Caliper restoration 2
02-22-2009, 06:12 PM
#1
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Caliper restoration 2
P*ssed off...
Bought 2 C4 calipers to refurb and fit....great condition, had screws removed at cost££££
Seals all good, pad plates good..luckily dont need parts
But today whilst fitting new shocks I removed my front calipers only to find severe corrosion, on what were supposed to have been rebuilt a couple of years ago by prev owners mechanic, so I have no choice but to replace the parts.
Problem/question...what size torx head is in there, do the plates need to come out to fit dust seals?
Where in UK can you buy just dust seals and piston seals, dont need pistons and sets are £160
I found a supplier in US all 8 pairs of seals for $100, but $60 to send
and its onlt a small envelope!!!!
HELP!!!!!!!!!!!!!!!
Bought 2 C4 calipers to refurb and fit....great condition, had screws removed at cost££££
Seals all good, pad plates good..luckily dont need parts
But today whilst fitting new shocks I removed my front calipers only to find severe corrosion, on what were supposed to have been rebuilt a couple of years ago by prev owners mechanic, so I have no choice but to replace the parts.
Problem/question...what size torx head is in there, do the plates need to come out to fit dust seals?
Where in UK can you buy just dust seals and piston seals, dont need pistons and sets are £160
I found a supplier in US all 8 pairs of seals for $100, but $60 to send
and its onlt a small envelope!!!!HELP!!!!!!!!!!!!!!!
Last edited by Low 964; 02-22-2009 at 06:53 PM.
02-22-2009, 10:15 PM
#3
Instructor
On C2 front calipers, you will find that one edge of the dust boot on the biggest piston snuggles underneath the edge of the pad plate. Despite the tight fit, I can absolutely assure you that you can replace the dust boots without removing the pad plate. This is probably applicable to the C4 caliper as well. You will probably destroy/bend the old dust boot's edge when you remove it but nonetheless the new ones will go in just fine with the proper amount of lubrication and installation technique. I just rebuilt (and refinished as well) a set of C2 front calipers and replaced all the dust boots (all 8) without having to remove the pad plates, thank god. Oh, and then I put them on the rear of the car. Needed a bit more bias in the rear. It worked.
02-23-2009, 05:14 AM
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Thats good news...but the goove for the seal is corroded badly and am scraping out this week, they had lifted out a bit..
The plates were done 2 years ago....2000 miles so dont want to remove them.
Do you need to soak the seals in anything before install ,are they easy to fit?
Did you replace piston seals as well?
Luckily the rear 4 pots are ok.
How did you sort the bias....new valve???
The plates were done 2 years ago....2000 miles so dont want to remove them.
Do you need to soak the seals in anything before install ,are they easy to fit?
Did you replace piston seals as well?
Luckily the rear 4 pots are ok.
How did you sort the bias....new valve???
02-23-2009, 06:38 AM
#5
Nordschleife Master
When I took mine off to cure the plate lift I also had to scrape out some corrosion under the dust seals and then put some high temperature paint on to provide some protection. I thought about going the whole the hog and replacing all the seals but decided that since they were working fine (no leaks and pistons moved freely) and that I am more than likely to fit bigger brakes in the future, that it would be a waste of money spending a lot more on refurbing old calipers. Just my 2 cents.
02-23-2009, 06:44 AM
#7
Nordschleife Master
No, like yourself I could only find complete repair kits which were very expensive and as I said, there were no signs of leaks, no pitting on the pistons and the pistons moved freely. Good for at least a couple of years use before putting something new on IMO.
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02-23-2009, 12:14 PM
#10
Instructor
"Do you need to soak the seals in anything before install ,are they easy to fit?
Did you replace piston seals as well?
How did you sort the bias....new valve???"
Regarding the seals, I liberally coated both the seals and seal bores with the special paste that comes with the kits (or you can use the Porsche brake cylinder paste 000 043 17 00) after of course scrupulously cleaning out the piston bores and seal bores. In some cases I replaced the seals and in some cases I re-used the existing seals. It depended on what came with the kits. The seals are easy enough to fit, simply requiring a bit of technique which you'll eventually master. In cases where I had found the dust boots compromised with tiny tears, sure enough there was grunge underneath which had to be wiped clean off the bores. I had absolutely no evidence of corrosion anywhere; not on pistons, nor on bores. The integrity of the dust boots is a big deal. If your brake pad installer has been ham fisted and used tools poorly, then there's a good chance they have pinched a hole (which is incredibly tiny and very hard to see) in the dust boots. This will certainly lead to ingestion of crud (and corrosion in some cases) into the bore and will further cause the piston to effectively seize up and fail to retract properly. The voice of experience is telling you this, so heed the lesson well for what it's worth.
