Comment: i just had a th700r4 put in my 76 gmc 3/4 ton it came out of a 81 suberban didn’t get to drive it much this last winter but when i did get to it worked very well. until i stopped at an intersection and it wouldnt shift out of 1 gear need help to diagnose the problem!!
Answer: The transmission we are talking about is a General Motors T-700R4. This is a hydraulic transmission, pre-computerized. A very common problem that happens all the time. Even I am not immune to this problem.
That being said, it has to be a valve body problem or a governor problem. The valve body is the brain of your transmission, it has a valve in it called the throttle velocity valve (TV) and the TV valve controls all shifting activity. We discussed the jobs and duties of a governor before in this post. Understanding this transmission was phased out in about 1991 or 1992, this is considered an older transmission although millions of them are on the road.
The TV valve is in the valve body and strokes back and forth in it’s bore, freely when it is working right. Let me lay out the simplest, easiest and least expensive thing that can happen. The good news is that if the problem occurs, it does not mean it is terminal..The problem being the driven gear on the governor has concaved itself in the middle and the governor won’t rotate, or the valve in the governor is stuck.
A bad gear is not such a big deal, a stuck valve may be a big deal. Pop a gear on it and send the customer down the road, worth about 50 bucks and no guarantee, because it may happen again down the road. What is happening is that the output shaft bushing is getting weak and it allows enough movement of the output shaft to wear the governor gear or break it off. It will happen again. When? It may be a year or month, but it buys time.
Make sure the transmission is maintained or serviced at the same time. The broken gear or worn gear fragments should be removed from the tranny. BTW, the governor gear is plastic.. Use a new OEM factory filter and synthetic transmission fluid..
What is described in the comment could be etched in stone it has been said so many times. Before I get anymore technical, this is a problem for a transmission specialist. It should not take long to figure it out. No matter what the determination is, we have to know what the condition of the transmission is before we can render a verdict. So, here is how I would handle it if you were my customer::
After the diagnosis I would suggest we ‘drop the transmission pan‘ as in loosen and lower it, collecting the fluid responsibly, and inspect the pan for contaminants. Obviously there will be wear in the transmission, but it is up to the trained eye of a transmission mechanic to know how much is acceptable. If the pan is clean than most likely there is an isolated piece of dirt stuck in the TV valve, not allowing it to stroke back and forth in it’s bore.
If the pan is contaminated with brass shavings or metal shavings or shavings from anything inside your transmission like a planetary gear or maybe a worn pump,,, give the transmission it’s last rights and call GotTransmissions.com at 866-320-1182 for some help in devising a strategy for transmission replacement.
In regard to the comment, the 700R4 was not made in 1976, so this is a swap-over job, similar to the post I wrote on the subject. I will assume the job was done right,. 1981 was the first year of the 700R4, so you got an old one pal.
There is a special TV valve kit made by TransGo that specifically addresses this issue. It can be installed with the transmission in the car. it is a good idea to let a professional do it. However if the pan is contaminated this may not work at all or for long. Realistically, you probably need a replacement transmission, preferably one that is rebuilt and upgraded properly.
GotTransmissions.com Blog is your source of good quality information. Questions are welcomed on any part of your car. Please don’t be shy. As a matter of interest, at my shop, a rebuilt T-700R4 never left the lot without the upgrades I have mentioned. Want a better rebuilt transmission? Call the experts at GotEngines.com.
