Dragging front brakes.

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Stewart
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Dragging front brakes.

Post by Stewart » Mon Feb 21, 2011 7:07 pm

I'm dealing with a weird front brake issue. The front brakes will intermittently drag when cold you can feel the slight resistance when moving the car by hand. WHen they are warm they will drag enough to slowly bring the car to a stop and hold it on a mild slope. While driving the pads are being held enough against the rotor to hear them along with that lovely burning brake smell. Both front wheels feel to be at the same temp.

75 mgb with the brake booster

Heres what I've noticed

I can do a couple of hard stops and get the brakes hotter than the sun and they will still work perfectly with out dragging however if I get into city traffic a few stop signs even with cold brakes is enough to get them to start sticking. When the brakes start sticking the pedal goes rock hard. When they stop sticking the pedal returns to normal.

So far I've replaced the calipers, pads, front hoses and even the rotors. I'm I looking at a bad master or something else?

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Steve Simmons
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Re: Dragging front brakes.

Post by Steve Simmons » Mon Feb 21, 2011 7:48 pm

Since you've replaced both calipers and hoses, my guess would be the MC not returning properly. Does the pedal still feel normal?

I've had a similar problem but it was the caliper.

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Jimmy
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Re: Dragging front brakes.

Post by Jimmy » Mon Feb 21, 2011 8:36 pm

I'd agree with Steve; if you have good hoses and calipers it's likely the master. Could be as simple as that there isn't enough free play in the rod, or a "sticky" piston.
I had a car catch on fire after putting new brake shoes on it (yeah, they were a bit too tight, but I had no choice but to drive with them at the time) and, predictably, the brakes got tighter and tighter as they heated up.
With only 18-1/2 horsepower (a Fiat 500) it didn't take too many miles before even First gear wasn't enough. And once I got stopped the heat flourished, hence the fire.
Ended up driving the last several miles on a bare rim, which with your new wheels I would recommend against.
Since your problem is sporadic, I'd definitely look at the master cylinder (on sale at the B-Hive, by the way).
On the other hand, with your new blower you shouldn't need brakes - just put the rear end out at will and take the corners the stylish way.
In baseball, running into someone is apparently a "collision".
But doing the same thing in a car somehow makes it an "accident".

Stewart
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Re: Dragging front brakes.

Post by Stewart » Thu Feb 24, 2011 5:02 pm

Update

Changed out the master with a new replacement and checked the hard lines for kinks there were none.

With the booster connected felt great for a while then the brakes pumped up and the front started dragging again. Bad enough that you could not move the car using your foot to push with an open door. When the brakes are working normal no effort to do so.

Jacked the car up fronts locked up rear perfectly free.

Cracked the bleeder on the left front it spurted and the brakes released enough to move the car. Front brakes were HOT.

Started the car up and the over the space of 30 seconds the front brakes bound up. Shutting the car down and pumping the brakes to bleed off the vacuum released them.

Disconnected the vacuum from the booster.

Drove the car again and it felt fine for about a mile then the same old feeling of the system pumping up and the rock hard pedal and bound up front brakes returned.


I'm completely baffled.

Steve what was the issue with the caliper?

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Steve Simmons
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Re: Dragging front brakes.

Post by Steve Simmons » Thu Feb 24, 2011 11:50 pm

The caliper was just dirty. I removed the piston, cleaned things up and put it back in. I don't think your problem is calipers though.

You've changed everything AFTER the problem started, yes? If pressure it being held in the system then the problem has to be the MC not returning, or something acting like a valve. I don't know if the booster can cause this type of problem, and being unfamiliar with later MGB braking systems I don't know if you have one booster per circuit or one for both? I assume it's one per circuit. Can you swap them easily and see if the rears drag instead? Or bypass the front booster?

Before doing anything though, make sure the MC is returning FULLY, and nothing is holding it up. Check the circlips to make sure they're in place, all linkage is aligned properly, etc. You should be able to visually see if the piston has returned all the way.

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Re: Dragging front brakes.

Post by Larry Kluss » Fri Feb 25, 2011 10:46 am

Stewart,
Steve's advice is good. Pressure being relieved when you cracked the bleeder is almost always a sign of the master cylinder not returning all the way. Whether it's the push rod, the booster, pedal, or other related components, that is most likely the issue.

