700R4 no engagement any gear, ATF over-full

[backwoodsman]

Hi all,

700R4 in my '83 Suburban, was rebuilt around 75K miles ago and has been trouble-free, except for an occasionally sticking throttle valve.

Until today. I drove a half hour, it briefly disengaged while driving at low speed. I stopped and checked the ATF, and it was over a quart above full and burnt, both of which it wasn't before. When I went to leave it wouldn't engage in any gear (fwd or reverse) the first few seconds, then engaged and worked normally for long enough to get up to highway speed, then completely disengaged. I pulled over, it again wouldn't engage in any gear, waited a couple minutes, then it worked enough to move the truck a little more out of the way.

What's going on here? With the overfilled condition, maybe a blown torque converter seal?

I need to travel next week for a funeral, and here I was thinking the rig was all ready for a road trip. Sure glad it let go now rather than half way into the trip, but now I have to figure out how to get there.

 

[NickTransmissions]

Hi all,

700R4 in my '83 Suburban, was rebuilt around 75K miles ago and has been trouble-free, except for an occasionally sticking throttle valve.

Until today. I drove a half hour, it briefly disengaged while driving at low speed. I stopped and checked the ATF, and it was over a quart above full and burnt, both of which it wasn't before. When I went to leave it wouldn't engage in any gear (fwd or reverse) the first few seconds, then engaged and worked normally for long enough to get up to highway speed, then completely disengaged. I pulled over, it again wouldn't engage in any gear, waited a couple minutes, then it worked enough to move the truck a little more out of the way.

What's going on here? With the overfilled condition, maybe a blown torque converter seal?

I need to travel next week for a funeral, and here I was thinking the rig was all ready for a road trip. Sure glad it let go now rather than half way into the trip, but now I have to figure out how to get there.

Likely pump failure. Do a line pressure test to confirm or deny or simply un-do one of the cooler lines, route it into a bucket and see if the pump is moving fluid.

If no fluid flow or pressure, yank it for overhaul and send the pump castings out for machine work.

 

[backwoodsman]

Likely pump failure. Do a line pressure test to confirm or deny or simply un-do one of the cooler lines, route it into a bucket and see if the pump is moving fluid.

If no fluid flow or pressure, yank it for overhaul and send the pump castings out for machine work.

Thanks for the reply. I don't have a way to do a line pressure test, but when it happened I did feel the cooler lines to see if it was circulating fluid. The cooler's input was much warmer than the output, so apparently fluid is circulating.

I brought it home today. The transmission worked at first, drove about a half mile before it let go, so had to tow it the rest of the way.

 

[NickTransmissions]

Thanks for the reply. I don't have a way to do a line pressure test, but when it happened I did feel the cooler lines to see if it was circulating fluid. The cooler's input was much warmer than the output, so apparently fluid is circulating.

I brought it home today. The transmission worked at first, drove about a half mile before it let go, so had to tow it the rest of the way.

Either way it almost certainly has to come out based on the symptoms as described.

Pump will also need machine work as it's likely scored up; they all are.

If you own a 700r4, you absolutely need a transmission pressure gauge to conduct pressure testing. Not getting the TV cable adjustment right will burn a freshly rebuild transmission down in as little as five miles.

Harbor Freight sells one under the "Maddox" brand. It's a decent gauge at a good price.

 

[90Supurban]

Is this 4wd? Bad transfer case input seals can pull fluid from the trans. But your overfilled condition may have been from overheating as well.

 

[backwoodsman]

Likely pump failure. Do a line pressure test to confirm or deny or simply un-do one of the cooler lines, route it into a bucket and see if the pump is moving fluid.

If no fluid flow or pressure, yank it for overhaul and send the pump castings out for machine work.

Finally getting back to this after way too long... Need to get this thing back on the road before too much more time passes.

I got a pressure gauge kit and got some numbers:

P-N-D-3 70 psi
2-1 170-180 psi
R 110-115 psi

FSM says to check pressures at 1000 RPM, but pressures didn't change between there & idle. After a couple minutes the pressures drop way down, trans starts making a soft whine sound, and I can feel some vibration coming through the pressure gauge hose. At that point it's still pulling a tiny bit, but that stops in a short time.

As before, it works for a couple minutes, then quits and has to be shut off for a few minutes, then it'll work for another couple minutes.

Really appreciate your help. Does that help with a likely diagnosis?

Is this 4wd? Bad transfer case input seals can pull fluid from the trans. But your overfilled condition may have been from overheating as well.

Yes, it's 4wd. It wasn't overheated when I checked the fluid when this first happened. I don't have a temp gauge but I could hold both cooler lines at the time.

 

[NickTransmissions]

Finally getting back to this after way too long... Need to get this thing back on the road before too much more time passes.

I got a pressure gauge kit and got some numbers:

P-N-D-3 70 psi
2-1 170-180 psi
R 110-115 psi

FSM says to check pressures at 1000 RPM, but pressures didn't change between there & idle. After a couple minutes the pressures drop way down, trans starts making a soft whine sound, and I can feel some vibration coming through the pressure gauge hose. At that point it's still pulling a tiny bit, but that stops in a short time.

As before, it works for a couple minutes, then quits and has to be shut off for a few minutes, then it'll work for another couple minutes.

Really appreciate your help. Does that help with a likely diagnosis?


Yes, it's 4wd. It wasn't overheated when I checked the fluid when this first happened. I don't have a temp gauge but I could hold both cooler lines at the time.

Sound is probably pump whine, which occurs when something is damaged/broken inside the rotor/slide pocket. That unit almost certainly needs to come out for overhaul. That's my guess based on everything you've shared and described.

 

[backwoodsman]

Sound is probably pump whine, which occurs when something is damaged/broken inside the rotor/slide pocket. That unit almost certainly needs to come out for overhaul. That's my guess based on everything you've shared and described.

Thanks... Was kinda hoping it was the torque converter and the trans was OK, especially since it only has around 75K since the last rebuild.

I may look for a used transmission just to get the truck back on the road, then rebuild this one myself and put it back in. It's going to take time to do that, because of other demands on my time, and also being pretty remote, whatever parts or machining or whatever I need will take more time to get here. But at present I can afford the time easier than the money to pay someone else to do it.

So a question with that in mind: Since I'm pretty remote, and there are a lot more gas than diesel 700R4's around, can I use a gas one if I swap out the governor, or are there other differences that make it not that simple?

And now the NP208 I put in a couple years ago is leaking from the front output seal. One more thing to fix.

 

[NickTransmissions]

Thanks... Was kinda hoping it was the torque converter and the trans was OK, especially since it only has around 75K since the last rebuild.

I may look for a used transmission just to get the truck back on the road, then rebuild this one myself and put it back in. It's going to take time to do that, because of other demands on my time, and also being pretty remote, whatever parts or machining or whatever I need will take more time to get here. But at present I can afford the time easier than the money to pay someone else to do it.

So a question with that in mind: Since I'm pretty remote, and there are a lot more gas than diesel 700R4's around, can I use a gas one if I swap out the governor, or are there other differences that make it not that simple?

And now the NP208 I put in a couple years ago is leaking from the front output seal. One more thing to fix.

You can use a gas valve body though if you find shift points are too high, you'll need to swap the valve body to the replacement unit, along with the governor. It may be worth putting in a Transgo SK700Jr shift kit into whichever valve body you will be installing as well.

Beyond the governor and, to some extent, the valve body, there are no other differences that I am aware of between the gas and diesel 700s.