'91 2500 with 700R4 probs

[krcaddis]

I had (previous truck) a nice high end, but salvage title, a '91 4x4 2500 extended cab for about 4 years that had repeated problems- I know it’d had a tranny fluid fire, but the seller was a great body man and painter, did those for a living, and his Dad owned a tranny shop. All damage was replaced with new parts.
I was in moose county AZ (actually Show Lo) when I lost 4th and had it rebuilt. There were metal shavings off some part. Why does that happen? Shop couldn’t say. The seller actually guaranteed the truck and ACTUALLY PAID for the repair.

Six months or so went by, then the center ripped out of the flex plate. Why does that happen? Shop couldn’t say. I never abused the truck, no hauling, no towing. I paid.

Another 6 mo. and I'm losing gears again, limped into a shop in 2nd. Again, no "reason".

Then, another flexplate, and months later, the gears went 3rd time. This time I knew a local GM tranny mechanic and he rebuilt it in his free time. Hubby of a secretary at work, a friend who'd do it right. Tranny shops refused to exchange for another (why?). I'd not discovered Pick'nPull yet.

So I sold the truck and it's history, CHEAP, hoping it would never come back.

Those flexplates are actually pretty hefty steel plate, How the heck do they break repeatedly? And why would that tranny eat itself three times? Alignment issues? crooked crank flange? bad torque converter?

My '85 C20 is now a keeper - 41k miles with a perfect rust free body and interior, peeling paint. Now that I'm putting a crate 350 in, I’m wishing my Turbo 350 had OD) I'm tempted to find a 700R4 ,or newer AT with OD (now it's all about gas mileage). I hear an '89 tranny doesn't need a computer. I'm thinking of going to Pick'nPull, is it worth doing?

 

[1987 GMC Jimmy]

Maybe one of the guys who knows more about transmission innards can shed light on your repeated problems, but it sounds like a bad experience that most people wouldn't go through on a correctly rebuilt transmission. I can tell you two things. One, the TV cable has to be adjusted right. If it's sloppy or (worse) disconnected, your transmission will burn. Two, it can't run hot for protracted amounts of time, or it'll cook itself. Functioning lockup and an auxiliary cooler are two foolproof ways to ensure it never runs hot.

With your question about getting one from PAP, none of the 700R4s needed computer input, but the ones in trucks got a little bit starting in 1987 to control the lockup. The good news is that if you have a TH350C, the vacuum controlled lockup circuit should just be plug and play. I don't know how comfortable I'd be just installing straight out of the yard without rebuilding it, but that's just me.

 

[4WDKC]

Only thing I can think of is a bent input shaft to break the flexplate, as for the gears, those werent the strongest of transmission and many people think they can build them correctly. a bug heavy truck with highway gears would be hell on one.

 

[Old77]

Moved to the proper subsection

 

[yevgenievich]

Tv cable adjustment, 86 and older stock 700r4 or internal leaking issues that never been noticed during rebuilds. Good rebuild on a 87+ 700r4 should last for some time, even in a truck unless really abused.

 

[rpcraft]

I don't want to say a cracked flex plated is normal but it is surprisingly common on 4x4 trucks where the rubber has perished, especially when it comes to the engine mounts and then also when the support rods have already been removed.

 

[krcaddis]

My tranny was rebuilt by 3 different AAMCO shops in 3 different cities, guaranteed for a year each time. Flexplates replaced by 2 different AAMCO shops in 2 cities. Every time I'd emphasize the entire history of those parts and the salvage title,asking for special attention to ANYTHING that might cause each problem and no one could say. I asked about run out, bent shafts, and told a story about a friend who had similar tranny problems with a manual tranny that turned out to be a crooked part. No joy, obviously. I wanted an exchange tranny,but no one would do that.

 

[rpcraft]

My tranny was rebuilt by 3 different AAMCO shops in 3 different cities, guaranteed for a year each time. Flexplates replaced by 2 different AAMCO shops in 2 cities. Every time I'd emphasize the entire history of those parts and the salvage title,asking for special attention to ANYTHING that might cause each problem and no one could say. I asked about run out, bent shafts, and told a story about a friend who had similar tranny problems with a manual tranny that turned out to be a crooked part. No joy, obviously. I wanted an exchange tranny,but no one would do that.

Did you ever figure out what the problem was?

 

[krcaddis]

No luck finding out why it was happening; I'm hoping someone on the forum would have an answer because I'm thinking of putting an 700R4 in my '85 while the engine is out.

 

[rpcraft]

Was it ths same transmission housing each time? if so then I would venture the problem is with the transmission body overall or perhaps what you have going on is maybe the flexplate you keep using is a mismatch to your engine???? I mean, in the realm of possibilities there are only so many things that can cause a flexplate to collectively fail so many times where you have to rule out an installation issue.

 

[krcaddis]

It kept the same case throughout, so if that can cause those kind of problems, that might well be it. The backstory was that the truck had a trans fluid fire. That apparently caused the demise of many AT equipped pickups (true?) until GM changed the dipstick. Old wives tale? Anybody heard that story? Anyway, the seller bought them up on a regular basis, rebuild and resell as a business. He was an excellent body man and painter and his dad had a tranny shop while he was growing up and learned the trades by building hot rods and custom cars.

 

[animal]

@HotRodPC any input here Mr. Transmission GURU?

 

[rpcraft]

Fire is bad MMMMKay???? That being said having a fire in the engine compartment isn't always as exciting or bad as it sounds, especially if it is trans fluid on an exhaust manifold. I know what you are tlaking about with the older dip tubes that didn't have the expansion holder, in fact I have one now and it reminds me I need to upgrade it, lol.

 

[rpcraft]

I'd still think I would swap the housing out if it continues to cause problems, especially after the third time. Once is a fluke, second is suspicious, third time is time to move on for sure.

 

[krcaddis]

I did move on; sold the truck cheap to a friend who did trannies for the local Chevy dealership. It's just bad experiences now and I'm considering a 700R4 for my current '85 C-20. Looking at the fence not even on it yet...