I don't know the brake system particulars for a '75 B, but I think it uses a tandem master and single inline booster, right? Is there any kind of shuttle valve or other device between the outlet of the master and the front calipers?

Is the brake pedal return spring installed?

Not knowing the history of your car, I assume the brakes worked properly at some point? Do you recall what if anything was changed when this problem arose?

Larry

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Re: Dragging front brakes.

Post by Larry Kluss » Fri Feb 25, 2011 10:47 am

One more question. Are the symtoms after replacing the the M/C the same as before you replaced it?

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Re: Dragging front brakes.

Post by Stewart » Fri Feb 25, 2011 7:13 pm

This all started just before new years day 2010 when I redid the front brakes with new rotors calipers and ebc red stuff pads. Brakes were fine before hand but relying on calipers that are older than I am made me nervous hence the rebuild.

Progress made today though I think it's a bit dpo'ish for now.

Took the car out and got the brakes nice and hot and like clock work they bound up when pumped.

Loosened the nuts on the master to booster and the front brakes released

I then used a metal shim to space the master out drove the car till the brakes were hot and no binding.

Took the master off and looked at adjusting the push rod however I need a 9/32 or a 7.5mm wrench and then some way of securing the rod. The one thing thats baffling me is why after 36 years would it now need to be shortened?

Made a paper gasket to fit between the master and booster hooked up the booster again and drove the car till the brakes were hot with no binding.

Need to drive it some more to make sure but I think I'm on the right path now.

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Re: Dragging front brakes.

Post by Larry Kluss » Sat Feb 26, 2011 10:15 am

Stewart, Good work, it sounds like you've narrowed down the issue.

It is possible that when bleeding the new front calipers, something happened internally to the old booster not allowing it to return consistently. When bleeding using the pedal, you typically push the pedal to the floor. I'd bet that pedal had not been pushed to the floor in many years before that.

Again, verify the pedal return spring is in place and that the pedal is completely returning at the time of the problem.

Larry

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Re: Dragging front brakes.

Post by Stewart » Sat Feb 26, 2011 11:20 am

Pedal returns as normal and the return spring is working. I use an ezbleeder so I don't have to pump the pedal to bleed the brakes.

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Re: Dragging front brakes.

Post by Stewart » Sun Feb 27, 2011 7:07 pm

I might be on to something

After a ton of searching ran into a post where someone was having a similar issue. Front binding up and the rear fine. His problem appears to have been the brake light switch was screwed to far in and not allowing the pedal to fully release.

Went out and checked and the clearance was fine. However after looking closer I noticed the pedal was hitting on the slanted portion of the pedal box opening not allowing the pedal to fully retract. If you pulled the pedal to the right you could get another 1/8th inch or slight more of movement. Went ahead and used a Dremel to extend the strait portion of the opening. Now there is just a touch of free play before the pedal hits resistance. I'm going to pull the shim/gasket between the master and booster and see if that does the trick but I'm pretty sure that was it.

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Re: Dragging front brakes.

Post by Larry Kluss » Mon Feb 28, 2011 11:15 am

That's good news...at least good that you've probably solved it. :)
I wonder why that interference is only showing up now?

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Jimmy
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Re: Dragging front brakes.

Post by Jimmy » Tue Mar 01, 2011 10:00 am

The "rubber boot" (gasket) that apparently goes between the master cylinder and the booster is on sale at the B-Hive for $3.65.
Could be a worthwhile investment, I think.
In baseball, running into someone is apparently a "collision".
But doing the same thing in a car somehow makes it an "accident".

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Re: Dragging front brakes.

Post by Stewart » Tue Mar 08, 2011 12:21 pm

Brakes hate me

New master is now leaking through the brake pressure failure switch :hammer:

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Re: Dragging front brakes.

Post by kiwimark » Tue Mar 08, 2011 5:24 pm

Hi Stewart
I had this problem when I rebuilt my calipers on my 69 BGT. What I did was distort the dust seal keeper ring when I assembled one of the calipers causing the seal to push too hard against the piston, stopping it from releasing. There is a special tool for fitting these rings which I do not have so they fought me every step of the way. As they are thin metal they bend out of shape real easy.
Regards
Mark

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Steve Simmons
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Re: Dragging front brakes.

Post by Steve Simmons » Tue Mar 08, 2011 7:58 pm

Mark, I have a caliper seal tool in case the need arises again.

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