Caliper rebuild question

[Blaise]

I am finally digging into my brake system and giving it some TLC. I will be going through the suspension at the same time (just basic checks and bilstein install).

I have the front calipers off and am cleaning them up.

I was reading the couple of articles on firstfives and noticed the link to the ferarri brake article. Apparently they use the same calipers.

http://www.r-design.net/308/techtip2.htm

In particular, this quote jumped out at me:

"If so, the pistons are not in the correct position. Taper wear is caused by the leading edge of the pad "gripping" the disc more effectively than the trailing edge. In a four piston set up, manufacturers like Brembo and AP use a differential bore where the pistons are smaller on the leading edge than the trailing edge. In this two piston set up, taper wear is controlled by a cut out in the side of the piston. If this is not aligned properly in relation to the disc, your brakes will either pull to one side or not work as efficiently as they should. The pistons should be offset 20 degrees. Please see figure two for details. This taper problem does not apply to the rear brakes as the pistons are symmetrical."

At first glance, I do not see a difference in any of these eight pistons. Any insight into this?

[T.Hanson]

1 thru 5: do get the vice grips brake fitting tool ( see FAQ ). Best ever. No boogered fittings, which a six point with a notch in it will do on any old crunchy ones. Unless you want to replace the tubes, bending, etc.

I rebuilt a set of '79 528i. First big trick was working the pedal with the pads removed to get the pistons out against the discs. Not much left in the bores to wrestle out.

Most kits do not include the baby O ring that seals the two halves together. For some reason more than a few posts express terror at splitting the calipers, but my Kart experience thought it routine to not know it was supposedly a big deal. It wasn't, save for the kit, O ring omission. The old one looked, worked fine.

As far as the pistons being asymmetrical, mine were not. Or no notches, anything to cause suspicions. My opinion: trying to reassemble, add the dust ring with the calipers assembled would have been stupid extra work. Not to mention the long assembly bolts/nuts got soaked in toilet bowl cleaner to de rust.

Tape over the innards, paint (high temp) red or Chevy Orange. Inhibits surface rust, looks nasty racery, says you rebuilt them.

Except brake fluid removes paint really great when it drips off the fittings.

Fittings aim up.

[Blaise]

1 thru 5: do get the vice grips brake fitting tool ( see FAQ ). Best ever. No boogered fittings, which a six point with a notch in it will do on any old crunchy ones. Unless you want to replace the tubes, bending, etc.

I rebuilt a set of '79 528i. First big trick was working the pedal with the pads removed to get the pistons out against the discs. Not much left in the bores to wrestle out.

Most kits do not include the baby O ring that seals the two halves together. For some reason more than a few posts express terror at splitting the calipers, but my Kart experience thought it routine to not know it was supposedly a big deal. It wasn't, save for the kit, O ring omission. The old one looked, worked fine.

As far as the pistons being asymmetrical, mine were not. Or no notches, anything to cause suspicions. My opinion: trying to reassemble, add the dust ring with the calipers assembled would have been stupid extra work. Not to mention the long assembly bolts/nuts got soaked in toilet bowl cleaner to de rust.

Tape over the innards, paint (high temp) red or Chevy Orange. Inhibits surface rust, looks nasty racery, says you rebuilt them.

Except brake fluid removes paint really great when it drips off the fittings.

Fittings aim up.

I liked the idea of those vice grips, but I looked around locally and could not find any. A few days of PB Blaster pre-soaking and everything came apart without a hitch. I would have ordered some if I was dealing with a corroded car.

As far as getting the pistons out, the fronts all popped out with compressed air. Actually they shot out. I am glad that I read about how aggressive that can be, as I might have thought to catch them with my hand. For those who have not done this before, do not put your fingers in the way of a piston that is being forced out with compressed air.

The rear calipers each had one stuck piston. A little PB Blaster, a C-clamp on the opposite piston, some compressed air....and they each creeped out.

Now I have everything apart.

Front pistons all look alike. Rear pistons have a raised portion that contacts the pad. These were not all oriented alike. I will have to figure out how these are supposed to go back in. I will post a photo.

All of my dust boots were torn and shot. All the seals were still holding. Though the brake fluid ran clear during bleeding prior to this overhaul, the internals of the calipers were nasty.

I imagine that this overhaul will make a noticeable improvement.

I am cleaning the calipers and getting ready for paint. Definitely not necessary, but it will make me happy. I am using the POR-15 caliper kit. It should be resistant to brake fluid.

As for splitting the calipers, I agree that it must not be a big deal. I just do not see a need for it in my case. They were not leaking and the bores look clean enough to perform. I would have split them if the bores needed honing, or they had leaked.

