The Stovebolt Site Forums The Shop Area Driveline Noise from transmission when coasting and breaking

First - sorry for the empty posts !
I used copy/paste and spell checking before posting and that did not work out well - so now you would have to live with my spelling .....

We would really appreciate your view and input on the below!!

The truck is a GMC 1/2-ton long bed with a 235 from 1954 and 4-speed tranny - all lokks stock. We got it on the road this summer after it had been sitting since 1980 and it has been running nice since the beginning of July when we got it on the road.

Since last week we sometimes get some loud noise from the transmission.
Well, it is kind of hard to describe sounds ... usually it starts with a "klunk" and then a "RRrrr" - like a gear slipping or a "peg" hitting the case.
We can also feel some vibrations in the truck when the noise is present.

The noise is only present when letting of the throttel or when coasting in constant speed and it goeas away when accelerating but comes back when you let of the throttel.

When the noise is present it does not matter if the gear is in or not - neutral, same sound, clutch, engaged or not, same sound - but it change with speed.

Our feeling is that the noise comes when "engine breaking" - stays for a while and then goes away ....

We have no problem shifting gears - with or without the noise - and the gears do not slip.

It seams like the noise comes from front of the "stick" but it is hard to say exact.

We have lifted the lid with the shifting mechanism - all gears looked ok and no play in bearings on the out-going shaft [perhapps you can not feel any play that way even if the bearing is shot ...].

So - do you have any idea of the issue we have - bearings on the out-going shaft - u-joint, speedo gear [we removed the out-going gear for the speedo to be sure] etc etc ?

We would really appreciate your feedback and input !!

Thanks in advance.

//d

Welcome!

The condition you describe sounds like a pinion bearing going bad. When the bearing fails, the pinion will slide back and hit the carrier making the noise. Mine too started on deceleration and got worse.

Drain the differential remove the cover. If it looks like THIS then its time for a differential overhaul.

Thanks for the input Sweet!
We had the cover off this winter since we had to replace the seals for the drive shafts - it did not look like that.

The noise we have come and go and sure seams to come form the gearbox - did you have the same symptons ?

//d

The exact ones. I thought it was the u joint (I have a closed driveline) and the noise was coming from what appeared to be the front of the transmission. Lesson learned is that these driveline noises can translate and appear in places far from the problem.

ok, thanks - the cover is going off this evening for a check!!

A pinion bearing will start making noise long before things get bad enough to cause pinion/carrier contact. The first telltale indicator will be a loose nut at the front yoke. Tightening the pinion nut will dramatically increase the noise if that's the source of the problem!
Jerry

A GMC 1/2 ton long bed has a short stub shaft between the transmission and the torque tube. It has a front and rear U joint and a bearing and bushing. It is very common for that area to give the noise you have.
Most of the time pinion bearings when going bad give their first noise on the pull, as that load is what it most receives.
After a while running with a pitted bearing will chew up the ball separator and the bearing will start to fall apart, then anything can happen as far as noise.

I'll remove the tube and check that as well - Pre'68 Dave ! In fact it was my next question - if the long bed had one or two u-joints.
Is the rear-end the same after the rear u-joint ? I have a complete rear-end from a Chevy 1/2-ton 1950 short bed [got it from my friend ... street rodder you know ;)] and I was thinking to swopp with that one if the pinion bearing is shot.
I guess I have to remove the rear u-joint first and lower the tube and then remove tha clamps holding the short stub shaft and then remove the front u-joint - or do you have any trick for this ?

One mroe thing - how does that read u-joint get lubrication - througth the small "pipe-plug" at the rear of the transmission [and how much oil gets in there ?] ? Maybe it has run dry for a while ....

thanks a lot !

//d

1948-54 are the same length except for the ones used with a Hydramatic.
The fill plug is for initial lubrication, after that trans oil works its way back to lube.

Dave,

Does a 1954 long-bed GMC have the same driveshaft as used in a 3/4 ton truck, and is the driveshaft on a 3/4 ton GMC the same as on a 3/4 Chevrolet truck?

It is my understanding that all 1954 Chevrolet trucks larger than the 1/2 ton had completely open driveshafts? I could be wrong.

I am not a GMC expert but growing up my Dad had a 54 GMC 1/2 ton with a stub shaft and torque tube.

I would suspect 3/4 ton Chev and GMC are the same.

I believe you are correct that anything larger than 1/2 ton was open in 54 up. Before that the front half was inclosed and the rear half was open.

Today I had some time to check the pinion bearing and the u-joint on the stub shaft.

Started with the pinion bearing - looked ok - no metal in the oil and no play.

Moved over to the rear u-joint ....
Removed the cover and found that one bolt had gone loose and made the noise !!

Some pics of the culprit and the damage it has caused !!

[IMG]http://i495.photobucket.com/albums/rr315/Fogelgren/GMC%201951%20U-joint%20issue/bild-13.jpg[/IMG]

[IMG]http://i495.photobucket.com/albums/rr315/Fogelgren/GMC%201951%20U-joint%20issue/bild-16.jpg[/IMG]

[IMG]http://i495.photobucket.com/albums/rr315/Fogelgren/GMC%201951%20U-joint%20issue/bild-15.jpg[/IMG]

[IMG]http://i495.photobucket.com/albums/rr315/Fogelgren/GMC%201951%20U-joint%20issue/bild-14.jpg[/IMG]

No wonder we had noise !

The front u-joint looks ok so now we just have to find a new and replace the broken one.

Hope to find one in Sweden else I have to order from the US - any good source in the US for this part ?

Thanks all for your input!

//d

Look like holddown tab spum around and made a little mess. If the bushings and trunion are ok, you can probably re-use.

Question is, why did it fail in the first place???

No - the u-joint is not reusable - the bushings are worn and there is play. I guess the vibrations did that !

Not sure if we ever will get to know why it failed - was it mounted in the wrong way with a broken looking tab ?

The other side was loose as well but the looking tabs was ok ....