Saturday, August 1, 2009

Refurbishing the rear differential.

Part of my big buy from OpenTracker was a set of rear leaf springs, shocks, shackles, and U-Bolts. Unfortunately, like everything else that was below the rocker line on this car, the rear differential was a real ugly piece of work.

I started by removing the rear brake lines, housing vent, and brake tube bracket. I then removed the 4 nuts from the axle tube flanges but was unable to remove the axle from the passenger side since the bearing was rusted to the inside of the housing. I happened to have a 20% off Harbor Freight coupon handy so I went down and bought a slide hammer. The cast axle puller attachment didn't fit the standard 4 1/2 x 5 wheel bolt pattern of course, so I had to use a die grinder to wallow out the appropriate holes until it would slide over the axle studs. The hammer weight was 5 pounds but I had to slam that sucker HARD several times to break the bearing loose. Finally, it slid out:

Oddly, the driver side axle literally fell out of the axle tube and I merely removed it by hand. I was then able to remove the drum brake assemblies from the axles. Very little fluid escaped from the ends of the axle tubes. It was pooled up behind the seals.

Removing the "pumpkin", or "gear carrier", was an adventure in itself. As far as I could tell, it had never been cracked open in it's 40 years. I expected the nuts to be rusted badly to the studs but after shooting them with WD40, they came off fairly easily.

I then attempted to separate the carrier from the housing but it would not budge. I tried tapping a chisel in between to crack the seal but was only succeeding in dinging the edge of the carrier so I took a different approach. I hung the carrier from my engine hoist and cranked it about 2" off the ground with the jack stands strapped to the housing.

I then whacked down against the housing with a dead blow rubber mallet and eventually the old gasket cracked and tore away. I then carefully worked around between the studs evenly was able to separate the carrier from the housing. The hoist was also great for keeping me from tweaking my back lifting the carrier because that sucker is HEAVY!

Here's the broken down rear differential with old, nasty, smelly, original fluid still pooled in it:

Here's a better shot of the fluid. I think it might need to be changed.

After I dumped the fluid into a waste bucket, I used the seal puller attachment for my new slide hammer to pop out the axle seals:

Here's what the end of an axle tube looks like.

Here's the cleaned out housing. Now it's off to the sand blaster with the housing and the carrier. I carefully sealed the gears of the carrier with a heavy plastic bag and coated the mating surfaces with several layers of duct tape over masking tape to protect it at the blasters.

While the differential was away at the blasters, I concentrated on cleaning up the axles. The passenger side axle bearing that was rusted into the housing also happened to be worn and had play in it. I opted to take both axles to a local shop and had the old bearings and their collars removed and returned to me so I could clean up the hubs and bearing retainers. Here are the axle hubs before cleaning.

After cleaning. Well, the left one is anyway.

After cleaning and paint and ready to go back to the shop to have the new bearings pressed on.

The shop did a good job but I was a bit sticker shocked when they handed me a bill for $100 to remove and replace the bearings because I provided the bearings. Folks on the VMF told me that they got it done for a "case of beer" or "$20 an axle" so I felt a little taken.

When I bought the car, the brake pads and springs were new but I still felt the need to tear them apart and clean them up and paint them. Here's the "before" picture.

After disassembly:

I ran the backing plates through the blast cabinet. These took awhile and I had a problem cutting through the heavy layers of rust on these.

After cleaning, priming, and painting the plates and miscellaneous parts:

The "after" picture:

A week later, the housing and carrier came back from the blaster. I also had the drive shaft blasted but that's a story for another time.

Since I was going to prime the carrier with red oxide PPG DP74LF anyway, I figured it wouldn't hurt to prime the housing as well with the "better" primer.

I then painted it with several coats of Rustoleum Satin Black 7777. The problem is that the two aren't completely compatible. The black removes easily from the DP74LF. I just gritted my teeth and ignored it hoping that the Rustoleum would eventually set up and harden.

