87 gta. As far as I know bone stock. Has 350 engine 700r4 trans and 3.23 rear gears. Transmission seems to shift good. But won’t go into 4th gear until about 50-55 mph. Any ideas? I tried adjusting tv cable the proper way. No difference. I have a corvette also and it shifts into 4th around 40-45. So this doesn’t seem right.

 

Is the ATF level full (while the engine is running, in the Park position, and fully warmed-up)?
Is the ATF clean, and red (Not burned/ dark, and not containing debris).

A fluid and filter change is most always a good place to start.
The TV linkage and Valve-Train would be next to look at.
Then inspecting the Valve-Body next.

What is the ring and pinion ratio for the Corvette?

 

my corvette has 3.07 rear. I literally just changed the tv cable. Found an ac delco NOS on eBay got lucky. Results were the same.

 

Did someone install a TransGo Shift kit? Or has this problem always been there? If someone installed the TransGo Senior Shift kit, then most likely they put in the stiffer 3-4 shift valve spring. This will cause the 3-4 shift to be late, while the 1-2 and 2-3 shifts are where they are supposed to be occurring.

 

So, like I said in my previous post... The Valve-Body needs to be looked at next.

Also if the Valve-Body or Transmission has been modified (shift-kit or other)...
Then Dana (Pro-Built Automatics) made a very good suggestion.

Changing the 3-4 Shift Valve-Train Spring to a firmer Spring... would help delay the shift up into 4th gear from 3rd gear.
TransGo sells a 3-4 Shift Valve-Train kit with multiple Springs of varying firmness.
This kit is a "1988 and up" style Valve-Train with 3 different springs (can be used in any year Valve-Body).
TransGo part number: 7-4-V.

I would very highly recommend two other changes (if not already done).
Line pressure and TV pressure both really need to be increased over stock.
These transmission are old now, and both of these pressure decrease with wear and tear.
Low TV pressure will cause Low MTV-UP pressure and may be the cause or part of the cause, for your early 3-4 up-shift.

TransGo produces parts and corrections for all of these things.
I would high recommend that you give Dana (Pro-Built Automatics) a phone call (fastest way to reach him)...
Discuss all of this with him.
I consider him to be the most Knowledge person regarding this Transmission (outside of Engineers from GM, TransGo, Sonnax, Etc).

Call 909-435-5360 or 909-795-1876
He is a One-Man Business... so leave him a message if he can't answer.
He will call you back, if you leave your Name and Number.
He is easier to reach in the Late-Afternoon/ Early-Evening, PST/ California time.

 

Yeah I am questioning what’s been done to this transmission. Car has 180k on it. So very hard to say if it’s original. I know the engine has been pulled. Orange paint gave that away. I’ve put in the pro built kit in my corvette. Among other goodies when I rebuilt it. Not sure when I’ll pull the pan on this car. At the moment working lots of hours.

 

I have a 700R4 that came out of a 1989 Caprice 9C1. It also shifts into 4th @ 45 mph. I believe this to be the original transmission for the car as it has a similarly calibrated valve body to the Z28/Trans Am/Corvette. Anyway I got some transgo springs from Dana and swapped one in the 3-4 shift valve, bit am waiting on exhaust parts, so truck is not running yet.