Brake Pads Won't Fit..Help Please

[Robert Coats]

'91 C4, I'm trying to install new brake pads, but I can't seem to get the pad to drop/fit down into the caliper. The outer metal backing of the new pad is a bit larger than the metal plates on the caliper. As a result, the pad won't go down/seat, even with pretty good pounding. It just seems to wedge tighter and tighter.

I double checked the pads, and they are (OEM) and the same size as the ones that were removed. I put some grease on the edges of the pad backing, and that didn't help one bit.
Something's not right; I can't see grinding the pad backing to "make" the pads fit; what else can you guys suggest?

[jmohn]

Have you cleaned, really well, the area in the caliper where the backing plate on the new pads is binding? While I've never had the problem, I have heard that brake dust build-up can prevent the new pad from sliding in unless the old caked on build-up is scraped off. The backing plate on the new, full thickness pad occupies a different place within the caliper than the old, thin pad, there could be a build-up, at the ends of the caliper opening, right where the backing plate must slide in. Just a further suggestion, I also install one new pad at a time, finding it easier to press back one piston at a time.

Good luck,

Jerry M
'78 SC

[Robert Coats]

I have sprayed 1/2 can of brake cleaner on this caliper alone, and can see clean, mostly bare metal plates (yellow boxes), but will have another go at it.



The old pads required a pair of vise-grips and a bit of grunt to get them out, but these new pads don't even start to go in without a bit of hammering, and then they only get tighter, which ain't right, I'm sure.

It just shouldn't be this tough/tight!

[jmohn]

You're quite right, they shouldn't be that tight, and, from the pictures, it does look pretty clean in there. My only other offering is, when I was on the 951 list, a couple of guys posted they had to "dress'' down the edges of the backing plate on their new pads to get them to fit, they both thought it was due to poor manufacturing tolerances. If it were me, I would get a different brand of pad and see if they exhibited the same problem. I put new "Metal Masters" in my SC last year with no problems and never had a problem changing pads in my 951, it took a little wiggling and prying to get the old ones out, then, a little clean up, and the new ones slipped right in.

Jerry M

[jmohn]

Another thought, it looks like there's a metal shim (?) at each end of the pad locations. Are they removable? If they are, be sure to clean behind them as well. They aren't familiar to me, but I do recall the 951S guys (mine wasn't an "S") talking about "spacers" at the ends of the pad locations on their calipers and how difficult it was to get these areas clean enough. Sorry, I'm not more familiar with "modern" Porsche calipers.

Jerry M

[Bill Verburg]

There are 2 removeable ss spring plates at either end of the pad slot. They serve as guides(for transverse movement of the pads) and stops(to position the pad radially). What happens (especially when driven on salty roads) is that corrosion (and other gunk) builds up between the steel plate and the Al. caliper body making a tight fit even tighter(you can see the gap due to this in your pics).

See if you can remove the plates and clean the area behind them. This is often difficult to do. If you can't get them out, profesional help may be required.

It is a sort of press fit to get the pads in anyway(remember they are spring plates). So use some h/t brake caliper lubricant to ensure free movement once in place. It doesn't help if you are trying to use the anti squeel buttons(I never use them partially for that reason)

[john walker's workshop]

it's not unusual to have to dress the metal ends of the pad with a file. paint, glue, or a rough edge where the metal was cut, often need to be removed. it usually doesn't take much. just don't take so much off that you get end play, or you will hear a knock when the brakes are applied.

[Robert Coats]

Originally posted by jmohn
Another thought, it looks like there's a metal shim (?) at each end of the pad locations. Are they removable? If they are, be sure to clean behind them as well.

From what I can tell, these metal spring-plates pretty much hold the pad in place, so it does not fall against the rotor/hub. I've blown air and sprayed cleaner as much as possible, but the pads are still too tight.

Looking closer, these spring-plates can be removed, and I'm sure I'll find lots of grit/dirt/dust/rust/etc. behind them, which is probably why they won't spread open enough to let the pad fall in place. Trouble is, to get the spring-plate out (red ring) you have to remove an allen-head bolt(green ring), which, from what I can tell, can only be done if the caliper is pulled off first.



The only gripe there is I'm gonna have to crack open the brake line to get the caliper off the hub, and then bleed the brakes. If that's all it takes, fine. We'll see.

[john walker's workshop]

use the file! i've never once had to pull those plates.

[pwd72s]

Originally posted by john walker's workshop
use the file! i've never once had to pull those plates.

Geeze! The fit has become that bad?

[911pcars]

Robert,
Maybe it's an optical illusion, but it looks as if the piston seals have been eaten up by ... carb cleaner.

