Dunlop Caliper rebuild questions.

[JAV]

Sorry for all the questions but I've started rebuilding my brake system and the Dunlop calipers are a bit different than I'm used to so here goes.

1. Can anyone describe the function (and proper fit) of the pin that goes into the backside of the piston?
2. Does this feature require removal or service if the bore is in good shape?
3. What maintains the orientation of the flats on the piston face to the long axis of the housing?
4. Are the seal, bellows and pads readily available?
5. I've read of folks are doing both nickel and zinc plating on these parts... is one preferred over the other?

Thanks in advance

[Chris Coios]

John,

Neither nickel nor zinc is correct. The correct finish for most of the major pieces of the period Dunlop calipers is clear cadmium (silver in color not gold). Some of the bits are black oxide like the bolts that mount the caliper to the upright or axle.

Chris

[JAV]

Chris,

understood but I'm told Cad plating in generel is impossible to source and that bright Zinc has been used instead, as well as nickel, hence the question.

[Chris Coios]

Appreciate the problem of sourcing cadmium, but it is still available from good industrial platers and electronics platers, just expensive due to handling the environmental controls.

[JAV]

thanks for the tip, I'll look into it with some of the regional platers. Any guidance on the other questions?

[8339]

John, here's what I can tell you about the Dunlop calipers:

1. The center pin fits inside the piston and actually causes the piston to return after application. The piston seals are square cut and don't provide piston return. Most newer caliper piston seals are cut on angle and return the piston. Keep in mind we are only talking about a few thousands of an inch return. Without the slight return the pads would wear prematurely and overheat the brakes.
2. The center pin does not have to be removed even if you are honing the cylinders.
3. There's nothing really to rotate the pistons so the flats don't move. In thirty five years of repairing cars I've not seen one rotate unless someone did not rebuild them properly.
4. Pads and seals are available, call Partsource 207-236-9791
5. The calipers did come originally in silver cad, call John Whittington at 540-335-9443. John does all the cadmium plating for David Carte.

Richard Garre, Radcliffe Motorcars

[JAV]

Richard,

many thanks for the info.

this morning I found a decent manual online for the Jaguar xk-150 Dunlop brake setup and it looks identical to whats on my Lusso. There's a local Jag parts house that may have the rebuild kits in stock and I may go down just to have a look at the kit parts.

The Jag diagram shows a screw down keeper plate for the piston seal that I don't recall seeing on initial disassembly. Do you know if the seal is stretched over the piston or retained by a keeper?

[8339]

The seal should be stretched over the piston. Do yourself a favor and find a tube of PBR rubber grease to assemble the seals in the calipers. HRP Racing Products carries it, call 866-851-7223

[Suebian330]

Hello wrenching guys,

I am quite new at this forum also this is my first Ferrari I own. Because of some skills and not a big wallet I try to repair as much as I can at my Ferrari (like Tom, when he started with his 250). For this your forum is very very valuable.
As I now do some overhaul and rebuilt work on my gt 330 . I searched this forum for hints about pot , piston and caliper overhaul. I found many threads about the correct plating, but nothing how to replace the piston sealing and dust cover. It seems to me that the dust cover can not be streched over the assembled piston. As I looked closer at the piston I realized that the piston at least at the dunlop front brakes is an assembly of 2 parts with press fit. So I used a iron bush and squeezed the piston part out to replace the dust cover, sanded and polished all moving surfaces (except those of the press fit) in a lathe and reassembled.

Here 2 questions:
My pistons where brass made and nickel or something plated, was this standard?
Also the pots had a brass bush in. Where they already resleeved, or was this also standard to protect for corrossion?

Luckily my pots still look quite good, so I do not need any surface treatment. It seems to me they where replaced some day by new ones, because the calipers look worse.

The weekend I will try to rework my rear brake pots.

Dieter

[John Vardanian]

Hi John, can you describe the heads of the four bolts to the pots? Mine appear to be not black oxide, but silver cad, but I wondeedr if there are any marks or lettering on the heads. Thanks.

john

[tyang]

Hello wrenching guys,

I am quite new at this forum also this is my first Ferrari I own. Because of some skills and not a big wallet I try to repair as much as I can at my Ferrari (like Tom, when he started with his 250). For this your forum is very very valuable.
As I now do some overhaul and rebuilt work on my gt 330 . I searched this forum for hints about pot , piston and caliper overhaul. I found many threads about the correct plating, but nothing how to replace the piston sealing and dust cover. It seems to me that the dust cover can not be streched over the assembled piston. As I looked closer at the piston I realized that the piston at least at the dunlop front brakes is an assembly of 2 parts with press fit. So I used a iron bush and squeezed the piston part out to replace the dust cover, sanded and polished all moving surfaces (except those of the press fit) in a lathe and reassembled.

Here 2 questions:
My pistons where brass made and nickel or something plated, was this standard?
Also the pots had a brass bush in. Where they already resleeved, or was this also standard to protect for corrossion?

Luckily my pots still look quite good, so I do not need any surface treatment. It seems to me they where replaced some day by new ones, because the calipers look worse.

The weekend I will try to rework my rear brake pots.

Dieter

The original caliper body was cast iron, so if you have a brass sleeve, someone probably resleeved the piston body before.

Tom

[Suebian330]

Tom,

thanks a lot for your always very quick response.

As reworking the pods and calipers my next question occurred : brake disk thickness.

In the manual I read that regrinding for a maximum of 1 mm material removal is allowed. I checked all the manuals, but there is no information about the original thickness. My front disks have 11,5mm, rear 12mm. Surface still quite good and runout of outer diameter gaged by indicator below the given 0,08mm so I do not intend to replace them if not required.

Does any body know the original width?

Dieter