1972 car with S (aluminum) front calipers on 911T struts.

Installed new pads and rotors on the front to solve a steering vibration under hard braking (warped rotors). Had to remove the calipers to do this since the hard lines don't just unclip from the struts on this car.

Now when I stomp on the brakes, the car pulls left, enough that I need to correct for it or I make an unintended lane change. Most obvious on the highway, not really noticable on the city streets, except that the front left wheel locks first if I panic stop.

Bled brakes, no improvement. Also tried trading brake pads between the front calipers in case I somehow glazed or improperly broke in one side - no effect.

Other work done at the same time - pulled the top of the struts out from under the wheel well to tighten the big nut that holds the shock insert on. One was loose. Drove car after I did that and didn't notice any change in handling or brake performance.

Could I have damaged the brake lines somehow when I tightened the nuts on the shock inserts? Or is it more likely that one caliper is acting up for some reason? Maybe pushing the pistons back into the caliper has caused one to get stuck??

Going to try replacing the brake lines tomorrow, if that doesn't fix it I'm not sure what to try next short of tearing open the calipers.

alignment?

Sounds like a sticky piston.

I did check them for movement and they seemed to move freely. I doubt that moving them would have caused this in the first place. I also don't recall one being harder to move than the others ...

When was the last time they were checked/rebuild?
Andy

I completely rebuilt the calipers about 5 years ago. Took the halves apart, replaced the pistons, seals, dust seals. Never had a problem since, but the bores had some scuffing so I swapped the calipers left/right on the car (and swapped the hardline that connects the halves of the calipers together).

pro 4 wheel allighnment?? tires/balance ect..? mal-allighment will be exagerated at braking forces w/ hihger speeds./..

You change the rubber lines? Have you flushed the brake fluid every 2 years? Bleeders on the top?

The Cap'n

It's Kylie's fault. Did she take a big insurance policy out on you recently?

Rubber hoses do this every time.

Lines were fairly new, but I changed them this weekend.

Still having the same problem, although it seems to be more intermittent now.

Mark and I suspect that one piston in the right caliper is sticking, although when we removed the pad we were able to get the piston to pop out without too much difficulty.

Couple of things:



S-Calipers don't fit t-struts.



Aluminum S-Calipers are a single unit, the 1/2's don't separate.

Regardless, it sounds like they need to be rebuilt. One of my very first caliper rebuilds ended in the same result. I had to rebuild them again. Luckly they were for my car.

It would be good to know what the actual calipers are, easier to diagnose issues. S-Calipers always have piston problems.

Eric,

Thanks for the tip - it must be the rears that I remember separating! Memory is fading now...

I'll see if I can find any more info about the calipers. I'm not sure what year the calipers and struts are, was told they were 911T, guess not! Definitely early 911 stuff though.

When I rebuilt them, I replaced the pistons with the aftermarket stainless ones. (Stomski)

I remember noticing that the bores were scuffed up, so I swapped the calipers left/right (and moved the hardlines) to try to even the wear. Seemed to work ok for 5 years, it's only now that I am having issues!

Will get more details when I can get under the car.

Orange would be Koni
Green Bilstein
Black Late Model Boge (for SC's)

Those are the only struts that S-Calipers fit on. All T struts were 3" spacing.

Onward... check for any dissimilar metal fusion issues. Look for white corrosion around the outer edge of the dust seals. Factory pistons were nickel plated to avoid this. Not sure how SS holds up comparitively. If it hasn't been driven regularly that might be it. I doubt it though... seems like 5 years with a regularly driven car would be fine.

Another thing to look at is the pad cavity on these. Many times you'll need to file the edge of the pads as paint build up can make them fit very tight in the pad cavity causing them to stick. You probably would have noticed this when swapping your pads though.

When rebuilding the calipers do you recall using the knockback mechanisms in the new pistons? Aftermarket pistons can be tricky with the c-clips if you re-use them. The c-clips will distort (collapse) and although they may seem fine when you reinstall them, they could very well have come loose and you now have the knockback mechanism flopping around in the back of one of the pistons causing the issue. (this would be my bet... sticky or malfunctioning knockback mechanism)

You can elect to remove them altogether or keep them in. If that's the problem, make sure you stretch the c-clips if you decide to re-use them. You can get new clips as well. I noticed this with Harvey Weidman's calipers we just finished. There was a big difference with new c-clips in all pistons.

You'll probably need a new rebuild kit as those dustcovers are almost impossible to remove without damaging them.

Hope that helps.