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MG MGB Technical - 68 B Complete Brake system Overhaul

Need Help

Did a complete brake system overhaul, all is new except the steel lines
We have bled the system according to the manual and have clear fluid from every bleed screw. We can build preasure by pumping the system, however, just after a few seconds the brake pedal goes to the floor.

Any suggestions??
MGC Crandall

Sounds like the master cyl seals aren't doing it or there's still air in the lines. Assume you checked for leaks at all connections including engine bay and all three flex hoses? Good luck

Paul
Paul Hanley

What did the "complete overhaul" entail?
Wade Keene

Wade is correct. To really help with such a question we need more information, of a detailed nature, than is provided by the comment that one has performed "a complete overhaul". However, these thoughts might help.

Did you replace the copper washers used with the flex hoses or did you re-use the old ones? If the old ones, did you anneal them before re-use?

Are all of the bleed nipples tight and sealing properly? Did you rebuild the rear wheel cylinders or replace them? Did you rebuild the front calipers yourself or have them rebuilt elsewhere?

There were some problems with the master cylinders a few years back, but the ones I have received recently have worked well. Do you know how old the MC you purchased is?

What fluid are you using? The silicone fluids can be somewhat more difficult to bleed properly than a non-silicone fluid.

Have you tried attaching paper towels (masking tape works well) around the various junctions and bleed nipples, then pumped up the system to see if you can find any leaks? Les
Les Bengtson

As Les asked, many things can become a problem. I just finished bleeding the brakes on my C. Complete rebuild. New hoses copper washers, wheel clinders etc. Rebuilt boosters everthing execpt some of the original steel lines. Found one juction from the master cylinder to the rear leaking. Used a MiniVac and pulled the fluid from the master to the individual lines did not completely work. Front brakes were fine rears were another story. The twin master cylinder system goes rear first then front. I believe that the B is the same. Finally had the wife pump up the brakes and then I opended the bleeders farthest from the master towards the closest. I never did have the pedal sink all the way, half way and the fronts would give pressure. Did you get a new master cylinder or just new seals? These have a chrome bore, body is what I would call pot metal. Any pits will give a leak. Try pumping up the brakes and bleeding again. I finished the old fasioned way, push.. hold.. release.. This with a line in a bottle 1/4 full of brake fluid.
HTH
Ron
Ron Smith

Thanks to all

This is a car we got that had been in a fire and set for 17 years (only 29k miles)
The brake system overhaul: new Moss master, new slaves in the rear new shoes, drums turned, new rubber hoses (3)with new copper washers and adjusted till we could not turn then backed off till able to turn
Front: new disks, new caliper kits and new pistons that I rebuilt, new rubber hoses with new copper washers, Also, new re-build kit in the front/rear distro. No leaks in the system

When we pump the system we can watch the fluid level go down into the system. then when we stop the fluid comes back into the master, is this correct?

Mike Crandall
MGC Crandall

This really sounds like the master cylinder.
However, first make sure the rear wheel cylinders
are not leaking. They will suck air in even if the
leak is minor. Check for moisture on the rubber
cylinder boots.

Just because the master cyl. is new doesn't mean
it's ok. The seals and/or bore could be
defective. There was a similar problem for a while
with midget dual MCs -- the bores were incorrectly
machined leading to leaks.
Ronald

Mike,

Are you versed in the proper techniques of bleeding the brake lines? Depress, tighten, release. Repeate until no bubbles in the jar. Start from furthest point, LR, RR, RF, LF.

I still vote MC seals

Paul

Paul Hanley

Did you bleed the MC before you installed it?
R. L Carleen

Ronald: Will check the rear slave cylinders
Paul: Yes on the proper technique, using a bleerer kit

RL: No, we did not bleed the master, how is this done?

Thanks
MGC Crandall

There are instructions for bench bleeding the master cylinder on my website at www.custompistols.com/ . Go to the MG section, then articles. Daniel Wong, a long time member of this BBS has written a rather good article on how to do this. Les
Les Bengtson

I've never done brakes on an MG, but on a GM you can install the calipers backwards meaning drivers on the passenger side and vice versa. My brother done it on his car, brakes wouldn't work, pedal would hit floor also. Switched them around and fixed the brakes. just a thought.....
JWK Kerr

Or along thoes lines, something went wrong with the front caliper rebuild? I know till a few years ago, rebuild kits were not available. Subsequently, I know zip about them. Anyone? Mike also rebuilt his "Distro"--both front and rear? What's that?
Paul Hanley

Les: I will check your web site, looks like I am going to try a re-build kit for the new master

Paul: In this model roadster there is a brass distribution unit/splitter that connects the lines coming from the master to the wheels. it has a small valve in it in case you loose preasure on the front or rear it shuts the bad system so you don't loose all your brakes
The front caliper re-build coould be an issue, I am not a professional, however, all went well according to the directions and the manual
MGC Crandall

This thread was discussed between 26/01/2004 and 27/01/2004

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