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MG MGB Technical - new brake shoes creating too much drag on drums

With the installation of new brake shoes, I had to tap my brake drums on with a rubber mallot. I've got the adjuster all the way out and there is WAY too much drag that I can barely turn the drum. Has anybody ran into this before? I am thinking about having the ID of the drums turned on a lathe to make the ID slightly larger so there is minimal if any drag. My car is a 67 MGB. I'd put my old shoes back on but they're worn out completely. Any experience or ideas on this welcome. Thanks. -Rod

Rod in NC

Have you got them all the way on? The drums tend to rust around the back edge creating a ridge that is tricky to get over new shoes, but once fully home the shoes are lined up with the normal working area and shouldn't interfere.

If you've got them all the way on and your cylinders are okay then perhaps you've got a bad set of shoes... I'm sure others can advise on US brands that work. I use Ferodo brake products and have had no problems.

fwiw.
--
Olly
Oliver Stephenson

I had this problem once and I have changed lots of B brakes (Rear), turned out to be bad or the wrong shoes. The parts guy said he got me a deal, I told him it wasn't much of a deal if they wouldn't work. They exchanged them no problem even though I had beatem them up trying to install them, never thought that the shoes could be wrong
Bruce

Rod. I have, over the last three years, purchased brake shoes from Brit-Tek and my local BAP store. All fit fine. Hence, I believe that Olly and Bruce are in track with the theory the shoes are either incorrect or the lining is too thick. (Either would be "the wrong shoes".) Can you compare the shoes you have installed to the shoes you removed? Are the metal parts exactly the same? If so, you either have some problem with the shoes not moving into the correct postion (as per Olly), or the lining is too thick. If you have a set of dial calipers, measure the thickness of the lining to see how thick it is and post that. I have a couple of spare sets of brake shoes (currently buried under furniture), but can dig them out tomorrow and see what the lining thickness is. If the metal portions of the shoes are correct and the lining proves to be too thick, a good brake shop can grind the shoes to fit the drums. I do not recommend turning the drums unless they are out of round. They can only be turned so far, then have to be replaced. Brake shoes are far less expensive than drums, hence that is what I would modify, if necessary. Les
Les Bengtson

Rod - Do you have the shoes fitted correctly? If they are on backward (if that can be done on an MGB as on a TD), you will not be able to adjust the shoes in far enough. If everything is correct and there still isn't enough room, I agree with Les, get the shoes ground to size rather than the drums turned. Good luck - Dave
David DuBois

I bought the shoes at my local Autozone store. I did a quick visual comparison against my old ones then tossed the old ones in the trash. I had taken a polaroid of the assembly before I took the old brake shoes off so I feel confident the new ones are installed correctly. Les, I will bring my calipers home from work tomorrow and give you a thickness of the shoes. I'll get a price to grind them down versus buying a new set from Brit-Tek. Thanks for the help guys. -Rod
Rod in NC

Are the shoes correctly centered?

The adjusters and brake cylinders are slotted to allow the brake shoes to float up and down a little
against the backing plate. If the shoes are off-centered, by just a bit, then the drums will be difficult
to install and they will bind.

I use a rubber mallet to tap the shoes up and down until I find the point where the drums simply slide
on with the lease effort. Then, I'll stomp on the brake pedal a couple of time to help "set" them in and
then adjust the shoes before setting the car down. After a day or so of real world driving, I'll adjust the
brakes, yet again,

--------

If fiddling with centering the shoes fails (unlikely), then maybe it's the shoes themselves.

As Les (Arizona) also noted: if the drums are OK, I wouldn't turn them to make the shoes fit.

This takes off precious metal and makes the drums thinner and more subject to warpage, especially
if one is over-enthusiastic when setting the parking brake while the drums are warm.

Take both the drums and the shoes to a good brake shop and have the shoes "arched" to the
drum ID.

Any brake person worth his salt will test the drums for out-of roundness and will measure their exact
inner diameter. If they pass this - the shoes are then mounted on a machine that has a swiveling
mandrel and drum sander. The linings are then shaved to match the inner diameter of the drums.

The brake parts will then be handed back to you as a "matched set". Do not mix up the shoes and
drums after this.

This has the dual benefit of letting your drums live longer, and it removes any high spots in the new
brake lining material - all giving you much better friction contact and shortening any "bedding in" period.

