Spontaneous 700R4 Problems. SOS-Please Help!

[1987 GMC Jimmy]

Hey, all. I think I know what I'm gonna check, but I wanted to get some secondary opinions before I dug in. I've got an '86 model 700R4 with 248,400 miles on it unrebuilt. It's been shifting crisply and without flaw, but that's not the case as of an hour ago. I thought that I had burnt up my transmission when I made a trip to town, but after driving it, I'm not so sure. Basically the problem is that it's struggling to shift, but it'll do it if I get the RPM's up there. This is in all gears. It's hard to get it out of first and really hard to get it out of second. I didn't try past third. I know it's pretty much you lose reverse, or you lose 3-4 in a 700R4, but wouldn't 1-3 still feel relatively normal in the latter case? The only transmission that I've seen and felt burn up while in the truck was a Ford E4OD, and the truck wouldn't even move. I know that's an electronic animal and mine isn't, but whatever just happened to me wasn't very catastrophic. I'm praying for my governor to be stripped or my throttle valve to be stuck. Before I pop the governor, can I test the throttle valve at all by pulling on the cable? Any ideas or suggestions? I know the transmission's old, and it's not the best year (however not the worst, either) for the tranny, but I would like to squeeze a few thousand more miles out of it.

 

[yevgenievich]

Sounds like a stuck throttle valve. Tug on the tv cable few times and see if it will be better. Not a solution but a way to check

 

[74 Shortbed]

Sounds like a weak spring behind the throttle valve, my neighbor had similar problem his car a while back I believe it was an 85(IIRC)I changed the spring and it was back to normal, just something to check, also make sure the cable is still adjusted properly..

 

[HotRodPC]

First off 248,000 actual miles on a 700r4? And then an 86 year model one at that? Just quitcher bitching now. I think I'd just take that one out, gold plate it and hang it over the fireplace mantle.

I agree with all of the above. Sounding like the TV Valve has hung open, either by weak spring, peice of trash in the valve cylinder, or bind in the TV Cable. For whatever reason, sounds like the transmission thinks the truck is at WOT and likely via the TV valve since that's its purpose.

Also, check the governor. Look for a hung valve in the governor or damaged teeth.

Governor and TV Valve via TV Cable are the only 2 things that determine shift points on the 700r4.

 

[1987 GMC Jimmy]

Sounds like a stuck throttle valve. Tug on the tv cable few times and see if it will be better. Not a solution but a way to check

I tried this first. It worked! Shifted up and down many times between 1 and 4 perfectly smooth.

Sounds like a weak spring behind the throttle valve, my neighbor had similar problem his car a while back I believe it was an 85(IIRC)I changed the spring and it was back to normal, just something to check, also make sure the cable is still adjusted properly..

TV cable's good. It could be adjusted a little tighter, but not much. Geometry is good, as is the overall movement.

First off 248,000 actual miles on a 700r4? And then an 86 year model one at that? Just quitcher bitching now. I think I'd just take that one out, gold plate it and hang it over the fireplace mantle.

I agree with all of the above. Sounding like the TV Valve has hung open, either by weak spring, peice of trash in the valve cylinder, or bind in the TV Cable. For whatever reason, sounds like the transmission thinks the truck is at WOT and likely via the TV valve since that's its purpose.

Also, check the governor. Look for a hung valve in the governor or damaged teeth.

Governor and TV Valve via TV Cable are the only 2 things that determine shift points on the 700r4.

I knew this was coming. I might consider it when it hits 300,000 miles. I say this half-heartedly serious knowing what the transmission is but thoroughly impressed by how it feels and performs with that kind of mileage.

I'm guessing the potential exists for this problem to repeat itself, and I'm also guessing I should pull the pan and address it so I don't have to tug on the TV cable to free it. Would that be the plunger sticking, a bad spring, etc.? What should I do? I'm not too reluctant to service the transmission because I see it's been done before. I don't want to kill it prematurely.

 

[HotRodPC]

So are you saying it's working Ok again? If so, it might not repeat itself again. It might have just been a piece of debris hanging a valve, either the TV or Governor valve. It may not even happen again. Find you a good strong magnet that's basically flat and slap it on the bottom of the pan if you don't want to pull the pan. This way any metal particles will stick to the magnet through the pan and keep the particles from re entering the transmission critical parts and hanging something up. Keep in mind, some rough terrain you might drop the magnet off the bottom of the pan. Maybe a piece of duct tape to help hold the magnet in place for the occasional rough pot hole or something that might cause you to drop the magnet off the pan.

As far as the TV valve being hung up, you should be able to tell by pulling on the TV cable. Disconnect it from the linkage on the carb. Then pull on it. If you don't feel engagement, resistance or spring tension on the cable at all or toward the end of the full pull then it's safe to say the cable is either broke, or the valve is hung. If it's shifting late or not at all instead of way to early, then it's safe to say the valve is hung up and not a broke cable. If it was shifting way early and no tension or resistance on the cable, then I'd say the cable is broke and it's not engaging the TV valve at all.

 

[74 Shortbed]

Drop the pan and check the plunger, it should move smoothly back and forth, and at idle position the lever should be up against the plunger against the spring no clearance, with cable properly adjusted.

 

[yevgenievich]

If it keeps doing it again, then you would need to replace the spring and install the antistuck spacer(both are in a jr shift kit). You might never feel the difference by feel on the plunger to tell why it is hanging up. It would require dropping the valve body, so you would need those gaskets as well.

 

[1987 GMC Jimmy]

Thanks for the info, guys. I'll see how it goes the next few days, and if it does again, I'll do the magnet. If it keeps doing it more, I'll drop the pan, replace the requisite components, and do the fluid/filter. We'll see if it makes it to the big three-double o.