Warped brake drums

[davidsfirth]

I have within the last month or so, replaced my front drums as the older ones were so warped i could feel it 'pulsing' through the brake pedal. I've done around 500 miles on the replacement drums, and these seem to be doing the same thing? When trying to adjust them with the cam, I have high spots where the drum is locked, but then areas of the drum where there is no resistance at all. So this is making correct adjustment impossible. Also, in the last Fortnite I have replaced the rear drums and shoes and I can't adjust them up enough to lock the wheels. In the past I've struggled to get the drums back on when replacing shoes. What's going on?

[myoldjalopy]

Sub-standard parts? I have had issues with the micro-adjusters in the past with new shoes where there were no adjustment issues before changing the shoes. The reason I changed them was because I spotted the old shoes were worn close to their limits.....
I can't see how drums become warped.

[philipkearney]

About 5 years ago, I bought a brand new pair of 8" drums from a well known supplier, to replace the original drums which had become worn, slightly warped and the outer edge had started break off. The new drums were worse than the old ones and have been warped/out of balance since fitting. I have since searched through my S/H parts and fitted an old pair which are much better. New parts are not always better.
In theory, it would be better to have an old pair re-surfaced on a lathe but if you take too much material off and you have the issues you describe with your rear brakes and insufficient adjustment.

[svenedin]

I would complain to the supplier. If is the well known supplier I am thinking it is, they sell two different qualities of brake drum with one being considerably more expensive. The more expensive type is made in Germany (I bought some recently).

Avoid "pattern" parts and always buy the best you can. With brake shoes, buy branded shoes if possible. If not possible, consider having old shoes re-lined. This can be done with premium friction materials (Ferodo/Mintex). New old stock parts are often the best option or known good second-hand.

When you adjust the brakes, make sure the drum is fully tight against the hub. Sometimes, even though you have tightened up the 2x brake drum screws, the drum is not fully home (give it a thump with a rubber mallet not a hammer or the drum can break). The drum not being fully home can cause the drum not to run true and cause the tight spots you describe. Of course when the wheel is on, the drum should be fully home from the clamping of the wheel nuts. Also, you must not have the brakes binding on high spots in normal driving. If this is happening the drums will overheat and.....warp. A light sand of high spots of the brake shoes can address binding in places. When the wheel is back on rotate it by hand to check for free running.

Stephen

[davidsfirth]

Hi Stephen, I ordered 'original specification' drums, the most expensive of the two kind supplied (other type were pattern) as I've had issues with the quality of parts in the past. I'll re-check the fitment of the drum, and have a look and deal with any high spots on the shoes. Thanks for your time and advice.

[svenedin]

You're welcome. This is Phil's advice I am regurgitating but it has served me well. Don't be too obsessed with the adjust until the drum locks solid and back off 1 click. If it still binds (and you have addressed any high spots on the shoes) then back off 2 clicks. The result should be a drum that spins freely or has minimal catching. This will give a slightly longer brake pedal which can feel a bit disconcerting but it also means that the cylinder pistons get more "exercise" (they move forward and back further) which reduces the chances of them seizing.

While you are on the brakes, do check the 4x brake back plate bolts are tight. I had trouble with mine working loose and it causes the brakes to judder.

Good luck!

Stephen

[davidsfirth]

Will check that out too while I'm in the area. Many thanks.

[philthehill]

Do not expect drum brakes to be perfect after fitting new parts. You have to let them bed in i.e. wear off the high spots on the lining. Also make sure that the leading edge of the brake shoe lining is chamfered i.e. has a slopping edge.
As regards the drums - to determine if the drums have ovality/run out they do need to be mounted in a lathe chuck with outside jaws and a dial gauge used to measure any ovality/run out of the drum. Unless you are able to measure any ovality/run out of the drum you cannot determine if the drums are the cause of the problem.
Just replacing the drums may cover/mask additional problems.

[Bill_qaz]

Not on a minor but on other drum braked vehicles I have bolted the drum on backwards using nuts and washer to fully secure the drum on the hub. You then can easily check the run out, magnetic based dti on an axle stand is a good platform.

[svenedin]

Good advice there but remember the drum may be true on the hub but the shoes and cylinders are on the backplate so if that is not true to the drum it will cause trouble or if the cylinders are not tight on the backplate. New parts are often blamed but they are in fact totally correct. What is not correct is the other parts they are attached to!

Incidentally, I was going to clean up my rear drums (which are modern replacements) and so I put my old original MOWOG drums on and there was no way the shoes would go near touching the drums even on maximum adjustment. I know for a fact that those old drums were a bit scored (from me running the car as a penniless student and letting the linings wear down to the rivets) but they did adjust up. There is a mismatch at times. I was going to dig out my old Mintex shoes but I couldn't be bothered because the rear shoe pull off springs are so strong and such a faff. I think I had to take the Mintex shoes off when I put the modern drums on because they couldn't be adjusted low enough. The opposite problem.....Anyway, if you get the original shoes re-lined you will not have a problem with original drums. It's expensive but still cheap compared to a modern car and how often do you wear out the linings these days? Discs and pads for my Audi (front only) were nearly £1,000 recently.



Stephen