front brake caliper fluid passages

Hi Wade,

The fluid enters the rear of the piston bore cavity via the external steel tubing and a passage that is internal to the caliper (inboard caliper half). Once in the bore cavity, the fluid travels through another passage that is in the side wall of the piston bore cavity. That passage goes through both halves of the caliper (via internal passages) to the rear of the piston cavity in the other half of the caliper (outboard caliper half). There are separate passages for each pair of pistons that are joined together via the external steel tubing and the external tee.

John

Hey John -

What keeps 'em from leaking - there's no gasket there (between the two caliper halves), right?

Any suggestions on the best source for caliper rebuild kits (front / rear)?

Thanks

Chuck

Hey Chuck,

Will this work ??

The seals are in the other half of the caliper.

A word of caution: Don't lose those two square rings. They don't come with the kits, and they are hard to find.

Shop the vendors for price on the kits. There used to be a seller on eBay that had them, but I don't see a current listing. There is one eBay listing for the kit and pistons, but you shouldn't need the pistons. Seal kits (for two calipers) should run ~ $55.

John

Perfect timing on THIS thread. Brake seal kits are in transit even as we speak.

thanks jb for the info/photos! snaponbob, there is a video on the poca website by asa jay on installing the kit. rocky i got my kits ;frt/rr from wilkinson. the square o-rings in the transfer holes i got from mcmaster carr
thanks

Thanks, all!

Regards -

Chuck

quote:

Originally posted by markIV/ 4280:
thanks jb for the info/photos! snaponbob, there is a video on the poca website by asa jay on installing the kit. rocky i got my kits ;frt/rr from wilkinson. the square o-rings in the transfer holes i got from mcmaster carr
thanks

Any idea what the part number is for McMaster Carr o-ring?

edit - searched their web site. Are these square Buna-N o-rings?

Anybody know the dimensions of that o-ring?

quote:

Originally posted by snaponbob:
Anybody know the dimensions of that o-ring?

The only square o-rings that McMaster-Carr lists is the Buna-N. Temp rating is -30*F to +212*F, which wouldn't be high enough for lots of really hard braking.

I measured the old o-rings, not knowing just how much "crush" they may have retained after 40+ years.

Used square o-ring:

OD = 0.493" (12.54mm)
ID = 0.320" (8.15mm)
Ht = 0.073" (1.86mm)


O-ring bore (spotface) in caliper:

Bore = 0.504" (12.8mm)
Depth = 0.058" (1.47mm)


Closest in McMaster-Carr is P/N 4061T117:

OD = 0.504"
ID = 0.364"
Ht = 0.070"


John

The little square profile o-ring for the caliper fluid passage costs a great big $1.80. There are British car vendors that are swimming in these things!!!! British Parts Northwest gave me dimensions of .490 outside, .275 inside, and .075 thickness. Given the picture on this thread, it will (SHOULD) work perfectly.

I've got these bad boys. I heard (through a reliable source) that there is a standard mod that can be done to get rid of the external hardline? Is this what seems to be going on here?

Thanks

Chuck

Side View

quote:

I heard (through a reliable source) that there is a standard mod that can be done to get rid of the external hardline? Is this what seems to be going on here?

Yup. Those are the ones. It takes the same seal kit and square o-rings as the non-modified calipers. If you remove the two hex head bolts, there is a copper washer between the under side of the bolt head and the caliper. If you do remove those bolts, you will need to either anneal the copper washers, or replace them. You should be able to find a suitable replacement at most auto parts stores or DIY stores.

John