After a trip to the Jag dealership, I had a note that a caliper Piston was binding on the left front caliper.

The recommendation was to replace the caliper, both rotors and all pads for $2700.

I was immediately suspicious because less than a year ago I replaced all pads and the front rotors. I keep an good eye on the brake pads so at the time of replacement the rotors were ok. It was just time for new pads and I didn’t like the rust visible on the wheel hub. So I replaced the pads and installed new disks that were powder coated.

Also suspicious, less than a month ago I had the car in the same dealership to get my fob reprogrammed and their “world class” inspection said the brakes were fine.

Now three weeks later the whole front end braking system was trashed? No.

So the first thing I did was go and check the disks. They were perfect. Pads looked good too.

I could feel something going on with the brakes, occasional drag that indicated binding so I didn’t doubt the diagnosis. The troubling parts were:

1. The idea of replacing parts that did not need replaced, and at double the price I could find the parts elsewhere.
2. They did not mention the pedal intermittently sinking almost to the floor when braking, with reduced braking power, likely a master cylinder problem.

So, I decided to rebuild the front caliper first. If the caliper body was bad then I would get a new caliper. My guess was a bad inner seal, or the aluminum alloy caliper pistons expanding with corrosion (thus, binding). Either way, I know the dealer didn’t take the caliper apart... so I will.

Ordered new seals/boots from rock ( ) auto along with a power bleed kit and the sl.6 brake fluid from Amazon. Took the caliper off the disk, and found the inner large (44mm?) piston jammed up. Creative placement of the old brake pads allowed me to use the car to push out the bound piston.

On a side note, I was teaching my 14year old Son how to do this. Helping out with pumping the brake pedal likely brought an end to an already failing master cylinder, as in the mix of things I did not put a block under the break pedal to prevent over extension of the master cylinder seals. I realized this later. Anyway...

Removed the caliper from the car and went to the bench to rebuild.

Upon removal of the pistons I found corrosion on two of them that was bad enough to warrant replacing them. The inner seals were in beautiful condition, as were the caliper bodies. A slight amount of gumminess was easily removed with steel wool on the port that was sticking. This left a perfectly smooth surface.

The aluminum alloy pistons expand and bubble up when they corrode. The chrome flakes off, so even sanding with increasingly fine sandpaper/steel wool left unacceptable surfaces. Unfortunately I did not have replacement pistons, so I did my best and reassembled the caliper. The original inner seals looked of better quality than the ones on the rebuild kit, so I put them back. The new dust boots fit perfectly.

I reattached the caliper to the car, power bled the system and pumped the brakes. This is when I realized the boy had probably pumped them to the floor earlier. Oops.

Anyway, the pedal went all the way to the floor every time. No matter how much I pumped. The final nail was attaching the power bleeder to the reservoir. Under some pressure, there was a bubble lingering in the tallest bend of the clear tube running from the bleeder to the reservoir. Pushing the brake pedal made the bubble move toward the power bleeder. This showed any pressure created by pushing the pedal was moving fluid backward past the master cylinder seals and into the reservoir. So the seals in the master cylinder were finally done.

Sigh. Still no brakes.

So here is where we are:

• I ordered a new master cylinder and new o-ring (they threw the o ring in for free
• I am currently looking for a source to order new caliper pistons. Any thoughts on this would be appreciated. Zeckhausen Racing carries the pistons but they are currently closed until late July. (You would think living in Indianapolis, the racing Capitol of the country, I could find these pistons lol)
• Would like to replace the bleed nipples as well. Hopefully whoever sells the pistons will sell the nipples too.

links:

mastercylinder: https://www.jaguarclassicparts.com/u...braking-system
seals and boots: https://www.rockauto.com/?carcode=1410635&parttype=1720
power bleeder: fluid catch bottles: brake fluid:
the pistons I want: https://www.zeckhausen.com/catalog/p...roducts_id=514 and https://www.zeckhausen.com/catalog/p...roducts_id=517

 

You may find it easier to get a second hand caliper from a scrap STR?

Mellow

 

​​​​​True, and a good idea.

My thoughts:

1. If one pops up in my area I will probably go pick a lot of parts from it. As for right now, there isn’t even an S-type in any Indianapolis area junkyards. Let alone an STR. I went looking for a vanity mirror from any vehicle in one large junkyard, hoping to find one that was exchangeable with mine. Walked the whole place with no luck.
2. The caliper body is ok on my STR. I wonder if the caliper pistons would be in better shape on the scrap car? That would be an interesting mystery to look into.

 

Replaced my master cylinder and brakes are back

Zack Racing reopened and sent me my caliper pistons, I had the new dust seals from rock auto and my power bleed kit.

Rebuilt the driver-side Caliper and used a spring compressor for the first time to move the strut enough so I could replace the drivers side upper control arm while I was in there.

Reassembled, bled and tested. All works perfect, but there is some vibration when braking hard at higher speed. Audibly coming from the drivers side, but little to no steering wheel shaking when braking at high speed.

My guess is the uneven braking created by the binding caliper Piston caused uneven heating that slightly warped the rotor.
So I assume replacing the rotor will eliminate the vibration.


Old caliper Piston above, sanded corrosion shown... new caliper Piston below

 

It is good you have your brakes back again.

When you change the rotor, it is a good idea to either change the pads or flatten the surface of the old pads. This is because the old pads would have worn to the shape of the old rotor and when using them on a new smooth rotor there will be high spots on the pads that can overheat areas of the rotor and, you've guested it, warp the new rotor!

Also before you change the rotor have agood look at your tyres, I have known worn areas on a tyre or slightly distorted tyres to also give brake judder.

Mellow

 

You could also have just plain build up of pad material on the rotors. Mine were great for a while after new rotors and pads but eventually I got that little bit of shudder. It happens on every one of my cars.

They make kits for cleaning off your rotors but getting to the inner side is the hardest part. I think you have to pull the caliper off again and I'm not sure working from that location is all that easy?

One vintage car of mine uses a 4 piston drop in from the top style Ate caliper off of a BMW. Much like the Brembos and for that car I took the suggestion I read about of putting a set of aggressive racing pads to put in long enough to clean off the build up. I hope that works but I haven't had a chance to try it as yet. The suggestion came from a racing team because they experience the same issue.

 

I replaced the rotor and pads on both side and brakes are no longer vibrating

When I took the pads off the drivers side I noted a strip of metal looking stuff on the leading edge of the outer pad. Also noted a couple lines perpendicular to rotation. This is likely from the warped rotor.

Replaced rotors and pads: Good feeling brakes!

Win!

Lines on the old rotor.

 

Yes, there are often small visiable medallic particles in some brake pad material, this is not unusual.
It varies from make to make and graphite is usually the main component, but other common materials as well as metllic particles include ground rubber, carbon black, cashew nut dust and antimony trisulphide. These usually make up between 5 to 29 % by mass of the brake lining materials.

I could be wrong but the dark marks on your disk are consistent with the location of a brake pad in a car that has not been used for a while.

What happens is that the rest of the disk will get surface rust, but the section where the pad is located will not. Depending on the length of time the car is left and the level of corrosion this can cause bake vibration when the car is put into use again. This may stop with use, but it may not.

Mellow

 

What you say is true Mellow, however this has remained my daily driver throughout this adventure. So the vehicle has not sat any longer than overnight.

And I had no idea cashew Nut was part of brake pad composition... that’s nuts! 😜