Thread: Rebuilding a Discovery 300 TDI front brake calipers

Originally Posted by twr7cx

Any advice or tips on rebuilding the front brake callipers in a Discovery 1 with the 300 TDI motor? They look to be 4 piston units (2 pistons per side). A mate just got back from holidays for 2 months and upend starting the car again it dumped fluid from the left front side calliper.

DO NOT split the caliper, compressed air the pistons out carefully, best to order piston and seal kit, as the main reason the seals leak is because the piston surfaces are kaput. Clean thoroughly in water and then dry with compressed air, then clean again with brakecleaner or similar, assemble with rubber grease or brake fluid, and refit and bleed. The dust seal rings are quite difficult to press back into the caliper body, I use an old brake pad and a g clamp to do it.
(Or better still, get Michael to do it, if its his vehicle we are talking about... )
Enjoy

JC

I've just finished doing a rebuild on all 4 calipers. Here's a couple of things I noticed:

- You'll need 12point sockets size 1/2inch and 9/16 for the bolts.
- The cause of the fluid leak is more probably the rotor worn too thin. When the pads get thin too, the probability is that one of the pistons protrudes too far and fluid leaks out. Aftermarket rotors are reasonably cheap.
- the cost of a seal kit for each front caliper is about $24. Search on evilbay and you'll find a few deals. One front caliper kit will do both rears.
- Consider buying new pistons. After 400,000 k, mine were a little pitted (and that was with a clean out when I first got the Disco at 265K).
- Getting the pistons out will require air pressure. I used one of those tyre inflaters with the accessory to blow up airbeds & toys. Don't use vicegrips as you'll mark the contact surface of the pistons.
- The seals have a metal shield first up, and when you lever it out be aware you might have to reuse them. The new metal shield sometimes deforms as you press it in.
- Do not split the halves. It's PITA but a bigger PITA to reassemble later.
- I worked on the one-at-a-time method on removing, cleaning, installing new seals and reassembling each piston. You'll need a something to hold the opposite piston in whilst you extract the other with air.
- Figure on installing new hubs seals whilst your at it.

With an assistant, say an easy days work each axle.

EDIT : And what JC said....

Originally Posted by justinc

DO NOT split the caliper, compressed air the pistons out carefully, best to order piston and seal kit, as the main reason the seals leak is because the piston surfaces are kaput. Clean thoroughly in water and then dry with compressed air, then clean again with brakecleaner or similar, assemble with rubber grease or brake fluid, and refit and bleed. The dust seal rings are quite difficult to press back into the caliper body, I use an old brake pad and a g clamp to do it.
(Or better still, get Michael to do it, if its his vehicle we are talking about... )
Enjoy

JC

Hey Justin, thanks for that (I was actually going to call you and ask tomorrow morning). You are correct it is Michaels vehicle - but you probably knew that as it was only about 2 and a half months ago that you told him it looked like he had a leak! He just got home today, went to start it and it dumped fluid out of the front left calliper and he had no (or very little brakes).
It's at my place now. I've got the calliper removed, chucked a piece of timber between the brake pads, and had him push the brake pedal. I have found the leaking piston, but assume that if ones gone, then all 4 need to be redone and the drivers side too.

Do I remember right that you recommended not to rebuild them and instead to chuck a second hand set in?
If so, what is a fair price to pay for a second hand set? Any ideas on where I could get one ASAP in Tassie?

Alternatively I assume Allen at JagSpares is the place to get the rebuild kit (with all seals and the new pistons).

Thanks again!

Originally Posted by langy

- You'll need 12point sockets size 1/2inch and 9/16 for the bolts.

Woops, I just used a 13mm...

Originally Posted by langy

The cause of the fluid leak is more probably the rotor worn too thin. When the pads get thin too, the probability is that one of the pistons protrudes too far and fluid leaks out. Aftermarket rotors are reasonably cheap.

Any idea what the minimum thickness is of the rotors? The Haynes manual doesn't have it specified. The pads in it I estimate are only half worn at best.

Hi twr7cx;

JC is absolutely correct about the plating on the surface of pistons deminishing . this is my D1 front caliper pistons before i replaced them with the stainless ones





the retaining ring for the seals are quite easy to press back in, I used the big washer from my trailing arms

Originally Posted by twr7cx

Hey Justin, thanks for that (I was actually going to call you and ask tomorrow morning). You are correct it is Michaels vehicle - but you probably knew that as it was only about 2 and a half months ago that you told him it looked like he had a leak! He just got home today, went to start it and it dumped fluid out of the front left calliper and he had no (or very little brakes).
It's at my place now. I've got the calliper removed, chucked a piece of timber between the brake pads, and had him push the brake pedal. I have found the leaking piston, but assume that if ones gone, then all 4 need to be redone and the drivers side too.

Do I remember right that you recommended not to rebuild them and instead to chuck a second hand set in?
If so, what is a fair price to pay for a second hand set? Any ideas on where I could get one ASAP in Tassie?

Alternatively I assume Allen at JagSpares is the place to get the rebuild kit (with all seals and the new pistons).

Thanks again!

Hi, yes sometimes it is cheaper (read quicker) to fit a good used caliper, BUT seeing as you have got this far, may as well fix it. You will be replacing alll the bits that give trouble anyway, pistons and seals so it will be as good as new.
Yes, make sure you use the 'I told you so' phrase regularly with Michael!! and get him to do all the dirty work

Allen may well have the kits on the shelf, you can get a complete overhaul kit now, a box with 4 pistons and all the seals, IME stainless isn't really necessary unless operating the vehilcle in salty or corrosive conditions, just more exxy.

JC

I had heaps of trouble getting the new dust seal rings in and ended up taking the tiniest of edges off the outer lead edge with a bench grinder. The pistons responded well to a rub with 400 grit wet and dry and kerosene. I made a lot of work for myself by letting the reservoir run dry whilst purging the fluid.
Tim