90 Silverado transmission -- violent shaking

[az10sbum]

Hello all

I have a 90 Silverado that has 320000 miles on it. The 350 engine is original with no major work done to it. The transmission had been replaced once before I got the truck.

About a week ago I noticed that the transmission was starting to jerk rather than apply torque smoothly from a stop. It was as if there was no torque until the engine was reved higher than before, and then it lurched forward. Not violently, but noticably different than usual. Except for accelerating from a standstill, it seemed to run normally.

Last night, I had the same symptom upon driving, but a few minutes later at about 20 mph, a horrible violent shaking happened that is hard to describe. It sounded close to the noise I heard once when I lost a rear-end and the pinion gear was hitting the case. Bam bam bam bam bam at 5 or 10 times per second. I tried giving a little more throttle and then letting off the throttle, but the noise continued. Also no change with light application of the brake.

At that point, I thought I would have to get towed. Since I was going about 25, I put it in neutral to coast to a better spot. The noise stopped completely in neutral and I coasted smoothly with the engine running and everything sounded great. I made it around the corner to a stop sign about a half mile from my home. I put it in first gear to see if I could limp home. To my surprise, the truck ran fine except that it had the issue of lurching a little from the stop described in the beginning. I put it in second, and it seemed like it shifted late, but it did shift with no more of the violent noise. I didn't try to go beyond second because I was just trying to make it home. I made it home without further incident and checked my fluid. It looks good and clean. I have not tried to drive it since.

I am not sure what transmission is in it yet -- perhaps someone can tell me what came in a 90 Silverado. I am hoping to find the problem is a vacuum modulator or a transmission control solenoid or something I can fix. It it turns out to require a rebuilt tranny or major work, then I guess I will have to part with the truck since I can't put too much into a truck with 320000 miles on it. (My dog will be crushed -- he LOVES that truck )

Any tips or advice on this issue are greatly appreciated.

Thanks

Dave M

[gmctrucks]

All I can help you with is I hope it's something small. But I do know that those transmissions don't last to long how many are on it? Also like I wrote the other night look on craigslist.org you might get lucky and find a cheap one there. I remember before my flex-plate went out it felt like my trans wasn't shifting correct even the engine felt like it was missing on the next stop light the plate fell down onto the trans inspection cover so you might check yours look around to where the bolts attach that's where they start cracking so if replacing the trans check it out there dirty cheap.
Good luck! GMC

[leolkfrm]

either drop the pan yourself or have it done at a tranny shop, and evaluate what you have. if it runs good it's cheaper than a new truck

[az10sbum]

Thanks. I will drop the pan and do whatever inspections I can. My strong preference is to keep the truck going of course. I do have the factory shop manuals for this truck but I have no experience with automatic transmissions so I don't know what to look for.

I appreciate the info.

[hotrodpc]

Guys, with the violant shaking he is talking about, I am going to guess its the torque converter. And I will go a bit further and suggest its the TCC (Torque Converter Clutch) for the lock up in the converter. Also makes sense since he mentions it seems better in 1st and 2nd. Get into 3 or OD and its going to start looking for the TCC lock up. TCC lock up is disabled in 1st and 2nd.

[hotrodpc]

BTW, I wouldn't get rid of it. 320,000 miles and only a tranny been done to it??? Come on, its been a good truck to you, so be good to it. No need to heart break your dog either. I am sure he's loyal dog too, so keep both the truck and the dog happy !!! Your dog is more forgiving than your wife/gf, so don't let him down. If you don't beleive me, lock both the dog and the wife/gf in the trunk of your car for about an hour, then see which one is happy to see you when you open it up.

[az10sbum]

I agree -- this has been a great truck, and I definitely don't want to let my dog down! ( hotrodpc -- I read your response to my wife but she didn't seem to laugh quite as hard as I did)

I have a couple of questions. First, if it is the Torque Converter Clutch, can that be fixed, or is it time for a rebuild?

Second, I am just getting to dropping the tranny pan now. My manuals are not easily accessible right now, and I have never done this before. It looks like I need to move the rear tranny mount cross member back to clear the rear pan bolts. This would require me to jack up the tranny up to clear the stud on the mount so that the cross member can move. Anyone out there done this on a c1500? If so, can you tell me if I am on the right track?

Thanks

[batty1214]

I too would say you may want to look into the torque converter.... But pulling the tranny pan and looking for wear debris is a good thing to do...... you can pull the torque converter and replace it without the trans being rebuilt. as for if they can be rebuilt? I dunno

[az10sbum]

If it is the TCC, and the TCC doesn't lock up except for 3rd and OD, does that mean that the function is controlled electronically by a solenoid in this tranny?? If so, could it be an electrical problem?

[hotrodpc]

The Torque Converter would have to be replaced. The A and B solenoid in the trans has nothnig to do with the Torque converter. The TCC has its own solenoid and that is NOT your problem. The violant shaking is the TCC is worn, out of balance and just jumping around in the converter. It has probably come apart from the shaft inside the converter. Probably could be fixed by simply replacing the converter. If your pan has only normal wear signs in it, and fluid is otherwise good then, IF you want off cheap, just replace the TC, but then your trans could last another 50,000 miles or it could last 50,000 feet. No telling. If your trans is not in bad shape, a rebuild would probably be cheap. Just replace clutches and seals and upgrade the Sun Shell to the beast while at it. Once you get that done, you should be good for another 100,000K or better. Its worth the repair. Also probably time for U joints if they have not been replaced.