Caliper condition opinions

[deano]

After soaking in WD40 and some coaxing with a C clamp and block of wood, I managed to remove the pistons from a stuck rear brake caliper with an air gun.

Can anyone say for certain from my photos whether the caliper and-or pistons need to be replaced, or can be re-used once greased up properly with new (Big Red) seals?

The piston surfaces are pretty good, but tiny bits of the top edge of the chromium plating are chipped off or corroded away. Yes, these are cheap to replace.....

The inner surfaces of the caliper piston cylinders seem to have more of a 'raw' finish that isn't as smooth as the plated piston surfaces. Nevertheless, there is no corrosion or scratching below the inner seal. Above the inner seal, the inner surface is significantly rougher but, to me, looks as if it might have been made this way.

Any advice greatly appreciated...

[Nine One One]

A lot of people on here use Classic Car Automotive for calliper refurbishment - very affordable, and come back looking like new - there are plenty of posts about the excellent service they offer.

[PeterK]

Bin the pistons. Calipers look OK in the photo

[AndrewSlater]

Another thing to consider if using CCA ( or most other restorers ) is that they will remove the knockback mechanism pin from your calipers.
Similarly if you buy new pistons you will need to remove the pin yourself.

A previous discussion about it here.
http://www.ddk-online.com/phpBB2/viewto ... er#p573154

Regards
Andrew

[profblue]

Andrew, I have been told that the piston "only" rides / touches on the inner seal, hence as long as the surface does not have protruding highs (rust), then I think you should be fine with the caliper.
The piston edge on the right appears damaged on your picture (which could potentially harm the brake pad) so I would vote for replacement (not sure about the pin situation though).

I'm just going through the same refurb, and going for stainless pistons (later style A calipers in front, M calipers in back).

[911hillclimber]

Fwiw
You have done the tough bit of getting the Pistons out, but for the cost and the reliability for future years, have them refurbed by that specialist.
If the car does few miles, a full refurb will be esp effective.

[deano]

Really appreciate all of the advice.

I noticed from pics that the new Big Red pistons were hollow and wondered about their compatibility with the caliper pins - I thought perhaps new pistons might simply fit over the pins anyway (and the pins would become redundant) but it sounds like this might not be the case.

I'll look to see if the pins on my rear's are removeable and if so will buy new pistons and seals, otherwise I'll just put this one back together as it stands with new grease and seals and see how they go. Got to find two of the long bolts that hold the caliper together, as the first thing I did was cut off the two that had rounded-off allen heads - doh!

At least now I know what to do in the future, so thanks all

[gridgway]

Just curious as to what grease you are thinking of and where you put it?

[deano]

Just curious as to what grease you are thinking of and where you put it?

I watched a couple of Youtube videos specifically on 911 caliper rebuilds, which demonstrated smearing the grease on the inside of the piston cylinder walls.

Planned to purchase a 'Big Red' seal kit that included the grease, which was labelled as 'silicone grease' in the associated photograph.

Kit without pistons: https://www.ebay.co.uk/itm/284483374440 ... p_homepage

Kit incl. pistons: https://www.ebay.co.uk/itm/312884269676 ... p_homepage

[deano]

It seems that new replacement calipers are widely available and quite cheap, starting from £55 each or £105 for a pair of rear's on Ebay for 69-83 cars.

https://www.ebay.co.uk/itm/166157730066 ... %3A4429486 These will actually fit 69-83 cars by the looks of it.

Lots more choice available on Design911, including from Brembo at £119 each, JP for similar money and £92 each for their OE Match Classic brand. Some of these include the brake pad fitting bits...

Obviously, the 'genuine' ones are crazy money!

[PeterK]

Just curious as to what grease you are thinking of and where you put it?

Typically red grease, but never any petroleum based grease as that will cause the rubber elements to swell. I always apply all over the seals, both when fitting seals onto pistons and then pistons into calipers.

[911hillclimber]

The Genuine oneraises a smile as Porsche don't make their calopers or pads etc, suppliers approved by them do.
So, an ATE calliper from ate is the same technically as the Porsche part.

On modern Porsche's, occasionally their prices are lower than Des911 etc, so just might be good to ask Porsche too?

I have revealed my rear M callipers on my 73T (which are original to the car) 3 times in 35 years before any leaks or seizing can take a grip, they have never leaked, original Pistons too with rust where the dust seals locate, all good.

Seals were real ATE parts with their red rubber spec grease which I fully used on each calliper.
Same for the larger A type callipers fitted in 1992 when I installed Bilstien dampers and struts.

New callipers at those prices are a great deal.

[gridgway]

Thanks for the commentary on the grease. When my dad taught me how to do calipers he used brake fluid as the lubricant, letting the be seal sit in brake fluid before assembly. That's what I've always done.

[911hillclimber]

Iirc that was the instruction for many years.
I only used the grease because it came in the ate kit, wonder if it still does.

I really dislike the feel of brake fluid, and cv grease and hypoid gear oil...

[deano]

Just capping off this thread. I decided to rebuild the caliper with new seals and silicone grease from Big Red. Very pleased with the job.

Still miffed that I bizarrely split the caliper and chopped two of the bolts up (that had rounded heads) in the process - these are proving a bit difficult to find. I thought I had found a set, but when they arrived, they were too short (50 and 55 mm M6 with 10 mm nuts), and I think perhaps for an earlier model caliper. The bolts on my caliper are 70 and 75 mm long M6 with an 11 mm M6 nut.

I made a cardboard tool to set the pistons at 20 degrees, but found deciphering how to set the angle a bit challenging because the diagrams are generic and do not show which is top and bottom, or front and back. As usual, I had taken pictures before disassembly, and found that the angle of the piston before disassembly was at odds with what the Ate instruction sheet and other info online images seemed to be suggesting. Even now, I am still not 100 %
sure if I got it right... you can just about make it out in my pic (brake pipe comes out bottom left, bleed nipple would be top left). Did I get this correct?

Interestingly, the oil and dirt that were covering the caliper, before I cleaned and degreased it, had done a fantastic job of preserving it. Once the gunk was removed, a small amount of surface rust appeared. At some point I might remove all of the calipers and paint or plate them, but I will coat this lone one with ACF50 for now.

I managed to put up some genuine Ate front seals too. Here are the part numbers, if anyone needs them:
Ate front seal kit (no grease or bleed nipple cover) - 13.0441-4819.2
Big Red rear seal kit (includes silicone grease and nipple cover) - 3805S - https://www.ebay.co.uk/itm/284483374440