MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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limey222
Michael Cubbon
Portland, OR
(129 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: limey222
Date: September 02, 2015 08:20PM

Took the car around the block to check out the clutch and T5...all is now good but the car ground to a halt and I discovered that the front disc brakes had locked up. Fortunately I had a small wrench with me and used the bleed screw on one side to quickly bleed of the pressure in a quick squirt. It was enough to get me home using only the parking brake to stop. The brake stop switch is backed all the way off so its not that. The slave cylinders are less than 6 months old and the master cylinder is new. Please help me to discover reason for this last glitch.


mgb260
Jim Nichols
Sequim,WA
(2477 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: mgb260
Date: September 02, 2015 08:28PM

Michael, did you see if you could wiggle the master cylinder pushrod? You may have to put washers between master cylinder and mount to get a little free play.


88v8
Ivor Duarte
Gloucestershire UK
(1049 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: 88v8
Date: September 03, 2015 04:14AM

Another possible adjustment, don't know what servo you have in there, but I recall from years ago problems with my Landy and my TR6, there is an adjustment to the servo pushrod, locknut arrangement..There has to be a clearance between the servo pushrod and the master cylinder to ensure that the master returns fully when hot.
Otherwise when the system gets hot and the fluid expands, it has nowhere to go and the brakes will lock.

So whatever car your servo came from, check the service manual and see what the end float should be.

I seem to recall there is a setting in the Haynes manual for the TR6, but it's in the garage and it's raining, I'll have a look later.

Ivor
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ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1166 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: ex-tyke
Date: September 03, 2015 09:09AM

Quote:
There has to be a clearance between the servo pushrod and the master cylinder
A quick test is to see how much pedal freeplay you have - should be about 1/8"
Edit: Wow, should have proof read that freeplay.... now it sounds right!



Edited 1 time(s). Last edit at 09/03/2015 06:52PM by ex-tyke.


RMO 699F
Mike Maloney
SW Ohio
(531 posts)

Registered:
12/09/2007 12:28PM

Main British Car:
1974 MGB Sebring GT, 3.9 Rover V8

authors avatar
Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: RMO 699F
Date: September 03, 2015 09:13AM

Michael, did you put new flexible brake lines on when you did the brakes? I learned a few years ago through my own false economy that locking front disc are allmost always the old hoses collapsing...when this happens, the fluid is locked between the brake and the collapsed hose and can not return to the MC.


limey222
Michael Cubbon
Portland, OR
(129 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: limey222
Date: September 03, 2015 10:58AM

Ok, some responses to your suggestions.
New stainless braided flexible hoses installed about 6 months ago.
I couldn't get the darn nuts off the Brake master cylinder flanges to add spacers so I did the next best thing and notched out the brake pedal where it was hitting the pedal box. This gave me perhaps another 1/4" of movement which helped take pressure off the cylinder rod clevis. I still don't have what I would call "wiggle room" perhaps I should take another look in that area.
My servo is separate from the master cylinder and on the opposite side of the engine. I don't believe that it has any adjustment.


88v8
Ivor Duarte
Gloucestershire UK
(1049 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: 88v8
Date: September 04, 2015 02:36PM

No, probably it hasn't. The adjustment would be between the servo pushrod and the master.

Presumably one day you'll need to replace the master and at that point the nuts will danged well have to come off, so I guess another visit to the nuts now may be in order. Are they jammed or rounded or inaccessible?

Ivor



limey222
Michael Cubbon
Portland, OR
(129 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: AAAARrrggg! Clutch is fixed now front brakes are locking on
Posted by: limey222
Date: September 04, 2015 03:33PM

While the problem might still be with the MC push rod clearance another factor has emerged, on checking the PDWA valve I unscrewed the plunger switch and discovered there was no plunger in there. In addition the switch hole was full of brake fluid which to me means that the seals are shot on the shuttle. I suspect that the shuttle has moved one way instead of being centered and that is why the front brakes have locked. I have purchased a reconditioned one from a UK supplier and will pick it up from my sisters home next week when I visit the UK. Won't get to install it until after the 22nd....more then.


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