Brake caliper repair on 300 SDL right rear - PeachParts Mercedes-Benz Forum

werminghausen · #1 12-31-2010, 03:53 PM

Sorry...This is my 300SDL! My fault.

I have ordered the ATE repair kit and new rubber hose for my rear brake because I believe one piston is stuck. I have squeeking noises once in a while, sometimes in curves and I hope to resolve these.
I am confident that I can do this job. I am just not sure how to handle the open system.
I need to disconnect the caliper from the hydraulic line for a while and also need to replace the rubber line.

How would you do this part if you don't want to empty the system? I have replaced all brake fluid last fall.
I could cut the old rubber line and plug it with a sheetmetal screw or such, do the repair on the caliper but then how would you change the rubber line without spilling a lot of brake fluid which is a mess?

Is there a way to do the exercise without draining the system?

leathermang · #2 12-31-2010, 05:36 PM

You only mention one rear brake...
remember that the rule is that you do brake work to One axle ... not one side..
so whatever you do with that ATE repair kit must be done to the left side also..
There is a difference between some fluid dripping out during one of these repairs and ' draining ' the system...
sometimes just a ziploc bag over the end with several rubber bands will be enough..
since you are not going to press on the brake with the line disconnected you are only dealing with gravity... and in a tube air must get in for the fluid to leak... so as fast as you can seal up the ability of air to enter the open line... then just flush as usual when done with the job...

vstech · #3 12-31-2010, 09:58 PM

would putting that ziplock bag on the MC reservoir stop the air from entering, and seriously slow down the exit of fluid out the open line? also, you could get a threaded cap from the hardware or auto parts store that matches the threads on the replacement line.
and if I replaced any rubber hose in the car, I'd replace it all...

newtodiesel · #4 12-31-2010, 10:08 PM

When I did mine recently, after I took off the rubber hose, I pushed the metal hard line into the bracket it came out of and it slowed down the brake fluid flow/drip, also put a bucket under the line...yea it makes a mess...

JimSmith · #5 12-31-2010, 11:50 PM

Brake fluid is cheap. Only one chamber will drain (the aft one). Only one line will be adversely affected - the one you disconnect - if you don't pump the pedal after before you refill the reservoir.

Jim

Brian Carlton · #6 01-01-2011, 09:31 AM

Quote:

Originally Posted by werminghausen

I have ordered the ATE repair kit and new rubber hose for my rear brake because I believe one piston is stuck.

This is not a fun job and will take forever if you don't plan it out.

The stuck piston may not come out with compressed air. If it doesn't, you're somewhat screwed.

The solution is to remove the stuck piston with the vehicle's hydraulic system. Get a suitable C-clamp and secure the GOOD piston. Be sure the stuck piston has a clear shot out of the bore. Return to the driver's seat and press the pedal about 10 times and the system pressure should dislodge the stuck piston.

Of course, now you've got the distinct pleasure of trying to plug the bore so that you can remove the opposite piston with compressed air. I used a piece of rubber held in place with a piece of wood. A second piece of wood is used as a backing plate behind the caliper and two C-Clamps keep the two pieces of wood secured to each other.

This is not one of those jobs that I care to repeat. I'll give them the $150 for the pair to avoid all this BS. And, I need to do the exact same thing on the SDL front calipers. Outboard LF piston is frozen solid.

Maki · #7 01-01-2011, 10:38 AM

I'm repeating myself, but to replace the hoses, get one of these: http://www.sjdiscounttools.com/vgp4lw.html

Use it to hold the flare fitting in place while loosening the hose fitting. Do not turn the flare fitting while the hose fitting is on tight. Don't be reluctant to apply plenty of clamping force with the Vise Grips; it will not damage the fitting, and you don't want the wrench to slip.

I changed the brake hoses on a buddy's '72 250c last year ... they were original, I believe. I cut the hoses off at the fitting, plugged them with a drywall screw and used a 6-point deep socket and 12-inch 3/8 drive breaker bar to free the hose fittings. Even with the bar it took some grunting!

leathermang · #8 01-01-2011, 12:10 PM

VStech, no, that will not stop the air from being able to exchange a few drops at a time from the lower end... and would be much harder to accomplish an air tight fit even if it would. You can pick up liquid with a straw by closing off the top... but at larger diameters that is not possible... something about gravity,surface tension and other unknowns.. LOL but the air will slip by a little at a time and it becomes a back and forth exchange..

*** Compressed Air *** to move the piston. WARNING, be careful if using this procedure as a lot of force can be built up and RELEASED like an explosion...
Do not let any fingers be close to where the piston might be ejected TO...
and wear both goggles and face mask is my suggestion...

JimSmith · #9 01-01-2011, 01:51 PM

If the caliper piston is truly frozen, it is corroded. A new seal won't last if it is in contact with a less than nearly perfect finish, and when you push the old piston back in, it runs most of its length over your brand new seal. Get a new set of rear calipers and always change both sides - fixing one side will make for uneven rear braking which can be fun in some instances but is most likely going to be unsafe for you and other innocents on the roads or sidewalks. I believe rear calipers are available from decent remanufacturers for under $100 ea.

