73.5 - 87 rear brake caliper design question

I’m looking at Girling rear calipers and I find there are two maybe three types of calipers. The calipers are for a 73.5 to 87 Jaguar xj6. Can you please explain the difference between these 3 calipers?

Thank you for any help.

Boot & Spring Design

Balloon Boot Design

Spring Design

Rock auto jag calipers

They all look the same…
My 87 has the boot and spring design.
You could also rebuild the old ones with new seals boots and pistons. Inox would be better.

Thank you for the reply but I’m trying to determine exactly what these three terms pertain to. Is it the parking brake, the rubber around the pistons, etc. I have no idea.

Also what is the difference in functionality and which is superior.

Their are only two styles of caliper used in that period, the later circlip retained dust cover is a “cheaper” design and is easier to service.
Functionally there is no difference,

Thanks both Aristides and Norman for your Replys.

Norman, which of these is the Circlip?
Boot & Spring Design
Balloon Boot Design

You call it a spring, it’s actually called a circlip.
I actually convert the early type to the circlip style, because it’s easier to assemble.
The early type requires the dust boot to be assembled to the caliper then the piston has to be pushed thru it, very easy to damage the boott.

perfect! Thanks a ton. I’m using xj6 calipers to convert a 1963 Iso Rivolta. I was afraid to order the calipers until I was sure the difference.

Bruce, were the original calipers Dunlop, if so what piston size?
And what about the front?
Make sure you get the later style calipers.

Yes they are Dunlop - 2 1/8" and 1 1/2"

I was looking at calipers that fit a 1986 xj6. Otherwise how do I differentiate between old or later style. I know about the Circlip in the later ones thanks to you and the others on this site.

I can see some problems here. The 86’ XJ6 has 4 pot front calipers that will require an adaptor for the calipers, the rears are a direct replacement.
You will have a great improvement in brake performance as the front calipers are 1.89" x 2 and the rear are 1.69".
You could also use “Wilwood” Corvette C4 front calipers with 1.88" x 2 pistons that weigh nearly half of the XJ ones. An adaptor is still required but I believe it will be a much simpler one to make.
That is the way I am going on my XJS and my E race car.

Do you know if the front discs are Jaguar or not? because the XJ and C4 are ventilated ones. The XJ are 285 x 24mm. and the C4 are 305 x 30mm.

someone is almost finished with the caliper bracket for the front. We were looking at the Wilwoods but they are a lot more expensive then the Jaguar xj6 calipers. We also want it to look as period correct as possible.

We also changed the Servo to the big dual diaphram ATE as used in the early 250 Mercedes.

Thanks a ton for all your input Norman.

Note that the force on the disc is proportional to total piston area - and that both sides of the disc requires the same force, of course…

That the rear callipers have two different piston diameters is just to more easily accommodate the handbrake set-up…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Of course, I recommend the rear brakes be upgraded to vented rotors:


Frank, rear piston size has nothing to do with hand brake accommodation, it is only base on brake balance from front to rear systems.

The Iso uses the add on e-brake with it’s own pads.

As per Jaguar.
With the modular design of the DUNLOP caliper it is possible to fit the front piston assy of up to 2.25" as used on the MK X 3.8 front.

I know, Norman - I was just trying to find a facile explanation why the 3-pot rear caliper was retained when the front was changed to a 4-pot set-up…:slight_smile:

The gist is that for Bruce’s purpose either version of rear calipers would work.

xj6 85 Sov Europe (UK/NZ)

You’ve got 3-pot rear calipers?