17 replies to this topic

[[email protected]]

1. 1991
2. carb'd Mainstream Mini Cooper with 8.4" disks up front and built-in spacer drums in back
4. No pictures yet, will take some tomorrow/Friday

3. Experiencing what I can only describe as horrific brake shudder / judder / or even "banging" under anything other than VERY light braking.

It is almost like the early anti-lock systems where it is a rhythmic "clonk-clonk-clonk..." And I could swear it is coming from my rear left drum.

History: have had the Mini for about 7 years now. About 3 years in, the right rear wheel suddenly started locking up under braking. I stripped it down and found the wheel cylinder leaking and contaminating the shoe. One new wheel cylinder and new Mintex road shoes all around and it was like new. (New Greenstuff pads up front at the same time).

Flash forward to this past winter. On wet days under light touch, "easing up to a traffic light" kind of braking, I was getting a squeal from the right rear. Time for new pads and maybe new drums too, I thought.

Replaced all that along with a seized wheel cylinder (left side this time) and all seemed good. I noticed a light rhythmic scrape on the rear left but assumed it was the pads bedding in.

Flash several months later and I started to hear an actual worrisome scrape under light braking that would quiet if I applied more pedal, and a light rhythmic pulse in the pedal, so I opened every thing up again and found nothing out of place, and adjusted as per this video: https://youtu.be/M02bqqNOlkY.

Once again, all seemed right in the world: no scrape, good pedal height, great braking. And all through this, my front disks have had plenty of meat.

Then came yesterday. Had to slam on the brakes. Immediately afterward: the jackhammering began every time I braked. I tried just pulling up on the emergency brake and believe I replicated the banging (that's why I think it is the back drum). I engine-braked and coasted as much as I could for the rest of the trip.

Going to get in there tomorrow (or Friday depending upon when real work allows) and just wondering if there are any suggestions from the community re: what to check and/or how to diagnose (one man only, no friend to press the pedal!).

Could I have gotten a warped drum new?

Thanks in advance for your thoughts!

[richmondclassicsnorthwales]

Hi

 

Just going to throw a couple of items in the hat here for you - There will be plenty more to come from other members though I'm very sure of that.

 

You talk of a scraping noise at the back, when was the last time it had new rear springs?  These really get over looked a lot, and can cause the "scraping sound" asthey are not pulling the shoes back enough

 

Then the front, have you had a look at the Tie Bar rubbers, these do perish, and can cause all sort of problems.

 

Probably worth a look at these primarily

[Cooperman]

Are the rear shoes in the correct way round. It is easy to get it wrong - we've all done that I would guess.

 

The return springs rarely need replacing, but if one had broken there could be some funny issues inside the drum.

 

Let us know what, if anything, you find when the drums are off. 

 

In case it is not the rear brakes, are the drive flanges tight on the front both sides?

[Spider]

Are the rear shoes in the correct way round. It is easy to get it wrong - we've all done that I would guess.

 

This is a likely cause

 

 

As a matter of course, I replace the springs when replacing the shoes as Richmond suggested. They don't often loose tension, but the bent ends that hook over and in to the shoes do wear and will eventually break off.

[richmondclassicsnorthwales]

Moke has put it perfectly,     I am not always putting it the way I should - but spot on with that one - think the general idea is there though round about way with me

 

Rear springs do serve their purpose

Edited by richmondclassicsnorthwales, 22 April 2019 - 07:35 PM.

[imack]

Could be that the lower brake shoe return spring is on upside down so that the spring was fouling the hub causing the scraping noise and has now rubbed through allowing the shoes to float about.

[[email protected]]

Thank you to everyone who has posted!

 

Here's my catch ups / feedback:

 

richmondclassicsnorthwales

I did put in brand new springs, top and bottom when the new shoes and drums went in mid-winter (and I ensured the bottom springs were NOT scraping the rear hubs) - and they all looked like they were in good positions when I pulled the drums to diagnose the slow speed scraping noise.

 

I have not looked at the front tie-rod bushings - hadn't even thought of that, but definitely will inspect them Wednesday!

 

Cooperman

It's interesting that you raise this point - on my first ever shoe change several years ago I found that I had simply mimic'ed the original shoe installation and that was incorrect.  But this time I was very conscious of the leading/trailing scenario with the shoes because the Steveston folks made such a big point of it: how the "bigger exposed metal end" of the shoe should be leading and the end where the pad goes closer to the end of the metal shoe should be at the trailing edge...  like a "ying-yang" symbol. 

