Oddball Dragging Caliper Issue - PeachParts Mercedes-Benz Forum

Skippy · #1 03-10-2013, 08:12 PM

'83 300D 325,000 miles. Recently I replaced the left rear wheel bearings. I failed to fully seat one of the bearing races on the first try, so after I drove it a little, I had to reset the bearing preload. Then it loosened up on me again, so I reset it again. Yesterday I replaced the brake master cylinder and bled the brakes.

Afterward I took it for a test drive in which it seemed like it still had a little of the "wiggle" upon dropping the accelerator like when the wheel bearings were bad or loose. However, the magnitude of it was quite small and I wondered if my lower than usual tire pressure might be contributing. There was also a very slight drift to the left. Other than that it drove fine. Brake performance was back to what it was before the MC went. Following the test drive, I decided to air the tires up to a higher pressure. While doing this, I noticed the left rear wheel was much hotter than the others. I jacked the car up and found the wheel hard to turn. I then opened the bleeder screw on the caliper and got no improvement. I decided to pull the wheel off, put a jackstand under the car, and proceeded to start loosening the wheel. Once I had all the lug bolts loose, the wheel became easy to turn. I re-bled the caliper, manually retracted it, finding it not sticky in the least, applied brakes to put the caliper piston back in place, and found the rotor with no wheel on it still easy to turn. Once I reinstalled the wheel, it became difficult to turn again.

I'm thinking warped rotor, but it doesn't pulse the pedal on a hard stop like you would expect from a warped rotor. Did I manage to warp the wheel hub somehow? Any other ideas?

macdoe · #2 03-10-2013, 08:18 PM

I thought you were suppossed to re-stake that rear bearing job when complete?

Skippy · #3 03-10-2013, 08:22 PM

The special nut was locked in accordance with the procedure. The loosening happened because I didn't get one of the bearing races seated all the way. Initially I was using a 24" pry bar to tighten the bearings, but bent it. On the third try I found a 4 foot length of 2x4 that I used to finally get the thing in spec and presumably fully seated.

The procedure I used:

PeachPartsWiki: Replacing the Rear Wheel Bearings

macdoe · #4 03-10-2013, 08:36 PM

Oh, I understand....I think we used a couple of hockey pucks with a hole drilled and piece of threaded rod through them to pull it all together, but it has been awhile....
We had one of our rear calipers doing strange things one time. How did the back side of the rotor look? I finally took a closer look with the rotor off and saw the back side of the rotor really badly rusted and almost like the metal was peeling.

Skippy · #5 03-10-2013, 08:48 PM

Back side of the rotor looks good. Front side got scored a bit when the hub suddenly had 1/4" of play the first time. The small amount of use it's had since then is smoothing that out.

macdoe · #6 03-10-2013, 09:08 PM

....another time I found the perfect sized pebble wedged in the casting behind the pad and catching up in the casting bore and pad back. It seemed like it would hold up the rear part of the caliper, I am not sure if it was the cause though I cleaned it out anyways. I wonder if the rubber piston surround could have an unseen cut or tear in it that could cause dirt or ice to jam things up if it packed it's way in there.

macdoe · #7 03-10-2013, 09:17 PM

there is a thread on here that shows a cut away of a caliper cylinder and the rings. There is a good explaination of what happens when those rings wear to the limit and how the fluid dynamics are changed to cause a dragging caliper. I think from age and use, those cylinders can get glazed too not allowing complete piston retraction. My plan if the problem reoccurs is to get the kits and rebuild the whole calipers. I am out of ideas and thats all I can think of. New calipers are big $$$$.

I put new hoses on and that did seem to help....for now after getting that pebble out. They can act like one way valves when they are weakened and collapsing.

Skippy · #8 03-10-2013, 10:14 PM

Rotors, calipers, and hoses on the rear were replaced about 30,000 miles ago, however that was seven years ago.

I got fed up with the thing and went to the gym. Between sets I think I figured out what the problem is. During the bearing replacement, I used the rotor as a slide hammer figuring that if I damage it in the process it should be readily apparent, and new ones are $22 at NAPA. I think what happened is I bowed out the rotor enough that it is now pushing the inside piston to max compression with a little force left on it. I'll replace the rotor and see if that fixes the problem.

Stretch · #9 03-11-2013, 04:21 AM

Why not measure the hub and then the brake disk with a DTI clamped onto the trailing arm? Then you'll know for sure.

Skippy · #10 03-14-2013, 04:58 PM

Replaced the rotor today. Same problem. Wheel easy to turn with the lug bolts just snug, very tough when torqued down. It seems cyclic-easier to turn at some times than others when making a full rotation. I wonder if I bent the hub (unlikely) or somehow have it in there crooked. What/where to measure to find out?

rscurtis · #11 03-14-2013, 05:08 PM

Install the lug bolts without the wheel and see what happens. I would suspect the bolts are too long and interfering with the parking brake, or the wheel is contacting something, in which case it probably wouldn't turn at all.

I don't see how the clamping force could bend the rotor, it's sitting on a flat surface to begin with.

Stretch · #12 03-15-2013, 04:15 AM

Quote:

Originally Posted by Skippy

Replaced the rotor today. Same problem. Wheel easy to turn with the lug bolts just snug, very tough when torqued down. It seems cyclic-easier to turn at some times than others when making a full rotation. I wonder if I bent the hub (unlikely) or somehow have it in there crooked. What/where to measure to find out?

Remove brake disc (caliper etc).

Clamp a magnetic base to the side of the trailing arm (I assume you don't have aluminium ones fitted!). If this doesn't work then get something big and heavy that won't move {tool kit?} and position it at a suitable distance from the hub so that you can...

...Position your clock gauge / DTI so that the probe will run on the surface of the hub. Turn hub by hand and watch how far that little needle spins. As it isn't a really smooth machined surface you will get some variation in needle output (?!).

If the hub is OK then check to make sure that the bearing clearance is still good => pull hub towards you and away from you - in and out towards and away from the differential.

If that is OK put the disk brake back on and repeat the test above.

Alternatively you might find it easier to check run out on the end of the hub - that would be checking for out of roundness in a vertical direction instead of lateral direction.

Runout check - YouTube

Stretch · #13 03-15-2013, 04:19 AM

Oh look Roy's been thinking of you (or someone else) have a look at these threads that I've just noticed further down my "New Posts" lists

how to check rotor runout

Reading and Using a Dial Indicator

(He da man - isn't that what you New World people say?)

Skippy · #14 03-15-2013, 04:25 PM

Will try those checks tomorrow.

whunter · #15 03-15-2013, 09:11 PM

Quote:

Originally Posted by Skippy

The special nut was locked in accordance with the procedure. The loosening happened because I didn't get one of the bearing races seated all the way. Initially I was using a 24" pry bar to tighten the bearings, but bent it. On the third try I found a 4 foot length of 2x4 that I used to finally get the thing in spec and presumably fully seated.

The procedure I used:

PeachPartsWiki: Replacing the Rear Wheel Bearings

In the procedure, did you note:

Install grease into the wheel carrier. Total grease installed in the assembly is 50G. This is split between the outside and inside bearings.
Place the crush washer on the hub.
Install the Outer radial seal into the wheel carrier
Install the hub into the wheel carrier.

**********************************

Did you know?
You need a NEW one to correctly set the bearing pre-load.

rear axle tension crush spacer availability?
rear axle tension crush spacer availability?

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