Rob Edwards

Let me start by saying that this was likely more trouble that it’s worth, given that the bores in my calipers were all in good shape and the seals all looked fine. I also managed to make a mess of the refinishing process, more on that later. Still, I now have freshly rebuilt calipers, new brake lines, pads, and freshly bled fluid.

Here are the parts I used:

brake cylinder paste/sliding lubricant 000.043.117.00
36 mm piston front repair kit – need 4 951.351.919.10
44 mm piston front repair kit – need 4 928.351.919.10
28 mm piston rear repair kit – need 4 951.352.919.10
30 mm piston rear repair kit – need 4 951.352.919.11
brake caliper bleeders (pairs, with dust cap)- need 8 (4 pairs) 930.351.919.00

front brake pad wear sensor- need 2 928.612.365.01
rear brake pad wear sensor – need 2 928.612.363.01
large front brake pad damper- need 4 965.351.096.00
small front brake pad damper – need 4 964.351.096.01
large rear brake pad damper– need 4 964.352.096.00
small rear brake pad damper– need 4 996.352.086.01

Front brake caliper bolts –need 4 900.067.154.02
Rear brake caliper bolts – need 4 900.087.077.02
front brake hose need2 928.355.081.02
rear brake hose need 2 928.355.080.02
Front brake line banjo bolt copper washers – need 4 N 013 806 2

Caliper rebuild kits – they each include a piston, a dust seal, an inner seal, and a packet of Kluber grease. I ended up using the Kluber grease packets, just 'cause. (We can have a discussion of Brembo’s supplied grease vs. the Porsche spec’d stuff).






For caliper finishing, I bought Zip Strip, some good chemical resistant gloves, a G2 epoxy brake caliper painting kit (black), and two white 3.0 x 0.21 inch Porsche caliper decals for rear brake calipers from Xenonmods.com. The archives are full of comments about how nasty the G2 paint fumes are. The comments are true, so I also bought a 3M charcoal mask, #7193.

I didn’t replace the rotors at this time (still well within spec.)

So here’s the ‘before’ shots:






S4 Caliper removal is straightforward- remove the wear sensors (small angled pliers or a small flat screwdriver), then undo the pad retainers (squeeze the center of the spring with large channellocks, you may need to use a screwdriver to help the top of the spring clear its retainer). Pull the pads (I use the points of a needlenose pliers), and then unbolt the calipers- the fronts use a 10mm hex socket and the rears use a 19 mm bolt. Here's me removing the front caliper bolt that I stripped 'cause the last person here used a lot more than 63 ft lbs to tighten it....



Next, unscrew the hard brake lines from the brake hoses, 11mm open end wrench; counterhold under the bracketwith a 17mm wrench. Then pull the clip that holds the brake hose in its bracket. The fronts are easy as there’s plenty of room. Even so I needed to use vice grips to pull it:



The rear brake hose mounting clips are a PITA to get at, the E-brake cable gets in the way, though it can be pushed out of the way. The other issue are the resonator heat shields- you can remove the rearmost three 8mm screws on each side and the shields will drop 1-2”:




so you can turn an 11 mm wrench (stubby’s easier if you have one) to loosen the fitting on the brake line while counterholding with a 17mm on the other side of the bracket:





There’s not much space for the rear brake line clips-I ended up putting a small (4-5”) vice grip on the clip, and then pulling on the end of the vice grip with a channellock from underneath:




So once the calipers and hoses are off, I plugged the inlets with some 10 mm grease fittings, found at Kragen:



Then I taped off the inside of each caliper, and hit them with Zip Strip, let them soak for 30-60 minutes, then used a combination of brass brushes, my steamer, and the garden hose to remove the stripper. The stripper took off most of the coating, but not all, so I did a second round:



NOTE: I have to confess that I really screwed up on the refinishing. Let this be a caution to anyone that wants to refinish their calipers. Note in the pic above the areas that are incompletely stripped. I should have known that they would look like crap when painted, but I was sick of stripping, so I went ahead with painting anyway.