 

But that said, oddly enough, my new Mintex shoes were pretty "symmetrical" without one side being "less pad" than the other.  So I simply matched the backings to the old shoes off the car (flat vs. triangular ends) and then installed them "Asymmetrically" as if they were like the old shoes.  I think I might have gotten poorly manufactured shoes.  

 

If by "drive flanges" you mean the "rotor shields", then my clearances there have been good for a long time (I caught a stone in between disk and shield once years ago - thought I'd wrecked a bearing!) but I will definitely check that as well.

 

Moke Spider

I think you and Cooperman might have spotted my issue - like I noted above, the new shoes were very "symmetrical" or "centered" in how their pads were glued on - but it seems very important that these leading and trailing edges be respected.  I may have simply gotten defective shoes. 

 

I have mocked up a drawing based on Moke Spider's great image and will take actual photos when I get under the Mini on Wednesday.  Unfortunately my old shoes are up at my brother-in-law's place, so I can't just swap them back in, but maybe I can find a better placement for these until new ones arrive.

 

 symmetrical-shoes.png   258.52K   0 downloads

 

And last but not least, imack - I actually was very careful about placing the bottom springs and I even double checked them when I made the recent adjustment that got rid of the slow speed scraping noise, but I will double-check that as well again on Wednesday when I open everything up to re-seat everything.

 

You've all been absolutely terrific and I feel like I'm going into this with much less guesswork now.

 

Thanks a bunch!

[Spider]

Many of the replacement shoes do now seem to be supplied with the friction material more central than they used to be.

 

I work off the cut outs in the frame of the shoe to work out which is the leading and trailing edges these days. One cut out is a slot and the other a delta shape.

[[email protected]]

Yes Mike Spider! There's a "D" with a bump that the pivot side of the parking brake lever needs to fit through.

Although I'm pretty certain that I conformed to that arrangement, that is one thing that I'll be looking for tomorrow for certain.

I still have my old - likely factory - drums up at my brother-in-laws, so although they are quite "lipped" (with a 1/8" trough in them from years of use) I can swap them back in to see if maybe the drum is warped.

I also read that I should check for a "carbon nub" as it could be that the hard braking left a piece of pad "bonded" to the inside of the drum, and the shoe pads are now striking it with each rotation.

All good stuff to check on!

Hopefully it will be one of them!

[[email protected]]

Spoke to one of my mentors here in NYC, Andre of Barnett Auto, Long Island City, and he says he has seen the pad tear right off the metal shoe due to poor bonding glue in the non-riveted manufacturing process.

Guess I'll be looking for shards of brake pad material as a good clue as well!

[Spider]

Another thought I just had (yes, that's what that noise was).

 

If the drums have been machined on an ordinary lathe, the finish left can cause the shoes to shudder. This happens if the feed rate is a bit (or a lot!) heavy and it leave a spiral finish that the shoes effectively 'screw' themselves in or out until they reach a point that they let go and bang back in to place, then the cycle repeats.

[[email protected]]

Geez! For something so simple in design, amazing how execution can ******* it up!

I will look for a spiral machining too!

[[email protected]]

Okay, so here's my report:

 

I opened up the rear left side expecting to find the pad sheered off the shoe and rattling around inside the drum, but everything looked fine (with the exception of the "centered" pads) and the machining, although having visible "ringlets", none were deep enough to catch a thumbnail, so I figured I was not spiraling:

 

 left-drum-clean.JPG   60.46K   1 downloads

 

I did notice the shield a bit close to the drum on the right side, so I gently used a flathead screwdriver to increase the gap in that one spot.  And then I swapped all the gear left to right. 

 

Then I did some "spirited driving" back and forth on the block testing pedal braking and then testing only yanking on the hand-brake and I found that I didn't get the same judder with the hand-brake actuating the rear drums ONLY as when I slammed on the brakes via the pedal triggering the up front disc brakes as well. 

 

So contrary to my earlier suspicions, it is not the rear, but must be the front where the issue lies.

 

I rang Andre/Barnett and he thinks it might be warped rotors, which might not be unheard of since that has happened before when the front wheels were air-gunned on too tight by a shop and I was definitely doing some very spirited driving, heating up the discs to the point that when they cooled, they warped like a Pringle chip under the heavy torqueing on the lug nuts.  A new set of solid discs back in the summer of 2014 (5 years ago) plus always hand torqueing my own wheels on - even at repair shops - plus a conscious effort not to cook my brakes ever again (except when I was at Watkins Glen last fall for the "Drive the Glen thang - see: http://www.theglen.c...e-The-Glen.aspx - solved that round of vibrating pedal for me.

