Constant brake squeal driving me INSANE!!! :-)

[Ulf]

Sometimes it's the little things that drives you mad, so recently I had my car in to fix a few annoying sounds - a squealing fan belt and a front brake that would begin to squeal semi-constantly when getting hot (sounding like a very large grasshopper/cricket), but disappear for a few seconds after tapping the brake pedal. My mechanic found out that the master cylinder only pressurised the front brakes (my car is a 1964 230 SL with discs up front and drums rear), so he replaced that and also changed the brake hoses for the rear brakes. But the sound is still there, only now it seems to have moved from the front to the rear and gotten more constant and even louder (people stare and NOT in the good "oh-look-what-a-lovely-old-car-way") and the sound will no longer disappear after tapping the brake pedal. Also the pedal-feel seems quite a bit softer. He claims to have done everything by the book and bled the brakes thoroughly. I could just send it back to him and just demand that he gets it right, but the reason I'm asking you is to give him a few pointers as I don't want him to spend hours/days barking up the wrong tree :-)

Br

Ulf

PS: All pads were recently replaced

[wayne R]

ULf, A couple of things you can do,there is a anti squeal  lube that comes in small plastic  tube, this is applied to
the backs of the front  disc pads before fitting , strange  most brake workshops dont use it because  most modern pads
have a thick  black anti squel on back already.Also its sticky and probably can not be bothered to use it,----but it works great.
Also especially with front pads new as well, most modern ones come  with the leading edge  has a approx 1/4 inch chamfer
or bevel, but alot of older classics like our SL do not have this chamfer on pads, so its very easy to do with a File placed carful in
a vise, just bevel it  ,i do all  around,about 1/8 inch. See photo of my front i just did month ago,sorry pads are in,But showing the
Anti squeal lube from a Porsche about  a year ago.Also rear linings can
squeal on edges of linings against backing plate as breaks are applied ,so a little anti squeal  can be applied. 

[450sl]

MB ,seems to think the position of the pistons is important...see attachment  ;there is a small cutout that has to be positioned right.

Mark

[Ulf]

Thanks, I'll definitely try that, but the brakes are not squealing when braking - actually that's the only time they are silent. It's more of a constant whine when driving and only after the car gets hot and after braking a few times. And now the sound has moved back to the to the left front brake again...weird :-/

U

[Cees Klumper]

Could it have something to do with the brake proportioning valve (if the 230 sl has one)?

[Ulf]

Could it have something to do with the brake proportioning valve (if the 230 sl has one)?

I have no idea, where is that situated? The master cylinder is new and is the one for 230 SL which retains a little constant pressure for the rear drum brakes, yet the pedal feel is much softer than before...

[UJJ]

Besides using the lubricant on the back of the pads, I agree with 450 SL. The position of the pistons is important concerning the squeal.
Regards, Urban

[swood1]

there is a small cutout that has to be positioned right.

Are you talking about the small step in the piston?


I am just wondering if one of your pads/ pistons is sticking..  When you had your pads replaced they should show even wear on both pads.  Can your mechanic confirm this? 


Steve

[Ulf]

Will ask him as soon as the front brake hoses that I've ordered arrives :-)

[Ulf]

UPDATE: Apart from the main brake cylinder, the front brake hoses have now been replaced too, left caliber is restored with new seals, both brake cylinders for the rear drums have been replaced. And for the first hour or so, the squeal was gone, then it slowly returned :-(
It's not constant anymore though and not nearly as loud as before, and it seems to disappear in slight turns or when I wiggle the steering wheel a bit. Could it be wear in a bearing causing it?
The pedal is quite soft too...

[Ulf]

My mechanic claims that this little t-piece could be blocked and the culprit behind the soft pedal, I find that very hard to believe...

[Ulf]

Update: New mechanic has fixed the soft pedal, by replacing another rear brake cylinder (was under the impression that my previous mechanic had already done that). He has also taken the front brakes completely apart, cleaned and re-assembled them. Yet, the squealing from the front left brake persists under driving when the car is warm - but more subdued and in a less irritating tone... I'm still completely clueless :-/

[Bonnyboy]

Were the front brake hoses replaced as well? 

On another car I had a similar problem and it turned out to be the brake hose. The hose was really twisted probably when they put on the caliper.  When I replaced the hose the squealing went away -  When I cut through the hose the centre was swelled as well so I don't know if it was the twisted hose or just that it was swelled up internally that caused the issue.

[Tomnistuff]

MB ,seems to think the position of the pistons is important...see attachment  ;there is a small cutout that has to be positioned right.