Which was a disaster. I’d read Nicole’s thread on caliper refinishing, and had gotten a G2 kit, four Preval sprayers, some acetone, etc. I hung the calipers on wires and hit the first one with the Preval sprayer. Well, the spray pattern just spattered globs of crap all over the caliper, then stopped as it got cold. I went through all 4 sprayers in rotation and managed to spackle the caliper:



So I gave up and used the supplied brush and painted the other three. I am not at all happy with the result, tho. Brendan’s got a beautiful picture of his powdercoated calipers in this thread (https://rennlist.com/forums/928-foru...nt-brakes.html) and I would strongly support going this route unless you are really good with brush painting. The other no-no I committed was using scotch tape to mask some of the caliper hardware. The epoxy turned it to goo that shredded it during removal. Use the blue painter’s tape for masking…




I decided that I’d make the best of it and sanded off the logo a la Tony Harkin:



So now that I have screwed up the cosmetics, time for rebuilding. The first issue is piston removal. Everyone says use compressed air, which is fine, but the details aren’t clear. I can sort of help with this, though I couldn’t tell you the specifics of the adapters in these pics. Whoever came up with the measuring conventions for pipe and flare and NPT threads clearly was looking to protect thier industry from amatuers like me..... The first pic is the pile of brass bits I had in order to connect the 3/8" (?) air valve to an M10 meteric fitting that screwed into the calipers:



Here’s the combination that worked:






So I set the compressor on 50 psi and started pushing out pistons. The tendency is to push out the piston closest to the inlet, so you have to be creative to selectively push out the piston you want. You will never get all 4 to blow at once, so the routine is to blow out 1 or 2 pistons, drive out the dust seals, remove the inner seal, clean the hell out of the bores, lube up and install a new inner seal, lube up and install a new dust seal on the new piston, and install it into the cylinder. Repeat a total of 16 times. I must have gone through 20+ pairs of gloves in order to have clean hands for each seal/piston installation.

I had a 2x3, a 1x4, and a stack of cedar shims that came in handy. Blowing out 1 piston:



Blowing out 2 pistons:



Dust seal removal- I used a small screwdriver and tapped it GENTLY between the outer lip and the caliper body, then pried the seal up 1 mm or so, just enough to break the seals’ tension on the outer bore. Then you can take a large needle nose pliers on the flexible part of the seal and pull up to release the seal. STAY AWAY FROM THE BORE SURFACE……



For the inner seals, I found an angled pick in a cheap set from Powerbuilt that worked perfectly- you can drive the pick into the middle of the old seal and turn it out.







Here’s 2 bores cleaned and ready to re-build:



When the inner seals come out, they’re sort of trapezoidal in cross section; the new ones are square. Must be 20 years of pressure on them…..






A few times the piston didn’t pop all the way, but if the groove in the piston is out of the dust boot, you can pry it the rest of the way out:



The inner seal installation is easy, just make sure they stay absolutely clean. I do not believe (well, I HOPE not) there is a directionality to the inner seals as they seem to be symmetrical in cross section when new.

Once the inner seal is in, I coated the I.D. of the new dust seal and slipped it over the piston, then greased up the piston. You get some resistance when sliding the piston in past the inner seal, but with some (3-4 lbs of force?) firm finger pressure they slide right in. At first some of the dust seals seemed to be a little cocked in their bores (above, lower left), but somehow after 10-15 minutes they all 'relaxed' and laid flat on the machined surface of the caliper.

Anyone need 16 junk pistons?




After what must have been 4 hours of fiddling:



I remounted the calipers (62 ft lbs for calipers to carrier, both front and rear, 9 ft-lbs for the hardline to hose joints, and 13 or10 ft lbs for the hoses to calipers, front and rear, respectively) and installed new vibration dampers and PBR pads that Mark Anderson recommended. Here’s a rear (2 cutouts) damper with the backing partially peeled before installation:



Damper pads in situ:



PBR pads:



The front brake lines have a D-shaped barrel that fits in the D-shaped mounting bracket, presumably to resist torsion of the line as the front wheels turn (?). The rear lines just fit through a round hole in the mouting bracket and are held in by a clip medially and the 17 mm counterholding hex laterally. Installation of the front clip:





Finished:



I ran out of time and haven’t bled the brakes yet. Yell if anyone sees any grave errors before I kill myself in my brake-less car……

RyanPerrella

WOW ROB THAT IS ONE HELL OF A POST!

Since we are friends i know you will take this in only the best light. I dont like the finish on the calipers? And i have to imagine that you could have come out ahead if you sold your S4 calipers and just bought the new GTS ones.

hey what a great learning experience though

(Damn this is 2 giant threads i want to read now, yours and the one on changing the rear axle ratio) 2 great threads in one day, THANKS.

StratfordShark

Fantastic post and pix Rob. I'm planning a brake refurb soon so really useful for me.

I'm working on new shocks at rear just now and had noted that the rear flexible hoses look very difficult to get at, so interested in your tips. I may just leave the rear flexible hoses and just change the fronts, but obviously I'd prefer to change everything.

