Brake Piston Removal.

jonboy

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Local time
Today, 06:04
Joined
Jan 22, 2021
Messages
10
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Age
67
Location
portugal
My Ride
T140v 1977
I cant use the simple action of the hydraulics to push the pistons out as the rebuild kits haven't arrived yet and I thought I'd get on with the stripdown anyway. The master cylinder is seized but i havent started that yet, and using air I pushed one piston out of the caliper and the other is not seized but only about 2mm of the piston showing, and its in the main body half.
Can't get grips on it or maybe just,.. but was scared about damaging the edge, though it isn't going to be inside the cylinder. before I drill a hole in the caliper and push the piston out, then seal one way or another, any tips on how to pull the piston out?
 
Ha ! Result!!. onto the drill press, 2mm pilot then 5.5 followed by 6mm x 1 tap. the tap actually gently pushed the piston out. I'll blank the hole with a 6mm panhead , copper washer and loctite blue. not purist, but hey it took me less than ten minutes after spending all afternoon buggering about with no success.

Watch this space for the woes of dismantling the master cylinder.....
 
using air I pushed one piston out of the caliper and the other is not seized but only about 2mm of the piston showing, and its in the main body half.
onto the drill press, 2mm pilot then 5.5 followed by 6mm x 1 tap. the tap actually gently pushed the piston out. I'll blank the hole with a 6mm panhead , copper washer and loctite blue.
Ummm ... if "using air I pushed one piston out of the caliper", why didn't you just do the same to the other piston? One piston always comes out first, move that one until it is nearly out of the caliper, hold it in the caliper with a small clamp, "using air ... push [the other] piston out of the caliper" then release the clamped one and pull it out.

Sometimes easy access to drill presses, lathes, etc. is as bad for old parts as big hammers and pipe wrenches ...
 
The master cylinder is seized
The first thing to remove is the grub screw in the cast mounting. Originals on your bike were No.10 UNF, only 1980-on (a replacement on your bike) are M3. If it is messed up and you use spark erosion to remove the remains, ime the spark erosion bath helps to remove corrosion between master cylinder and mounting casting.

The flats at the small end of the master cylinder are 0.6"AF as standard, which is the 3/8" British Standard or 5/16" Whitworth spanner size, a 15 mm. AF open-ender is a tight fit, as is a good quality 12" adjustable ...

Unless the threaded end of the master cylinder was left open or the reservoir was left off, you will probably find just the lever/rod end of the piston is seized in the cylinder. Once the piston is extracted, while any damage to the cylinder's surface likely makes it scrap, an undamaged original piston can be reused inside a new stainless cylinder.

If you intend to try and save the original cylinder, while the unthreaded part is 1" OD, the thread is M25 x 1.0.

Whether you buy just a new stainless cylinder or a complete master cylinder and mounting, check the ID to ensure especially the vent holes to the reservoir have absolutely no burrs whatsoever, maker L.F. Harris is a little careless about this, trying to bleed an assembled brake system with a damaged master cylinder seal is frustrating ...

only about 2mm of the piston showing,
Can't get grips on it or maybe just,.. but was scared about damaging the edge, though it isn't going to be inside the cylinder.
I replace pistons with either stainless or anodised aluminium as a matter of course, both types are easily available. If you have a lathe, it is cheap to turn stainless replacements from round bar.
 
Good morning Rudie, and Bom dia Todos.

I'd already split the two halves when I used the air to get one piston out . and it slowly crept out until BAM! and shot out across the workshop. In retrospect I should have put it back in a bit,, reassembled the caliper and done the same but the trying to get the air in the main caliper half wasn't successful and so I went down the above mentioned route.
The grub screw doesn't seem to be there......In my experience dissimilar metals are always a B' trd to get apart especially ally and steel, and those fine threads.
Soaking in a 50 50 acetone and ATF helps and a little heat,
Hey ho back to the workshop in a bit...
 
Bom dia para você também, Jon,
already split the two halves when I used the air to get one piston out . and it slowly crept out until BAM! and shot out across the workshop.
If you ever have to the job again, wrap the caliper in an old towel to catch the piston.

The grub screw doesn't seem to be there.
(y)

I always fit stainless, with a smear of grease on the threads.

In my experience dissimilar metals are always a B' trd to get apart
Yes, had the cylinders been assembled into the mountings with grease ... :(
 
Well, steep learning curve, as I do have to do the job again as the rear brake also doesn't work.

Also the grub screw was broken off in the cylinder and as I finally managed to unscrew the cylinder from the handlebar clamp a tiny raggedy pice has nicely removed .the threads as it came out. :(
But the inside of the master cylinder is ok as far as I can tell, but if the mess of the innards is anything to go by maybe its a whole new master cylinder as there's not going to be the pieces in the rebuild kit , I fear. The plastic check valve at the end of the piston assy is for the bin and the spring retainer likewise... .

More to come I'm sure , but still waiting for the repair kits to come so I can see exactly what Im getting.
 
waiting for the repair kits to come so I can see exactly what Im getting.
If you bought the AP Racing repair kit (not the cheapest), you get everything inside the master cylinder except the piston and spring, plus the special fat O-ring that seals between the reservoir and the outside of the master cylinder.

"AP" was Automotive Products, that supplied several well known 'brands' (e.g. Lockheed brakes, Borg & Beck clutches) to the British motor industry, AP Racing was originally another part but was always the part that had all the information on the Lockheed disc brakes supplied to Triumph. When AP folded and the various 'brands' were sold off, 'Lockheed' went to one buyer and AP Racing became a separate company.
 
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