C60S Transmission Question

[Phil Waterman]

I have notice a new vibration or catch in the transmission on my C60 (which I just installed a new engine). The problem only occurs during deceleration in 3rd gear on steep hills. It takes the form of a intermittent catch felt through the gear shift lever. As anybody else noticed a similar occurrence, if so did you discover a cause.

When I had the transmission out I did disassemble it to check for wear (it has been 18 years since the truck was restored) there was no metal chips in the case I strained the gear oil and ran it through fine filter with strong magnet to see if there was an unusual amount of metal particles which there were not. The only part showing wear was the pilot bearing area of the main shaft. I'm wondering if it is just bearing chatter on the pilot bearing. See picture.

I sort of expect the response - of course that is the problem, I'm already looking for new main shaft and bearing, but I looking for input so I can fix it once.

[cletrac (RIP)]

Phil, the only time you get any movement in the pilot bearing is when the clutch is pressed so that's not your problem. The problem would have to lie either with the 3rd gear on the main shaft or in the cluster gear bearings or the center bearings on the main shaft.

[Phil Waterman]

Originally Posted by cletrac

Phil, the only time you get any movement in the pilot bearing is when the clutch is pressed so that's not your problem. The problem would have to lie either with the 3rd gear on the main shaft or in the cluster gear bearings or the center bearings on the main shaft.

Hi David

Thanks for the response, my picture choice was poor resulting in a difference in part terminology, I was referring to the Pilot Bearing 4.352 the picture I posted is unclear it is of the Main Shaft 4.403 and not the Main Drive Gear 4.351. (see exploded view picture) Good point though the I did replace the pilot bearing in the flywheel of the new engine so that it would mate correctly with the original transmission.

The pilot bearing on the main shaft is turning in all gears accept 4th, which adds to the confusion because I only have noticed the "catch" or single chatter in 3rd gear when going down fairly steep grades 6-8% (steep for on road).

[Alex Blair (RIP)]

Originally Posted by cletrac

Phil, the only time you get any movement in the pilot bearing is when the clutch is pressed so that's not your problem. The problem would have to lie either with the 3rd gear on the main shaft or in the cluster gear bearings or the center bearings on the main shaft.

Hi Phil..
I agree with David..some good close up's of third gear and the cluster may tell the story better..sounds like wear on the gear faces..straight cut gears will show this wear and are more susceptible to this than angular cut gears,although all gears wear..prolonged usage of third gear would would induce wear that would only show on those gear faces..
And unfortunately the wear is can not be adjusted ,as shimming the crown and pinion to adjust for proper load clearances..
But it is measurable..put in the old bearings and reassemble the transmission..
Then turn the transmission slowly by hand and feed a length of plastigage through the teeth of third gear...record your clearances..
Then replace the bearings and do the same thing and the difference in clearances should be measurable..If there is no difference it will be the gears..
The consistency of the clearances,which will show up on the plasticgage will also tell you if a shaft is bent or a gear is warped
Enjoy..

[Tony Smith]

Or wear on the splines in the bore of the third sliding gear and/or on the splines on the splines on the mainshaft in that area. I see that the reflection on the mainshaft appears different in that area of the spline. This will cause the gear to cant over or twist and decrease clearances, thus binding up, or else radial backlash will cause the crown of one gear to mesh higher up the face of another gear rather than centrally in the valley. Is there any signs of galling on the faces of the teeth?.

[Phil Waterman]

Hi Guys

Thanks for the comments I working on getting the pictures posted. Be back later today with the internal photos.

Cheers Phil

[Phil Waterman]

Hi Guys

Well it took me awhile to figure how to post the pictures of the inside of the transmission in a meaning full size image. In the end I posted them all to my web site, left column has the pictures and the right column as discriptive information. http://www.canadianmilitarypattern.c...ansmission.htm

[A. Hudson]

I had no sooner finished reading your opening sentence, when I was pretty sure what was going on. A very good friend used to haul cement out of Marulan and Kandos in the 40's and 50's using Maple Leaf and Chev trucks. He explained to me in the 70's, when I was having the same problem with my C101 4x2. He told me that back then they used to carry a bag of spare bearings and when it got too bad, he could pull the box apart and be back on the road in 30minutes. Now I have never had any reason to doubt his words and he was a very clever man.
At the same time there was a number of 4x4's getting around carrying anything up to 5 ton of water and yet they did not seem to suffer this as the 4x2's. This got the better of me and I started observing propellor shafts and bearings under load. The universal joints on the 4x2 would always twitch when starting off. So where is this going..
I believe that when the propellor shaft exists the gearbox at an angle at the universal joint it is unable to turn with a constant velocity as the angle creates an uneven moment at the joint. The universal is attempting to straighten the rear mainshaft in the gear box, and the only thing stopping it is the pilot bearing between itself and the input shaft. Hence the wear.
On the 4x4 it is not so much of an issue as it travels in nearly a direct line to the transfer case.

[Phil Waterman]

Thought people might want to know what next step was. Well after various people confirmed my fears of a bearing chatter, see the chatter marks on the pilot shaft end. I went hunting for NEW parts and I found them at Obsolete Chevrolet Nashville, Georgia. Bit pricey $215 but not really if you think what the same parts for a modern truck would cost.

Any way then had all the parts new in the box. So now it is drop the transmission out and replace the shaft and bearings.

[Harry Moon]

I never did find a source for that cage bearing so i used a used one again. I'll make a note of that parts source in georgia. Good thread, I learned a lot.

[Grant Bowker]

Assuming that you are talking about the long thin, one - I found it easily at a local bearing supplier, current production.
I have also done business with www.obschevy.com or Tim Tygart's obsolete Chevy - your choice of names for them. Look specially at their NOS parts section. You have to search on part number, not a problem if you have the parts book. For example, they were able to source the early rubber covered gas pedal for the cab 13 (shared with some civil pattern) for me.

[Phil Waterman]

Hi Harry and Grant

Yes, I've used both parts sources before with good success. Obviously with NOS parts their stock fluctuates. I even found a NOS 4x4 engine oil pan for the 261 Chev engine that went into my `42 C60S, a part that I had been looking almost a year for and one day they had it.

The bearings are available relatively easily the main point of this exercise was getting a new main shaft. On the old shaft given the chatter marks where the cage bearing runs I was not hopeful of regrinding and finding a different bearing to fit. Even considered smoothing the shaft and re-machining to fit a speede sleeve.

Now I have to decide do I pull the transmission or see if I can pull the shaft in the truck. Either way it is going to wait until after November 11th veterans day event. Want to get another couple hundred miles on the truck to see if I've got to do anything else since the engine swap.

Cheers Phil