400 will be a nice unit for you. If you plan on doing much highway driving, the 200R4 will eventually pay for itself in the saved gas money.

 

OP, all the above comments are correct, and if you restored the car doing most of the work yourself, you CAN....with some reading, and a bit of study ....rebuild your own 200 4r tranny and it's damn near a bolt in swap for the 350, unless you have a super HP engine, it will last fine, as I did my own which is in the '72 vert here for some 3 years now....runs like a charm.....

PM me or 6'er Danny for the lo down on how to build one, and what/where to read.....not as hard as it looks, seriously....

you can get it done for 5-600 bux or so, maybe less....

 

my 350 is leaking like anything the 400 was givin to me thats my i would like to know if there is any major modification that needs to be done and im running about 435hp i was told it was a stronger tranny

 

The 400 would be better than the 350 for your application. However, if you want reliability, you should do a good rebuild on the 400 or purchase a beefed-up 700R4 to manage that much HP. If you don't intend on going WOT all that much, the 400 should do fine....if it is in good condition.

 

To answer your original question, to swap the 400 in where the 350 is now, you will need to measure the over all length of the 350 and the 400. this will tell you if you need to adjust the driveshaft length. The 400 should bolt in on top of the existing crossmember. It will use the holes bolting in the 350 tranny bracket. You will need to obtain the 400 tranny yoke for the corvette. The standard "press in the universal joint syyle" wil not work and the 350 yoke will not fit the 400. This will most likely be your biggest expense. The shifter will work and so should the interlock if it is still there. I am not sure about the speedo gear in the tranny. You may need to use the one from the 350 to get everything reading right.

 

thanks alot .ihave the 400 yoke