machining caliper bores

[Offcamber1]

I have 4 old (likely early 1980s) JFZ 4 piston calipers on my Lola 340 D S/R. The pistons are pitted and corroded and no longer usable. Unfortunately, replacements are unobtainium.

The closest I can find are some wilwood stainless steel pistons; the problem is that they are a few thousands too large diameter.

JFZ Piston 1.733 x .85

Wilwood 1.740 x .88

JFZ Bore 1.735 x .90

Does anyone know of a machinist that could bore the holes in the caliper halves to 1.742?

I've bought several used JFZ calipers on-line to try and scare up the right pistons but the used ones are worse than the ones I have.

Alternately, I am looking at some new Wilwood calipers but cannot find any that will spec for my 9.50 inch diameter rotors.

Thanks in advance for any assistance!

Kip

[Garey Guzman]

The diameter of the piston and the caliper bore are sized to fit the appropriate o-ring. If this were my car, I would contact a good machine shop (maybe Richard Pare at ICP?) and have him duplicate the pitted pistons.

[Offcamber1]

correct seals are NLA as well. Wilwood has some seals that fit the caliper bores and the wilwood pistons, the pistons are just a wee bit too tight...

[tlracer]

Instead of machining the caliper bodies, would it be possible to have a machine shop grind the Wilwood pistons to the required diameter?

I'm thinking somewhere that grinds camshaft profiles may have the capacity to do the work and reduce those pistons to the same size as the JFZ ones.

Addendum - I hadn't spotted your post about seals when I wrote the above!

However digging around further, I found some references to 1.75" seals being correct for JFZ, Wilwood and Strange calipers, eg:

https://swracecars.com/product/calip...wood-130-2655/
https://www.lambcomponents.com/brake...d-caliper.html

Could it be your calipers may be nominal 1.75" and the pistons are worn? What is the current bore diameter in your calipers?

I found an old Apexspeed post that JFZ were bought by Sierra, but they don't seem to exist now. However as the above kits also mention Strange Engineering, who are still active, I wondered if you could match up the seals from within their rebuild kits?

[Offcamber1]

Gary,

Richard is a good thought. I'll be in Indy a few times over the next month and will bring some pieces to him for him to see if he thinks it is a viable strategy to bore them out a few thousanths.

TL,

Bores are 1.735, as close as I can measure. my thought was to bore them to 1.742, or to whatever the wilwood spec is for their piston. if that is the way I go I will likely buy a used wilwood caliper for the machinist to get a truly accurate measurement on.

You're right, the wilwood seals do cross over for use in the JFZ calipers. If my current pistons weren't junk I'd be in business!

Also, JFZ was acquired by Sierra Racing Products. Sierra was evidently purchased by Joes Racing Products in Everett, WA a few years ago. Unfortunately Joes does not reference either Sierra or JFZ on their web site so that was a dead end as well.

The bummer about this whole thing is that I've been working on this project for almost a decade. Got the engine going, webers rebuilt, shifter refabbed and rerouted, and clutch working. I finally got the thing off the 15inch stands on the ground to work on a seat, belts, and fire system and damned if it wouldn't roll. Jacked it back up and the LF caliper was locked up. I'll probably get this thing sorted out and track ready about the same time I file for Social Security benefits...

[tlracer]

Wow, I thought I had it tough with my 3-year Van Diemen rebuild!

Thanks for the additional caliper info. My first thought is the bore is an odd size as it doesn't seem to stack up against a logical 'imperial' measurement.

However I got to thinking (dangerous occupation!) and, not sure if this helps at all, but your 1.735" caliper bore is almost exactly 44mm.

Could it be the calipers are metric sized? 44mm is a common Brembo size, so maybe that avenue is worth a little Google time?

[R. Pare]

Grinding or turning the pistons will be the easiest - You just grab them by the ID on an expansion collet and turn at a very fine feed rate.

Reboring the bores would be a real PITA - you would have to make up a fixture of some sort to hold them perfectly square. Not something that any machinist would want to get into for the price you would be willing to pay.

[Offcamber1]

TL: Yep, I already went down the 44mm highway! Brembo/PFC/AP all have 44mm pistons but none of them are shallow enough depth. I found some 43mm stainless steel pistons the correct depth on an obscure English motorcycle site, but figured they would be way too small.

Richard: If I bring you an old JFZ piston, 16 new Wilwood pistons and 1 caliper half with a couple of new Wilwood seals, would you be able to turn the pistons to fit?

Thanks for the suggestions guys!

Kip