Hey All,

I opened up my recently acquired Mk1 front calipers yesterday, and noticed scoring in the piston (water accumulation and neglect I presume). I cleaned them took some extremely fine steel wool to them and slapped them back together to find the cylinder leaking. Yay! Now I am left with what seems to be a common conundrum:
1. Sleeve them
2. Machine, build up and machine again, or
3. Replace

Any thoughts?

 

Sleeving is fine, just make sure who ever dose it has a way to bond the sleeve into the bore.
Apple Hydraulics glues them in there with a permanent thread glue.
If they are not in there well enough the pressure in the system can force the sleeve out, so an interference fit isn't good enough.


New ones can be made of stainless steel, but expensive, but will never rust inside and out.


Replace the crappy hydroscopic brake fluid with silicon, but that's a huge job.
Brake fluid that absorbs water is the number one culprit here and requires a heated garage for long term storage. Replace with new fluid depending on how long the car is being stored and/or driven.


Also, did you check the pistons for rust where it seals on to the rubber seal ? They can leak there too.


I've never heard of anyone machining out the damaged bore, adding material and machining down to spec. _ seems more trouble then it's worth.

 

Thanks Jeff.
Apparently the 2 1/8" brakes were used by some makers who wanted to keep the original cylinder metal. I read about the process on a Lancia site. I was going to use either Apple Hyd. or White Post to send them to.
I was curious about the piston itself leaking, actually. The "bad" scoring seems like it would not interfere with the gasket on the piston (i.e. the piston seal would remain above/outside that spot). Thanks for the info, I will try and attach a photo(!).

If it doesn't appear, clicking on it should bring it up...
New to me sorry...

 

The flat broad seal on the piston (when removed) seals against the piston on the seals flat area on the seal itself.
The piston can rust in this area and the rust can't be seen until the seal is removed.
Someone at some point rebuilt my pistons by replacing the steel with brass.


When you remove the seal, you will see what I am talking about.


If not I will post some pictures.

Some people will go to great lengths to keep things as original as possible _ like the people on the Lancia site _ pretty much to the point where it becomes impractical. I would think that type of repair will just rust out again _ wouldn't it ???
I know of a guy who is a retired air plane mechanic where he insists upon using the original Rolls-Royce pistons when rebuilding an engine (a car engine not one for a plane). The original pistons were fine in their day, but technology has come a long way since 1950 and using those antiquated pistons is just ridiculous _ and I am going to say the same for the people over at the Lancia site. (at the risk or being smacked in the head for criticizing them I am sure).

Hmmm... Your piston doesn't look that bad _ I've seen much worse that don't leak...

 

Honestly I didn't think it looked too bad either. I was surprised that it began leaking. I haven't had a chance to pull the rears or open the left fronts yet, probably a project for tonight/tomorrow. I emailed the White Post rebuild folks and they were friendly and quick with a reply. Depending on my findings with the rest of the calipers, I may just mail them the lot and let them do their magic.
While I am discussing brakes, can someone tell me about the pins that go through the brake pad backing plate? On my cylinder, one side has some sort of coiled bushing (like a permanently compressed spring) and the other side just has the pin. Part diagrams seem to indicate they both should have the spring-like bushing, and some posts even say it is a real spring to pull the pad away from the disc.
Thoughts?

 

If you could post a couple of photos it would help, but as I recall, there is a piston retraction device inside the piston housing. This involves a pin secured to the back of the cylinder, and a "gripper device" on the piston. Retraction is achieved by a deformable washer where the pin locates in the cylinder. The piston has the "gripper device" to compensate for wear. As the pads wear, the piston gradually moves outwards along the pin. The gripper device is overcome by the much larger force of braking, once the distortable washer has distorted to its maximum extent. Modern calipers use the piston seal for piston retraction. These early Dunlop designs showed how the pioneers dealt with the problems, but development soon led to cheaper alternatives.

 

I will try for pics. I am travelling this week, and havent touched the car in sevefsl dsys. I am suffering withdrawal, frankly.

 

Hey all, thanks for the info. I have finally gotten the rear calipers off and ordered all the rubber from XKS. Still looking for the retractor pins and bushing/springs. I only had 8 out of 16. For the next question, I am wondering about the rebuild and lubricating the rubber on the pistons. I have seen both "you have to do it or else!" and "don't do it or else!" opinions on the inter-tubes. Any recommendations?
Secondly, I managed to shear off the remaining bolt head for the bolt attaching the parking brake arms to the caliper. I'm not certain it matters unless I need to replace the parking brake arm at some point. I am planning on putting it back together as is, thought?

Thanks as always,