700R4 Transmission Questions/Issues

[NickTransmissions]

As odd as it is… the rig did sit for 15 years and it could be kinda stuck/dry/goopy in the transmission. I’m gonna keep driving it and if it doesn’t get better I think it’s the valve in the transmission. But im seeing minor improvements with each drive.

PS: it does manually downshift just fine and kicks down occasionally now

Perform a line pressure test - see my 700R4 Information Thread on how to do this. You're flying blind without knowing where your baseline transmission pressures are at the current TV set up and adjustment. If your line pressures are within spec, drop the pan and see what's at the bottom...If there's quite a lot of burnt clutch material, put the pan back on w/a few bolts and yank the unit out for overhaul.

 

[Burbinator86]

Haven't read the whole thread, but have you dropped the pan and changed the filter and filled with new fluid?

I haven’t. That’s my next step

 

[David King]

Welcome from the FL Panhandle!

 

[BadBowtie]

I'd drop the pan for inspection. Replace the filter, add the big bottle of Lucas Transmission Conditioner, and top it off with regular Mercon/Dextron IV. This will be a 50% fluid change. Then drive her a bit, let Lucas go to work....

 

[Nardulli]

I have just gone thru this with my '86 GMC build. There are a LOT of 'opinions' regarding how to adjust the TV cable. Here is what I learned as the surest method .

1. Remove the transmission pan.
2. Cuss and bitch about the trans fluid mess you just made. Resolve to get a pan with a drain plug.
3. With the throttle at the idle position, check the lash between the cable end and the plunger . It should be as close to zero lash as you can make it. The result is that ANY movement of the throttle moves the plunger . The plunger should not be depressed at all at idle. Nor should there be any free play between the cable and the plunger.

I'm anticipating many of the knowledgeable folks on here to disagree with this. This is not the only way, but in my experience, it is a sure way. I've done at least half a dozen in this manner and never had an issue and experienced good shifts at the right time.

 

[Burbinator86]

Thank you all for your help. I was finally able to drop the oil pan and there is definitely black sludge in it but no metal shavings. Keep in mind this probably hasn’t been changed in 10 years.

And yes…. It was a disgusting mess i made getting it off… and also smells awful (burnt/old smell)

 

[Burbinator86]

Filter too

 

[NickTransmissions]

Filter too

Yank it for overhaul. Install 97+ 4L60E bonded pistons and corresponding ret spring assy in the forward drum. Ensure the pump is vacuum tested, particularly the pressure regulator valve.

Let us know what you find once it's torn down.

 

[Burbinator86]

Well now i have a new problem that started before i changed the old fluid, and hasn’t changed after i installed the new filter and fluid.

It was driving like before, 1-2,2-3,3-4, and seemed to be getting better. I drove it 10 mins to a parking lot, let it sit at idle for 15 mins roughly, then went to drive it home. Then it started shifting 1-2 per usual… and won’t shift past 2nd gear. It’ll hit around 3000 RPM in second and then go WAAAAAAAH (high rpm like trying to pass someone) and stay in second…

Never has done this before, and I don’t think it’s a bad transmission. I say that because it was just fine and wasn’t being driven crazy, and the inside with the pan off looks new. I’m thinking governor but I don’t know if that’s it. Others have said a stuck TV valve but it was shifting before just fine and getting better, then this.

I’m losing my marbles. And before someone says I need a new transmission, I’d rather hear any other possible ideas. Because needing a transmission just doesn’t add up

 

[Broken85]

I had one that acted the same way after a service. 2-3 clutch was smoked. Fine the day before, then ruined. People can give you some opinions, but unfortunately, there is no way to find the real problem without getting into it. And judging from how much clutch material is in there, there is no way to fix that trans from the outside. Piece of junk blocked something somewhere, the TV cable didn’t line up with the flux capacitor, No one is going to be able to suggest a magic part for it. It’s gotta get pulled either way.

