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Old 05-25-2011, 09:44 PM   #1
ray0427c
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1990 GMC Rally Possible TC issue?

Yesterday my van was driving like it was stuck in 2nd or 3rd gear for most of the time I drove it. Get up to around 30mph runs ok not full on though. believe it or not I made home to my driveway and couldn't get it to go no more (how often does this happen?). Started it this morning and was able to get it further up the driveway. started analyzing. Pulled rear part of split driveshaft, jacked up rear end, turned the yoke on the rear end all seems fine, turned other half of driveshaft going into tranny in all gears and turned ok (slightly better in one direction than the other), pulled the drums on rear and all seemed normal, put it back together and tested forward gears still seemed like the parking brake was on or something. Later pulled pan on tranny, fluid reddish brown of course, fine sludge on magnet (average amount for 148,00 miles, magnet just covered over) never notice any slippage, have noticed it seemed like the torque converter would never drop out at a complete stop (motor would bog down like it was still under a load, instead of like a nuetral), heard a loud pop about a week ago when on the interstate and i had let off the accel., wasn't sure if it were me or someone else, I did notice gas mileage was getting worse during the last week. All signs seem to point to a bad torque converter from what I have been reading All Day Today. Never had a torque converter go bad and never seen these symptoms before, I'm clueless. Anyone know the answer to this issue, I would greatly appreciate any info. considering buying a new TC but would hate to waste the money unneccisarily. Thanks in advance.

Forgot to mention; When I had the driveshaft lose I ran it through all gears and driveshaft turned with no load, didn't hear anything abnormal, actually couldn't tell it was turning until I looked underneath. since it's a 1990 I'm assuming it's a 3L80 (turbo 400) short tail, single wire TCC solenoid, not sure if it's HD or not (don't know how to tell). measured the TC best I could while still mounted at 12". I would think being a 1 ton 15 passenger van it would be HD. I took out all the seats when I got it and use it as my work van ( I have a lot of tools)

Last edited by ray0427c; 05-25-2011 at 11:13 PM. Reason: Forgot to mention
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Old 05-26-2011, 02:07 PM   #2
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Re: 1990 GMC Rally Possible TC issue?

What engine and what trans, the 400 had no lock up conv.
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Old 05-26-2011, 02:22 PM   #3
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Re: 1990 GMC Rally Possible TC issue?

5.7 eng., 400 turbo? unmounted the tranny today. This things been worked on before supposedly by gm. it's ran like it had a parachute behind me since I've had it. when I was pulling the tranny I noticed it had a 6 pad converter with only 3 bolts in the flywheel. the other 3 holes didn't line up with the holes on the TC. thats to say there are 6 holes in the flywheel but they're not in a circle, like 3 holes of one circle are smaller than the other 3 hole circle ( hope that makes sense). trying to figure out what TC matches the tranny. GM is not much help even with the serial number. Of course they want you to go to the dealer. need to know how to determan what the right TC is.
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Old 05-26-2011, 06:39 PM   #4
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Re: 1990 GMC Rally Possible TC issue?

Post the pics of the pan or google "GM trans identification", the shape of the pan will determine the trans, the flywheel is probably drilled for more than one trans/ conv.
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Old 05-26-2011, 09:04 PM   #5
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Re: 1990 GMC Rally Possible TC issue?

Went by the hole to hole measurement. Hope this fixes the problem. I know it's a THM400 just wasn't sure which TC is the right one. you never know when someone else has been under the hood what they did. still not sure what they did. I'll find out tomorrow when they deliver the new one. I'm so looking forward to climbing back under that van and putting the tranny back in by myself, seeing how I had so much fun getting it out. One of the aligning pins wouldn't let go (need I say more). Just didn't like the stall out speed of 1360rpm seems like an awfully small number. I'll post once I'm back together.
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Old 05-27-2011, 07:53 AM   #6
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Re: 1990 GMC Rally Possible TC issue?

To make it easier to put back in, make up 2 guide studs, get 2 more bellhousing to block bolts, cut the heads off screw them into the block a few threads by hand this will help guide the trans.
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Old 05-27-2011, 09:00 AM   #7
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Re: 1990 GMC Rally Possible TC issue?

That's a good idea. The biggest problem is the space limtations on the underside of the van, since it has to slide up through the opening in the floor and for some unknown reason they always put the exhaust in the way. May try to drop the exhaust. I always end up busting those bolts.
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Old 06-06-2011, 07:31 AM   #8
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Re: 1990 GMC Rally Possible TC issue?

