MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Rear brake squeal - time to turn the drum?

I replaced the shoes on the rears 2 weeks ago, then went off to the NAMGAR Solomons Island Regional GT last week. Did a total of just under 1000 miles, but just before reaching home I began to get a squeal in the left rear brake. The drum has some rough spots (see pictures. I used emory cloth on when I replaced the shoes. Looking at the drum, I'm thinking it may be worth it to have it turned, but not sure where I can find someone to do it nowadays.

Barney's site says you can turn a rear drum about .040, and these are original, so I'm sure I can have that much removed without worry.

Two questions:
1. Anyone had drums turned recently and if so, what type of shop did it?
2. If I don't turn it, I may buy a new drum. Anyone had experience lately with Moss, VB or Scarborough Faire replacement drums?

- Ken



Ken Doris

2nd picture


Ken Doris

Ken,
normally drums can be turned by engineering firms who do work on vehicles engines, such as cylinder boring, cam & crank shaft grinding, etc. They would have a machine specially made for turning wheel drums and such like.

Frank
F. Camilleri

Around here most of the "serious" auto parts stores (NAPA for instance) have a brake lathe to turn drums and rotors, as the turning process is still cheaper than replacement drums and rotors.

Squeal in disc brakes is commonly caused by dirt or rust behind the metal backing plate of the brake pad. Sand the back of the pad clean and apply some high temperature sticky stuff like this:
http://mgaguru.com/mgtech/brakes/bt109.htm

Squeal in drum brakes is commonly caused by friction linings that are too hard (intended to increase wear life). You used to be able to choose between soft linings for quiet or hard linings for longer life, but I haven't seen this choice advertised for decades.

Turning the drums to get a smoother surface may well eliminate the squeal, or reduce it somewhat. Also a few repeated panic stops in a row from highway speed may rub a glazed surface off of the linings to stop the squeal. Worth a try before having the drums machined.

There is not a lot of material allowed for machining on the MGA drums, perhaps 0.040" (dia) for rear drums and 0.060" (dia) for front drums. Take out more material and the adjusters won't work. As such, and considering the current replacement cost of the drums, I would only have them turned as a last resort.

Some years ago I had a different problem. When I was autocrossing regularly (every week end) I would use the brakes heavily for short bursts from speed. I'm sure this would heat the drums considerably. Eventually this repeated heat cycling will change the grain structure of the metal at the friction surface, similar to flame hardening. Some carbon from the iron will coalesce at the grain boundaries to create carbon nodules (which might be see under a microscope). This makes for a wear resistant surface, but cause other problems.

For instance, I once had a front brake locking up at low speed (about 10-mph) with light pedal application. This was bad news for competition. No matter if I eased off the brakes at the anticipated moment, it would lock up anyway. Cleaning the drums and shoes, sanding the parts, and replacing shoes made no difference. Eventually I gave in and had the drums turned, even though they were perfectly round and smooth, and that cured the problem.

A point of interest was that the cutting tool would chatter like crazy with a shallow cut, so the technician had to cut 0.015" deep to stop the tool from chattering. So I recon the hardened surface must have been at least 0.010" deep. That was the only time I have ever had the drums turned in 240,000 miles. They do not otherwise seem to wear out, as long as you keep good linings on the shoes.
Barney Gaylord

I'll try Barney's suggestion of a couple of hard stops to see if that cures it. If not, I'll try to find a shop (we have NAPA here, but I don't know if they are as "serious" as those near Barney) that can turn the drum. Buying a new one at about $75 will be the last resort.

Still curious if anyone has gone down that route of buying one of the aftermarket drums - I'd like to get an idea of the quality.

- Ken
Ken Doris

I would think that is more likely to be your linings - looking at the marks on the drum . I would just try using the emery cloth on the drum again and then wire brush the linings to remove any glazing - maybe even try a different set of linings.
Cam Cunningham

Cam - these are new linings. The radial marks you see are just surface dust - its the pitting marks that I'm concerned with. They are probably the reason the radial lines of brake material are appearing. The pits are potentially there due to the leaking wheel cylinder or perhaps from the car sitting for over 30 years.
- Ken
Ken Doris

I changed both rear drums a few years ago, seemed to be fine from a quality perspective
dominic clancy

It was just a thought Ken, considering that the squeal has only started after fitting new shoes - although if the "rough spots" are actually pits and not bumps then a skim of the drum might solve it. .
Cam Cunningham

Cam - you're right that this is a new issue, but I'm thinking it is the combination of new shoes against old pits. The previous shoes were soaked with brake fluid, so that probably was an effective way to avoid squeal (and also avoid stopping!).

