Ray Calvo

OK, got done with another job; not all that bad. I'm drafting this for our PCA Region newsletter.

Thoughts/screwups appreciated.

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REPLACING BRAKE PISTON SEALS
By Ray Calvo

Well, with the mileage increasing and increasing on the 993 (over 70,000 right now!) I figured it was inevitable that something else would go. This time, when changing the brake pads after a track event, I noticed the rubber brake piston seals were bad.

If you look on Figure 1, you’ll see what looks like a cover just below the tops of the brake pistons. These are rubber dust/dirt/water seals that protect the brake pistons from damage and corrosion (actually, the walls of the brake pistons and the caliper piston bores plus the rubber seal ring between the brake piston and caliper bore that is the only thing holding the brake fluid in the piston under braking pressure). On mine, due to time and heavy track/autocross duty the rubber seals had dried out. I figured I should replace these before the pistons or rubber seals get damaged. It’s something you might want to do also on a high-mileage car.

First, the unfortunate news on parts. On early model 911’s at least (up thru 1989) these dust seals are readily available. On later model cars (and ones with 4-piston brakes) you have to buy a complete piston repair kit, which includes the brake piston. These kits can cost upwards of $25 PER PISTON, so with as many as 16 total pistons (4 per caliper – high level math, I know!) you’re faced with some expenses. For now I just did the fronts; the rears are still OK.

For you 993 owners, part numbers are:
Small brake pistons: 951-351-919-10
Large brake pistons: 928-351-919-10

Now, you “Shadetree Mechanics” CAN handle this job. Here is what I did:

1) Loosen lug nuts on left front wheel
2) Raise left front wheel, remove lugs and take off wheel
3) Turn steering wheel to left so that caliper is facing out
4) Remove ONE brake pad. Tie the spring hold-down clamp out of the way (I used light picture hanging wire to tie it to a front spring coil. You can now compare what you see to Figure 1.
5) Use a jewelers or small hobbyists screwdriver to pry the piston seal out of the caliper bore. Once the outside edge of the seal is free of the bore, you should be able to work the seal off the piston with your fingers. Repeat on other piston seal on that side.
6) You might want to force the pistons out of the caliper for this next step. I used an old brake pad with all the old lining knocked off to insert in place of the brake pad, then withdrew the pistons by slowly and partially pumping the brake pedal (i.e., NO LONG strokes; use many short pumps). I did this till the whole dust shield mounting surface was visible on the piston.
7) Use some brake cleaning spray and a toothbrush to clean the pistons.
8) Apply some of the lubricating paste that should come with the above piston repair kits on the piston and caliper mounting surfaces of the dust shield.
9) You can now force the seal into position over the piston and into the caliper bore. Make sure the entire outer edge of the seal is totally and evenly pushed into the caliper bore.
10) Use the above noted brake pad with no lining and a pry bar to force the pistons totally back into the calipers. Now wipe down the piston, rotor, and dust shield surfaces free of all of the lubricating grease.
11) Reinstall the pad, commence on to the other side of the same caliper.
12) Reinstall wheel, lower car, repeat on other front caliper.

In case you’re interested, for comparison I’ve shown you a new and one of the bad/used piston seals in Figure 2.

JasonAndreas

Two suggestions;

(a) If the spring plate has been pushed out enough (with brake spooge/etc.) to overlap the dust/pressure seal (so you can't get it out/replace with a new seal) you'll need to use heat to remove the allen head screws that are locktited to the caliper.

(b) If you completely disconnect the brake lines from the caliper use an air compressor to push the pistons out. (i used an air compressor from a toyota 4x4 with the "beach ball" attachment; i had disconnected the battery previously so as to NOT take any chances of re-pressurizing the abs system (in the porsche) and the toyota was just sitting there plus I didn't want to take a chance with pushing my brake pedal in too far and possibly screwing up something else (i'm a newbie)


-- jason andreas
1993 964RSA

Ray Calvo

[quote] a) If the spring plate has been pushed out enough (with brake spooge/etc.) to overlap the dust/pressure seal (so you can't get it out/replace with a new seal) you'll need to use heat to remove the allen head screws that are locktited to the caliper.
<hr></blockquote>

HUH???? Guess you lost me on this one, Jason; don't know what you mean by "spring plate" or "brake spooge". If you mean the piston is forced out too far, that's why I recommend using an old worn-out brake pad between the pistons and rotor; if the pistons come out too far you can force them back easily using a pry bar between the backing plate and the rotor. Also, my pads were fairly new when I did this; pistons were only extended out a bit from the caliper, making acces relatively easy as shown on pretty picture.