 

[NickTransmissions]

Well now i have a new problem that started before i changed the old fluid, and hasn’t changed after i installed the new filter and fluid.

It was driving like before, 1-2,2-3,3-4, and seemed to be getting better. I drove it 10 mins to a parking lot, let it sit at idle for 15 mins roughly, then went to drive it home. Then it started shifting 1-2 per usual… and won’t shift past 2nd gear. It’ll hit around 3000 RPM in second and then go WAAAAAAAH (high rpm like trying to pass someone) and stay in second…

Never has done this before, and I don’t think it’s a bad transmission. I say that because it was just fine and wasn’t being driven crazy, and the inside with the pan off looks new. I’m thinking governor but I don’t know if that’s it. Others have said a stuck TV valve but it was shifting before just fine and getting better, then this.

I’m losing my marbles. And before someone says I need a new transmission, I’d rather hear any other possible ideas. Because needing a transmission just doesn’t add up

Another possible idea - overhaul the transmission. It's shot. Not sure why you refuse to believe or accept that but common sense is telling you to yank it, throw it on your tear down bench and go through it.

 

[Ricko1966]

Another possible idea - overhaul the transmission. It's shot. Not sure why you refuse to believe or accept that but common sense is telling you to yank it, throw it on your tear down bench and go through it.

Reminds me of the people that would bring in carry in engine rebuilds. We had a set price for labor to disassemble and reassembly. All parts and machine work were additional. We'd tell people we can't give you more info than that until we tear it down and see what it needs. I have no idea how many times I heard,oh it shouldn't need much it was running great,just before it quit running.More than once Denny said yep you should have brought it in then.

 

[Burbinator86]

Well it turns out that the 3-4 band is bad and it’ll be around $2k to have an actual trustworthy shop fix it. So that sucks

 

[gsuburban]

Haven't read the whole thread, but have you dropped the pan and changed the filter and filled with new fluid?

Hello all. I’m new to the forum and new to Squarebodys. I have a 1986 GMC Suburban K1500 with a 350 and a 700R4. I’ve had it roughly 2-3 months and it hasn’t been a daily running rig in 15 years (not my doing).

I bought it and got it to running and driving shape but im having some issues that I need help with. Before I get into it i’ll mention nothing Tranny related has been touched besides filling the ATF back up and replacing the tv cable.

The issue: When I drive it, it seems to rev a little high before shifting. Granted I don’t have a Tach but I’d Guess-timate around 2500-3000 rpm. It shifts 1-2 at around 15mph, 2-3 at 25, and haven’t tried fourth I don’t want to damage anything. Added to that is it seems to shift really soft. Like almost not able to tell it’s shifted at all. More between 2-3 than 1-2. And this is light-moderate on the throttle in speed limits 30 or less.

And when I go to look at adjusting the TV Cable, it’s to the point of no more adjustment (pulling it out). I have the Edelbrock TV Cable mounting bracket on my 1406 carb.

My thoughts on what it could be is:

Something related to the TV Cable? A vacuum line issue as some little ones are disconnected?

Any help is greatly appreciated.

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If the TV cable is not adjusted correct, just going around the block will damage the transmission. That TV cable has to be spot on. Most transmission builders will say the 700R4 has a weak third gear clutch from the get go. Likely, a rebuild is necessary and seems to be the best practice to take considering the issues it is having. A decent rebuild should include a new converter, a corvette servo, TransGo shift improvement kit, wider bands and a good trans builder who won't cut corners. Good idea to have a decent trans cooler up front too. Precision Transmission in Amarillo Texas has a YouTube channel that has much information about the 700R4 and the later 4L60. There really is no other remedy, its having issues that are internal.

 

[gsuburban]

BTW, the cost of rebuilding a transmission won't be accurate until it is taken apart and inspected. If it needs a pump, more $$. A new shell, more $$. A new planet, more $$$$. The 700R4 is a good trans...worth investing in but not cutting corners and doing it right.