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Brake Diagnostic Help needed

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Minor1000y1962 Carsten Gubelt
Dusseldorf, Germany   DEU
Dear all,

first of all, let me quickly introduce myself. After having owned a MG B for >20 years, my wife and I have looked for a four seater to take along the kids.
We fell in love with a 62 Minor and now have owned it since last year.

Last week we ran into some issues with the brake system: all! wheels locked up at the same time and the brakes have not fully released since.
The brake pedal returns properly and I have not identified any brake fluid leaks (neither at the wheels nor the master brake cylinder).

Given all wheels are locked up my prime suspect is the brake master cylinder (maybe the return spring?). After looking at Haines and the Workshop Manual removing the master brake cylinder appears to be a lot more painful than on other cars, so I would like to be as certain as I can be that I have to do it.

So here is my question: Any idea what else could limit the return of the brake fluid? What diagnostic should I run before taking on the master brake cylinder?
The braking system is standard drums all-around, but a brake servo has been fitted by the previous owner. Anything I can checl on the brake servo?

Thanks for your support - much appreciated!

Best wishes from Germany and have a nice weekend
Carsten

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emjay Jim English
Marietta, PA, USA   USA
Welcome aboard. Are the wheels locked or just drag? The first thing to check is thee free play of the brake pedal. If you don't have a remote reservoir, you can take the cap off the master cylinder and watch through the hole in the bottom of the reservoir for movement of the piston as you slowly push the pedal. You need to be able to move the pedal a little bit before the piston starts to move. You should be able to tactically feel the free play if you can't look into the reservoir. Of course that assumes the piston has fully returned, which is required in order for the brake fluid to relieve any pressure back to the reservoir.

0123 Mike D
Biddulph, Staffs, UK   GBR
I think

Does the return spring on your brake pedal pull the pedal all the way up?
Check to see if you can lift ir by hand.

If no, you need to replace the spring.

If yes, do you brakes stay on if you remove the vacuum pipe to the brake servo?

If no, you need to recondition your servo

If yes, you need to recondition your master cylinder.

After that, GOK :-(



Edited 1 time(s). Last edit at 2018-05-05 08:43 AM by 0123.

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
crack a. led valve on any wheel, tighten and see if all wheels now turn. If they do it's master or servo. If it's master the piston isn't returning all the way or hole that lets fluid in and out is blocked

0123 Mike D
Biddulph, Staffs, UK   GBR
My pleasure Jim smiling smiley

In reply to # 29921 by 66jalopy crack a. bleed valve on any wheel, tighten and see if all wheels now turn. If they do it's master or servo. If it's master the piston isn't returning all the way or hole that lets fluid in and out is blocked

66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
That's what happens when you can't sleep at 4:00 am and go looking for trouble.confused smiley

0123 Mike D
Biddulph, Staffs, UK   GBR
smiling smiley

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pixelsmithusa Avatar
It's most likely one of two things. The first thing to check are the brake flex hoses. They collapse internally and can prevent fluid from returning to the master cylinder. The second, which has been suggested already is that the fluid return port is blocked. This can happen when the master cylinder pushrod adjustment has been made incorrectly. The latter adjustment can be made without removing the master cylinder, SImply remove the cover plate over the MC and loosen the locknut on the pushrod. Adjust the pushrod as to shorten the length in very small increments and test for a remedy. You probably won't need to adjust it very much of this is the problem. I've never known a master cylinder piston to get stuck on a regularly driven vehicle. It would have to sit unused for years for that to happen.

Unless the locknut was loose on the pushrod or if you've made any adjustments to it before this began, this issue doesn't usually develop spontaneously. I'm more suspicious of the brake hoses since that can develop suddenly. If the hoses are more than 5 years old, and certainly if more than 10, they should be replaced.

It's possible it could be servo related, but I'd check those hoses first.



Gerard

http://gerardsgarage.com/



Edited 3 time(s). Last edit at 2018-05-05 03:44 PM by pixelsmithusa.

Minor1000y1962 Carsten Gubelt
Dusseldorf, Germany   DEU
Thank you all for your helpful ideas - much appreciated.
I will take some time tomorrow to run through the diagnostics proposed by you and hopefully find it's not the master cylinder.

I really do not feel like removing the torsion bar ...

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66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
Good news: you do not need to dismantle the suspension. This is covered in many posts, but what you need to do is to lever the torsion bar downwards.

You can put the bolts back in the other way to avoid having to force the torsion bar down. I suppose you could buy 2 new bolts and cut the heads off the old ones and slide them out the other way.

0123 Mike D
Biddulph, Staffs, UK   GBR
You may find the bolts have been inserted from the other side.

If not, it is possible to cut the bolt heads off with an angle grinder.

Insert new bolts from the other side when you refit your master cylinder.

emjay Jim English
Marietta, PA, USA   USA
I missed there being a servo. I would suspect that first it's actually another master cylinder.

Flipping the master cylinder bolts is okay ONLY if there is enough room between the bolt and the torsion bar. You want a decent amount of clearance because you don't want any nicks.

pixelsmithusa Avatar
The bolts used on the master cylinder are not a regular bolt; the head is very thin so as to keep a good distance from the torsion bar. They can be replaced from the other side with a standard bolt, but a standard nut, especially if used with a washer, will put you in close proximity to the torsion bar; a somewhat risky proposition. Nicking the torsion bar will create a stress point for it to crack. At the very least, you will want to be sure that the threaded portion of the bolt does not extend past the nut. If you use an angle grinder for anything, you should use it to trim the height of the bolt and the thickness of the nut.

Personally, I wouldn't recommend you go anywhere near the torsion bar with an angle grinder; one false move and you'll be replacing more than the bolts. A proper fulcrum point and a long lever, i.e. a good length 2x4 and a short block, makes this a pretty easy job.

In reply to # 29929 by 0123 You may find the bolts have been inserted from the other side.

If not, it is possible to cut the bolt heads off with an angle grinder.

Insert new bolts from the other side when you refit your master cylinder.



Gerard

http://gerardsgarage.com/

usmh3 Avatar
usmh3 Rob Thomas
Cardiff, Wales, UK   GBR
I made some wooden wedges from a piece of Spruce (the long sides of a ladder) and used 2 hammer to knock the wedges together between the torsion bar and the floor about 10cm from the master cylinder bolts. This gave enough room to remove the 2 bolts. Pine wood breaks apart too easily. The wedges were about 25cm (1 inch) square with a 1-3 taper.

0123 Mike D
Biddulph, Staffs, UK   GBR
I didn't realise you were a "Fred in a Shed" too Rob smiling smiley

I used to take the locating washer off the back end of the bar.
Put an axle stand under the torsion bar
and let the weight of the car do the business.



Edited 2 time(s). Last edit at 2018-05-06 03:24 AM by 0123.

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