Refurbing calipers

[gs.davies]

I have a pair of 7 inch calipers (yes I know, I know, TLS drums better, terrible brakes etc... ) but anyway, I need to split them, paint them and fit them.

I have all the parts, new pistons, new seals and new bolts but I've got a couple of questions;

- I'm going to paint them, is it best to wait until they're assembled before paining them, or should I do the caliper halves while they're apart?
- Does the section that the pads run in get painted too?
- What torque setting should the bolt be done up to?
- Should there be loctite on those threads?

Cheers,
Gary

[Peter Laidler]

Gary......, please don't listen to the doomsters who continually slag off the little and much loved Cooper 7" brakes. As a bit part, inexperienced engineering grad from the early 70's I despair when I hear some of the horse sh.., er..., manure repeatedly repeated about thee brakes. Anyway, here's my take on your Q's

They're going to get hot so prime and paint in high temp paint and put them in the oven (when wife is out) for an hour or so to cure it
Paint while stripped apart but before assembly, THOROUGHLY clean the mating surfaces. Yep, I'd paint the pad bearing surfaces. Why not?
Torque settings. Don't know off-hand but the S torque is a good safe bet
No lok-tite on the threads because you might want to undo them again in a few years (?). Loc-tite is a double edged sword but you could use a semi lock. Use new bolts unless you are in a position to stress-test your old bolts

Simple job and looked after and well maintained with modern pad material, they'll be fine

[Dearg1275]

Painting. If done in two halves carefully mask the joint surfaces. It’s easier to do the fiddly bits this way. If painting once assembled you do get the benefit of sealing the joint area from the elements. I paint the pad slots but make it just a light coating - no heavy build up.

Torque 37 to 38 nm (about 28ftlb). I haven’t seen any trace of locking compound on the old bolts I have removed but can’t see the harm in a small dab in the female thread so that it doesn’t spread onto the mating surfaces of the two halves.

D

[gs.davies]

Gary......, please don't listen to the doomsters who continually slag off the little and much loved Cooper 7" brakes. As a bit part, inexperienced engineering grad from the early 70's I despair when I hear some of the horse sh.., er..., manure repeatedly repeated about thee brakes....

Haha, well, I'm also using the self exploding, smoky, powerless, non revving 1098, AND all atop a wand box with it's terrible gear selection... doomsayers may protest, but these ears are deaf to it!

Good point about the oven too - I have some VHT paint, but it's white labelled so says nothing about baking and temperatures (I have an oven in the garage which was bought to heat up the transfer case to enable a bearing change, I'd be glad to get more use out of it). I'm guessing somewhere around 150 degrees C or so?

Dearg1275, thanks for the tip on the torque settings. I do have new bolts, but presume the old ones simply relied on the spring washer to keep them done up. I think I'll try the sem-lock that Peter suggests, having them separate wouldn't end well I don't imagine..!

[Peter Laidler]

Please don't doubt the ability of spring washers to retain bolts Gary. If BSF/W and UNF/C bolts were fully retained by spring washers throughout the Centurion and Chieftain tanks that vibrated like demented kango hammers, I'm sure that they'll cope with loading of the calipers.

[mk1]

My choices would be & for that matter have been:

- I'm going to paint them, is it best to wait until they're assembled before paining them, or should I do the caliper halves while they're apart?
I paint the whole thing once they are back together, masking off only the bleed nipple & pistons.

- Does the section that the pads run in get painted too?
Yes, everything.

- What torque setting should the bolt be done up to?
around 40 ft/lb same as any other 3/8UNF Bolt.

- Should there be loctite on those threads?
I do use loctite.

[Peter Laidler]

Mmmmmmm the question of thread lockers is questionable in this instance because those calipers get pretty damn hot and heat will break down some locktite. The calipers ain't going to get hot enough to break down some thread-lock. But it's the other perma-lock stuff that's the problem - eventually - as we used to say.

Good question Gary

[mk1]

Not a bad point re temperature.

However, I have never seen an original S calliper with a spring washer on the bolts that connect the two halves.

The early 997 callipers had lock washers, but never anything on the S ones.

s-callipers.jpg

[GraemeC]

All the S callipers I have stripped have had a slug of nylon in the bolt, perpendicular to the thread - sort of a male Nylok I suppose.

Like this:
https://www.ndindustries.com/products/i ... d-pell-it/

[Dearg1275]

I also have not seen spring washers used on the clamping bolts.

This from Minispares.

http://www.minispares.com/product/Class ... o%20search

This fitting advice from 920E the successor company to AP Lockheed. Note the torque requirement.

1AFE11C3-8C63-4745-9F78-91645E044468.jpeg

I don’t see any sign of a locking compound on the bolts.

1187054C-0361-4E15-A158-83CFBD8D2A4B.jpeg

However in the Minispares illustration there does appear to be a dab.

75CAD907-ED39-40AC-A760-D715ABF9EF8C.png

D

[mk1]

38nm = 28 ft/lbs

[gs.davies]

Here is one of the calipers - they both have spring washers. maybe the 7 inch are different the 7.5?

45F60D7D-BB9C-4A4C-92BA-91B7D77B6F94.jpeg

[Peter Laidler]

All GOOD advice and good input too. The question of lock washers did get me thinking. Not on my S but have just rebuilt a set for Clever Trevors '66 998 and they're on them. Won't do any harm.

Don't forget to slather the seals and pistons red rubber grease if you're not going to use the calipers soon

[Dearg1275]

Lock washers. It all depends on the quality of the lock washers. Unless you know they have been made to a recognised standard you are probably better off without. I have bought and thrown away lock washers so soft that they splay at recommended torque and do not recover when the bolt or nut is released. Frightening to think of a brake component relying on such a piece of rubbish. And if you have bought nuts and bolts from the same source don’t trust those either!

D

[gs.davies]

I just looked back at the invoices for the parts I bought (which given the glacial pace of my rebuild was some time ago now..!)

https://www.somerfordmini.co.uk/bolt-ca ... orque-conv

So, this says to use loctite.