'94 W124 Parking brake scraping - a diagram please - PeachParts Mercedes-Benz Forum

dtf · #1 07-28-2003, 08:04 PM

I think the parking brake pad in the '94 wagon is scraping on the right rear wheel. Can anyone supply a diagram of that region of the car. It sounds loose and I want to see if it can lock up the rear tire if it gets worse or comes loose.

400E_FAN · #2 08-25-2003, 09:19 AM

What I thought was a bad caliper turned out
to be parking brake shoe sticking....Anyway,
I have replaced both sets of shoes and springs
on both sides BUT now the driver side rear
will not rotate freely. Looks like the "retractor"
on that side will not "release" fully keeping the
shoes apart (i.e. rubbing the rotor). I have
tried to adjust the cable but no luck yet.
I squirted some wd40 into the hole from where
the cable enters the wheel area...maybe there is some rust preventing from letting go completely.

Those parking brake shoe springs are a PITA to put on!

Anybody have any ideas on what else I should be looking at?

csnow · #3 08-26-2003, 02:08 PM

Sorry, no diagram for the original post,
but for the 2nd post:

Assuming it was assembled right, it would seem that it would have to be that the shoe adjustor is set too tight, or the cable is too tight.

The shoe adjustor should be rolled back prior to assembly, since the new shoes are likely fatter (less worn) than the old. They are then adjusted for proper clearance after the rotors have been fitted. If the rotors go on hard, the shoes are too tight. On my older model, I believe the adjustor is tweaked through one of the wheel bolt holes (if I remember right- I work on a lot of cars...)

Parking brake cables are generally left alone, unless they were previously adjusted to make up for worn shoes. If the cable is not taught when the brake is released, this is not the problem.

Generally, the adjustors and any moving parts on the actuator lever are pretty frozen up by the time a rear brake job is needed.
A thorough cleaning and lube with moly 'brake grease' usually restores function. Sometimes it's less hassle to simply replace the adjustors, depending upon the design.

Every metal-to-metal sliding surface (including where the shoes rub on the backing plate) should be cleaned, and lightly lubed with brake grease to ensure good lasting results.

Spraying oil into the brake mechanism is a bad idea.

Best of luck.

400E_FAN · #4 08-26-2003, 03:07 PM

Csnow...Thanks for the pointers...my responses
below...

>Sorry, no diagram for the original post,
> but for the 2nd post:

> Assuming it was >assembled right, it would seem that it would have >to be that the shoe adjustor is set too tight, or >the cable is too tight.

> The shoe adjustor should >be rolled back prior to assembly, since the new >shoes are likely fatter (less worn) than the old. >They are then adjusted for proper clearance after >the rotors have been fitted. If the
> rotors go on hard, the >shoes are too tight. On my older model, I believe >the adjustor is tweaked through one of the wheel >bolt holes (if I remember right- I work on a lot >of cars...)

I made sure the adjusters ( I am assuming in MB lingo this is the "star wheel"?) were "closed"
i.e...they were not pushing the shoes apart.

> Parking brake cables are >ge>adjusted to make up for worn shoes. If the cable >is not taught when the brake is released, >this is not the problem.
>nerally left alone, unless they were previously

I have not really done anything to the cable yet.
I am noticing that the cable on the side that is
not letting "go" has more slack than the one that
connects to the other side and is operating fine.

I am not sure how to take up a little slack in this one to see how that may play....or should I leave it alone and look for other issues...

I will clean out the WD40 behind the "retractor"
and then apply break grease and see whether that
helps....

csnow · #5 08-26-2003, 03:39 PM

Slack is good. Tightening cable could only make binding worse.

Perplexed by your binding issue. Retractor springs are pretty powerful, particularly new ones.

400E_FAN · #6 08-26-2003, 05:37 PM

Yes, the retractor seems to be "strong" enough. I think I have narrowed it down to the little contraption with a "lever" that attaches to the cable. This thing has an the upper and lower shoes resting in notches with this lever in the middle. As the parking brake is applied it pulls the both shoes "in" and "out" i.e spreads the retractor spring thus pushing the shoes out and
in contact with the rotor. This works as desgined.

The problem occurs when the parking break is released...that lever's "elbow" is not popping out completely (hence the thought that the cable may be "sticking" somewhere) thus not allowing the retractor to compress and pull the two shoes together.

I put the old retractor spring back in just to check that the new one for some reason could not maintain tension.

I wish I had a digital camera and that would make it easier to explain.

Thanks.

csnow · #7 08-26-2003, 06:16 PM

Straining my memory to envision the mechanism. Done too many brake jobs to remember this one...

Is the lever the cable pulls on hinged?
Perhaps it the pivot point itself that is seizing up?

400E_FAN · #8 08-26-2003, 06:45 PM

You are right...it does have a pivot point!
Now that could explain the intermittent behavior I have noticed. i.e. once in a while in the past two days that elbow has popped out when I released the brake. But I could not replicate it....I am not experienced enough to have picked up on that.....I will check it out tomorrow...

But would the WD40 have freed it up? Or would it require brake grease?

I presume if either of those do not work then I would need a whole new brake cable...because it appears the brake cable seems to be attached pretty securely (perhaps soldered I cannot tell unless I take it apart)?

Thanks again! I was beginning to dread that if I could not fix it I would have to tow it to mechanic before winter rolls out around here in sunny Massachusetts!

400E_FAN · #9 08-27-2003, 07:50 AM

Got a chance to look at it this morning.
I lubed the "hinge" and it seems to be
working. You were right on the money
about that being the potential source
of the problem.

The rotor slips on easily but the shoe still touches it ever so slightly so I have to
figure out how to get the shoes closer
together when the parking brake is
released.

csnow · #10 08-27-2003, 11:00 AM

Well, that's good news!
The WD is good for unsticking and cleaning, but does not last long.
Grease would be better, or even motor oil would last longer.
The rear cable is generally a very cheap replacement part if you need to go there.

Slight shoe contact with rotor upon install is not really a problem, so long as it does not drag much. The shoes 'self-align' to some extent the first time you apply the brake. You may even find that the rotor rubs a bit going on, then the clearance is actually too great after brake is applied and released.

Shoes should get final adjustment after brake has been applied and released.

400E_FAN · #11 08-27-2003, 02:23 PM

Csnow,

Thanks again. I think this may work i.e. let the shoes seat themselves...I will re-assemble the calipers/brakes next week and then see if the shoes are seating themselves. If not then a new parking brake set will be the next option.

Much appreciated!