Well, after checking everything else, I finally tore into the heart of that turbo 400 tranny. I pulled out the forward clutch assembly and noticed a ring about 1/4" wide wore down on the direct clutch driving hub, right about were the last pressure plate would be. everything inside the forward clutch looked good, even the pressure plates. Then, I pulled the direct drive clutch assembly and (holy crap, putting it lightly) the center support guide the direct clutch assembly rides on looks like a sarated blade, seals twisted, the bore in the direct drive clutch had canals in it. This would explain the intense vibration while driving. I happened to notice some parts with white splotches of paint close to the center support area, indicative of junk yard parts, but the center support had none. Now the funny part about this is that the church I bought this van from told me only GM has worked on this van and it was serviced every three months and it was in perfect condition when asked about the service history and what was wrong with it, $2300.00 later on top of the purchase price it was road worthy. I guess you just can't trust anyone these days. Anyway, I opened the direct drive clutch assembly about and found that the wave ring inside was broken into three pieces and the pieces had bunched up together to one side, which I'm sure created a great inbalance. I checked the pieces out pretty close and noticed this was no fresh break and by the looks of the center support guide and bore this has been going on for some time. Yes, the tranny was "rebuilt" and so I was told by the church and certain evidence along the tear down. So, I'm on a mission to find the select parts I need to put this thing back together. I spoke with a guy at a salvage yard yesterday (actually i spoke to a couple of guys there who told me something different each time) and his final words were "if you want the parts you'll have to buy the entire tranny at $350.00", keep in mind this is a u-pull it place, you know were pull what you need and pay for what you need, LOL, I was told by the first couple guys that if I pulled the parts they would make up a price for them, LMFAO. Now I've worked at a couple junkyards and know how the business works and I also know that at a u-pull place a tranny is usually around $130.00 including core. I wanted to write a review on my experience and see what other people had to say. Turns out I'm not the only one who had a bad experience with these people. A lot of reviews said they were told one price for their parts on their way in and after pulling the parts and going to pay for them (you guessed it) the price increased and when they would confront them about the price change they got rude. Well, time to hit the phone and find my parts. Will update later.
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Old 06-13-2011, 08:41 AM   #9
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Re: 1990 GMC Rally Possible TC issue?

I lucked out and found the parts for my transmission. It appears there is a tranny parts Internet company based here in Fort Myers. They sell used tranny parts and at a great price. I didn't think I'd find the parts for that 3L80 anywhere and if I did I was scared I'd get the whole tranny in the rear Bell first with no fluid if you know what I mean. The company is Sun State Transmission, AKA, Transmissionpartsusa.com. I ended up needing the direct driving hub from the forward clutch, the direct drive drum, the dish plate out of the direct drive clutch assembly and the center support. Got it all for $30.00. Not a bad deal in my eyes.


Well, I was up that entire night going through the gruelling process of cleaning every piece of the tranny. Crashed out around 6:30 in the morning, back up at 9:30 a.m. and finished reassembling the 3L80 slid it back under the van and put everything back together under there, filled it, started it, said a prayer and took off down the road. Amazing, what a difference, this poor van has never run so good. I did notice during the reassembly that someone had added a shift kit at some point and I was curious what effect it would have and I soon found out when it hit second gear and the tires chirped a little, nice. It's going on a week since I put it back together and all is well, so far. Still trying to get used to the extra power I have. If I don't pay attention to the speedometer, I find myself driving rather fast through the local streets or when I step on the gas it sets me back in my seat and making turns is going to take some getting used to. Keep in mind this is the largest van GMC makes (15 passengers), it's like driving a bus, literally.

This has been a great experience, besides the aggravation of being sold the wrong parts in the beginning (was sent the wrong torque converter, FYI, always check your new converter bolts to the old one before you reinstall the entire tranny) and tracking down the problem (procrastinating doesn't help). It wasn't nearly as scary as I anticipated or as complicated as it was made out to be, although being mechanically inclined and not knowing how to quit helps a little. I did learn that the dish ring in the direct drive assembly has a tendency to break and gather to one side creating an imbalance and wearing down hard parts of the tranny. I hope this helps someone someday.
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Old 06-13-2011, 11:45 AM   #10
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Thumbs up Re: 1990 GMC Rally Possible TC issue?

Good work, but remember the shift kits tend to stress the stock hard parts.
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