Rear disc brake questions

[waqas]

Hello all,

Today I decided to replace my rear disc brake pads. I removed the calipers and discs in order to examine the condition of the parking brake shoes. The left side seemed in order, but I was dismayed at what I found on the right side:

• One disc pad is worn almost down to the backing, but the other one is still ok.
• The rotor is pitted in the pattern of the pads. The thickness is > 10mm as per spec.
• The right axle seal seems to be leaking slightly (see photo-- sorry for being out of focus)
• One of the spring retainers for the drum brake shoes is broken.
• The right brake shoes seem to be worn out of spec (but I already have replacements on hand)
• There is a lot of brake dust on the right side. The left side is relatively clean.

I had changed all the flex hoses and replaced all the brake fluid as soon as I bought the car, but the pads looked ok at that time (did not dismantle back then).

My questions are:

• Regarding the disc pad wear, assuming the PO replaced both inner and outer pads together, does the unequal wear indicate a sticking caliper?
• What caused the pitting on the disc? Are the discs still usable? (photos coming soon)
• How bad is the axle leak? Is this something I absolutely need to take care of before driving up to PUB? (I suspect I already know the answer to this one)

[waqas]

Here are close-ups of the right brake disc. The pitting is found all around the disc and are shaped exactly like the pads.

The disc thickness is still within spec ~ 10.3mm.

[waqas]

One other question:

I removed the brake shoe retainer springs from an earlier parts car (see photo), and they look very different from my later retainer springs. One of mine is broken (see photo), and the earlier springs look like they are better quality.

• Does anyone know why MB made the change?
• Are the early and later springs interchangeable?
• Is one type preferable over the other?

[ja17]

Hello Waqas,

The inner rear axle seal is leaking 90 w oil into the sealed bearing section of the alxle before it leaks out. This will wash out the packed grease in the bearing and will eventually cause bearing failure. It may take a good while to fail however I would do it before heading out on a long trip. It can only get worse.  Check the vent in the diff. just to make sure it is not plugged up, just in case it is causing pressure build up and leaks.

The brake problems are somewhat typical of a car that has been stored for a  long time. The pitting on the discs will cause faster pad wear, however rear pads last a long time. You may get a slight uneveness, or pulsating from the pedal as the pads hit these rough areas.  You can actually see a "pit"  outline of the pads in the rotors.  This happens during long storage (most often in a not so dry environment).
 
Uneven pad and shoe wear is can also be the caused by things sticking and hanging up after long periods of storage.

Ideally, replacing or reconditioning all the questionable items is best. However, calipers and discs will often times clean themselves up and begin to function properly again after some "exercise".  When i come across unequal pad wear I exercise the calipers by removing the pads, pushing the pistons back, installing the worn pads back in temporarily and then press the brake pad until the calipers return, then repeat several times. You need to remember to cover the brake fluid resevour with a rag or you may squirt fluid as  you push the pistons back in the calipers.  Understand that the pistons in the calipers may spend many years at the "one end" of their cylinders. Exercising them will clean and lube the areas where they have not been for years. You can also observe their movement as you execise them.  Don't forget to install the old pads or the pistons will pop out.  I usually just temporarily slide the pads  in on their sides without the pins to do the exercise.

 It's your call. The item which would be most likely to put you at the side of the road is the leaky axle seal.

[waqas]

Joe, thanks for the reply.

Part of my dilemma is that I don't want to do much to the axle until I replace it with a 3.27. However, any brake work will easily carry over to any new axle.

I think I'll ignore the leaky axle for now, and ratchet up my search for a 3.27 axle. The idea is to prepare the axle with all new seals/bearings/etc before installation, so anything done to this axle is a waste (for me at least).

If anyone knows about a 3.27 axle around central Texas, let me know!  (I have 3 spare axles-- 3.92!  )

[Raymond]

I did my rear brakes two weeks ago.  They only had 5,000 miles on them but their was an intermittent groaning sound from the left rear after 20 or so miles of driving.  I too found a broken shoe retainer spring with that failure.  In mine, it was wedged at the bottom of the shoes.  Those shoes were half the thickness of the other side.  It too had more wear on the outer pad than the inner pad.  The outer piston was sticking.  I don't know whether the sticking piston or the broken spring came first. 

I replaced the calipers on 40 year-old general principle.  Those were almost $400 each.  I wonder if that cheap retainer spring will cause another problem.