Sherwood Lee
http://members.rennlist.org/911pcars

[Porschedude]

911pcars,

The items you are speaking of are the vibration dampers that have a self-adhesive surface on the pad side, and a multi-fingered spring that slips into the caliper piston.

Robert,
I converted my ’91 C2 rear brakes to four piston calipers. The set of caliper were used that I rebuild and they had been cannibalized. The screws that hold the spring plates on were internal allen wrench button head screws. They are real soft and are lock-tite'd in pretty well. I had to deal with some stripped out screws and drilled the body of screw out and used an “easy-out” to remove the screws. If you are determined to clean behind the spring plates, be prepared to drill out the screws and have replacements on hand. Use an allen wrench that is sharp cornered, rather when one with radius or rounded edge. The newer the better. When I drilled mine out I had to use an angled head drill motor “aircraft type pneumatic”. It was the only way to get into the cavity.

How hard were the old ones to come out? Compare the old pads with the new ones. The old ones came out; the new ones must be oversize. If you sand down the width of the backing plate to make it fit, make sure that the surface is square and not tapered. Also make sure that the surface is smooth, to prevent it from hanging up so that it will float in position.

Good luck, Keith

[Bill Verburg]

I have to agree w/ Sherwood on this, those seals appear to be toast, A total rebuild appears to be called for here. This is what those seals should look like;


Here is a pic of the anti squeel/vibrationn dampers, they are only glued on and can be discarded w/ no ill effects;


Another thing to look at on brake pads is the co-efficient of friction indices on the back of the pads, there should be 2 letter ratings such as "EE", "FF", "EF", etc. The first letter is the cold temp coefficient rating and the second letter the hot temp coefficient. The higher the letters, the higher the coefficient of friction. The Repco deluxes are a "FF" as are the Pagid T-compound pads. The Repco Metalmasters are a "EE". The ones in the pic are oem Textars from a 964T "FF"

[andyjboy]

Bill/Sherwood, what you thought was damaged seals appears to be the vibration dampers which have become detached from the old pads & are still in the pistons. Robert, you need to remove these before attempting to fit the new pads - they may be contributing to the tight fit. It is not uncommon on many cars to have to 'dress' the ends of the new pads for the reasons that John Walker has already mentioned - build up of paint, poor finishing of the metal edges, etc .

Andy Boyle (UK)
'69 911E

[Bill Verburg]

Andy, you are probably right! I am so used to not using them that it never occured to me that they would come apart if the pad was just pulled out in the usual manner.

[Robert Coats]

Originally posted by 911pcars
Robert,
Maybe it's an optical illusion, but it looks as if the piston seals have been eaten up by ... carb cleaner.

No, those are the anti-squeal "hats" that fit inside the pistons and are glued to the back sides of the brake pad. The surface is gummed up with dried adhesive and brake dust in the photo. The seals are okay, and I'd NEVER use carb cleaner on brake parts.

[Robert Coats]

Okay, taking johnwalkersworkshop's advice, I took a bit of material off the edges of the pads, using my handy-dandy-Sunday-morning-milling-machine:



After a few test fits/grinds, I got the pads to drop in okay. I noticed the inboard pads seemed to need more trimmed to fit than the outboard pads, but they did go in okay.

Brakes work great on the test/seating-in drive. However, I've got some squeal now, even with the anti-squeal hats glued onto the new pads. So, a question: Should the anti-squeal hats fit loose or snug into the pistons? I spread the legs on them ever-so-slightly to make sure they grabbed the inside of the piston, and I'm wondering if they should (instead) be a bit loose.

Finally, a "I learned about car repairs from that" tip-of-the-day; be sure nothing is under the car before you lower it off the jack:

[cstreit]

I have to file mine down right to the edge of the pad material every time... Standard process...

[Porschedude]

As Brembo intended, the manufacturer of the Calipers, the anti-vibration "damper plates" should be changed every time you change the pads. I know, I know, some people don't. The dealer that I bought my C2 from used a "Copper Anti-Seize Coat" between the pad and the pads he put on before I drove away. He explained that he has used this for years and it stays put and absorbs some of the vibration and actually helps the problem squeal.

When I put my four piston calipers on the rear of my C2, "Didn't Come With 4 Piston" I replaced the pads, virbration damping plates, etc. I had the calipers off the car, inserted the damping plates, took off the cover paper on the damping plate self-adhesive surface and installed the pads, then I installed the caliper on the car.

The best pad I have found that is a very good performer are marketed by many names, but made by Bendix Austraila. PBR Metal-Masters, Repco Metal-Masters, Bendix, and a couple of others. They are low dusting so you don't have the cleaning problems associated with the ATX and Textar pads.

I have run these pads on many cars and had great luck.

Keith

[jc]

I've got those calipers and just today I pulled my pads. Pagids went in effortlessly.

Cheers,
jc