I will be doing the swap and was wondering if anyone here has done it? It would be good if someone could sketch out the cross-member modification. I plan on making the cross-member myself.

Tom

 

Unless you want to modify the exhaust you do not need a new crossmember, just a bracket like this to make your original work.

Since yours was a 400 and it was bolted on top of the crossmember, you would have to add the tabs to the lower side of the crossmember as shown in the pic.

 

I'd suggest a search of the fourm. This has been done many, many times.

 

If you want to keep the same crossmember, you will also have to cut the top plate (where the 400 mount connected) to clear for the bottom of the 700's output housing and relocate the E-brake idler wheel mount. But, if you weld, none of that should be a problem.

As far as the 400 to 700 conversion goes, there are several "headaches": modifying the brackets from the 400's oil pan rail so they will work on the 700 (or buying new ones); changing the driveshaft length (must get a new tranny yoke with same 'strap' type connections) and positioning everything on the output end of the tranny & driveshaft to fit in the tunnel area without hitting anything; connecting and adjusting the throttle valve system cable {if you need advice on how to do this RIGHT, PM me}; changing the tranny dipstick tube so that it fits well (you cannot reuse the one from the 400 and a new aftermarket tube is too long...my solution was to use the 'new' tube, but cut it to the length of the 400's tube and reuse the 400's dipstick).

One final thought for you. I made my swap and immediately had a small but bothersome oil leak that I could not find for several days. After a torturous diagnosis process, I finally located the leak: one of the three oil gallery [blocking] pipe plugs located on the back face of the engine block just above the cam pocket had a very light leak. After 40 years of not leaking, the work done in converting the tranny had apparently caused the joint to separate enough to create the leak. Since there was no access to properly identify which plug was leaking or actually get to it to fix it, I ended up having to back the tranny out...again...to fix that leak. Moral: Remove and reseal those plugs while you have the tranny out.....THE FIRST TIME!!

 

7Tvette, I just put a 700r4 core in the frame with a spare 400 crossmember and the bracket for the ebake did not hit and the output housing clears by approx 3"??

c69vete,

Thanks for the picture. I had envisioned a bolt on bracket like that but without the drop in the front. It seems alike the bracket you have puts the 700 mount lower then the 400 mount had been. Is this for pinion angle or is it for body clearance? With the 400 mount modified to fit the 700, i get about 1 degree diff. down pinion angle if the bottom of the mount is at the same height as the original mounting pad.

Thanks
Tom

 

If you could fit a 700R4 into your car with the same crossmember (and located at the same height), you were able to do what I could not. I really wanted to do the minimum modification of the crossmember that could be done, but I ended up having to buy a BowTie unit, rather than just cut the heck out of the stock one.

 

The step on my bracket is the same as the bracket used for the 4 speed. The mounting slots had to be moved back from the original position to get the tranny mount to the right spot. As for the parking brake wheel,when you reinstall the parking brake cable, if you have not moved the wheel over about 1/2 in. the drive shaft, universal joint will hit the cable.
The above picture is my 69 with the 700R4 and the stock welded in crossmember.

 

What did you do for an exhaust? It looks like my trans pan is going to make routing of the passenger side pipe through the crossmember difficult. I have an extra 4 speed crossmember that I might jus weld in the right location, but that would make the exhust pass through closer to the pan.

A custom cross member might be easiest but that means waiting untill the body is on to make sure it does not hit the floor.

Tom

 

PM sent

 

A couple of pic of the 700 in the frame to help anyone doing the swap visualize how it mounts in relation to the cross member and ebrake wheel.