Dominick - where did you purchase the new drums?

Just dropped the drum off at a local NAPA (thanks for the tip Barney). Their machinist is off today, but will look at it tomorrow and give me a call to tell me what he thinks.

I'll report back when all this is done and I have it back on the road, hopefully next weekend.

- Ken
Ken Doris

Really should have used more elbow grease on the emery. More drastic/less work methods:
The non-woven "surface prep" (brown) or paint removal (black)wheels you use in a drill or angle grinder, or a flap wheel. Try to keep it even; sometimes you can mount the drum reversed on the hub and put the car in gear/running = ghetto lathe.
More ghetto, but from a Mercedes Benz WSM: glue emery to the old pads/shoes, drive the car with gentle brake applications to clear up glazed discs/drums. Don't even need to drive for the rears.

I intensely dislike turning drums, and it is very rarely necessary. In theory, both drums on an axle should be turned to the same size at the same time, to maintain brake balance. Sheer mass is important in brake function, and turned drums are frequently less round/true than the old ones were. Only time I've ever turned drums is when they have been allowed down to where the rivets cut grooves in them, and I have done an awful lot of these cars. I've not found MGA/B etc to be prone to noise, even with rust pitted drums, so long as the drums are otherwise clean and smooth.

However, the actual noise is usually generated where the shoe contacts the backing plate or anchor points. These should be clean and smooth with a very light smear of Lubriplate or similar. Were you the guy with missing hold down springs? Might be rusty contact points.

Also, linings should have a chamfer filed on the leading end; this edge is a known noise generator. I do it as routine on all lining replacements. Loosely riveted or bonded shoes will also do it - check carefully for voids in the bond.

FRM
FR Millmore

FRM - Yes, I am the one who found no anti-rattle springs when I opened up the drums a couple of weeks ago. By contact points do you mean where the shoes fit against the cylinder and abutment?

The pits I have are beyond emery cloth. I used it to smooth out the edges of the pits, but couldn't remove the actual pits. I could have used a dremel, but that would surely have resulted in an unbalanced drum.

I like all your low-cost suggestions, but for now I'll see what the machinist says - the drum hasn't been turned yet.

- Ken
Ken Doris

Ken-
Those springs, as well as the others if they are correctly installed, cause the shoes to lean against the backing plate at a couple of points. Since the contact was iffy at best without the springs, there may be rust or roughness there. Vibration of the shoes against the plate is what ultimately causes the noise. So, anyplace the shoes touch anything needs to be smooth and lubed. When I have (rarely) had trouble with noise, I lube every place there is contact, including where any of the springs hook into or touch the shoes. Just be sparing, so that the lube does not get on the lining or drum surface.

You are not removing the pits except by turning, but they rarely if ever cause trouble, so long as they are not covering a very large area, are not accompanied by high spots, and are not harbouring grease, oil or other contaminants that cause the linings to glaze.

FRM
FR Millmore

FRM - good info. I will thoroughly clean and lightly lube all the contact points - I agree vibration is the key here, and now that I've added more force with the anti-rattle springs, I may have caused more opportunities for it to arise.

- Ken
Ken Doris

Barney was right (again) - the local NAPA store has a machine shop. They turned the drum 0.013 and it looks like new. Back on the car, took about 4 clicks on the adjuster, and so far, the squeal is gone. Price = $16 (NYC vicinity prices in effect).
- Ken


Ken Doris

Nice job Ken. That drum should now last a few thousand miles. I'm a little surprised that it only took 4 clicks on the adjuster, must be the first turn it had in its entire lifetime.

Frank
F. Camilleri

Frank - hopefully more than just a few thousand more miles! Only 4 clicks on the adjuster was because the shoes have only 950 miles on them.

And, yes, this has to be the first time it's been turned - we've owned the car since 1968 and bought it when it had 33,000 original miles on it. More of the story can be found here: www.waterviewgroup.com/MGA
- Ken
Ken Doris

This thread was discussed between 09/10/2011 and 22/10/2011

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.