Lee

I recently converted my '75 from a TH400 to a 700R4, using bowtie overdrives conversion kit and a local tanny builders 700.
The low gear is great, the 1-2 shift is great, the 2-3 shift clunks and the 3-4 shift is fine, but goes right to lock up.

Also, when you manually shift down from 3rd to 2nd, even at reasonable speeds, it feels like the rear end is about to come out of the car. Hold the car in second, back off the throttle, it vibrates and shimmies. It does that a little in 4th lock up when you back off the throttle, but nothing like in 2nd.

So, I torqued everything up again, changed all the bushings, verified driveshaft is strait and balanced etc, but no impact on the clunk or 2nd gear off throttle vibration.

Any ideas? I am thinking driveline alignment, or worse, bad tranny. (The tailshaft appears to be a bit to the right, but with some grinding and adjustment it is now close to center.)There is only about 50 miles on the car since the conversion.

Thanks, Lee

pauvil

what kind of driveshaft?? could be out of balance??

Lee

Stock driveshaft, cut to length and balanced, then re-checked. Its OK.

bobs77vet

perhaps your TV cable is not adjusted properly....i have no clunks in my 700r4 and my 4th gear and lockup happens only after 50MPH + and then only if i'm backing off the gas pedal....did you do the pressure gauge check and get pressure readings on all the gears? i spent alot of time getting my TV cable set properly.....and yes down shifting manually is very firm, but i have no shimmies or vibration.

rosslato

and lockup happens only after 50MPH + and then only if i'm backing off the gas pedal..

my 200r4 does the same thing, is that the way they're designed? seems weird to me

Sharky Guam

yep, it sounds like the tv cable is out of adjustment. Mine in one of our cars did something similar. I changed the trans and could not solve it. I finally had a friend adjust the cable properly.

Lee

I think the TV cable may be the 2-3 shift and lock up issue. But the clunk and vibration are something else. Both are bad, and at their worst when backing off the throttle.

Driveshaft is good, so now i am looking at alignment. I want too fix this so I can take full advantage of the stroker and bang it around a bit without breaking it. Any other ideas?

Xakk

This is something I've been wondering about ever since I did my 700-r4 swap. How can you tell when the lock-up engages?

Lee

Took my car to the tranny builder today. He took it around the block and laughed. Seems the converter was starting to lock up in second gear. He gave me a 6" wire harness from "shift rite" that he had kicking around and said "try this". I plugged it into the tranny, then pluged the tranny wire into that and went for a drive. Fixed! Nice crisp shifts, locks up on the highway, unlocks with light application of throttle, no clunks, goes like stink.

Now I need to find out why the harness from bowtie overdrives did not work right...

at any rate, with a strong stroker, a 700R4 and a vette brakes suspension kit, this '75 will give a C5 a run for its money. What a treat to drive.

Thanks all for the suggestions.

Lee

bobs77vet

it will lock up automatically in 4th....and should disengage when you apply the brakes if its got the brake light relay.....you will feel the difference ...in lock up the engine and trans are linked together and they do not have any slipping so the tach is little more steady.......put your foot on the brake and step onthe gas at the same time then take your foot off the brake and lock up will happen...you should feel it....also take it down to about 35-40 and slowly step on the gas pedal the car will be at the low end of the RPM range and the car will lug a little....