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TR2/3/3A tr3 front caliper cleaning

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sp53

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Hi all, I remember reading a post from one of the members that rebuilt front brake calipers professional and wanted to know how they clean them. Do they class bead, or hot tank, or acid dip, or ….Anyways, I guess my question to all is how do you clean a front brake caliper on an early tr3. It is the one with the plug, but I thinking I might leave the plug alone because, I am afraid, I might have trouble resealing it.

Sp53
 
I work for an automotive parts rebuilder, and one of the items we handle is brake calipers. We clean most of our calipers with heat. 750-800 deg. F. in an oven for about four hours. After that, they are steel shot blasted and dipped into a rust preventative that is compatible with brake fluid. That is beyond what the home mechanic could do.

If you have access to glass beading equipment, that is the best alternative. The calipers themselves can be de-greased with mineral spirits followed by a cleaning with some of that Brake-Clean stuff to get rid of any residue. If the calipers aren't that dirty, the Brake-Clean stuff might do the job of de-greasing. The glass beading will get into the all important bore area. Specifically the square O-ring groove and boot groove. The seal groove after cleaning should look smooth. Any obvious pits will cause problems. My past experience shows that these grooves hold up very well. The boot groove is thin, and all the crud must be removed, or it will be difficult to get the new boot in. Again, glass beading cleans this out real good. The bore itself is not an issue, as the square O-ring seals on the exterior of the piston. Just so long as the bore is clean. If there is any pitting on the pistons, they will have to be replaced. You cannot accept anything other then a perfect finish...that's where the seal seals.

Now for the threaded plug on the early calipers. There is an O-ring that seals it, and it is threaded in. When I did mine, I took out the plug, and just used an appropriate sized O-ring I got from work. Any EPDM O-ring that's the same size as what's in there will work. I would imagine, that there are a mess of those calipers out there that have been rebuilt a half a dozen times and never had that plug out. Besides, who has a screwdriver that big?? /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

So, why is that plug there??? I thought about it for awhile and came to a conclusion that I feel is correct. Anybody have any thoughts on that??
 
martx-5 said:
So, why is that plug there??? I thought about it for awhile and came to a conclusion that I feel is correct. Anybody have any thoughts on that??
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That's easy. The housing is a single casting, so the plugged hole is the access to machine the bores.

The later 'split' calipers were two separate castings, so no more plug.

Do you really use steel shot on the bores ? I would think that would bung up the sharp corners on the grooves, but obviously I've never tried it. Glass beads should be fine tho.

Yeah, I've never had those plugs out of my calipers. But I also quit having to rebuild them when I switched to DOT 5, so maybe they've only been done a dozen times or so /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
TR3driver said:
Do you really use steel shot on the bores ? I would think that would bung up the sharp corners on the grooves, but obviously I've never tried it.
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The steel shot we use is size S-110, (0.011") which is next to the smallest available. We process a barrel of parts in 6-8 minutes in a Wheelabrator type machine. Except for the darker color (glass beading imparts a whitish tinge), the result is virtually the same as glass beading. We also shot blast all of out aluminium parts using the same size shot with no ill effects.

And yes, there is no other way to machine those one piece calipers without having a hole in the back of the casting. BTW, that is the only caliper I have ever seen with such an arrangement.
 
Hi Art and thanks much for your input. Do you think it would be ok to use 70-weight silica sand for the medium when I blast them or would the sand cause a problem? And do you have any clever ideas for someone who does not have that big of screw driver.

Sp53
 
I really don't know what you mean by 70-weight silica sand, but if you are refering to screen size or Mil Spec #, then that will be fine. Any type of fine glass bead will be OK. Glass bead polishes more then it abrades. You just want to blast off all the rust and crud.

Unless the threaded plug is leaking, just let it be. Also, take off the cross-over tube and bleeder, as you will get sand in the passageways, and it will be easier to blow out without those items in. Besides, you want to clean those areas also.
 
martx-5 said:
BTW, that is the only caliper I have ever seen with such an arrangement.
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Me too. But then, I don't believe I've ever seen another caliper designed in the mid 50's either. American cars didn't get them until the 60's, when the early TR3 caliper was already obsoleted by the later split caliper.

I would guess the early design was tough to machine, especially accurately cutting the seal groove in the inner bore. Even with an automatic boring head, you'd have to reset it every time the tool wore a bit; and probably switch tools twice for every caliper.
 
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