Tranny chattering noise.

Zach.Marsh · November 15, 2015

Hey guys, need some help. I just recently purchased a 91 silverado 1500 ext cab 4x4. It has a 350 with a 5 speed manual. I bought it thinking it need a throw out bearing because it was making noise. It would make a chatter in noise while the clutch pedal was realeased but when i put pressure on it, it would shut up. I decided while I was in there just to put a whole clutch kit in. The old clutch looked worn so I never thought of checking anything else I just put every thing back together with the new clutch plate, pressure plate and throw out bearing. Got it all put back together and it's still does the same exact thing. When sitting at an idle with the clutch pedal to the floor it is quiet, but with it released it makes the chattering noise and driving down the road it makes it in all gears. Even with the clutch pushed in it still makes the noise while driving. So I believe it's something in the Trans, but don't know a dang thing about them so that's what I need your help with. Thanks in advance!

Doug_Scott · November 16, 2015

You don't say if the noise only happens when the vehicle is moving, or if it makes it anytime the clutch is released. to add some logic to your troubleshooting, you are good to think it is in the transmission(or it is at least after the clutch assembly). The system has a natural break inside the transmission to help diagnose this.

If the noise happens when transmission is in neutral, with engine running, vehicle stopped and clutch pedal released, then it is something in the input shaft area of the transmission, possibly the needle bearings between the input and output shaft. Did you take a look at the pilot bearing in the crankshaft while the transmission was out for the clutch replacement? Pilot bearings make noises at odd times.

If the noise can be made to appear while truck is stopped it should be fairly easy to isolate.

txab · November 16, 2015

You don't say if the noise only happens when the vehicle is moving, or if it makes it anytime the clutch is released. to add some logic to your troubleshooting, you are good to think it is in the transmission(or it is at least after the clutch assembly). The system has a natural break inside the transmission to help diagnose this.

If the noise happens when transmission is in neutral, with engine running, vehicle stopped and clutch pedal released, then it is something in the input shaft area of the transmission, possibly the needle bearings between the input and output shaft. Did you take a look at the pilot bearing in the crankshaft while the transmission was out for the clutch replacement? Pilot bearings make noises at odd times.

If the noise can be made to appear while truck is stopped it should be fairly easy to isolate.

Check this.

Zach.Marsh · November 20, 2015

I only paid 900 for the whole truck. If I were to just buy a transmission from the local junkyard, would you recommend swapping it out for a different trans? Or put the same one back in it?

Zach.Marsh · November 17, 2015

Yes it happens when the truck is sitting at an idle and pedal released. I checked the pilot bearing and it seemed fine. I couldn't get it out so I just left it.

Doug_Scott · November 21, 2015

Swapping to a different style trans will impact a lot of other parts, especially when it is a 4wd. You are best to stick with what you have. Not sure how readily available it would be at a wreckers though. It is over 20 years old, anything at a wreckers will likely already have a large number of miles on it.

Wreckers will almost always gaurantee the part will work, but, the problem is they never cover the labour to replace the defective part, even when it was delivered to you DOA. If the truck is in good shape body wise, and engine wise, and if you like the truck, even if you paid a shop to repair the transmission (that you remove and install) a thousand dollars, you are likely still ahead of the game. Having $2k into a 4wd truck that lasts you a year before having to repair it is still cheaper than just about anything else out there. The big question is, what sort of shape is the truck currently in,

You have what is likely one of the more popular used trucks these days for those that like to play with their vehicles. You have the more traditional higher torque/lower rpm plus the manual transmission.

Zach.Marsh · November 20, 2015

If it is the bearing between the input and output shafts, how hard is that to change?

Doug_Scott · November 18, 2015

Generally the easy way to change the pilot bearing is to use the dummy shaft and some heavy wheel bearing grease, the thicker the better. Pack the bearing and the space behind the pilot bearing with the grease, take the dummy shaft and a dead blow hammer (area is too close to your face to use metal hammer on an old input shaft), put the shaft in the bearing, it should not go in very far due to grease, and whack it with the hammer, The grease will pump the bearing out pretty easily. Note that I never tried this with one of those nylon alignment tools, but have used the metal ones successfully.

When the trans is out, you can also check the input shaft for any play. The shaft should be virtually movement free.

Doug_Scott · November 20, 2015

Depending on how bad the bearing is worn, and also how the bearing is worn, it may not be just as simple as changing the bearing. Bearings have inner and outer races with hardened rollers, needles or balls between them. A typical input/output shaft bearing is made up of a bunch of needle bearings, with the outer race being the input shaft, and the inner race being the output shaft. If your transmission is made up that way, you can pretty much count on a complete teardown to repair.

There is also a support bearing in the front of the transmission case that also could be bad. I realize this post is not really giving your what you want to hear. I would be looking for someone in your network of friends that may have the experience to help you with this repair if I were you.