Brake pad thickness : MG Midget Forum : The MG Experience

Brake pad thickness #1 This topic is about my 1965 MG Midget MkII
Mick B Michael Bayes Derby, Derbyshire, UK Sign in to contact 1965 MG Midget MkII	Topic Creator (OP) Apr 30, 2017 10:31 AM Joined 7 years ago 59 Posts

Hi to all. First of all thanks for the help on my clutch slipping problem. I adjusted the M>C rod all the way back and took 3/16 of the slave pushrod which was too long according to the info given.
So my new problem is the front disc brakes binding after a couple of miles and a couple of applications. I have adjusted the m.c rod right back but the pads have no movement in the caliper even at cold. The pistons do not retract any further they are flush with the caliper . The pistons and pads are new.
Are there different pad thicknesses

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Re: Brake pad thickness #2
S1 Elan Kurt. Appley Akron, Ia., USA Sign in to contact 1964 Lotus Elan 1965 MG Midget MkII	Apr 30, 2017 11:02 AM Top Contributor Joined 11 years ago 8,034 Posts

Did you change your brake hoses? Not uncommon for them to swell shut and not let fluid back after brakes are applied. After that MC push rod adjustment and if that doesn't do it I would guess you have swollen seal's in the MC.

Having said that I just bought a new set of front pads that were very thick and had to grind a bit off of them to keep them from dragging with the pistons all the way retracted.

Kurt.

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Re: Brake pad thickness #3
Mick B Michael Bayes Derby, Derbyshire, UK Sign in to contact 1965 MG Midget MkII	Topic Creator (OP) Apr 30, 2017 11:25 AM Joined 7 years ago 59 Posts

Hi Kurt,
No the hoses are the ones it came with that look fine. Not a nice experience, one minute you're doing 60 or so and then it feels like it's going to die, changing up gears and each time the sensation of the brakes being applied, finally a smell of burning friction material and on pulling over, the vision of smoke coming from the N/S wing.
At first I thought it was around the carb/ fuel area.
I have a feeling the heat has effected the bearings as well as there is play in the wheel.
I'll take the pads out, check piston movement, see if the bearings will nip up on a torque and take a couple of mm off the pads.

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Re: Brake pad thickness #4
TheLastDeadMouse Tim Vollmer Potsdam, NY, USA Sign in to contact 1972 MG Midget MkIII	Apr 30, 2017 11:56 AM Joined 13 years ago 756 Posts

Replace the hoses. These hoses will go bad from the inside out, so they'll look fine on the outside, but the inside of the hose has probably collapsed. When you apply the brakes, the pressure expands the hose and pushes the fluid, then when you let up the hoses contract again and the fluid is trapped, locking the brakes on.

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Re: Brake pad thickness #5
pixelsmithusa Gerard C San Francisco, USA Sign in to contact 1937 Chevrolet Master Deluxe 1946 Austin 10 1953 Morris Minor Series II 1960 Austin-Healey Bugeye Sprite & more	Apr 30, 2017 12:33 PM Joined 13 years ago 2,859 Posts

As several have suggested, the brake hoses are the most common cause of this issue. However, you might also have the pushrod at the master cylinder adjusted incorrectly. It's possible to have them adjusted in such a way as to block the return port. If you master cylinder, which should be a 3/4" bore, was replaced at some point with a 7/8", you could have the wrong pushrods there too. Replacement 3/4" bore master cylinders were not available for several decades, so it's not uncommon to find they have been replaced with the incorrect one.

Gerard

http://gerardsgarage.com/

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Re: Brake pad thickness #6
tomshobby Tom Smith Windsor, WI, USA Sign in to contact 1974 MG Midget 1976 Triumph TR6	Apr 30, 2017 02:37 PM Joined 14 years ago 1,881 Posts

Mick, here are 2 possible causes;

1) You may need to back off the pedal free play. When I first got my car back on the road I had the pedal adjusted to match the clutch pedal. The result was that the brakes were not always able to completely release. Backed off the free play and all was well.

2) There is little room for error when new parts are used, pads, bearings, and rotor. So if the bearings don't fit correctly there could likely be a problem with contact from the pads not being being to back off completely.

I would suggest cause #1. Here are some drawings and explanations. Bearings

Tom Smith
1974 Midget
1976 TR6

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Re: Brake pad thickness #7
jimbenedict Jim Benedict Waterford, MI, USA Sign in to contact	Apr 30, 2017 07:36 PM Joined 7 years ago 486 Posts

I would never use old brake hoses. I just had the new rotors installed with new brake pads. Of course, replaced the old hoses too. Pads are Duralast brand from AutoZone and did fit without dragging on my 1979 MG Midget..

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Re: Brake pad thickness #8
Mick B Michael Bayes Derby, Derbyshire, UK Sign in to contact 1965 MG Midget MkII	Topic Creator (OP) May 1, 2017 01:11 PM Joined 7 years ago 59 Posts

Just checked the pad thickness and get .533" to .543" with an anti squeal shim in that makes for a skin tight fit either side of the disc and no room for movement.
I have ground them down to .5" and that gives them the movement by hand and room for heat expansion.
It did alter the n/s bearings which I am hoping will just need a nip up .
When everything had cooled down the wheels turned easy so I believe it was down to heat expansion and thick pads.
When both sides are done i'll give it a good workout and let folks know

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Re: Brake pad thickness #9
S1 Elan Kurt. Appley Akron, Ia., USA Sign in to contact 1964 Lotus Elan 1965 MG Midget MkII	May 1, 2017 02:08 PM Top Contributor Joined 11 years ago 8,034 Posts

Your posts lead me to believe more and more that the problem is the hoses. You could probably test that without getting the brakes hot by just jacking up the front and seeing how the wheels turn before and after you apply the brakes.

Kurt.

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Re: Brake pad thickness #10
TheLastDeadMouse Tim Vollmer Potsdam, NY, USA Sign in to contact 1972 MG Midget MkIII	May 1, 2017 02:34 PM Joined 13 years ago 756 Posts

Well, you'll have the chance to test this for sure now. Jack the car up and reassemble. You'll have wiggle room with the pads now. Then with the car still in the air really stand on the brakes. If you can't turn the wheels freely by hand afterward, its the hoses.

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Re: Brake pad thickness #11
Mick B Michael Bayes Derby, Derbyshire, UK Sign in to contact 1965 MG Midget MkII	Topic Creator (OP) May 7, 2017 11:34 AM Joined 7 years ago 59 Posts

Looks like Kurt and Tim could well be right. I've only looked at the N/S at the moment. After standing on the pedal the wheel is stiff to turn. after releasing the oil at the caliper bleed it turns fine.
I've ordered a set of braided hoses and stripped the M/C as I wanted to check the release valve at the back of the spring on the brake side. I doubted that I had put it back in.

if I understand correctly the actuating rod should have 1/8 free play off the piston. how long is the rod.
Dot 3 or 4

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Re: Brake pad thickness #12
ice Larry Ice Lawrenceville, GA, USA Sign in to contact 1971 MG Midget MkIII	May 7, 2017 04:09 PM Top Contributor Joined 12 years ago 6,114 Posts

While you are at it replacing the flex hoses up front don't forget and not replace the one in the rear over the rear end also. Many forget to replace the rear one because it's out of sight but it can cause trouble as well.

Iceman

Atlanta GA

71 MG Midget

62 AH MKII
67 Midget
71 Midget

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