Opel GT Forum banner
1 - 20 of 20 Posts

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #1 ·
I have new 1975 Manta/Ascona "Big Brake" calipers and rotors on my GT (adapters and braided hoses from OGTS), with new anti-rattle clips and pins. I also have the OGTS 22 mm Master Cylinder and 9" booster.

The brakes are awesome.

But after a few hundred km, they started squealing. Just a bit at first, and then more, and then they wailed like an almighty banshee.

I followed the normal course of action:

1) made sure that the edges of the pads that contact the calipers were clean and lightly greased w/ proper brake lube

2) beveled the leading and trailing edges of the pads

3) noticed that the stock backing plate might have been slightly touching the inner pad edge, so I bent it flush to the spindle bracket

4) Sprayed CRC Disc Brake Quiet on the backs of the pads. Twice.

That solved the problem. For another couple hundred km. Then the banshee was back.

The pads don't come with any "damping shims". Nor are they listed for the 1975 Opel Manta/Ascona pads. But they are listed for the 1979-1981 BMW 320i ATE caliper pads, which are identical (and these technically are those).

Shims are only $4 per set from RockAuto, but shipping is $10. Damn COVID shipping increases. I'll try additional brake pad anti-squeal and re-beveling. I highly doubt that will endure.

Anyone tried the shims, or any other ideas?
 

Attachments

·
Registered
Joined
·
1,023 Posts
I’ve always loaded up the pads with shims on my stock calipers with a very thin layer of the brake quiet that comes in that little squeeze packet. The shims are critical I think. I’ve always had good results going with that method anyway.
 

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
I've never had squealing brakes through all of the GT's I've had over 40 years. For most of that time I had stock brakes, but during the past 10 years I've had the '77 BMW 320i wide vented calipers and rotors. I ALWAYS buy metallic pads.

Check that your sheet metal spring clips aren't dragging on the rotor. I had a problem getting the proper clips for my BMW brakes and they dragged and screeched from rubbing the rotor.
 

·
Senior Contributor
Joined
·
1,644 Posts
Sounds like the Calipers are Sticking and Brake Pistons not retracting, if this has happen twice.

I would try to retract the brake pistons fully, (Maybe Metallic Pads, am using too) and give it another Go
The Big Brake Manta and BMW Calipers use Different Brake hold down clips, The notch in the pads
( attach pic)
are BMW pads used for the brake sensor, those not 75 manta pads
 

·
Opel Rallier since 1977
Joined
·
2,278 Posts
I looked in the GM Opel parts catalog, and it does indeed list the backing shims behind the pads for the '75 50 series front brakes. So proper shims might be your ticket to solve this.
 

·
Registered
Joined
·
544 Posts
Stainless shims are a must. That will probably do it. Although, just in case, for the most difficult cases I found another cure.

First, you have to understand what causes disc brake squeal. It is a high frequency vibration being transmitted though hard parts that act as a sounding board. You need something to dampen the vibration. Fixed caliper disc brakes tend to squeal more than floating caliber brakes.

I have never seen a spray on solution that lasted. The surface eventually gets squeezed out by the piston until there is nothing left to dampen the vibration. Back in the 80's I started using very thin gasket material placed between the shim and the pad, with a VERY LIGHT coat of adhesive to hold it to the pad. It needs to be a really tough gasket material, not just paper. My first couple of attempts, I used material that was too thick. It quieted things down, but resulted in a mushy pedal. I wish I could tell you exactly what material I ended up using, but hey, it has been 35 years. It may take some experimenting.
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #7 ·
I phoned around auto supply stores today after doing some web searching for damping shims for the Big Brake caliper pads. I couldn't find ANYTHING about sourcing separate damping shims for the '75 Ascona/Manta Big Brake calipers and pads, other than what I showed above from Rock Auto. Some of the listings for pads have shims listed as included (the OGTS pads show shims on the back of the pads), but many do not. I have three sets of brand new pads, none with shims. None of our local supply stores even showed a listing for separate shims, and even the pads would have to be special ordered. While it may be that GM/Opel intended the pads have damping shims, the availability of same is deminimus after 45 years.

So I pulled the pads (yet again), beveled all the edges with a coarse file, sanded the friction surfaces a bit to get to fresh material, re-coated the back of all the pads with more CRC Disc Brake Quiet, generously lubed the pad edges and backs, and put the pads back in. And hit the road.

No squeals for the first few km, but then the banshee returned, and didn't vacate the premises after a spirited 10 km brake-pad-break-in run. My wife heard me turn the corner down the street. VERY annoying....

While these ATE Big Brake calipers were used in a LOT of BMW 320i's (some 1.3 million made, many with these calipers!), the last ones were built in 1981, and as I mentioned, the only listing for separate damping shims was at Rock Auto. I had a few other items I needed for our Daily Drivers (not that we're Daily Driving much these days...), so I ordered up three sets of shims. At $4 a set, I figured I could always flog them to the other folks with squealing Big Brakes.

The shims will be here by the weekend. Stay tuned for an update.
 

·
Registered
Joined
·
2,286 Posts
Are you using that thin film spray? We used to use some blue spray stuff but went with some thicker compound with the texture of caulk that worked much better. Had to cure for 10 to 15 minutes before assembly, we'd wait an hour if possible. Damn CRS, I cant remember the name, sorry.
 

