Specs for renovating/rebuilding/restoring brake calipers

[ricky8664]

I have reposted my last post in the thread about variations in parts prices under a separate heading in this message as I've digressed a bit from the issue of prices and got into the details of what we actually get for our money when our calipers are restored/rebuilt/renovated.

Below is the substance of my latest message in that other chain which, under a specific title about restoring brake calipers, I hope will be drawn to the attention of someone who knows about the process of caliper restoration, which I now realise I clearly do not! And they might then clarify what is the industry standard for restoration etc or, indeed, that there is no industry standard and we just take pot luck, which would be a bit concerning given we're talking about something of pretty great importance, safety wise.

Anyway, this is the text from the other thread. I hope someone can cast more light than I've been able to.

Power Brakes in Aus also do not state that they reline/rebore calipers. They expressly state that they reline and sleeve wheel and other brake cylinders but on the pages dealing with brake calipers, they just talk of "guaranteed restoration", without saying what they actually do to the calipers or giving a spec for what they do. So only the firm in Suffolk have said what they actually do to the calipers as part of renovation or restoration (i.e. honing) which to me does not seem a method to deal with rusty bores.



So if anyone knows of a UK brake caliper restoration firm that actually re bores/relines/re-sleeves brake calipers then please let me know, as there does seem to be a bit of confusion about what actually gets done to calipers that are rebuilt/renovated/restored. Whilst the definitions of what gets done are a bit ambiguous, one thing none of those sites I've looked at actually state expressly, is that they re bore/re sleeve/ reline brake calipers but do expressly state that they do that to wheel, master, slave cylinders. That makes me think that calipers don't get relined etc by any of the firms I've checked out.



However, internet searching is fairly imperfect and I don't expect members to search the net for me. I'm more than happy to research particular companies myself. I just need members to give me the company names they have used where they believe their calipers (for the P5B) were re bored/re lined etc and I can try and find out what their actual restoration spec is.



It's of particular importance to me as I've now got the calipers and wheel cylinders off the car. I'm happy to take the wheel cylinders to Suffolk as they have stated they expressly reline those, so happy to let them do it. Obviously need more clarity on what happens to the calipers before entrusting them to anyone.



Sorry, if this comes across as a bit ungrateful for the info provided but I think there is a lack of clarity on what actually gets done to "recondition" calipers and I suspect that there may be a number of people who think they have had them re lined etc., when they actually haven't. I've also seen reference on a couple of sites that say the calipers must be serviceable, which also suggests there is a limit on bore wear/damage over which the calipers are not "restorable etc., which also suggests re-lining doesn't happen at those firms. So I think it's in all our interests to know exactly what were getting when we have our calipers restored.

[enigmas]

I fitted a set of disc brakes (Mercedes solid disks & MK2 Jaguar rear calipers) to the rear of my modified MK3 P5 Coupe years ago. The rear calipers were relined with stainless steel inserts.

Here availaible on a C/O basis fully reconditioned

www.ebay.com.au/itm/184872699984





PS.
The seller states "CNC turned with new stainless pistons."
The caliper bores have been machined fractionally oversize to clean the surfaces.

[westoz]

Hi Ricky. Reconditioning the calipers should be pretty straight forward. I think you might be overthinking it a little. As long as the bores are rust free there should be no problem. The pistons need to be perfect. The calipers operate the opposite way the master cylinder works in that the seals are fixed in the bores and the pistons move in the seals; in a master(or drum brake slave) the seals are attached to the piston, which moves in the bores, hence the need to resleeve sometimes. A polish with some emery of the caliper bores is sufficient unless there is serious pitting.

[westoz]

Further...and if there was serious pitting then the calipers would be discarded. I think relining calipers would be limited to calipers that are exotic ie high end restorations on rare vehicles.

[ricky8664]

My previous experience of rebuilding hydraulic cylinders was limited to a couple of wheel cylinders for a Mk2 cortina in the 70s and my p5b in the 80s. On both types my recollection was that the rubber seal was on the piston and that travelled up and down in the bore, so bore condition was relevant. These rebuilds all failed due to bore scoring and new wheel cylinders were needed.

I assumed the calipers operated in the same way. However, after the last 2 messages I found a video of the P5b caliper being dismantled, and there is no seal mounted on the piston. Instead the seal is on the top of the bore and the pistons travel up and down through the seal, so I can see now that the bore condition is not paramount as with wheel cylinders.

I'm still awaiting a call back from the company that have said they "replate" the calipers, as I'd like to know what that means.

[Sam Bee]

Try MGBD Parts in UK, Mark Grey - details on his website. He is a P6 supplier but does P5 calipers and servos. He relines with stainless steel whilst using standard steel pistons and will have then plated at modest extra cost. They come out looking like new.

[enigmas]

Wow! This topic is certainly entering something of epic proportions. Westoz covers the point accurately.

With this type of fixed head caliper the piston works against a square section seal fitted within an internal annular channel within the caliper bore. The piston surface is the sealing medium, not the bore of the caliper. This is the reason this style caliper uses hard chromed or replacement stainless steel pistons. A rebuild generally includes new pistons being fitted if any surface defects are apparent on the original set. The hard chrome surface layer is often found to be compromised given 50 years of use in a very hostile environment.

