rebuilding front brake calipers

[sp53]

I was rebuilding front brake calipers on a tr3 and used a little bit of Rust Mort (phosphoric acid) to clean out that little rubber grove that the boot goes into. The product worked fine; however, I am concerned about possible residue that might be left over. Does any know if that would be a problem? I plan to use some of that red rubber grease and figured it would dilute any possible problems or if the slight amount of acid residue would even have an effect on the rubber. In addition, does anybody have any tips on putting that little rubber boot ring in the grove.

George

 

[Camping57]

Put a little bit of baking soda and water mix into the groove. Putting the red grease over acid won't neutralize it; it will just trap the acid under the red grease (not a good thing). Any type of product that is a mild base will take care of the acid residue.

 

[Alan_Myers]

Hi George,

One procedure is to wash the inside of the parts with clean brake fluid, which also provides some lubrication, so there are no concerns about compatibility. However that's nasty stuff and if the job is done in advance and the car or just the parts sit unused for a while, traces of brake fluid quickly cause surface corrosion (not to mention the damage it does on exterior parts/paint).

So, instead of brake fluid, I coat everthing very thinly with Raybestos Brake Lubrication oil.

For cleaning, I use spray cans of disc brake cleaner a lot. It dries very quickly and leaves no residue. It's a superb de-greaser and will even remove old paint. Work outdoors with it, if at all possible, and wear gloves.

I do think it's a good idea to first do as already has been suggested, neutralize that acid. Just be sure there is no grit of any kind left behind inside the caliper.

There are some tricks to getting the rubber boot to pop into place, but let's take a step backward, first.... The pistons in particular need to be in good shape. They were originally chromed steel and the plating is prone to flaking. Any flaking can be a problem and send bits into the brake system where it's hazardous. Especially if any flaking has happened on the sides of the piston, where it rubs against and can damage the rubber seal in the caliper, the piston must be replaced. There are upgrade stainless steel pistons available that might be a very good idea for low mileage cars. (Daily driving is actually good for things like brake systems, lubrication, mild steel exhaust, etc. Cars that sit for longer periods might see problems.)

Installing the piston and it's seals can be a bit tricky, sort of like the proverbial greased pig. Here's what works for me (eventually):

First install the inner seal in the caliper, with a bit of brake lubricating oil on the surface the piston needs to slide past. Then install the outer rubber boot/secondary seal, into the caliper groove. Be sure it seats all the way into its groove and put some of that brake oil on the lip. Gently stretch the rubber lip a little with your fingers.

Next hold the piston squarely against the rubber boot. At this point, use gentle, low pressure air blown into the bleeder of the caliper to "pop" the rubber boot around the piston. I also use a dull edged tool I made from brazing rod, that's sometimes needed to start the piston into the boot. Continue to be very careful not to damage, dislodge or tear the outer boot at the same time the piston is being pressed into place, keeping it square so that it doesn't dislodge either the outer or inner rubber seals.

To accomplish this, three or four hands would be useful at times!

Also, you need to seal up the opposite piston in the caliper temporarily. If there are no piston/seals installed yet, I use a small piece of sheet rubber bought at a local hardware store, along with a flat piece of metal (actually a wide paint scraper) and a c-clamp.

If the opposite piston and seals have already been installed, I use the same flat piece of metal and c-clamp to keep it in place and prevent it from popping out while I install the other side. Be careful not to overtighten the c-clamp. Sometimes it helps to use a piece of wood shim to protect the piston and caliper surfaces.

Once the piston is smoothly and squarely started into the bore and the outer boot seal is snugly stretched around it, some hand or thumb pressure should be all that's necessary to push the piston the rest of the way in. As it nears the bottom, the lip on the rubber dust boot should be engaged in the slot on the rim of the piston.

Now that it's fully installed, you should be able to move the piston in and out pretty easily. There is no good way to get a grip on it to pull it out, so a little compressed air might be needed to push it out slightly (very gently, you don't want to pop it all the way out or blow the dust boot out of the grooves), and hand pressure can push it back into the caliper. If it's not easily moved, probably the inner/primary rubber seal is out of its groove and is interfering with the piston movement and/or the rubber dust boot lip/outer secondary seal is dislodged from the groove in the caliper.

Brakes are a safety critical item and *must* be done right and work every time. Not knowing your skill and experience, all I can say is be very careful and certain they are working 100% when you are done with this project.

 

[sp53]

Thank you Alan that is a very informative explanation of caliper rebuilding; I will surely utilize much of it. I like the oil idea because it will probably take another couple of years to get this running. I have a nice driver tr3 and I work on this one for a hobby.
George

 

[IKE]

Alan
I've been reading posts on installing the dust boots on my 1960 TR3. I like what you offer but have come up short when working to get the small lip into the groove. I'm beginning to think I may have bad parts. I ordered them sometime back from Moss. The only success I have had is to place the boot onto the piston and try to forse it down along the edge of the piston into the groove.

I upgraded to stainless pistons as well.

Any more suggestions or places to check.

Thanks

Don Eichner
Ames, Iowa

 

[Geo Hahn]

Don - I have always had success using air pressure as described above by Alan so I don't really have a Plan B, but I'll offer some comments.

The only success I have had is to place the boot onto the piston and try to forse it down along the edge of the piston...

I don't care much for that notion as the risk of damage seems greater. To make the air pressure method work you really need everything lubed up well - also the tool Alan describes is critical - I made mine out of a length of 12ga copper wire (house wiring) with a length looped to make a handle. I formed the tip into a little hook (like a button hook) and rounded the end so there was no chance it would damage the boot.

My wife runs the air gun so I have both hands free to manipulate the hook and the bits. Once it is all set up (boot installed in the groove inside the caliper, seal installed in the caliper, opposite opening blocked, air line connected, everything lubed & the piston perched on top of the boot -- she gives it air (low pressure) and I coax the inflated boot over the edge. The job take about 5 seconds (once you get the hang of it). Once the boot it over the piston then it is a simple matter to press the piston through the seal and home.

I wish I had a photo of the set-up (maybe next time) as I wonder if there is something amiss with how you're trying to do it.

 

[TRMark]

I put a section of tubing inside the bellows to make them easier to handle and slip into grooves.

 

[IKE]

Geo
Thanks for the quick response. Last night i figured out the problem. I pulled out the old brake parts and looked at the seal/dust boot. The new seal/dust boot had a much larger OD on the small "L" area. Measuring a rubber part is not easy but the difference was dramatic. I was truing to put 8# of stuff in a 5# sack.

The old seal/dust boots look pretty good. I was able to assemble them into the piston/caliper without problem.
I thought I bought the seal kit from moss, but the number on the bag (50965. ADFHG) does not match anything in moss, VB or the roaster factory. The bag even says made in England.

The kit also includes a very nice rolled ring with a beveled cut which fits nicely into the upper groove. So nice that I'm having a difficult time getting it out. Not sure what it really for.

I will proceed to reassemble with the old seals. They look so good that they can't be very old.

I did take the calipers apart before reading not to do that. Any advice on reassembly? Torques?
I think I can get Viton orings or Teflon coated rings for the seals.

At least I seem to be on the right road to assembly.

Ike

 

[CJD]

George? Where did Steve go?

 

[mikephillips]

I've used the same Girling calipers on a different make car and have always disassembled them. Easier to get everything cleaned out that way. I've used a Dremel tool with a small cutoff wheel to clen out the groove for the dust seal, gets all the old dirt, rust and old rubber bits out and it's practically impossible to cut the cast iron of the body. I use 45lbs for the smaller bolt and 50lbs for the larger ones when reassembling and never had an issue.