Brake / calliper Question..

Big Dave · Sep 30, 2006

I seem to remember some time ago there was a thread running about the calliper piston + seal kits..

Has anybody found a place where they can get just the seal kits from .I beleive Porsche sell ONLY the complete kit...[ piston + seals.]..
Im in the process of refurbing some callipers of my S2 + 968 + am in need of just the outer seal. I need seven of them...
Ide rather not have to buy the whole kit incl the piston etc,[ aprox £17 each.,], as i dont need them, the pistons are fine...I managed to catch the callipers b4 the pistons got damaged....

944psi · Oct 1, 2006

I found this supplier a while ago http://www.zeckhausen.com/Brembo/Consumables.htm#Rebuild . I haven't used them myself but I assume that since they are supplying parts for brembo caliper rebuilds there should be no reason why they shouldn't fit.

Seems as long as you know which sizes you need you should be able to order the seals without the pistons.

Hope this helps.

Phil

Diver944 · Oct 1, 2006

That's a good find Phil (I've saved it in my bookmarks)

Off the top of my head I think standard S2 and 968 callipers have 36mm and 40mm pistons (best to double check though [

])

sawood12 · Oct 1, 2006

But i believe that althought the front and rear calipers look the same from the outside the front calipers have larger piston sizes as I was looking to replace my rear calipers with my fronts but I think it was Andy Duncan who pointed out that the fronts have larger piston sizes.

Big Dave · Oct 1, 2006

Phil
Thats fantastic m8...[

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Just a pity there in the USA...[

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]

The piston sizes for the front callipers ARE 36 + 40mm.....

Im actually going to put the front callipers on the rear , So we,ll see if its either a help, car stops "flatter", or a hinderance,?? , the car swaps ends under heavy braking...!!!!!!!!!

Fen · Oct 1, 2006

I have a pair of 220 Turbo fronts to go on the rear of mine, too. I also have an adjustable proportioning valve and Big Black fronts though, so I'm pretty sure they can be made right with that combo. Not that I have great need of brakes at the moment of course.

morris944s2john · Oct 2, 2006

Yes, I got my calliper piston seals from Zeckhausen racing. There was some problem about credit card payment, but that was resolved.

I did , however find that I needed a couple of replacement pistons anyway, the Zeckhausen price is not so good on these.

If you need only seals, the Zeckhausen is cheaper, but the Porsche/ Brembo kit does include seals, pistons, dust seals and even brake grease. I would take the callipers apart (but no need to split) and remove the pistons with an airline (carefully). Any pitting on the pistons and they are scrap. The scrap pistons are likely to be the siezed ones anyway.

Replacement bolts for the stainless plates- Namrick do M6 dome/ allen bolts in just the iright length.

BTW, my brakes were and still are fantastic after the re-build, no problems with the Zeckhausen seals which look identical to the Brembo ones, even down to the coloured rings.

Hilux · Oct 2, 2006

the car swaps ends under heavy braking...!!!!!!!!!

Im actually going to put the front callipers on the rear

Hmmm....................if your rears are too efficient (or more efficient than they need to be) the wheels will lock and the rear will try and overtake the front. Do the rears lock up?

If so then uprating the rears will exacerbate the situation. The rears are not that heavily used its the fronts that do most braking.

Is there a line pressure imbalance?

Are the fronts working properly?

Are the front flex hoses ok? If they are old change them for braided.

Are the pads up to the job?

I managed to catch the callipers b4 the pistons got damaged....

In what sense?

Big Dave · Oct 2, 2006

OK so i need to explain myself,!!!!!!!!!!

The car , A 944S2, has M030 front callipers,Hubs + spindles, Pagid orange pads, Castrol SRF fluid [ THE best you can get ],Goodridge braided hoses all round, Pagid Blue rear pads. If you look at my sig youl see a 944S2 "track toy"..

What ive done is removed the front,"original NON M030 callipers" + am in the process of refurbing them....This is why i need some seals...
When they are finished they are going on the rear ...So at the mo ive got the "normal" rear callipers on the car.
The car brakes are FANTASTIC, im just trying to improve on them...[

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]

The car DOESNT swap ends at the moment. It must have been the way you read my post, or the way i worded it......

Regarding, " catching the callipers",,,,, the seals have split but havnt affected the pistons, So i caught them b4 the road corrosives got to the pistons....[

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Like i said b4 a BIG thanks to Phil for pointing me in the direction of the seal supplier...[

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Hope that helps you .....

944psi · Oct 2, 2006

Glad to have helped you BD.

I'm part way through a caliper rebuild at the moment and will need to replace some seals and possibly pistons. Actually when I say I'm part way through, I mean so far I have only managed to remove one of the bolts holding one slider plate to the caliper. [

] And that was with a hammer and chisel.

So I have decided to take the calipers to a garage / workshop and let them remove the bolts holding the slider plates as my domestic workshop facilities have (so far) been beaten by this task [8|]

Phil

sawood12 · Oct 3, 2006

ORIGINAL: Big Dave UK

Phil
Thats fantastic m8...[][]
Just a pity there in the USA...[][]

The piston sizes for the front callipers ARE 36 + 40mm.....

Im actually going to put the front callipers on the rear , So we,ll see if its either a help, car stops "flatter", or a hinderance,?? , the car swaps ends under heavy braking...!!!!!!!!!