[RonDwyer]

I've had good luck with the 4-piston split caliper rebuilds. First I pull the pads on each side and pump the brakes to get the pistons out as far as possible before removing the caliper. Previously if the piston was stuck after splitting an overnight dosing of KROIL loosens anything. In my years of doing CS Coupe restorations i never managed to find any wrong way to put the pucks back in. Single piston calipers are notched to orient the piston to the housing.

[Blaise]

Single piston calipers are notched to orient the piston to the housing.

I am not sure that I understand this.

Here is what the rear caliper piston looks like:

<table><tr><td><a href="http://picasaweb.google.com/lh/photo/oZ ... site"><img src="http://lh6.ggpht.com/_UZQuuBHQvx4/THX0r ... r><td>From <a href="http://picasaweb.google.com/blaisedesco ... bsite">E12 Caliper rebuid</a></td></tr></table>

<table><tr><td><a href="http://picasaweb.google.com/lh/photo/ij ... site"><img src="http://lh6.ggpht.com/_UZQuuBHQvx4/THX0q ... r><td>From <a href="http://picasaweb.google.com/blaisedesco ... bsite">E12 Caliper rebuid</a></td></tr></table>


Obviously it is intended to be oriented in a certain direction.

As an educated guess, I would think that I would orient the piston such that it pushes on the trailing side of the pad, as the pad is forced to dig in in the front while braking...and lift in the back. This is more obvious on old style bicycle brakes.

Anyone know for sure?

Some other photos form my progress:

http://picasaweb.google.com/blaisedesco ... directlink

[T.Hanson]

Haynes manual: Rear brake pistons must be positioned with the 20 degree cut out facing down.

I.e., against the forward rotation of the disc.

[RonDwyer]

Now I'm wondering if I rushed in my eagerness to write about the front 4-puck calipers. I do not recall seeing a trailing edge rotation alignment of the pucks. The rears with the alignment are obvious, as are fronts with the same mark. If there are marks on the 4 puck front caliper, wouldn't the trailing piston leading edge would work against the forward puck trailing edge.

Cheers

[Blaise]

If there are marks on the 4 puck front caliper, wouldn't the trailing piston leading edge would work against the forward puck trailing edge.

Cheers

I could not see any markings on the front caliper pistons.

[RonDwyer]

Nice looking caliper work there Blaise! I have had them plated yellow zinc in the past, but they start to white rust almost immediately. Nothing like good old factory plating.

[Blaise]

Well, the car is back in the road.

Brakes work well. At first, it still pulled to the left. But….I thought it might be due to the fact that I have two different tires up front. So, I swapped the front wheels. It appears to be fine now. I would have expected it to pull right, but it does not. The car tracks well at speed and does not pull in either direction.

I have three different tire makes on the car. Both rears are the same and the fronts are different. Not ideal, I know….I will address that in due time. If anyone has some matching stock tires that they want to give away….locally…let me know.

The heavy duty bilsteins are nice. They are a bit stiff, but I like it. The car still rolls in turns, but I am guessing that this is just how these cars were set up. I am used to my 2008 that feels like it is diving into the turns.

On another note, it appears that my odometer may be way off….I will do some testing and report back.

[Domingo]

Great job you are doing, should consider replacing the pistons as they are rusted and will fail.
I did the same and ended up buying the reman by Cardone.

[Blaise]

Great job you are doing, should consider replacing the pistons as they are rusted and will fail.
I did the same and ended up buying the reman by Cardone.

The pistons cleaned up fairly well and should be okay. The seals had not failed before the rebuild.

[T.Hanson]

Just for 2 cents, flat cornering vs. roll, the big jump is a fat front stabilizer bar. Having done the lowering springs, sport shocks, to notice the reason my 635 cornered flat(ter) had to be the bar.

That, then the tower bar, rear stabilizer and rear tower bar. Just keep in mind each step effects behavior, and diminishes cushyness.

Odometer Gears, Jeff Kaplan, is your one stop answer for perfection.

[Blaise]

Stabilizer bar makes sense. My understanding is that a stiffer stabilizer (sway) bar limits body roll, while also limiting the suspensions ability to act independently. So....a stiffer bar will also lead to an individual wheel being less likely to take a bump without effecting the other wheel.

But...that is in the future...but not now for me. I want to lower the back of my car first. Yea....just the back. I hate how the car is raked and want it to be level.

[garyinwestoz]

Now that you have done the calipers, I would suggest replacing the rubber brake lines.
I did mine a few eyars ago, made them much firmer, positive.