 

Inspecting the front, I found that my front tie-rod bushings are perished and need replacing, and I do have some uneven wear in the pads AND they too are due for a re-fresh:

 

 left-pads-uneven.JPG   34.55K   0 downloads

 

Right side very even:

 right-pads-even.JPG   42.08K   0 downloads

 

So I'm going to swap them out first and clean up the calipers in case it is the pistons binding up AND I'm going to inspect the backsides of the disks for any heat-bonded-on-pad-blobs in case that is what the issue is...  I have new bushings and new Greenstuff pads but they are in storage an hour north at my brother-in-law's place, so that job will have to be another day (don't ask - I moved from a brownstone with a basement "tool room" to a high-rise apartment where my wife didn't want any Mini parts bins "hanging around").

 

If it is warped rotors, the old ones are pretty pitted anyway:

 

 pitted-left-disk.JPG   54.75K   0 downloads

 

...so I might get the "upscale" cross-drilled and grooved rotors instead of solid discs in the hopes that they might dissipate the heat better.

 

Does anyone know if the cross-drilled and grooved actually improve cooling or at least don't warp as easily?  (or do you need to move to vented to get any substantial difference, which entails replacing the calipers as well?)

Edited by [email protected], 25 April 2019 - 11:19 PM.

[Cooperman]

I have often got my standard solid 7.5" and 8.4" discs glowing red hot on tarmac special stage rallies, but have never experienced discs warping. Actually they are very robust, but I always buy OE spec discs and use race pads, typically Carbon-Fibre or Mintex 1166.

You may not need new discs. Check the run-out of the existing discs with a DTI and if the run-out is within limits, just fit new quality pads (not necessarily 'greenstuff' which is not well regarded) and get the discs hot by driving at about 40 mph and giving it full throttle in 3rd gear whilst holding the speed at 40 by using your left foot on the brake pedal. Do this for around 1/4 of a mile, then drive letting the brakes cool. Repeat this a couple of times, letting the brakes cool between applications. This is called 'burning in the pads' and is necessary with a hard competition pad. After that try the brakes again after they cool by doing a firm stop from about 70 mph. 

[[email protected]]

I think you are right about it not being warping and not needing new discs this time around Cooperman.

 

In fact, I may have actually figured out where my Brake Shudder / Judder / Banging was (is) coming from:

VERY bad glazing on my right front disc on the inner side, hidden under the disc shield.

 

Before I swapped the new pads in, I poked my finger in through the caliper to feel the inner sides of the two discs and sure enough there was a high spot on the right one - with an actual lip on it that felt quite substantial.

 

Amazing how so shallow a deviation can cause so much disturbance.

 

Anyway, the old pads were about due for a change...

 

 new-vs-old-GreenStuffs-size.png   556.21K   0 downloads

 

...but since I didn't have any of my own power tools or even my own sandpaper up at my brother-in-law's, I couldn't set about removing the glazing, but I did have access to a Dremel (rotary tool) with a stone tip, and so I was at least able to poke it in through the caliper and taper the edge of the glazing a bit.

 

I had actually hoped that the break-in grit on the GreenStuffs might clear the glazing, but I realize that I still need to pull off the calipers & disc shields and then take some 1000 and 2000 grit to the glazing to remove it to get the disk surface true again.

 

(I'm actually hoping that I might only need to take the bottom half of the shield/cover off in order to expose enough of the inner side of the disc to rotate it and sand it all...we'll see)

 

The good news is the banging part of the behaviour is gone (due to the tapering - plus I am consciously braking very lightly at the moment so as not to ruin the new pads until I clear the glazing off) but for folks with similar symptoms, note that I am still getting judder and pedal vibration due to the glazing that is still in place. 

 

But that said, I think this particular mystery might be close to being solved!

 

Cooperman:

I really appreciate your tip re: burning in the pads and although this time around (simply because I have them), I've used the GreenStuffs that I had bought, for my next pad change I will look for the Carbon-Fibre or Mintex 1166 that you have recommended - thank you for that!

 

So once again, thanks to all who contributed their thoughts and suggestions - I'll say it once again, the members of this forum are tops!

 

(I just discovered the "Like" function - so I marked everyone's helpful suggestions as "Likes" too!) 

Edited by [email protected], 29 April 2019 - 02:29 AM.