Re: 81 R65 Brake Parts/alternatives

[Bob_Roller]

The BMW shop manual states a diameter for the  ATE wheel cylinder of : 1.417 in., the ATE #1 piston has a diameter of 1.3365 in.

That would give you a .040 in. clearance between the piston and caliper bore, does that sound about right .

[Justin B.]

.040 sounds a bit loose, but I really don't remember.  I need to troll e-Bay for an example of each.  I'd also like to get a "ratty" brake cylinder as I really would like to experiment with sleeving a caliper and master cylinder...

[Bob_Roller]

I contacted a repair shop that advertises in Hemming's auto   trader,White Post Restorations, they specialize in resleeving master and wheel cylinders.

In 1992, when I found my master cylinder leaking on the R65, corrosion and pitting in the bore area, I was quoted a price of around $100 to install a bronze sleeve, refinish the exterior, with powder coat, and replace the rubber seals on the piston .

Cost for an OEM master cylinder and reservoir at the time was about $125, so I didn't go ahead with the rebuild .

So there is an alternative to replacing brake components, seeing as how today, the prices for a master cylinder, and calipers, are getting into the overpriced area .

http://www.whitepost.com/

[Justin B.]

I don't want to have it done but toying with the idea of trying it myself but don't want to risk goofing up a "good" part...

[Altritter]

From Bob_Roller: <I contacted a repair shop that advertises in Hemming's auto   trader, White Post Restorations, they specialize in resleeving master and wheel cylinders.>

I'd be very interested in what they have to say.

Classic cage collectors probably are quite familiar with White Post Restorations; the company has at least a national, and probably international, reputation for doing like-new  total restorations of cars valued as much as seven digits left of the decimal  (or "comma", as our German members know it). WPR searches worldwide, and if unsuccessful, it reputedly (per enthusiast publications) has both the machinery and the expertise to manufacture to OEM specs just about any unavailable part or body panel needed, so long as the original specifications are available or an existing part can be physically spec'd out).

WPR is located in White Post, Virginia (near Winchester & Front Royal), about 70 miles west of me. An anecdote of a work colleague explains my interest:

My friend was executor of his father's estate about 10 years ago. Seems my friend's father had a 1955 Ford Thunderbird in near-but-not-quite Concours condition. He knew in advance that, alhough super nice, it wasn't a lunatic collector's car, in part because the transmission was 3-speed column shift, rather than a floor shift. My friend contacted WPR for a rough range of the cost of upgrading the 'Bird.

WPR did not give an estimate, but informed him that in order to get on a waiting list (about two years at the time, I think), he would have to pay an up-front cash deposit of about $100K, and sign an agreement to provide additional funds upon demand as the work progressed.    My friend thanked them and looked for a more practical alternative.

[Ed Miller]

The BMW shop manual states a diameter for the  ATE wheel cylinder of : 1.417 in., the ATE #1 piston has a diameter of 1.3365 in.

That would give you a .040 in. clearance between the piston and caliper bore, does that sound about right .

THAT's part of my hesitation, as I don't have my pistons out to measure, and the part that is exposed when you have the pads is the contact area, and is smaller in diameter than the part that goes into the bore, if I remember right.  And I think that outer seal would prevent me from being able to measure the thing in situ.  A friend of mine used to have an R65 and told me about this guy, said the pistons worked.

[Bob_Roller]

Does anybody out there have a brake piston out of their bike, and in possession of a precision measuring device, and reasonably competent in it's usage ??

[Ed Miller]

OK, 36 mm for a measured piston (from a different thread) comes to 1.4173".  (Obviously too many significant digits, but that's what I got from the converter.)  Now where's that guy's web page?

[Bob_Roller]

Ed,

The link is in the Trading section, the diameter that you gave is the same as the BMW manual has for the bore diameter of the caliper, the only piston that is listed that is close, had a diameter less than .001 in. smaller than the caliper bore .

I talked to a co-worker that rebuilds '60's-'70's muscle cars, and he said you want about a .010 in. clearance between the piston and caliper .

So I guess we really need to measure a piston, and then go from there .

I'll bet if someone was to order, say 100 pistons, that the individual cost per piston wouldn't be all that costly .

[Ed Miller]

Here's a copy and paste from an email exchange, just to update the thread:

Ed the dia. in my catalog is for the pistons  A piston that size should have a clearance of .003/.004 depending on appliation
 
Regards
John

----- Original Message -----
From: Ed Miller
Date: Wednesday, June 10, 2009 10:53 am
Subject: RE: piston catalog
To: John Farrell

> Hi John,
>
>
>
> On your flyer, is the diameter listed for our early R65s
> (1.415") the
> actual diameter of the piston, or the diameter of the bore? We can't
> find anybody who has a piston out and the ability to measure it
> accurately. One guy said "36 mm" but I would prefer to see at
> least 3
> significant digits there....
>
>
>
> How much clearance is needed between the piston and the bore?

[Bob_Roller]

So it looks like pistons for our bikes, would be a special order, and probably with a minimum quantity of pistons .

The Motobins price for the part, may be quite close to what it would cost to have them made up here in the US .

[Justin B.]

I haven't wanted to make and sell any pistons until I've had a chance to "field test" mine for a while.  So far, laps around the backyard aren't my idea of proper testing.  If I ever find any sand to finish up my rear wheel I'll tag the Dawg and start a proper test on the pistons.