Some brake shoe remanufacturers intentionally install a thicker friction lining - just for this purpose.
Daniel Wong

The drums are in good shape...they have the slight ridge that Olly mentions, but no deep scarring. Les, I borrowed my neighbor's calipers...the total thickness of the shoe, from the inside surface of the plate to the outer wear surface is .295". This was consistant on all shoes. I took the measurement at the middle of the shoe. Looks like I would need to take off about .05" per shoe (for a total of .1" on the diameter of the assembled shoes) to give my self some clearance to get the drums on easily. If anybody else has a thickness of their new shoes I'd like to verify that mine are too thick. Thanks. -Rod
Rod in NC

"A" owner poking my nose in the "B" pages - Rod, if you can get the drums on and the only problem is its a bit tight to turn, then you don't need to grind off .050 radial. Just smear sone blue on the drums and see where it touches, then take a good flat file and file it off a few thou till it turns freely.
Art

I actually had to bevel the leading edge of the shoe quite a bit to get the drum to even start going on. I will probably call around to a couple of british parts sources and see if the can measure their shoes before I buy another set. 2nd alternative is pad grinding but I am in agreement that the shoes are too thick. -Rod
Rod in NC

Rod. Just measured several brake shoes. The thickness of the lining is .145", plus or minus .003" on all six. The thickness of the lining and the brake shoe is .295" with similar tolerance to the lining. Hence, it would seem you have the correct shoes. You might want to check out the hand brake to make sure it is not holding the shoes out a little. Daniel has some very good thoughts and it would be worth doing as he suggests. If the brake shoes are correct, and it appears they are, then the problem lies in how they are installed or something is not allowing them to retract fully. Make sure the brake shoe adjuster is in all the way and not extending the shoes. If you have to remove .050 from each shoe, this would be equal to 33% wear. Not really very likely. Les
Les Bengtson

The thickness may be OK, but what if the radius is wrong? Or the distance between the faces of the shoe web that contact the piston and aduster and the face of the lining?
Paul Hunt

I have a new set of brake shoes for spare parts, bought from Bob Thompson, I think he gets them from Moss. They were made by Automotive Braking Systems in Warrington WA1 4SL England. Total thickness of lining and metal backing plate averages .275". The backing plate measures .100" making the lining about .175" I say averages and about because I found the dimensions varied as much plus or minus .005". Based on what Les and Rod measured my set is around .020" thinner. Perhaps someone in England knows if Automotive Braking Systems produces good quality brake parts.

To make things a little more confusing I just picked up a used brake shoe from my junk boxes of parts. The shoe has very little wear, the center 3" of the shoe was contacting the brake drum and the ends have no wear. The center measures about .300", one end measures .300" and the other end measures .280. The backing plate measures about .105" making the lining about .195 at it's thicker end. I don't recall which rear end this shoe came from, I bought a 71 parts car and a rear end from a rubber bumper car. It was installed and the drums would rotate, although based on the wear pattern it looks as if the drums may have been turned. That doesn't explain why the shoe is thinner on one end than the other.

After all this I know more than I wanted to know about the lack of consistency on different brake shoes. FWIW, Clifton
Clifton Gordon

I'm with Bruce - you probably have the wrong parts.

I had the same problem with my B years back - after hours of checking, rechecking, reinstalling and swearing, I compared the position of holes in the new shoes to the old. The new ones had the same pattern, but the holes in the new were offset about 1/8" from the old. Parts guy gave me another pair and all was OK.
Phil Collura

Rod,
One thing that I don't believe has been mentioned. Are the pistons in the wheel cylinder fully retracted? Some times I need to use a clamp to fully retract the pistons when installing new lining.
Bob
Bob

We'll, I verified that the cylinders were retracted all the way. What I ended up doing is grinding down the edge of each of the shoes where they seat into the cylinder and adjuster. I took off about a 1/32" off of each edge. I reinstalled the shoes and the drum slid on perfectly (just a hint of a drag). The springs are still taut and the shoes retract when I let off the pedal. As Clifton put it, I think I've learned more than I wanted to about brake shoes. I will drive them for a while and pull the drum off to see how they are wearing, since I may have compromised the full radius of the wear surface contacting the drum. Thanks again guys. -Rod
Rod in NC

Rod, Good to hear you got them on. Now that I think back I may have done some grinding on some brake shoes years ago, not MG, probably on GM brakes like in General Motors. Too bad the quality control standards are so bad on safety related parts. Regards, Clifton
Clifton Gordon

Rod,

When I went to reinstall the shoes on my 68b it was too tight a fit. I had reinstalled all the parts according to the manual. I was going to grind the edges but after looking carefully at another installation I found out that the emergency brake lever is shown incorrectly on the manual and thus takes additional space. Take a look at it and it could solve the problem. I just purchased a digital camera in order to take images before disassembly.
Armando Quincoses

Armando, which manual are you referring to? My Haynes manual shows the correct installation. -Rod
Rod in NC

Also interested in Armando's response. If the cable is fully backed-off or disconnected from the levers there should be no effect on the position of the shoes wrt the drum, this would be solely down to the slave pistons and adjuster and the distance between then and the face of the lining.
Paul Hunt

This thread was discussed between 15/12/2002 and 20/12/2002

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