Mark

I remember having a brake squeal about 20 years ago but it went away about the time that I discovered that M-B released an "anti-squeal" plate to install between the pistons and the pad backing plate.

I just finished restoring the car, including new brakes (everything).  I installed the left front wheel bearing loose, according to the M-B mechanic who double checked my alignment before the trip to Meeting of the Clans II.  The next day, after he tightened the wheel bearing nut,  the LF brake started squealing again and when hot, would squeal constantly any time I would not "touch" the brake pedal.

Yesterday, I removed the pads, sanded about a millimeter off, cleaned them and added high temp brake grease where it's supposed to go and reassembled them.  When it stops raining, I'll test them.

Wish me luck.

Tom Kizer

[Garry]

I also have the occasional chirp chirp chirp in a front brake and when touching the brake pedal it goes away.  It then comes back until i find a decent pot hole to make it thump a bit and it goes away until i brake again.


I just put it down to the caliber piston not retracting entirely allowing the pad to just touch the rotor lightly. Maybe my rotor is slightly out of round hence the chirp rather than a continuous squeal.  To me it’s not a big deal, more annoying than anything else and i will get it looked at on the next service.

[Tomnistuff]

I went back to my old books and found in Chilton's Repair and Tune-up Guide for Mercedes-Benz 1959 - 70, on page 182, a sketch of a Girling anti-squeal plate installation.  In the third paragraph of "Pad Replacement - Girling Disk Brakes" on the same page, is the statement, " Before pushing the pistons back, remove the inner heat shield, if present, to prevent damage.  These shields, by the way, can be replaced with anti-squeak plates, available at authorized dealers, if brake squealing is a problem."
The sketch appears to show that the anti-squeak plate appears identical to the inner heat shield except for a half-moon cutout and a slot in the remaining un-cut part of the plate.  I suppose it changes the resonant frequency of the inner heat shield.  I now will try to find an anti-squeak plate.  I can't scan it for the moment.

Tom Kizer

[Benz Dr.]

Try a slight weave from left to right while driving. This will move the brake pads back slightly and force the pistons back with them.

[Shvegel]

Just to clarify the picture 450Sl posted about the piston position the step down is on the leading side of the piston so the trailing side of the brake pad gets pressed into the rotor first.  This keeps the leading edge of the pad from chattering.

[Garry]

Dan,
That sounds a better idea than finding a big pothole to me.


😳😳😬

[waltklatt]

Ulf,
If the whining/squealing is still there, try deglazing the rotors and pads with steel wool on the friction surfaces.
Perhaps try to flip the pads from right to left.
See if that helps.
Walter

[Tyler S]

Have you tried a different pad? Some cars are sensitive to the material used in the pad. There are a few options. Semi-metallic, organic, ceramic, etc.

[stickandrudderman]

I've had occasions where after-market discs and pads have caused brake squeal. After several wasted hours implementing the various possible solutions as described here it was found that simply fitting original parts was the cure.

[Tomnistuff]

The work I described a few posts back, cleaning, sanding the pads to remove about a millimeter, adding new high temp grease where it's supposed to go and reassembling apparently worked for now.  The squealing is gone.  Unfortunately I didn't orient the piston notch because I didn't know about it until I had finished.

I find it strange that the noise only started s few kilometers after the M-B mechanic tightened the wheel bearing nut.  I still don't exactly know what the problem is/was, but I'm not going to look a gift-horse in the mouth.

Tom Kizer

[Tomnistuff]

Update:  A few days ago I reported that my cleaning, disk sanding to remove about a millimeter of material, and application of high temp brake lubricant on the non braking surfaces solved, at least temporarily, the constant non braking brake squeal.
I couldn't figure out why it started after the M-B mechanic tighten my loose wheel bearing nut.

I just realized that when he did that, he moved the wheel, hub, and brake disk inboard toward the kingpin that also retains the brake caliper.  In other words, he shifted the brake disk toward the inner caliper piston and away from the outer caliper piston by the amount of his bearing tightening.  After applying the brake, the outer piston would protrude from the caliper more than before the tightening.  At least I know something changed due to his adjustment, but I don't know why it might have had an effect on squealing.  I know that at the end of my brake restoration, the brakes (unapplied) were dragging to the extent that I had to sand them to get them to fit properly.  Every part was at its upper dimensional limit.  Maybe that was what was causing the squealing.

It's just something to think about.

Tom Kizer

[Benz Dr.]

Adjusting the spindle nut wouldn't move your rotor in very much and the pads would quickly self adjust after a couple of times using your brakes. I don't think that would cause brake squeal but you never know with old cars.