You will be increasing your rear brake bias if you put your fronts on your rear. The rear calipers are different from the front on the S2's and early turbo's. The rear calipers have 28/30mm piston size whereas the fronts have either 36/38mm or 36/40 (as you said) depending upon the year of your car so the last thing you want to be doing is to swap your calipers around.

Big Dave · Oct 4, 2006

The front + rear brakes [ standard ] have exactly the same size pad area.
The only difference is the piston size..

What ive done is fit larger callipers" larger pad area" [ M030 ] to the front. The front of the car NOW brakes WAY better than b4. Ive run this set up on numerous track days this year...To great effect...[

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The only reason for my wanting to change the original fronts to the rear IS to "slightly" increase the rear bias.
This is to try + reduce the nose of the car from "diving" under extreme braking. IE making the car stay flatter on the entry to the corner + also reduce a slight tendancy to understeer....

I know i can fit a different brake pressure proportioning valve [which i have " in stock"] to the "abs" brake block on the passenger side inner wheel arch, BUT they aint easy to fit...VERY fiddly to access. Also these work better when the BIG RED callipers are fitted...[ Overkill in my eyes]...

As i see it the pressure to the rear callipers is limited by this "proportioning valve". So THE only way i could unsetul the rear A LOT would be to fit BIG RED or M030 fronts on the rear thereby increasing the pad swept area....

I might be wrong + change it back to how it was, But itl be fun trying....[

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Guest · Oct 4, 2006

The only reason for my wanting to change the original fronts to the rear IS to "slightly" increase the rear bias.
This is to try + reduce the nose of the car from "diving" under extreme braking. IE making the car stay flatter on the entry to the corner + also reduce a slight tendancy to understeer....

Increasing the area of the rear brake pads or increasing piston size will increase your rear bias. Note the increase in piston size may also increase your pedal travel.
But this will not reduce the nose of the car from diving. The amount of weight transfer forward under braking is a function of the front/rear spring rates, the height of the sprung CG and the decceleration the sprung CG. The front and rear braking forces push backwards on the tires, which push on the wheels, which push on the suspension parts, which push on the rest of the car, slowing it down. But these forces are acting at ground level, not at the level of the CG. The braking forces are indirectly slowing down the car by pushing at ground level, while the inertia of the car is `trying' to keep it moving forward as a unit at the CG level.

Fen · Oct 4, 2006

We had a similar discussion on Titanic a few months ago - engineers got involved and everything, then someone (not me) pointed out the following:

Imagine you're on a motorbike. Grab a handful of front brake and the front forks compress - ultimately you could go over the handlebars. Grab a similar "handful" of rear brake and there is not so much front fork compression. So, clearly rear braking effort does not tend to cause front squat to the same extent as front braking effort. A function of the vehicle's CoG being ahead or behind the braking effort which is what forms the fulcrum about which the vehicle pitch changes I expect.

Suspension design will also work to pull the rear down under braking on many cars.

Guest · Oct 4, 2006

I think the motorbike case is quite unique and is very dependent on swing arm suspension geometry. My colleague next to me who rides motorbikes (I do not) says that using rear only brake can either cause front dive or rear squat.

In my experience of push bikes using front brake only stops you very quickly sometimes so quickly that the rider being the main mass is transfered over the handle bars onto the pavement. Using rear brake only does not transfer the rider over the handle bars but untilmately I think this is because I am decelerating much slower and weight is still transfered off the rear wheel causing it to lock alot easier than the front wheel.

In my experience of vehicle brake testing at MIRA during my Automotive engineering degree course. We had a experimental vehicle (modified Monedo) which allowed us to isolate the front and rear brakes. Front brakes only showed very little reduction in decceleration from both. Rear brakes only resulted in only a 1/3 of the decceleration of both axles brakes and it was very difficult to do without locking wheels. The weight transfer forward was related to the rate of decceleration rather than axle being braked. This was 5 years ago now and I have not used any of my brake design nor vehicle dynamics in anger since as my career has focused EMS controls and engine development.
Also I do not if there is any anti dive are squat characteristics in the 944 suspension geometry.

I am not in anyway suggesting that Dave should not try the bigger brakes on the rear. It sounds like a fun thing to try and would be very interested in the results. Just sharing my thoughts.

Fen · Oct 4, 2006

Similarly I am not disagreeing with what you say, but I tend to agree with Dave that more rear brake effort will neutralise the car on corner entry. To be fair I'm not sure it will do so by reducing dive, however.

I got left behind by the Titanic discussion to be honest. Logically though rear brakes must assist in vehicle stability and/or overall braking ability otherwise they would not be fitted to cars.

sawood12 · Oct 4, 2006

The only way to reduce dive is to stiffen up the front suspension or lower the car's centre of gravity. You are not going to significantly effect diving under baking by adjusting brake bias. How much do you want to modify your brake bias? No more than a 60/40 to 70/30 F/R split surely - unless it's for some unusual application?

edh · Oct 4, 2006

Dave

I don't really see that the "dive" and understeer are related? I can't see you're going to reduce dive by marginally increasing rear braking ability.

Maybe the best way to reduce understeer is to come off the brakes more progressively? (apologies if I'm teaching granny to suck eggs here [

] )
I know I'm prone to using the brake pedal like a switch, & coming off more gradually helps reduce understeer into the bend. The weight transfer backwards isn't so dramatic, the car is more composed & the fronts get a bit more grip.

Ed