Brakes are safety equipment. Do it yourself brake kits are only suitable for parts that don't have much corrosion at all - with a typical failure being the brake does not release. Frozen pistons typically damage the female bore on the way out. Resurfacing either the piston or the bore without real skill and tooling is a prescription for more serious brake failure. I have loosened frozen pistons by using a C-clamp, by the way, and once loose they can usually be removed by stepping on the brake with the caliper off the wheel to get them most of the way out, then you can pull them the rest of the way out with a rag and channel locks. Messy but it works.

And, Castrol LMA brake fluid is about $3 per pint. It should be replaced every two or so years to avoid corrosion issues inside the brake lines/calipers. I have a low threshold for dumping brake fluid and putting new stuff in there - it just isn't that wonderful a product, or expensive enough, to add any antics to the job to save the old stuff even if it was just poured in. Open the can and it is "used."

Jim

leathermang · #10 01-01-2011, 04:47 PM

We kinda got lost wandering around in the goal set by the OP instead of backing up and saying what Jim did. At the point you are at , OP, you just need new or professionally rebuilt calipers....It is easy to get fixated on one stupid little part which you have used all your available ' bigger hammers' on.. instead of realizing that that means it is not suitable for continued use by definition...

newtodiesel · #11 01-01-2011, 04:56 PM

Well...the OP symptoms are squeeking around corners and in turns..which to me does not sound like a frozen or sticking caliper, maybe we can get some more info from the original poster and help with the symptoms..or teach them how to check for frozen calipers before they replace something that might not need replacing.
I am by no means a mechanic..these guys have years on me..but just my thoughts

werminghausen · #12 01-01-2011, 10:13 PM

Quote:

Originally Posted by newtodiesel

Well...the OP symptoms are squeeking around corners and in turns..which to me does not sound like a frozen or sticking caliper, maybe we can get some more info from the original poster and help with the symptoms..or teach them how to check for frozen calipers before they replace something that might not need replacing.
I am by no means a mechanic..these guys have years on me..but just my thoughts

Well, thanks so much for all the information. I think I have a pretty good idea what is coming up here.
I'll do both rear caliper sides, left and right and I'll do new brake fluid...yes it is cheap.

Back to the symptoms: I have various noises at this particular rear caliper.
It is hard to figure out for me exactly what it is and in times I forget to focus. The most obvious noise was when I took turns. Let's say at left turns this caliper started making noise. My interpretation is that it is frozen or partially frozen. Maybe I am wrong. I even got off the car and let my wife drive slowly and the caliper make noise as if the brake pedal was pushed slightly when driving very slowly. But the brake pedal was not touched at all.

I don't think it is the parking brake...although I need to check the parking brake too as I don't see enough spring force pullling the cable and lever back when I apply the parking brake.

vstech · #13 01-01-2011, 10:16 PM

you could only need a new set of piston seals. if yours are torn up, it can cause a dragging type issue. pretty cheap repair, and they come in pairs of seals, so both sides are a no brainer.

werminghausen · #14 01-01-2011, 10:17 PM

Quote:

Originally Posted by Brian Carlton

This is not a fun job and will take forever if you don't plan it out.

The stuck piston may not come out with compressed air. If it doesn't, you're somewhat screwed.

The solution is to remove the stuck piston with the vehicle's hydraulic system. Get a suitable C-clamp and secure the GOOD piston. Be sure the stuck piston has a clear shot out of the bore. Return to the driver's seat and press the pedal about 10 times and the system pressure should dislodge the stuck piston.

Of course, now you've got the distinct pleasure of trying to plug the bore so that you can remove the opposite piston with compressed air. I used a piece of rubber held in place with a piece of wood. A second piece of wood is used as a backing plate behind the caliper and two C-Clamps keep the two pieces of wood secured to each other.

This is not one of those jobs that I care to repeat. I'll give them the $150 for the pair to avoid all this BS. And, I need to do the exact same thing on the SDL front calipers. Outboard LF piston is frozen solid.

Thanks Brian
Make complete sense what you are saying. I have the car standing on the driveway and don't drive...so I have enough time to do this job. I understand it is one of the unpleasant ones.

vstech · #15 01-01-2011, 10:31 PM

Quote:

Originally Posted by Brian Carlton

This is not a fun job and will take forever if you don't plan it out.

The stuck piston may not come out with compressed air. If it doesn't, you're somewhat screwed.

The solution is to remove the stuck piston with the vehicle's hydraulic system. Get a suitable C-clamp and secure the GOOD piston. Be sure the stuck piston has a clear shot out of the bore. Return to the driver's seat and press the pedal about 10 times and the system pressure should dislodge the stuck piston.

Of course, now you've got the distinct pleasure of trying to plug the bore so that you can remove the opposite piston with compressed air. I used a piece of rubber held in place with a piece of wood. A second piece of wood is used as a backing plate behind the caliper and two C-Clamps keep the two pieces of wood secured to each other.

This is not one of those jobs that I care to repeat. I'll give them the $150 for the pair to avoid all this BS. And, I need to do the exact same thing on the SDL front calipers. Outboard LF piston is frozen solid.

if it is a stuck piston, Roy has a great gadget for getting them out... air won't do it usually... and wood will not hold the other piston with roy's gadget...