Regarding the adjustment in the rear brake bias, there are many ways to reduce rear bias but there are very few ways to increase rear bias. Probably the most effective one (at least with a 964) is to install rear calipers with larger piston bores. Putting the 964 C2 front caliper on the rear will substantially increase rear bias but that increase in piston displacement is so great that you would have necessarily already installed a larger bore master cylinder (the 993 master cylinder and booster assembly works) to compensate. In my search for more rear brake bias I have long since removed the rear bias valve and use just the CUP straight pipe. However, that is probably not the correct solution for most 964's. The selection and use of the correct rear bias valve should be examined very, very closely because there is a very serious safety issue at stake which could lead to an unexpected emergency lockup of rear brakes with accident to follow.
Did you replace piston seals as well?
How did you sort the bias....new valve???"
Regarding the seals, I liberally coated both the seals and seal bores with the special paste that comes with the kits (or you can use the Porsche brake cylinder paste 000 043 17 00) after of course scrupulously cleaning out the piston bores and seal bores. In some cases I replaced the seals and in some cases I re-used the existing seals. It depended on what came with the kits. The seals are easy enough to fit, simply requiring a bit of technique which you'll eventually master. In cases where I had found the dust boots compromised with tiny tears, sure enough there was grunge underneath which had to be wiped clean off the bores. I had absolutely no evidence of corrosion anywhere; not on pistons, nor on bores. The integrity of the dust boots is a big deal. If your brake pad installer has been ham fisted and used tools poorly, then there's a good chance they have pinched a hole (which is incredibly tiny and very hard to see) in the dust boots. This will certainly lead to ingestion of crud (and corrosion in some cases) into the bore and will further cause the piston to effectively seize up and fail to retract properly. The voice of experience is telling you this, so heed the lesson well for what it's worth.
Regarding the adjustment in the rear brake bias, there are many ways to reduce rear bias but there are very few ways to increase rear bias. Probably the most effective one (at least with a 964) is to install rear calipers with larger piston bores. Putting the 964 C2 front caliper on the rear will substantially increase rear bias but that increase in piston displacement is so great that you would have necessarily already installed a larger bore master cylinder (the 993 master cylinder and booster assembly works) to compensate. In my search for more rear brake bias I have long since removed the rear bias valve and use just the CUP straight pipe. However, that is probably not the correct solution for most 964's. The selection and use of the correct rear bias valve should be examined very, very closely because there is a very serious safety issue at stake which could lead to an unexpected emergency lockup of rear brakes with accident to follow.
02-23-2009, 06:59 PM
#13
Regarding the adjustment in the rear brake bias, there are many ways to reduce rear bias but there are very few ways to increase rear bias. Probably the most effective one (at least with a 964) is to install rear calipers with larger piston bores. Putting the 964 C2 front caliper on the rear will substantially increase rear bias but that increase in piston displacement is so great that you would have necessarily already installed a larger bore master cylinder (the 993 master cylinder and booster assembly works) to compensate. In my search for more rear brake bias I have long since removed the rear bias valve and use just the CUP straight pipe. However, that is probably not the correct solution for most 964's. The selection and use of the correct rear bias valve should be examined very, very closely because there is a very serious safety issue at stake which could lead to an unexpected emergency lockup of rear brakes with accident to follow.
If you really want to increase rear bias(a reasonable amount, though still too much for most purposes w/ stock fronts) use 993 rear calipers. W/ stock fronts this nets you a hbr of 1.409, somwhat better than the worst 911 oem implementation('84-89 C3.2) which can be somewhat useful at A/X w/o a p/v. Though, usually these rears are used w/ the much more powerful 964RS/964t front calipers and rotors.
Additionally using the fronts, which want a 28mm rotor on the 24mm rear rotors opens the door to the possibility of hyperextended pistons if the pads are allowed to wear significantly.
02-23-2009, 07:21 PM
#15
all n/a 964 n/b(except RoW RS) use 28/30 rears which want 24mm rotors
all 964RS(not RSA) use 30/34 rears which want 24mm rotors. These calipers are the same as used on n/a 993rear
964 C4TL use 30/34 rears which want 28mm rotors. These are the same calipers used on 964t rear