·
Opel Rallier since 1977
Joined
·
2,278 Posts
Hope the shims do it for you. One thing discussed was a substitute: I wonder the metal cored exhaust gasket material wold be good. It has graphite surface on both sides of a steel core. Mr Gasket 5960 is a PN.
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #11 ·
Is the squeal only when braking or all the time?
The brakes only squeal when braking. They don't squeal when lightly pressed (but hard enough to feel some deceleration), but squeal louder as the brake force increases. Sometimes the squealing reduces as substantial force is applied.
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #12 ·
Are you using that thin film spray? We used to use some blue spray stuff but went with some thicker compound with the texture of caulk that worked much better. Had to cure for 10 to 15 minutes before assembly, we'd wait an hour if possible. Damn CRS, I cant remember the name, sorry.
The CRC product that the local AutoValue store recommended is a red spray. It forms a thick'ish film, rubber-like. I allowed it to cure overnight both times I have sprayed it on.
 

Attachments

·
Opeler
Joined
·
942 Posts
Sometimes new, out-of-the box rotors have a very smooth finish and need to be scuffed up a little before use. And/or, they have a protective coating on them that needs to be cleaned before use. Either one of these conditions can cause the pads to glaze very quickly.
 

·
Your Noble Friend ;-)
Joined
·
4,450 Posts
I haven't changed any pre-1975 Opel brake pads in a while, but I think to remember that the shims are actually "locking" into the pistons, and prevent them from rotating. The pistons have to be in a certain (rotational) position for whatever reason, or they squeal.

Dieter
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #15 ·
I haven't changed any pre-1975 Opel brake pads in a while, but I think to remember that the shims are actually "locking" into the pistons, and prevent them from rotating. The pistons have to be in a certain (rotational) position for whatever reason, or they squeal.

Dieter
The locking shims with the little dents are OEM for the stock calipers, and fit into the "notch" in the piston, ensuring that the piston notch is oriented correctly. Many aftermarket pads w/ shims are missing the dents, which can cause a problem with uneven wear of the pads.

The '75 Big Brake caliper pistons are flat, and don't have the notch.
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #16 ·
Sometimes new, out-of-the box rotors have a very smooth finish and need to be scuffed up a little before use. And/or, they have a protective coating on them that needs to be cleaned before use. Either one of these conditions can cause the pads to glaze very quickly.
I have read that, and I am going to give that a try. That issue seems to mainly with rotors that have a rust-proofing coating, which I don't believe these had. But it is worth a try.

CRC also sells a "De-Squeak™ Brake Conditioning Treatment"
(CRC CANADA De-Squeak Brake Conditioning Treatment UAE393 ( 75080) | Shop Specialized Lubricant | TENAQUIP)

which:

"Prevents brake noises before they occur
Contains aluminum and graphite to plate and protect metal surfaces up to temperatures of 1800°F
Smooth texture, fine particle sizing and dries quickly"
 

Attachments

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #17 ·
While I await the delivery of the damping shims from RockAuto, and since my employment is still delayed, waiting on a COVID-protocol to allow us to return to the Applied Research and Innovation Services at the educational institution that the project that has been occupying my mind, if not my person, I "cracked on" (in my best Edd China impersonation) at solving the banshee brake squeal.

Rather than trying a single solution to determine if that solved the squeal (which any decent research project would insist on...), I scatter-gunned my response:

1) Cleaned and re-coated the back of the pads with two generous coats of CRC Brake Quiet.,

2) Rounded the remaining edges of the friction material on the pads,

3) Lubricated ALL the contact surfaces, including the pad clips and pins,

4) Sanded the rotor surfaces, inner and outer, with 220 grit oxide sandpaper on my palm sander, ensuring that any glaze was broken, and did likewise to the pad surfaces.

The result: Barely a squeak, and then blissful quiet for the next 30 brake applications, of varying effort and effect..

I suspect that sanding the rotors had the greatest benefit, perhaps followed by lubricating the pad clips (as I noticed that the contact surfaces were a bit "fretted").

When the shims arrive Wednesday, subject to going back to earn money for the first time since March 16, I will install said shims, with a re-coat of the CRC polymer spray between the shim and pad.

Please stand by....
 

·
RyanY
Joined
·
4 Posts
You haven’t mentioned what brand pads you’re using - many cheaper pads have a harder compound for longer pad life that tends to be noisier than a softer high-performance brake pad. If you have sportier pads, was there a recommended pad bedding procedure for them?
 

·
Super Moderator
Joined
·
5,968 Posts
Discussion Starter · #19 ·
You haven’t mentioned what brand pads you’re using - many cheaper pads have a harder compound for longer pad life that tends to be noisier than a softer high-performance brake pad. If you have sportier pads, was there a recommended pad bedding procedure for them?
I do not know the brand of the pads I originally had that squealed badly, as they came with the rebuilt calipers I bought on eBay. They appear to be "organic-metallic" , with some metallic bits. Clearly not "ceramic". They are the BMW style pad, with the notch for the BMW wear sensor.

By the way, the pads that OGTS sells for the Big Brake calipers show as the notched BMW-style on their website. I believe they are interchangeable when used with the. Opel Big Brake calipers.

The 2nd set that squealed equally badly or worse (and are in now with no squealing after the changes listed above) are " Durilon" aramid fiber (aka "Kevlar" I believe , and again not ceramic) and are the Opel pad design, w/ no sensor notch.

I bedded both sets of pads with the proper technique of a dozen hard (but not locked) high'ish speed stops, followed by a few miles of driving and light stops to allow the pads and rotors to cool. The bedding procedure had no beneficial effect on the squealing.

The RockAuto damping shims arrived late today. They are the notched BMW style, and are adhesive-backed. I will remove the CRC Brake Quiet coating, and apply the shims to the pads. Then I will re-apply the Brake Quiet to the back of the shims and re-install and test them out.
 
1 - 20 of 20 Posts
Top