The carrier:

After finishing the paint, I strapped the housing down to the jack stands and cleaned up the mating surfaces with wire brush, lacquer thinner, and brake cleaner.

I strapped the housing to the jack stands to keep it facing upwards to lower the carrier back down onto it. I opted to take advantage of this and poured one of the two quarts of 85W-90 gear oil into the housing so I wouldn't have to squirt it through the hole in the side of the carrier later. I opted to only do one quart because I don't yet have the seals installed to this point.

At the recommendation of several VMFers, I doped the paper gasket with Permatex Indian Head Gasket Shellac on both sides and let it dry.

I then seated the carrier onto the housing and installed the nuts and torqued them to the specifications in the factory service manual remembering to reinstall the ID tag.

I next drove the seals into the axle tubes. I attempted to use a cheap Harbor Freight seal driver kit but it failed and the crappy plastic disks cracked. I then made my own driver disk out of 1" HDPE plastic and pounded the seals into place. Those seals were very difficult to drive in and have a kind of concave look to them. Honestly, I think the repro seals from NPD are a few thousandths too large OD.

I then applied gasket shellac to the flanges, installed a paper gasket, applied gasket shellac to the outside of the paper gasket, slid on the drum brake assembly.

After installing the drum brake assembly, gasket shellac was applied to the axle bearing retainers and a paper gasket was placed onto it and the gaskets outside face also had shellac applied. The axle assembly was then slid into the axle housing and 4 new retaining nuts were torqued down on each brake assembly though the hole in the axle hub.

It was definitely looking better but needed some adornments before I could let it go to the ball such as new brake lines and spruced-up emergency brake cables. I then squirted in the last quart of new gear oil.

Time to shove it under the car. Placed up on jack stands as high as it would go to allow the leaf springs to go below.

The rear suspension parts were purchased new from OpenTracker and consisted of:

Grab-A-Track rear shocks
4.5 Mid eye 1" drop leaf springs with new U-Bolt, front eye bolt and rear shackle kit

The leaf springs and shackles were bolted into place but not torqued down. They need to remain loose until the car is on its tires and then tightened. Otherwise, the car will sit too high.

I then lifted each side down onto the springs and oriented them over the centering bolts. The U-bolts and shock plates could then be installed and torqued to specs.

Finally, the shock absorbers were installed along with a brand new brake tube and vent tube.

The finished product.

Here's a picture taken at a similar angle a little over a year ago:

Update 8-6-2009: I ran the rear drums through the blast cabinet:

Hit them with a coat of etching primer:

And 2 coats of Cast Blast paint:

And the rear is wheel-worthy. We'll see how long they stand up repeated braking heat.
Update 8-22-2009: I put the original standard rear tires back on so I could torque down the leaf spring bolts. I needed more clearance so I could get under the car so I put it on heavy 4" blocks and blocked the front tires from the front and back so it wouldn't roll. Don't worry, I'm paranoid by nature so I tested the heck out of the stability by trying to roll the car back and forth but it didn't budge and inch so I crawled under.

Here's the torqued and wheeled rear differential from the business end.


  1. A lot of hard work! Good job and keep the updates coming.

    Thanks for following my 66 Convertible blog!

  2. great job and it looks good...

    bobby reyes

  3. what kind of paint do you use for the breaks and the differential

  4. where to buy new brake tube and vent tube ???? hugh 66 coupe in FL

    1. NPD sells both:

  5. Great job! I'm in the process of doing the same thing to my 67 fastback. Thanks for the great pictures to help me out

    1. You're very welcome. Good luck with your Fastback!

  6. Excellent write up. This will be very useful as I'm about to do that same thing. Thanks for the link from VMF

    1. You're very welcome. Glad it's helpful to you!

  7. Great Pictures and descriptions! Working on a 68 GT and needed some good pics of a finished rear assembly. Only question (as I have to do this) is why didn't you also change out the pinion seal? Mine is leaking badly.