This seems a little removed from the thread in parts interchangeability, as the main parts appear non-interchangeable with anything yet found.


Observations:

The brake pipe threads are 10mmx1.5, a somewhat rare thread pattern for brake fittings.

The hex heads on those brake pipe fittings are sub-12 mm, possibly 11.5 mm, just small enough to round off under a 12 mm flange nut wrench.

Someone at the factory really should have trimmed the caliper castings to allow more clearance for a wrench on the hose ends and the pipe ends between the rear and front halves.

The Dunlop/Sumitomo brake calipers have a center guide pin that runs up the middle of the piston. This makes trouble for what should be a simple task of making a replacement piston. The shaft to accept the guide pin is spring loaded into the back of the piston, at about 200 pounds, making for a very annoyed machinist when it comes apart and fires across the shop while chucked into the lathe to be cut out. Once all the parts are found, gathered up, reassembled, and examined, dialog and commentary goes something like:
"What the heck is it?"
"I don't know."
"What the heck does it do?"
"I don't know."
"Why the heck would they put that in there?"
"I don't know."
Repeat.

No progress on the caliper pistons as of yet. That may turn to an effort related to the hoses.

The local "hose guy", who has a Brake Quip franchise, and can build hoses for anything, Well, 10mmx1.5 hoses are not even available from the company headquarters in Australia.

I may be searching Japan for hoses, and caliper pistons.

Always something weird and non standard

Thanks for keeping us posted JT, hopefully you'll turn up something soon!

Cheers,
R.

Guys,
Try Burt Bros Automotive in Fairfield in Sydney, (early days they were known as Burt Bros Brakes) these Guys are great with brakes.
If they can't do the job they are a good chance of offerring another option, the best thing is they know Belletts!
I have had wheel cylinders and master cylinders re sleeved with stainless by them.
Try your luck
11

Hi JT191,
I'm kind of new on the forum and all the way from Holland.
The guide pin you talk about was only there in the early calipers. Later pistons were not guided that way and have the same measures. Getting the pin out and fit stainless pistons made on a lathe will work okay .....

As Dick said remove pin machine new pistons or leave old pistons in as pin hole does not go through macxhine out seal grove & fit Jaguar seal & boot kit ----readily avail. from most brake shops Has been working in our PR90 since 1989. Soon to do same to other P990
hope this helps ken

Dick and P.R.90,
I have some conflicting information on the pin.
For the 2 1/8 size pistons used in the Nissan Fairlady, the pin seems to have been used for the life of the vehicle, so they do not have early or late calipers. The US expert on rebuilding those gives a really grim caution of "Whatever you do, don't bend or damage that pin...".
The machinist who took the first piston apart pointed out that the spring in the back of the piston is basically acting as a solid cylinder when installed, because the coils are stacked.
And the comments about how bad the original brakes are/were have me curious if the original brakes in original condition are that bad, or the original brakes with 40 years age are that bad.
Wanted to put them back as they were in new condition, and find out. It's a really light car with really big brake pistons on the front, based on the numbers, it should be somewhere between remarkable and "don't press too hard on the brake pedal or you'll hit your head on the windshield".

At the moment, the 10x1.5 brake hose fittings are the most unattainable part. I can do a drawing and have them made, but the BrakeQuip dealer can't install them without violating his contract and insurance coverage which requires he use only BrakeQuip brand fittings. The machine to crimp the hoses would be something like $20,000, sort of expensive for six hose crimps after having the fittings made locally. Or, BrakeQuip wants an order for 500 fittings and a six month wait for manufacturing. 100 fittings would be out of the question, that would make 5 sets. 20 sets of hoses?... (Comment removed for the public good) I did not want to repipe the car with 10x1.0 thread pipes, or use unique hose fittings that would not fit any other Bellett.
Unfortunately, the left front brake pipe was damaged. The end had frozen solid, and I had to cut the hose end away from the pipe to get the assembly away from the car and into a vice. It is surprising how deep the pipe threads into the end so the cone will seat and seal...

With chrome pealing off the original pistons, no hoses, and one bad pipe, the easiest solution might be finding the hoses and pistons in Japan, and redoing the one pipe. Original pistons would probably be cheaper than having new ones machined.

Or, I might end up re piping the entire car with custom pipes and just going with the smaller 10x1.0 thread size. Then worrying about the pistons after that.

I should probably get a look at the rear brake cylinders first. And I have a couple other bigger things pushing the Bellett brakes to the side. I will wait and decide later.

I had my pistons re-hard chromed and polished to spec. Yes the threads are an oddball one. An option available is t have them tapped out to a stock hose maybe one size larger. then get the nuts on the pipe changed.

Try a small brake joint they may be willing to re-use the end fittings on a new hose. If they get uptight just tell them it is for a clutch. It works here. Not that I would encourage any one to do anything that could compromise there safety or any legal obligations they may be deemed to have.

The suggestions above are not intended as either legal or safe, but as options available to open discussion and further investigation.

Now I will sit back and wait for the "LEGAL" worry warts to bite.

A little further research...

The pistons in the original calipers have some impact or wear damage on the exposed ends. The rims are not flat or smooth and the little center pin tops are mashed. Not reusable, and not re chromable without removing the center pin receiver from the centers, that can't be chromed.

I found seven caliper rebuild kits (seal sets) for 2 1/4 inch piston sizes from various manufacturers. I was able to order six of these, the Chevy Luv seems to be unavailable.
I am unsure of what the original seal dimensions are supposed to be. I do not know how to anticipate the change in seal dimension when it is squeezed into the groove and how well it fills the groove after the piston is installed. All I can do is measure what is there. The groove appears to be .157 inches wide. My calipers are too big to fit into the caliper, so that is measured at an angle, and not overly precise. The piston seal measures .161-.165 inches tall, and .113-.118 inches deep. It has been soaking in brake fluid, squeezed between the caliper and piston, and dry rotting for 40 years. It is no longer accurate to the shape or size it was originally.
Of the rebuild/seal sets that I was able to obtain, most of the piston seals are .119-.125 inches tall, and .114-.122 inches deep. The one I believe to be for Toyota (Pickup) Truck comes a little closer, it measures .127 inches tall, and .117 inches deep. But I do not know if that is close enough to fill the groove of the Bellett caliper once the piston is installed.
None of the dust seals were close to the same design. It is surprising how many different ways there are to attach a dust seal.

I have not found any Jaguar 2 1/4 inch piston caliper rebuild kits. This may be a size or model not common over here.
I would like to know more details of the model these are from, and also what part must be machined to make these fit. Is the piston seal groove to be machined, or the dust boot retention groove?

If the Toyota piston seal is close enough, and the Jaguar dust boot does not require machining, the combination would be the easiest and cheapest solution.

I have no more progress on this other than cleaning up the bolts and washers to be replated and the observation that the bolts holding the caliper pieces together are 1/4 inch by 28 thread pitch, not metric, but SAE/Inch size! This was a huge surprise to me. I guess this puts the origin closer to the first borrowing of the European technology to Japan (the Dunlop part), than the Japanese refinement of the borrowed technology (the Sumitomo side).

I wonder if Bellett GT owners in Japan had just as much fun finding replacement inch size hardware as I have had (and continue to have) finding metric sized hardware...