MGB: Rebuilt my brakes, but...

Went to my mechanic today and he walked me through rebuilding my front brakes - how to pop the cylinders, what to clean, what to replace, what to check for and so on. So far, so good.

Came home after work and rebuilt my brakes - felt really good, but...

I noticed that the cylinders aren't symmetrical. About 1/3 of the leading edge is recessed about 1/16". (see picture) Does this recessed area go toward the hub, away from the hub, or does it matter? I can't see that this area lines up with anything in particular on the brake pads and I had all four apart before I thought about it... Which way do they go? Please enlighten me.

An extra 10 bonus points if you can tell me the purpose of the recessed area.

As always, thanks in advance.

The recessed portion of the caliper piston goes towards the hub (Haynes Manual). The recess was supposedly for anti-squeal purposes.

I had to look this up myself a couple of months ago.

Cheers,

Glen

Bob,

Glen has allready explaind anything you asked, but do yourself a favour: Buy new bridge bolts and new rubber gaskets.
The bolts are of a stretch type and must not be reused! Reusing the rubber ring, once seated, might become a problem sooner or later.
Retorque the bolts to the specs given in the manual!

Ralph

Ralph (or anyone else) - What are bridge bolts? I'm not familiar with that term.

Are those the bolts that hold the two halves of the brake assembly together, or are they the bolts that hold the brake assembly to the swivel axle?

I'm also not familiar with stretch bolts. Are those used anywhere else in the car I should be aware of?

Thanks in advance.

They're the bolts that hold the halves together. Make sure you get the correct grade bolts otherwise it could be even worse than reusing the old originals.

Timely post... for me anyway. I'm going to dive into the brakes pretty soon and have been studying the Haynes book for several days now. I saw the schematic for that cylinder and thought I had it envisioned properly but seeing your pictures cements the image for me.

Thanks,
Kevin

This is one of those areas that you really should know what you're doing before you dive in. Definitely get a new fluid channel seal, and don't go shopping at the Home Depot for an O-ring. Order the right part. The bolts can be reused, they do not get torqued to the limits of that size bolt. All bolts stretch, thats how they hold their torque, these are not torque to yield like some modern cylinder head bolts for example. The reason not to reuse them is because they came new with a threadlocker applied. Clean up the old bolts with a die and use fresh threadlocker with the proper torque.

The picture below is of NOS Lockheeed repair parts. Note the red stuff on the bolt threads - its threadlocker. If you buy new bolts, they DO NOT COME WITH THAT!

What am I missing? I thought you weren't supposed to separate the caliper halves unless you had the knowledge and tools/equipment to put them back together...

I didn't find it that difficult -

Work on one side at a time and keep the parts together:

Remove the clips and cotter pins holding in the pads
Remove pads
Unbolt sections
Remove small o-ring that is between the two halves
Remove cylinder using compressed air or specific wrench designed for the purpose
Remove the two rubber rings in the cylinder chamber (but not the metal ring in between them)
Clean all metal parts thoroughly
Check cylinder and cylinder walls for rust
Don't reuse a rusty cylinder - replace it.
LIGHT rust on the cylinder walls can be removed using very fine sandpaper
Where the two halves of the caliper will meet, lightly file the mating surface to ensure there are no burrs
Clean everything well again
Put hydraulic lube or brake fluid in the groove for the inner-most rubber seal (it is square in cross section)
Carefully install the inner rubber seal, making sure it seats well and flat all around
Put hydraulic lube or brake fluid in the groove for the dust seal (the outer-most rubber seal - it is U-shaped in cross section)
Carefully install the inner rubber seal, making sure it seats well and flat all around
Lightly coat the cylinder with brake fluid or hydraulic lube and push it into place (with the indented section facing toward where the hub will be)
Replace the O-ring with a ring DESIGNED FOR THAT PURPOSE - they are not generic, and they don't usually come in a rebuild kit - you have to buy them separately. Use the wrong ring and your brakes WILL LEAK.
Repeat the process with the other side of the caliper
Reassemble the two sides
Use new bridge bolts if you have them - otherwise you can reuse the old bolts (according to my mechanic) if they are clean and in good shape BUT make sure you use lock-tite on them and torque them to the proper specs. If you are racing your car, definitely replace the bolts.
Paint the calipers if you want, but mask off the bleeder valve and the cylinder area
Install the pads in the reverse order you took them off

Okay - now you guys that really know what you're doing - tell me what I missed. I haven't installed them yet, so it's not too late to correct my mistakes.

[quote=GlenP]
What am I missing? I thought you weren't supposed to separate the caliper halves unless you had the knowledge and tools/equipment to put them back together...[/quote]

Some find it easier to take it apart, some find it easier to leave it together. It all depends on what tools you have. As long as you have a way to install the new metal retaining ring that holds the dust seal in, I think it's very easy and faster to leave them together. Just personal preferance.