Function:
The square section seal also acts to withdraw the piston slightly due to elastic deformation. This is the method by which the pads release their grip on the caliper once brake pedal pressure is released. Calipers with age worn annular seals will often stick and cause premature pad wear.


Note:
This is not the case for all caliper designs. It depends how the Factory Brake designer/engineer originally formulated the method of caliper operation. eg. Early rear disc brake Jaguar/Daimler systems.

Early 1959-68 Jag/Daimler caliper.
Note also the term stainless steel on the caliper body.

[westoz]

Ricky. Re-plating just refers to the external finish (usually cad plated) . The internal bores will benefit from the re-plating also, but as i explained the bore condition is not critical in this instance.

[ricky8664]

Thanks for all your contributions.

Having checked out those companies named in the various replies, none of them expressly state in their listings that they re-sleeve calipers, though they do for wheel cylinders and slave and master cylinders. The only logical inference therefore is that they do not routinely re-sleeve calipers. That is not to say it could not be done for some valuable/ exotic cars as someone has suggested.

However, after seeing on Youtube a P5B caliper being dismantled, I can now see that the seal is not mounted on the piston and instead the piston travels up and down through the seal, so the bore plays a less important role.

Anyway, yesterday I delivered my calipers and wheel cylinders to suffolk for overhaul, so should be able to complete the brake reassembly in a few weeks. But thanks again for your insights.

[Sam Bee]

For future reference - MGBD Parts do not show renovation of P5 calipers on their site, you just have to talk to Mark Grey. Thus :

Attachment Deleted

[enigmas]

Jun 22, 2023 9:55:38 GMT Sam Bee said:

For future reference - MGBD Parts do not show renovation of P5 calipers on their site, you just have to talk to Mark Grey. Thus :

View Attachment

Hi Sam...who does the drilled discs?

[lagain]

Not sure why you would resleve the calipers. Just give them a good clean, never split them, then fit new rubber seals and stainless steel pistons. The pistons do not touch the calipers as they slide on the rubber.

[djm16]

I rebuilt mine a few years back.

I split them. It is almost impossible to re-insert the boot retainers without splitting them. Rejoining with a new O-ring is trivial, so I don't understand where the "not splitting" meme comes from.

With the caliper split it is much easier to see and deal with any corrosion inside.

I reassembled with new SS pistons, seals, boots and all has been well for 10y / 40,000 miles.

Purely incidentally, the new boots obtainable off the shelf from Perth Brake Parts are designed to be reassembled without the retaining ring, and probably glued in place instead.

[ricky8664]

Just got the rebuilt rear wheel cylinders back from Suffolk. They look just like the pics of new ones you see on ebay. Much better than I expected for rebuilt ones. And the pistons slide in and out too! Should be able to get the handbrake at least working next week so I can see if it will drive under its own power and not have to worry about running down the slope from the garage into the front gate!

Just waiting for the calipers now.

[lagain]

While you are at it, don't forget the master cylinder, servo and flexible hoses

[Sam Bee]

Apology Enigmas, I did not get back about disc drilling. Mine were by:

FOSSEWAY PERFORMANCE LTD
UNIT 8A, DRAYCOTT BUSINESS CENTRE
DRAYCOTT
GLOUCESTERSHIRE
GL56 9JY
UNITED KINGDOM

Tel. Simon. 01386 426249

[enigmas]

Thanks Sam. ~ Vince 👍

[ricky8664]

Now had the overhauled rear wheel cylinders back from Suffolk. Very impressed with the finish.

Of course when trying to do one job you discover another. Whilst re-assembling the wheel cylinders on the rear hubs we noticed oily deposits that could have been from the leaking cylinders or oil from the transmission/axle casing. 

Better safe than sorry, so rather than ruin the new brake shoes if it is the rear axle that's leaking, I've ordered new half shaft oils seals and "O" rings for the rear bearings.

Looking at the manual, it appears the half shafts can be withdrawn after undoing the 6 bolts that attach the half shafts to the outer axle casing as the wheel cylinders are not yet attached to the pipework/handbrake linkage. There does not appear to be any circlips etc securing the half shafts into the differential unit. However, I was wondering how easily the half shafts withdraw from the axle after 50 years? There's still oil in the axle casing BTW.

[Phil Nottingham]

The half shafts complete with hub and oil seal carrier should in theory just pull off when said 6 rusted bolts and nuts are undone.

The hub flange often rusts to the axle flange and some have had terrible times releasing it as they just try bashing it off in the wrong place.

All that is needed are light taps with a small narrow cold chisel on the narrow circumference edge of the HUB flange that overlaps the axle flange

Note once dirty swarf ridden diff oil has passed through the once "sealed" bearing which now will have some play, it washes the HMP grease out and wears faster creating more play to wear the new seal and the bearing will begin to rumble and fail. I think the seal can be done 2-3 times before the whole bearing needs renewing if it is not already noisy. That procedure is much more trouble - see SEARCH 

[lagain]

When replacing the O ring take care that it stays in place.
One of mine moved out of place and got damaged and leaked a little oil, fortunately I found it before too much leaked out. I used a scissor jack on the rear of the back plate to break the seal.

