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C4 Rebuild

bdpeek

New member
Maybe this will help someone rebuild a C4. This is my first time working on this particular rear end, using a book for a closely related but not identical piece of equipment. If you find errors feel free to point them out or correct them.

C4Small.jpg


I knew I would have to go thru this rear end as soon as the drain plug was removed and nothing happened. Ramming a wire through the layers of collected silt allowed the oil could drain, not a good sign.
 
After pulling everything apart and cleaning found the following:

Main shaft bearings had grit and would catch slightly
Pinion shaft bearings were also bad
Fourth gear bushing was scored badly (reverse looked great)
Cross pinion bushings sloppy and egg shaped
Carrier bearings bad
Drain plugs were smashed and threads distorted
Axle bearings bad (one was broken)
Slave cylinder linkage broken and adjustment bolt stripped


Disassembly is straight forward with the exceptions of:

The brake bands can be a little stubborn but with a little patience they will come out

BrakebandsSmall.jpg


The carrier bearings require a special tool to remove, if they are bad just cut them off with an angle grinder/cutoff wheel and a cold chisel.

The cross pinion gears are a tight press fit with woodruff keys in the shafts. I pressed the shafts thru the old pinion bushings after removing the retaining clips. This ruins the bushings by dragging the key through them in my case they were already bad. I’m sure there is a better way to do this.

The instructions I was using said a couple of alternating pry bars should pull these gears, not a chance.

Mark the cross pinion shafts keeping them paired, along with both case halves and the center section. Also mark the cross pinion gears as to which brake drum gear they belong. This keeps mating gears together.

It doesn't much matter which cross pinion gear goes with which shaft as long as the gear mates with the original drum gear. Mark the axle drive gears for side and orientation, as they will go in either way.

An easy way to mark this stuff is to mark everything on the ring gear end of the part. Then during reassembly all the markings should face the ring gear.

The cross pinion shafts, drums, axle gears, and center will fit either side or upside down. The cases and center can be stamped, the cross pinions and gears a paint marker works after cleaning. Don't wash the paint off in the parts washer.

I could not find the correct original bushings so made some out of SAE 660 Bronze stock of the closest nominal size available thru McMaster Carr, and then rough turned them to size.

Turned the OD to a press fit in the case.

BushingODSmall.jpg


Turned ID slightly under final ID. ID will shrink some when pressed into case.

BushingIDSmall.jpg



The original bushings, or at least the bushings in this, were a split steel sleeve plated bushing they have two oil grooves and a bunch of dimples for holding oil or in my case silt.:ermm: The bushings where replaced with solid bronze no oil groves or dimples. I don’t have the equipment to cut the oil grooves which are normally used for pressurized systems anyhow.

NewBushingsSmall.jpg


Other bushings that did not get replaced were the brake drum bushings which had minimal wear and the axle gear bushings which again showed minimal wear.
 
After installing the bushings an oil passage needed to be milled as in the original.

MillSmall.jpg


Temporarily reassemble the case halves. An adjustable hand reamer with a guide was used to ream both of the bushings inline with each other, reaming one side to size then reaming the other from the opposite side.

ReamingSmall.jpg


ReamerSmall.jpg


Reassemble the halves with the cross pinions and axle gears and check for binding.

CenterSmall.jpg


Crosspinion1Small.jpg


Replace the cross pinion gears, snap rings and safety wire all the case bolts.

PiniongearsSmall.jpg


Replace the drums and check it over before pressing on the carrier bearings.

Bearing2Small-1.jpg


It’s too late to turn back and fix something once the carrier bearings are pressed on.

ChunkSmall.jpg

 
 
To be continued.......
(sick of typing :biggrin:)
 
 
 
 

Snowcat Pat

Active member
Very nice work. Would you like to work for us? However....

In your first pic the diff carrier is in there backwards. THE MANUAL SHOWS IT WRONG. You would not believe how many people have called us asking why their Imp OC-4 they just rebuilt has 12 reverse and 3 forward gears.

Also, if you haven't already, you may want to replace the brake band pins, they are often bent and often break, the correct alloy clevis pins are available at Zim's, very reasonably priced. Saves the R&P (Very expensive). We just had a customer lose a R&P a few weeks ago because of those pins.

The cork gasket looks like it would seal well but will the cover squirm around due to the fact the the diff is mounted to the machine with that cover? OEM is paper.

I hope I'm not out of line here, just wanting to help, not to mess up your thread.

-Pat
 

bdpeek

New member
Thank you Pat.

Not out of line at all, I appreciate any advice.

I reused the old pins, one was bent slightly and one looked homemade from a bolt, will replace them all, cheap insurance.

Took that differential out about a year ago when I finally got around to rebuilding it I had no idea which way it went, should have marked it:doh:.

Didn't detect any play in the rear cover, but wasn't looking for it either. Silicone was used on it before I got it but it did leak. I'll replace it with a paper gasket when I flip the diff around.:biggrin: Glad I held off filling it with fluid.

Thanks again for the tips.

Bobby
 

Snowcat Pat

Active member
I have what I think is an important update......

.....for the Brake Band Anchor Pins.

I made a press jig and tested to destruction about 15 new and used pins for both the OC4 and OC12 diffs. They are both 3/8 inch pins just different lengths. I wrote down the pressure it takes to bend and/or break the pins. I took several readings as the pin was undergoing deformation.

Results showed that the OEM and Zim's pin for the OC4 is very weak, the weakest of all the pins I tested. They are NOT ALLOY as I thought, just 'file hard' CASE HARDENED MILD STEEL, zinc plated and they crack and BREAK easily just as they start to bend. Both the OEM and the Zim's pins test out the same. So we no longer use the new Zim's pins.

We've sent out sets of our improved High Alloy pins to all our previous OC4 customers, no charge. They are much stronger than any other pin I've tested and will bend without breaking.

I need to start a more detailed thread about this but the short answer to 'What pin should I use?' is that a Grade 8 bolt is much stronger and won't break. That's not as strong as what we use now but its much better choice than the OEM or Zim's pins.

I'll supply more info on new thread but this was important so I wanted to get something up on the Forum now.

BTW the OEM OC12 pin is much a stronger pin than the OEM or Zim's OC4 pins discussed but they still break and if they are bent should be replaced. We used to get the OC12 pins from Petersons but they have been out of stock for 6 months, so I sent an old pin out for metallurgical analysis and went from there.

I have replaced the pins on every OC12 rebuild with the Petersons pins, and they were expensive. The pins we have now are stronger yet, but not more money.

Why does it matter? Well if the pin breaks and falls out it usually ends up breaking teeth off the R&P. At the least it will tear up the ends of the brake bands. And possibly stranding you, the driver.

Upon initial disassembly, five of the OC12 rebuilds we've done have had at least one broken pin waiting to fall out onto the R&P, on one it had already happened

Just FYI

-Pat
 
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