Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

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Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

Post  David2010 on Mon Oct 15, 2012 10:14 pm


Am in the middle of a brake overhaul and am puzzled to have discovered some (small) play in each of the Caliper's pistons.
The pistons are Minisports stainless steel version - fitted new in October 2010.
The Calipers are Lockheed 7.5" as fitted to the Mini Cooper S.
The question is - how much free play should there be for each piston within its caliper ? Presumably there has to be some free play ?
And....does anyone have the manufacturer's official measurements for ; -
(a) The Piston - its correct diameter &/or the permitted tolerances plus and minus ?
(b) The Caliper - the internal diameter of the "bores" &/or the permitted tolerances plus and minus ?
David2010.
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Re: Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

Post  Big_Al_Smith on Tue Oct 16, 2012 2:14 am

beyond my expertise i'm afraid...anyone?
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Manufacturer's Recommended Tolerances for 7.5" Lockheed Calipers :

Post  David2010 on Tue Oct 16, 2012 4:52 pm


I brought one of my dismantled calipers complete with its stainless steel pistons to two of our most highly regarded Irish Mini experts.
Both agreed that I need not worry & that the very slight amount of clearance evident when the pistons are placed in their bores in the
caliper are " quite normal ".
So will now proceed with reassembly of calipers using Minisport caliper seal kits.
Will advise on the outcome in this forum - soon as I can.

David2010
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Re: Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

Post  catmint on Wed Oct 17, 2012 11:16 pm

Hi David

I seem to recall that they are reasonably loose in the bore, though it is a few years since I had a set apart. The big problem is getting them back in past the seals, which can be a real pain. Just a suggestion (sorry if you already know this) that came to me through a major restorer is to assemble the pistons using brake grease (not fluid), not only does it make things easier to go together, but there can be an issue with dry seals pulling the pistons back after pressure to give the effect of a soft pedal

Hows the engine doing now ?

Gordon

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Manufacture's recommended tolerances or 7.5" Lockheed Caliper Pistons.

Post  David2010 on Thu Oct 18, 2012 1:29 am


Yes Gordon one of Ireland's top Mini specialists - Lloyd Hutchnison - examined one of my Caliper/Piston asemblies when split.
He saw no difficuty in the slight free play between the caliper piston & its bore - this had been my biggest worry.
He cautioned me, however, on two points to be taken into account before re-assembly , namely ;-

(1) The importance of the small square-shaped o-ring seal inside each caliper - ideally these should be replaced but....
the Minisport Caliper O/Haul Kits contain a set of piston seals only - no o-rings.( Lloyd could only source these with difficulty once ).
(2) Similar to your advice - to use grease in the bores to faciitate reassembly and the positioning of the various seals.
He recommended that I use " rubber grease " (what's that you say ? - search me) but Lloyd says it is available commercially.

So you see it is not straight forward - is anything 1965 - Mini related ever.
If you or any of our readers know of a source for either the o-rings and/or the rubber grease - can't wait to hear about it.
Oh yes and the engine - running well especially up hill - very strong. No oil leakage whatsoever (!) but still using some oil - 250/pint.
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Re: Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

Post  catmint on Thu Oct 18, 2012 9:09 am

Hi

Mini spares sell the seals quite cheaply

COOPER S 7.5" CALIPER INNER RUBBER SEAL link

the last lot of grease I bought was from the local motor factors (unipart). If you get stuck I can see if they still sell it and get you a tube.

Glad the engine is working Ok, shame about the oil use though

Gordon

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MANUFACTURER'S RECOMMENDED TOLERANCES FOR 7.5" CALIPERS :

Post  David2010 on Sat Oct 27, 2012 12:04 am


Good news - for a change !
Got the car back on the road last night and did about 30 miles or so to-day.
The Caliper / Piston / Piston Bore size question having been answered by Ireland's top Mini mechanic - Lloyd Hutchinson - reassembly
went ahead and the overhauled calipers were reattached to their respective hubs without any further " drama ".
The only casualty sadly was my only 10% worn " Green Stuff " brake pads. They had started to delaminate (brake pad linings parting company
with their steel backing plates) due to brake fluid contamination. New brake pads were of course fitted to identical specification - EBC Fast
Road Cooper S - 7.5" Green Stuff (Part No.EBCDP2102 From Mini Sport @ GBP 29.84 + 20%VAT) .

Another (unrelated) problem was also corrected to-day. Since doing the Parade Laps at the Dunboyne Motor Sport Festival last month,
a persistent front end noise has become louder over the past couple of weeks. Coming from the front it got so loud last night that a failed
front offside wheel bearing was suspected. This proved to be the correct diagnosis. My friend Paul assisted me for this repair and he
showed me a new (for me) trick of the trade. When the hub had been cleared of its failed bearing, Paul using a hammer and small chisel
put several grooves inside the hub - about four or five in all. The object ? to dissuade the new bearing of any tendency to revolve
in its entirety - instead of as it should within its race. Silence now prevails - no more not so funny noises from the front.

David2010.
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Re: Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

Post  superworm on Mon Dec 17, 2012 11:56 pm

The correct grease to use on your brake seal parts is Castrol Red Rubber Grease... available from SC Parts,etc.....

http://www.scparts.co.uk/index/lang-2/lkz-195/markenid-24/katnr-106/kat_sprache-2/hrubnr-1744/rubrik-5453/functiontpl-virtueller_katalog.tpl,x-a.htm

at a tenner (gulp!) for a 500ml ca.

I once bought some in a tube for much less from a Brake parts Factor.......this is the stuff to use
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Re: Manufacturer's Recommended Tolerance for Lockheed 7.5" Caliper Pistons :

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