Minor question - what kind of socket are you using to remove the stripped front caliper bolts? Last time I had my front rotors off I remember these allen bolts got a little worn (I really should have fitted new ones at the time) so just want to be fore-armed in case they get worse this go.

Rob Edwards

Ryan-

Believe me, I am with you 110% on the finish, I don't like it either. I'm mad at myself for not just stopping and coming up with a better solution before just slopping on the G2 epoxy paint and moving on (the holidays were coming to a close and January is super busy for me). And I should point out that I'm not disparaging the G2 paint or even Preval sprayers, I just didn't figure out how to use them properly. I probably shouldn't even post such hideous pictures, but hell, sometimes you have to post the negative data with the positive data. Brendan's powdercoating looks like the best solution to me right now, though maybe if I had any painting skills at all I could have done a better job with what I had.

You may be right on the GTS calipers, but the total cost for all 16 caliper kits and 4 pairs of bleeders was $318. Mostly the benefit is the experience of doing it and knowing that all the bits are renewed. (Though like I said at the top, they probably would have been fine for a long time more without the rebuild- the brake hose re-fresh is probably the only thing that was really necessary....)


StratfordShark:

The extractors are from a set of Snap-On extractors I got off of Ebay. I've posted these pics in another thread somewhere on here. They just chock up in a 1/2" socket and you turn out the stripped bolt. For that brake caliper bolt I think I got it started by using the impact wrench on it, just to get a good bite on the bolt. That sucker was on there TIGHT....

If you're going to go to the trouble of re-doing the calipers, i would definitely do all four brake hoses, the rears aren't THAT bad. Clearance is tight, but dropping the heat shields an inch and using an 11 mm stubby on the fitting will work. The e-brake cable can be pushed out of the way without too much difficulty. Like so many things on this car, you just need to find the little pocket of space that just barely allows you to turn the wrench on whatever you're trying to remove.

BC

When we talked Rob, I thought you had used just the seal kits. I did not know that you had ordered the full boat piston seal kit. When you called, were those available too?

Rob Edwards

Brendan-

At the time I'd talked to Tom at 928Intl and Roger (IIRC) and neither had the caliper kits in stock, so I e-mailed Jeff at Sunset. Here's the text of my quote from them back in May 2008:

They didn't say anything about having to wait a month for stuff to come from Germany.

BC

You got pistons too for 20 bucks a pop? It was 50 when I checked and the seals weren't even that cheap.

Rob Edwards

Maybe they quoted the wrong price, but they honored them and the part numbers I listed got me 16 kits that fit the calipers on my car. Now I just need to find an hour or two (famous last words.....) to bleed them properly.

I'd be interested to see what the current prices are, the dollar's stronger (for now) than it was in May 08.

mark kibort

now its time to get the bigger GTS rotors and the spacers to make them, effectively, big blacks!
mk

Rob Edwards

You sellin' spacers, MK? I'm game. I'll need new rotors in another 7 years or so....

dprantl

So how about marketing these spacers, now that you know the exact measurements? I'm sure these would sell very well, even for non-racers. When it comes to replacing rotors, it's pretty much a no-brainer.

Dan
'91 928GT S/C 475hp/460lb.ft

Jim bailey - 928 International

Rob , Porsche NEVER adjusts prices LOWER because of exchange rates ! ...NEVER ! At least that has been my experience over the last 20 years... And yes the finish does look really bad Joe Fan painted his calipers with rattle can high temp engine paint and on his race car they still look fine. The calipers really do NOT get very hot especially on a street car.

StratfordShark

Thanks Rob. I wasn't aware of those extractors. I have a set of Snap-On extractors for hex heads which have got me out of a few jams. Can see how the multi-spline ones would work in allen head (in past if allen head has got chewed up I've filed flats on it to let me use the conventional bolt extractors). I'll look out for a set here.

mark kibort

When you go for the bigger rotors, you can do the spacers! (and get the GTS brakes equivilant)

yep, on a street car, the rotors should last almost forever. heck, my rears that still see a lot of high temp, have not been changed in 7 years and they look great.

Fronts, on the other hand, when racing, need to be changed 2 times a season. However, its not for wear, its for cracking. with out holes and only slots, probably once a season.

mk

mark kibort

I can do it. However, i need to do it with at least 10 folks.

A group buy for the kit would be $700 (rotors, race pads, spacers, GTS bolts, and instructions on the light dremel work)

Let me know if you guys are interested. Its a great modification. one of the cheapest and most effective Ive done in a long time!

Think about it. Basically, GTS brakes for $700!! (and no disconnecting your S4 calipers or any mess!)

mk