Need help with a vibration issue.

[CamoCody]

So I've got this 1982 Chevy c20 (350/th350) . It never used to do this when I bought the truck but it's done it for quite some time now. When I get the truck up to highway speeds (starts vibrating at 60ish), it will do a on and off vibrating as I hold the gas. As I increase speed it increases how fast it does it and will eventually turn into one single long vibration. Now if I let off the gas and leave it in drive it will still have the same on and off vibration but if I put it in neutral and coast for a bit it results in a non-stop vibration. For the record, by vibration I mean the entire cab shakes (not just steering wheel, etc). If anybody has ever strapped something down to a vehicle with a ratchet strap and went down the highway....yea it's kinda like that. Replaced carrier bearing and u joints hoping that would fix but it didn't. Almost thinking maybe it's torque converter shudder but I've never dealt with that before so I'm unsure. Anybody ever deal with torque converter shudder? I'll also note that since I've had all four tires replaced and had it aligned and it still does it.

 

[bedwards]

Transmission slip yoke bearing play or differential pinion bearing?

 

[CamoCody]

One thing I did notice when I had the driveshaft out was that the output shaft of the transmission was a bit loose. Are the suppose to be loose?

 

[bedwards]

The output shaft will be loose with the slip yoke out. It fits in the slip yoke which then fits in a bearing in the tail of the transmission. In other words, no slip yoke no bearing. With the yoke in place there will be up and down play but not excessive. You have to firmly shake it up and down to feel the play. There is a lot of play there but not enough to clunk. The slip yoke has to have enough play to move in and out when the rear suspension moves up and down. Vibration would be a common problem with high mileage trucks also more so 4wheel drive and trucks with 2 piece drive shafts.
I don't think your torque converter would cause vibration with it in neutral and or coasting. Just when pulling or a steady speed.

Upon edit, my son hit a 2x4 on the interstate years ago and bent his output shaft. It didn't vibrate so much as the bearing would get hot and the rear seal would back out and puke tranny fluid. Re-did that about three times before I figured it out. =[

 

[bucket]

The driveshaft could be bent or out of balance.

 

[chengny]

The driveshaft could be bent or out of balance.

That is the first thing GM recommends to check - after tires/wheels - according to their DLVD (drive line vibration diagnostic) charts:

TSB Number: 89-199-4A
Section: 4A
Date: June 1989
Subject: EVALUATING DRIVELINE VIBRATION


Model and Year: 1980-89 LIGHT DUTY TRUCKS
TO: ALL CHEVROLET DEALERS

The purpose of this bulletin is to provide a logical approach to evaluating vehicles for driveline generated vibrations and imbalance occurring between 50-62 mph. The following diagnosis tree is designed to be used as a guide, and when utilized properly can help isolate and identify causes of driveline disturbances.

Procedure:

Prior to road test, determine if disturbance is engine related by following the procedure below:

1. With engine at operating temperature and vehicle parked, set parking brake and place transmission shift lever in neutral.

2. Slowly accelerate engine from idle to 4000 RPM (diesels 3200 RPM), noting RPM at which vibration is felt (if any).

3. If vibration is felt, disregard use of this bulletin and isolate and repair responsible engine component (transmission, clutch/flywheel, torque converter, engine accessory, etc.).

Road test vehicle on a smooth level road to verify customer comment. It is usually beneficial to road test the vehicle with the customer present. Note the speeds and conditions at which the disturbance is most noticeable. Refer to Remark A in this bulletin for diagnosis information.

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