[ricky8664]

Upon removing the half shafts yesterday (neither of which required any hammering to free the shafts from the axle casing!) discovered that one of the O rings had broken up. Was a bit odd in that the ring had broken into several segments some of which remained in the groove and  looked like they'd been cut off with a knife. The missing bits were squashed flat against the hub. Don't know how that could have happened and I'm 99% sure I've never had the half shafts out, so must have happened in the first 10 years of the car's life before I owned it.

Anyway, new O rings fitted on each half shaft so hopefully my new brake shoes won't get oiled.

[percy]

Aug 12, 2023 22:51:18 GMT ricky8664 said:

Upon removing the half shafts yesterday (neither of which required any hammering to free the shafts from the axle casing!) discovered that one of the O rings had broken up. Was a bit odd in that the ring had broken into several segments some of which remained in the groove and  looked like they'd been cut off with a knife. The missing bits were squashed flat against the hub. Don't know how that could have happened and I'm 99% sure I've never had the half shafts out, so must have happened in the first 10 years of the car's life before I owned it.

Anyway, new O rings fitted on each half shaft so hopefully my new brake shoes won't get oiled.

[percy]

Leave the axle oil level slightly below the filler hole. The capacity is 1.75 Litres and I fill with 1.6 Litres which is more than ample to lubricate the axle gears. Doing this will keep the oil level BELOW the axle casing. Use a quality 85-140 EP diff oil. Don't use oil of lower viscosity. Ensure the brass breather on the axle casing is clear.

Consider this posting from 2008 referring to a post two years earlier

"Here is the posting from 2006

--------------------------------------------------------------------------------

I removed the n/s half shaft on Saturday and had enough side room as I was able to move it to one side as it came out of the axle casing

I have now brought the h/s home to my fully equipped garden shed and studied it in detail after removal of the oil seal sleeve.

My car has the original bearing and collar and the visible side of the bearing has an engineered sealing cap which looks as if it would prevent any ingress of water/oil/dirt. it is impossible to see the actual inside of the bearing.

The bearing is held tight against the flange of the h/s but is free to move within the bearing housing and it is possible to rock the housing side to side in relation to the bearing.

When the assembly including the oil sleeve is tightened up to the end of the axle casing, the bearing is held tightly in position to prevent it from turning in the housing.

My point is that any differential oil seepage past the seal should pass around the bearing and not through it.

The cross section on page 4 of section M of the 3 litre w/m shows the route the oil should take eventually exiting through the three drillings in the shaft flange to run down the OUTSIDE of the drum. Obviously, if those 3 holes are blocked then the oil will exit INSIDE the drum and ruin your linings.

Having said all that, on page 6 the modification to the early hubs is shown to prevent seepage and that text recommends the replacement of the bearing

In my view, the hub has been modified because Rover engineers accepted that some seepage is inevitable and they have put the "O" ring and the felt seal in to reduce the seepage but have also designed an exit route for any oil that has bypassed the "O" ring, the seal and the felt washer.

I suppose if you have actually dismantled the assembly and found the bearing to be full of oil,then my theory is wrong.Perhaps in the case of a really severe leak the oil would pass through the bearing but that bearing is well protected against the outside world from what I could see.

If I am wrong please put me right but,if so, what is the point of the drillings?"

Food for thought? 

[enigmas]

Try not to make a mountain out of a molehill. If the flange for the bearing retainer on your P5 doesn't incorporate a large O ring then purchase a tube of 515 or 518 Loctite flange sealer. It is an anaerobic sealer specifically designed for this type of engineering solution.

Although 518 specifies use on alloy surfaces it is also recommended for general metal to metal flanges to prevent leakage.
Google each product and read the literature. I use these products extensively when building or repairing engines and other mechanical components.

Here is an example of it's use.
The sealing of the engine valley is a critical area as it has to effectively seal against 3 mediums: Engine vacuum, Coolant and Lubricant, keeping each separate from the other.
This product is not silicon based and sets in the absence of oxygen.

Obviously you'll be fitting a new "modern" oil seal (item C) and not a NOS leather type seal. Sealing technology has moved on since the 1950s and 60s. Ensure that you coat the working lip of seal with oil prior to fitting otherwise it'll burn and fail.

Click on the link below.
Loctite 518 Pruduct Details

[ricky8664]

I'm quite content that the o ring replacement will deal with the leak which was minor and did appear to be on the outside/rear of the backplate on the l/h side, but as both wheel cylinders had leaked inside the drum it was difficult to see whether the contamination inside was just brake fluid or included axle oil. I won't get into the issue of the 3 drain holes on the shaft/housing, as we didn't actually notice them. We've corrected an obviously defective o ring, so that should do it.

When we drained the axle before removing the half shafts, the oil was in good condition and there were no bits in it, so fairly sure the diff is in good nick. It was also just over 1.5 litres, so not much had leaked out anyway.

As for refilling with oil, I'm planning to stick with the originally recommended EP90 for the back axle, which is what we took out, rather than the new variants that seem available.