1990 Corvette with some transmission troubles.

1. Today it started changing gears erratic. Sometimes it doesn´t shift from second to third gear. It just runs on second gear in 50 km/h (31 mph). It used to shift to third gear and stay there in those speeds until I pressed the pedal to the floor to get a downshift.
Sometimes it doesn´t shoft from third to fourth gear. (Or overdrive if you prefer that term)
And at least once it didn´t shift down as it should have done. I can´t remember which gear it had and which gear it should have shifted to.
It also sometimes seem to stay to long in first gear at wide open throttle (WOT) instead of shifting to second gear. This happened at least once with 6000+ rpm as as result.
And sometimes a "delayed" up-shift results in a very harsh up-shift. The harsh up-shift is probably not a fault in itself but merely a result of the late up-shift compared to the throttle opening.
All gears pull really hard at WOT so there are no signs of clutch slippage.
I have two theories:
A: A sticking wire between throttle axel and transmission. (don´t know what the wire is called in English)
This is easy controlled but I haven´t done that since I just got home and it´s quite dark outside. I live in Sweden and it´s 00:47 now. But I appreciate any comments on this problem until I get a chance to check the wire tomorrow.
B: The wire controls a plunger (via a spring) in the tranny. This plunger controls the shift points etc. It might be that this plunger sticks?

2. This problem has been there all the time:
It runs 206 km/h (128-129 mph) on third gear at WOT but it will not change to fourth gear in spite of the fact that the revs are approaching 6000 rpm.
If I let off the throttle pedal slightly it will shift to fourth gear and accelerate to 220 km/h (137-138 mph). If I then step on it again it starts to down-shift to third gear but I have always stepped off the throttle pedal in this situation since I have this image in my head showing valves, pistons, pushrods etc flying out of the hood if I complete that down-shift.
But I would like to be able to use WOT at fourth gear to get a higher top speed. Can this be done in anyway?

Even my Saab has a higher top speed than the Vette! Can´t have it that way, can I??

Sorry if I have spelled something wrong but I think you understand anyway. I´m better at Swedish but I guess that wouldn´t help here.

 

And I now see that I spelled "gear" wrong in the subject. IN THE SUBJECT!!! Quite embarrassing! And the subject can´t be edited and everyone sees it! :-(
Well, this fault and this drink is on me. Cheers everyone! :-)

 

Isn´t there anyone that knows anything about this?

Anyway, fluid level checked. It was a few mm below "Low" so I filled it upp to "Max" level. The fluid was red and smelled nothing but Automatic Transmission Fluid, just as it should i a good tranny.
That wire from the throttle to the tranny, the TV-Wire, runs smooth and is properly adjusted.
The fluid obviosly circulates through the pipes to the radiator, the pipes get warm, just as it should.

The problems is still there. It seems to get worse as everything gets warmer.
No up-shifts when expected, no down-shifts when pressing the throttle pedal half way down. It usually makes forced down shifts (kick down) when I stomp the throttle pedal to the floor.

No engine braking when coasting from 50 km/h (31 mph) despite the fact that the tranny has locked istelf in 2:nd gear. If I lock it in 2:nd gear with the gear shift lever it will engine break in that same situation.

Any comments?

 

Hang on someone will be along differant time zone

 

Some things you might post regarding the car/transmission. Is it a recent rebuild or rebuilt at anytime? Do you know? Was it done for you or a previous owner? Do you know if the governor was modified or if there was a shift kit installed in the valve body?

It seems that you mention you actually have all four forward gears. If that's a yes you might comment.

You mention TV is adjusted properly but your issue maybe contradicts that. I believe that it would be the first maneuver.

 

Thanks guys! Thumbs up!

I have had it some months and it has been running good while I have had it. It had a "loose" TV-cable when I bought it which was the reason it didn´t kick down as it should. I adjusted the TV-cable as described in the factory service manual which gave me much better response, a little later shift points and good kick downs. And most of all, a very big smile in my face.
I realize that a "loose" TV-cable might result in slipping clutches but I´m very sure that that has never happened and there are no signs of that in the color or the smell of the fluid.
I have also read this several times, all three parts:
http://www.tvmadeez.com/article/index.php
And this, but it is in Swedish, difficult for you over there:
http://www.rocket88.se/th%20700%20r4.htm
But it is also about the TV-cable and the importance of having it correct adjusted.
And I have another Vette, an -88 with a TH700 as well, so I consider myself aware of how to adjust the cable.

The background of the car:
The previous owner had it for nine years. He was 69 years old and most certainly drove it carefully.
He had the car at some mechanic (don´t know which one) for some kind of rebuild because it shifted to hard. He said that it was because the owner before him had had the tranny rebuilt which resulted in hard up-shifts.
I guess that the first of those owners had it rebuilt and some kind of shift-kit installed and the next owner (the one before me) didn´t like it and wanted softer up-shifts, more like the standard tranny.
So it is impossible to say exactly what has been done to the tranny but it ran very nice until saturday evening when something suddenly happened. It ran perfect last wednesday evening for 140 km (87 miles) and saturday evening it was a mess.

Yes and no.
Sometimes it refuses to shift into any fourth gear, or even one of the lower ones. But when it shifts into the gears, anyone, it pulls as hard as it should on that gear. No slipping clutches at all, and as I wrote above no signs of clutch slippage in the fluid either.
So the gear (and the clutch packs) obviously runs as it should but probably not the hydraulic pressure to them.

Done. Didn´t help.
And I have checked that the TV-cable runs smooth as well.
And a slightly loose or tight TV-cable can´t result in such big problems. Late or early shift points and at the extreme slipping clutches if the TV-cable is very loose. Right?
But here we have shift points that can be very late, and that might not happen at all etc.
For a while today it didn´t shift from 1 to 2 at all. I had 5000 rpm at first gear for maybe 5-10 seconds. No up-shift at all. Then I stomped at the throttle and lifted my foot immedately and then it shifted to second gear. And that was quite a harsh up-shift.

 

Here´s a picture of the TV valve. I stole it from the first link above.
To the left is the TV lever. And then comes the TV plunger, the spring and the TV valve. The TV Valve is always "balancing" its position between the pressure from the spring to the left and the oil pressure to the right.
My theory is that the TV Valve sticks to the housing for some reason, such as a foreign object that interferes with the free movement of the TV valve.

Does this sound right?
Has anybody had this problem before me?

 

Could the vss cause this?

 

VSS equals Vehicle Speed Sensor?

Probably not since the tranny only uses the governor for the gear changes and the Vehicle Speed Sensor is only (?) used by the speedometer, the ECU and maybe the ABS-system.
But I´m not sure, I´m the tread starter you know.

 

I just realized that I might have misunderstood your question.
In my first post I wrote on point #2 about fourth gear at WOT ("This problem has been there all the time:").
This problem is that it will not go into fourth gear at WOT. I have heard that TH700 does not shift into fourth gear at WOT but I don´t know if that is true. I have also heard that the TH700 in Corvette is the exception to this rule.
Does anyone know about this?
I´m wondering if this would help:
http://www.summitracing.com/int/part...illocation=int