[quote]
(b) If you completely disconnect the brake lines from the caliper use an air compressor to push the pistons out.
<hr></blockquote>

I was hoping like hell that I could do this job without removing the caliper; fortunately I could. If anybody runs into trouble with the caliper in situ, I would recommend removing it first with the brake lines attached, and use very gentle brake pedal pressure to withdraw the pistons (hold one side in place with a C-clamp and a brake backing plate). I guess the idea of using air pressure scares me a bit (also I don't own an air compressor - no need for it in 30+ years of car ownership).

Silver Bullet, the kits also contain a brake piston and a rubber pressure seal washer (fits between the piston and caliper bore).

JasonAndreas

[quote]Originally posted by Ray Calvo:
<strong>

HUH???? Guess you lost me on this one, Jason; don't know what you mean by "spring plate" or "brake spooge".</strong><hr></blockquote>



The red arrows are pointing to the two spring plates that are on a brembo caliper.

--spooge: sorry, I guess it is slang I picked up living in Wust-ah Massachusetts, west of Boston (k-ah, Mirr-ah, etc.) The way I used the word it was meant to describe brake dust, dirt, rust and anything else that managed to accumulate in the caliper. A search on <a href="http://www.google.com/" target="_blank">Google</a> will bring up the more common use of the word (I love my car but not that much.)

[quote]<strong>
If you mean the piston is forced out too far, that's why I recommend using an old worn-out brake pad between the pistons and rotor
</strong><hr></blockquote>
I brought my car in for its 105k service and I complained that the brakes were squeaking when turning the steering wheel sometimes without the brakes being applied and that there was an excessive amount of brake dust on the right front wheel. I got the car back and the Porsche dealer said everything was fine. Taking a right turn out of the dealership and the brakes were squeaking again. (all they had to do was turn the steering wheel while driving the car and they would have noticed it.) Now because my car had been hit in the dealerships parking lot(they fixed it) all I wanted to do was get out of there (and never return.) When I got home I took a look at the front calipers and noticed that the boots/seals were torn. I also noticed that brake dust/road dirt/rust/etc. (aka. spooge) had built up behind the spring plates enough that the plates were pushing outward, locking the brake pads in place, not just holding the pads. I had to use a can of 3m brake cleaner (per spring plate), a block of wood and a rubber mallet to knock the pads out. With the pads removed, the spring plates had bent out far enough that they were overhanging the dust and pressure seals and had to be removed to get the seals out. I ended up sending the calipers out to be rebuilt after I stripped the hex head bolts. Of course i've probably read the page in the workshop manuals that says the bolts are locktited in place at least 10 times but completely forgot at the time and had given up in frustration.

[quote][QB]
I was hoping like hell that I could do this job without removing the caliper;
I guess the idea of using air pressure scares me a bit (also I don't own an air compressor - no need for it in 30+ years of car ownership).
[/QB/]<hr></blockquote>

Pulling the calipers from the hard lines wasn't really that big of a deal. It took all of twenty seconds and the calipers had never been removed before. (replacing the soft lines was a completely different story; i ended up replacing all the hard & soft lines connecting upto the pressure thing in the trunk (i had stripped one hard line trying to remove a soft rubber line plus the hard lines are real inexpensive from porsche &lt; $30 and I was already there so I just did it.)
My porsche and I'm guessing most everyone elses comes with an air compressor to fill tires with air. I used one from a toyota (and a block of wood and a clamp) because it was sitting there but there is no reason I couldn't have used the one from the porsche. I put the wood in the caliper, held it in place with a c-clamp and applied air. The unblocked piston slid out (keep fingers away just in case.)
This was probably the first work I ever did on the car (or any car for that matter) myself besides changing oil so I was worried about pushing the brake pedal in too far and damaging something (working on porsches and cars was some mystical science to me at the time and I had absolutely no clue, i now know a tiny bit more and realize with right tools and a little education I can pretty much do anything. Of course my opinion might change when I drop the engine & transmission in the next few weeks.
If I had a C4 I definitely would NOT have touched the brake lines or removed a caliper.

--jason andreas
1993 964RSA

tom_993

We all like to complain about grumpy ol’ Ray, but he does make valuable contributions! Many thanks!