RE 220S Psfred or Mark please help - PeachParts Mercedes-Benz Forum

joshhol · #1 06-05-2003, 05:25 PM

Update:

quote:
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You must inspect the bore -- any scratches or corrosion, get rid of it. Under NO circumstances can you hone it, if you do, the seals will be undersized and it will either leak or fail quickly. For that car, a new master cylinder is MUCH cheaper than sheetmetal damage!
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- originally by psfred

I got both master cylinders out, and dumped them in a vat of ATF until I was ready to work on them. My mechanic looked at them both and says I should go get one of those 12 dollar brake hones at auto parts store and run it on the drill at low rpms just to "freshen" up the bore. These hones are the small two or three stone variety.
Peter, is this what you said explicitly NOT to do or are you referring to actually grinding it out larger inside at some sort of machine shop?
The clutch master cylinder looks really good inside, nice and smooth, no corrosion, I don't want to junk it up. The brake master looks borderline and it would just be prudent to stop fussing with it and get a new one. I've got the clutch rebuild kit on its way now, a mere $25 bucks. My mechanic knows of a place to remanufacture the brake master if I go that route, but it might not be that much more for a new one, I don't know yet.
I appreciate your advice.

psfred · #2 06-05-2003, 06:44 PM

Josh:

DO NOT, at any time, for any reason, ever hone a master cylinder with a drill motor!

The finish on brake parts is NOT the same as engine bores, you should only be able to just barely see any hone marks. If you see clearly visible crosshatch marks, as you are supposed to in an engine, the seals will be eaten off in a matter of weeks, leaving you with no brakes. The seals aren't cast iron or chrome-moly alloy, they are rubber, and any significant surface texture will ruin them very fast. If you procede to "clean it up" you will also, even with a proper stone, you will enlarge the bore, and the seals will leak, leaving you with no brakes........

Stay away from this idiot, he'll get you killed.

If the bore is clean, almost shiny, has no obviously duller or shiner spots, no pits, and no scratches, it's just like new, put the kit in.

Peter

joshhol · #3 06-05-2003, 08:28 PM

Amen,

I don't know why this talented mechanic with a high volume successful shop would tell me to do this. He's been working on these things when they were new, knows them like the back of his hand. I've been giving him my business for a long time and he's always giving me breaks and helping me out etc. Maybe I've bugged him a few to many times about how to fix something but I don't think he wants to see me rubbed out.

I'm :

Well, thanks a lot Peter, I'm not going to do a thing to the clutch cylinder, but I'd say that the brake cyl. is junk. Guess I'll bite the bullet and buy a new one. It's not that much all things considered.

psfred · #4 06-05-2003, 09:28 PM

Josh:

My friend the MB mechanic (Master Mechanic, which actually means something in Germany, has a framed certificate on the wall signed by the Mayor of Dusseldorf) says to never touch the surface of brake cylinders. I trust him -- he's been working on MBs since the late 50s.

It is a common practice in the US to hone brake cyinders every time you put a kit in them. Don't know the source of this idiocy -- if it was bad, making it larger won't fix anything (who has ever seen an oversized seal kit??) and if it needs honing, it usually has something else wrong with it.

The fun part is that all US manufactures relieve the ports with a little chamfer, while the Germans don't. Guess which brake master cylinder lasts longer!

Peter

joshhol · #5 06-16-2003, 10:50 PM

Here's the latest: Got the new Brake master cylinder on the way from the dealer as well as the clutch master cylinder rebuild kit.
My question is about re-assembling the clutch mc. Is there a brake cylinder paste that I need to smear inside the bore before installing the kit? What other procedures do I need to be aware of?
As far as I know I apply that paste, install the guts and re-mount the clutch mc. Then I have to fill and bleed the system. I know of the bleed screw on the resovoir I assume there's one underneath on the slave. I'm green at this stuff, so any common sense MB for dummies advice is not overlooked.
I'll probably be trying one of those one man bleeder kits.

Also, I liberally applied POR 15 in the affected area I'm working in. I wonder how that stuff holds up to brake fluid, not that I should have any leaks for a while.

Thanks

psfred · #6 06-16-2003, 11:41 PM

Josh:

New master cylinder will be complete, all you have to do is bench bleed it and install. You and can also bleed in the car after installation.

To reassemble, if you get a kit, you line up all the parts on a clean bench (there is a diagram with the kit) and then coat the rubber bits with the "paste" --actually a VERY slimy goo that lubricates everything nicely. Guts go in, in order, with piston seal lips pointing the correct direction (see insert). Be carefull not to cut the lips on the snap ring groove -- there is sometimes a little ring tool to use to slip them in past the groove, sometimes not.

Once all the guts are in, you need to insert the base seal and press down on the springs so you can put the snap ring in to keep them all in place.

To bleed, if you have the little hoses that go from the line holes to the reservior, you can bench bleed. Simply fill reservior and gently pump the pistons in and out until you have no more bubble coming out the hoses. If not, just install and open the front caliper bleeders. If you have a MitiVac, attach and pump until you get only a stream of tiny bubbles and close bleeder. Make sure the reservior doesn't go empty!

If no Mitivac, pump the pedal slowly a couple times with one bleeder open, then let gravity flow the clean fluid down and out until no more air comes out. If you have a helper, you can pressure bleed by opening the bleeder valve while your helper presses down on the brake pedal. Whent eh pedal hits the floor, close the bleeder valve and ahve the helper slowly let up on the pedal. Don't let it up too fast, you can suck air in around the piston seals.

Do the rears the same way, although they usually won't gravity bleed unless the lines have brake fluid in them.

Can't help with the clutch, the last car I had with a hydraulic clutch was the Toyota!

Peter

joshhol · #7 06-17-2003, 01:53 AM

Peter, thanks for your time.
Hopefully I can get it from here, and get this thing back on the road. I feel like I'm abusing it by not driving it.
I'll let you know how it goes.