How easy is Brake M/C R&R? My tale of woe... - PeachParts Mercedes-Benz Forum

micalk · #1 04-02-2009, 10:42 AM

I'm pretty sure I hosed the M/C when I had to drive it without fully bleeding it. Can someone point me to a procedure so I don't totally screw up again? Here's the quick story...

First my car. 84 300SD bought 6 months ago with 90 KMiles, garaged CA car so no rust issues. Had maybe 2-3 KMiles per year the 5-6 years. So it needed some regular running and maintenance to bring back to full working condition. Had the ball joints and front rotors/pads done at a highly recommended local mechanic. Turned out I also needed calipers since the old ones wouldn't release completely. That job wasn't done as this is something I knew I could do myself.

When I was discussing my brakes with the mechanic, he suggested I blow out the brake lines with brake fluid before bleeding the brakes, which I did. Yesterday I replaced brake hoses all around and front calipers at the Auto Hobby Shop on the Navy base I work at (I'm a DOD Civilian and we get to use it too!) Unfortunately, I took the mechanic's advice one step further and emptied the M/C, wiped it out, blew out the old fluid, etc. That was my big mistake. I ran out of time (go figger) before I could bleed the system. Managed to get enough fluid (power bleeder) in the lines to get me to my brothers house a few miles away. (The emergency brake is your friend!) But getting there, I had fully depressed the brakes, potentially damaging the seals. Once there, we tried bleeding brakes with power bleeder, and got lots of air out of lines, but some strange results. Front passenger brake had three huge bubbles in it, and this may be related to not bleeding M/C. But all other brakes bled fine - the usual bubbles, but eventually clearing out. Driving home the problem only seemed to get worse.

So now I figure I have to replace M/C. From reading here I now know I need to bench bleed the M/C (this is a great forum - give yourselves a hand ... ) but I only have this weekend to do it before I leave on a big trip. I plan to order an ATE M/C and the reservoir seals. Is there anything else I'd really need to order just to be safe? Can someone point me to the M/C bench bleed procedure? Is the r&r simply unbolt from booster then assemble in reverse order? Or is it more complicated than that? I'm a fairly competent mechanic, but I'm an engineer too, and I just overthought (underthought?) this one.

tangofox007 · #2 04-02-2009, 11:05 AM

It's entirely possible that all the you need to do is bench bleed the m/c and rebleed the brakes. You can bleed the m/c while it is installed if you elevate the rear of car so that the m/c is level.

Brian Carlton · #3 04-02-2009, 11:20 AM

Quote:

Originally Posted by tangofox007

You can bleed the m/c while it is installed if you elevate the rear of car so that the m/c is level.

I'd like to try this on the '86 as well. Any tricks to that procedure.........or is it the basic two man approach with pedal and fitting............done twice for each outlet?

Or is is preferable to get the kit with the hoses to return fluid to the reservoir?

mdlwolf · #4 04-02-2009, 11:35 AM

I have done two masters on 123's and have never had any luck power bleeding the front lines. The back lines bleed fine, but the fronts just keep sucking in air somewhere. Both times, and the times I have replaced calipers in the front, the old method of bleeding where one guy pumps the pedal and holds while another cracks the bleeder screw-and repeat, etc., is the only way I've been able to bleed the fronts. Give it a try-

micalk · #5 04-02-2009, 11:37 AM

Problem is that pedal fades to floor, won't hold pressure when pumped. I'm not losing fluid that I know of. Just happened yesterday so too soon at this point. Could probably rebuild, but at this point just looking for a plug and pray solution. Mainly looking for the answers to my questions so I can get the parts before weekend.

tangofox007 · #6 04-02-2009, 11:49 AM

Quote:

Originally Posted by Brian Carlton

I'd like to try this on the '86 as well. Any tricks to that procedure.........or is it the basic two man approach with pedal and fitting............done twice for each outlet?

Or is is preferable to get the kit with the hoses to return fluid to the reservoir?

The hoses and fittings are the better option. But, in a pinch, it can be done by using one's fingers to plug the m/c ports when the pedal is released. Either option is best done with a helper tp operate the brake pedal. If there is a trick involved, it woud be to actuate the pedal very slowly. Otherwise, the fluid in the reservoir gets churned up and air bubbles are introduced to the m/c.

tangofox007 · #7 04-02-2009, 11:55 AM

Quote:

Originally Posted by micalk

Problem is that pedal fades to floor, won't hold pressure when pumped. I'm not losing fluid that I know of. Just happened yesterday so too soon at this point. Could probably rebuild, but at this point just looking for a plug and pray solution. Mainly looking for the answers to my questions so I can get the parts before weekend.

A new m/c should come with new reservoir seals and a new seal for the m/c-booster interface. As long as the old reservoir is reuseable, you should not need any additional parts, except for the lines and fittings for bench bleeding the m/c.

Brian Carlton · #8 04-02-2009, 12:15 PM

Quote:

Originally Posted by tangofox007

The hoses and fittings are the better option. But, in a pinch, it can be done by using one's fingers to plug the m/c ports when the pedal is released. Either option is best done with a helper tp operate the brake pedal. If there is a trick involved, it woud be to actuate the pedal very slowly. Otherwise, the fluid in the reservoir gets churned up and air bubbles are introduced to the m/c.

I'm going to try to get the proper hoses and fittings. When I installed the m/c, I didn't have the proper fittings for it. Do you happen to know the size of that fitting?

micalk · #9 04-02-2009, 02:43 PM

Does anyone know the size of the fittings on the M/C for a bench bleeding kit? Or where I can purchase one? Really don't need an all inclusive kit, just really need it this one time. are the bleeders on the calipers the same size?

Rick Miley · #10 04-02-2009, 03:26 PM

I just bought a rebuilt MC from NAPA a month ago and it came with plastic fittings and hoses for bench bleeding. Also, reservoir seals and mc/booster seal were in already in place. Everything needed all in one box, and the price was around $50.

Of course this doesn't help you if you already bought a MC.

winmutt · #11 04-02-2009, 03:44 PM

Just picked on up at Oreilly's this AM, came with bleeding kit. Similar pricing.

Micalk, if your calipers were shot then the MBC was probably not far behind. When bleeding the brakes use SLOW light pressure on the brake pedal. Fast and hard will make for more bubbles or a blown MBC. It also does not hurt to let the system sit for a few hours and then rebleed.

tangofox007 · #12 04-02-2009, 09:12 PM

Quote:

Originally Posted by Brian Carlton

I'Do you happen to know the size of that fitting?

Sorry. I am not in the right place to get an answer at the moment.

Brian Carlton · #13 04-02-2009, 09:19 PM

Quote:

Originally Posted by tangofox007

Sorry. I am not in the right place to get an answer at the moment.

NP.......if you come across it when you get back.......post again, if you can.

mobetta · #14 04-02-2009, 11:08 PM

one should be able to fab up a set of bleeder pipes from metric bubble flare steel brake line.(the type which is closest to 3/16 OD-it actually uses 3/16 line w/ metric ends. the guy at napa said"this is the most common size"- so that's what I bought, and it even fit.)

buy one piece, shortest you can, and cut it in half. add enough tubing to get into the MC, and make sure that they stay submerged. pump away.