My rear brake pads were completely worn out so I had the shop throw new ones in the other day when I was having some other work done.

When I got the car back the brake pedal felt spongy even though they never opened up the hydraulics. They did tell me that screwing that caliper's piston back in was very very tight. The car is a clean one, and the brakes were flawless up to that point, now we found that the caliper is seized, and is applying very little pressure on that wheel.

My thought is that the piston was accidentally screwed out a little bit, and then cross threaded as it was screwed in - not sure how else a good caliper with good dust boot would have gone so tight, and not work correctly now. My thought is that if it was a rusty seized caliper it simply wouldn't release, where as with a cross threaded piston it can't rotate, and isn't adjusting out, therefore it is just barely contacting the brake rotor when applied. (enough to keep the disk from going rusty - but just).

So, first - hope for opinions on my theory...

Second part is the important part. The dealer charges $525 for the caliper; it seems they have a silver one or a black one - my car has black. When I check with after market companies they don't seem to list the colour. I am wondering if they are the exact same caliper just coloured differently, or were there two physically different versions.

I need to get the car on the road right away, and I don't want to wait for the dealer, as they will take a couple of days to get one in. Hope to get one on Monday from a local supplier.

Cheers,

Rob.

 

Sounds to me like they have wound the caliper piston the wrong way initially allowing air to enter the caliper. Before buying a new caliper i would try bleeding the brakes and see if that improves things, the fact that they have been able to fit the new pads suggests the theads are not crossed as it has to go a fair way back to create the space required for new pads. Also it is possible that the discs are worn in such a way that the new pads are not fully contacting the used discs, i would always change the two as a set ie discs and pads at the same time, not expensive as the rear calipers use saab pads! (£25 off ebay for ebc ultimax and the discs made by pagid only £60 the pair).

 

It is not uncommon for those calipers to be a problem. We keep a rebuilt pair ready to go at all times. They seem to be a weak link.

 

Thanks for the replies.

It wouldn't be so bad if I could get the mail order caliper quick, it is only $160 rather than $525.

I think I may try a quick bleed of that wheel only tomorrow before I go further, can't get a caliper until Monday anyway.

Fingers crossed - but the fact he said it took tremendous force to screw it in, when the other one was relatively easy just scares me. I think he cross threaded, and maybe it didn't screw all the way in, maybe he stripped it, or broke the bolt piece inside. If I do need to replace it I am going to have him pull the piston so we can both see why it failed. If it is corroded or something (unlikely) then my issue, if it is ruined by cross threading then we have another conversation to have. They also have another one of my cars in the shop getting $10k of body work / paint, and three other cars going in over the next month for various mechanical work... (good guys, I know in the end they will make it right but I am sort of venting here now under the assumption he got a bit ham fisted on this one!).

Cheers

 

Hi Rob,

I tend to agree with others that air has entered the system. Air is highly-compressible (unlike hydraulic fluid, which is highly incompressible), so if enough air was allowed into the system, that would explain both the spongy pedal feel and the lack of pressure on the rotor.


I'm not personally familiar with any brake caliper piston that is threaded. I just did the brakes on our '04 XJR, and the pistons in our Brembo calipers simply press straight into the calipers without rotating. If one is using a clamp or brake pad spreader/caliper press that incorporates a threaded rod, the term "screwing the piston in" refers to the action of the tool, not the motion of the piston. If someone knows of threaded brake pistons, I would appreciate the education.


My understanding is that, especially on vehicles equipped with ABS, it is poor practice to press the pistons into the calipers without opening the bleed nipples to allow some fluid to escape. Otherwise the rusty fluid in the piston cylinder is forced back into the brake lines, where it accumulates and can affect the performance of the caliper. That may be an additional source of trouble in your malfunctioning caliper, but I'm leaning toward air in the caliper.

Let us know if things improve after you bleed the brakes (in case you don't do that often, start with the wheel furthest away from the master cylinder (rear right on a LHD car), then do the next closest (rear left), then front right and finally front left. If your car has calipers with bleed screws on both the inner and outer sides of the caliper like our Brembos, opinions vary on whether to bleed the inner or outer nipple first. Some guys use a T fitting and two hoses to bleed both nipples simultaneously. To me it makes sense to bleed the outer nipple first, allowing more fluid than normal to flush out, then bleed the inner nipple, but someone with a compelling argument could easily change my mind.

Cheers,

Don

 

The fact that he had problems screwing the caliper in just reconfirms the caliper is bad. I don't think it is possible to cross thread the caliper. As I posted above this is a common failure with that caliper.

 

Well, I bled the brakes, it seemed to have some air at the offending caliper. I then unbolted the caliper just to swing it out and feel how the piston is. It turned easily enough I thought. I wonder if this extra force was to push the fluid, and possibly the other side had less resistance.

Anyway, put it back on, wheel back on and went for a drive.

Immediately the first time I touched the brakes I knew it was better. And after a short drive and retorque of wheel I went for a half our run in the country. Brakes are excellent - both sides are running at the same temperature (to the touch) and the world is a better place.

Thanks for all the notes. This is the first time I have ever had to deal with this type of caliper, I too have never seen them as all my other cars were the ones you could simply press in.

Cheers,

Rob

P.S. Will be talking to my mechanic in the morning. Thank goodness I didn't go ahead and order the $525 caliper yesterday!!!

 

Congratulations, Rob. In my personal experience, calipers very rarely fail, they just need periodic service. Jaguar offers a rebuild kit, so having to purchase a new caliper should be a rare occurrence unless a car has been neglected.

Cheers,

Don

 

Also a lesson for all, check the basics before being convinced into buying unnecessary and costly parts!