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MG TD TF 1500 - Brake cylinder inspection advice needed

After reading all 1000+ posts in the wonderful archives about brake cylinders I'm overwhelmed. But the BBS seems a little quite these days so why not just ask my question fresh:) So here goes:

I'm putting my rolling chasis back together and have all new brake parts (shoes, flex lines, pipes, copper washers and cylinder rebuild kits from Moss). I'm now taking the front cylinders apart to inspect and replace rubber parts prior to converting to Dot 5. (I am aware of all the pros and cons out there on that topic!)

Question #1-front piston removal: One piston fell out in my hand. The other 3 will not budge even with 80lbs of air pumped in! (I don't have a spare grease fitting like Larry S. would suggest here, or I would try that method.) I had to put the cylinder in a vise and use grips to remove - picture attached. If I have to use this much force how in the world have my brakes been working? I have previously confirmed while on jacks that all 4 wheels indeed stop via brake pedal when spun however.

Question #2-piston & cylinder condition. The picture shows the parts cleaned up with brake cleaner. Marks on piston are from my grips. What do you all think of the condition? (I would have just ordered new cylinders but $50 a pop is steep!). I put a dab of silicon grease on piston and reassembled. Seems to work as I would expect but then again, I've never done this before.

Are these things safe to use or not? All opinions welcomed! Thanks as usual,


efh Haskell

If the pitting isn't deep, perhaps a bit of honing...?
gblawson(gordon- TD27667)

Ed, the grease fittings are very cheap at most any parts store. Spend the couple of bucks, you'll never regret it. Your marks on the piston are in a very non-critical area. No sweat. IMHO, clean 'em up, do some honing to clean up the surfaces and install the rebuild kits. Reinstall the cylinder, bleed it, apply some pressure and look for leaking. Good luck. Bud
Bud Krueger (TD10855)

Ed, Seem to remember reading somewhere that you can attach the grease gun fitting right on to the brake bleed nipple, if you just grind a little off the perimeter of the bulb end to make it fit. You could also try depressing the piston back into the cylinder somewhat with a C-clamp, just to get things moving.
Since you are changing to silicone brake fluid it might be better to get the cylinders sleeved in stainless steal, rather than trying to recondition the bores, by honing, as Dot5 is known to seep through the slightest imperfections. Hope this helps. Phil
Phil Atrill

Ed if you get another one stuck like that just put the assembly in boiling water for about 5 minutes. Don't take the vice to them lest you do them fatal damage. Hone the bore till there is no sign of pitting and you should be good to go. Sand the piston walls smooth so yo don't score the walls.
LaVerne Downey

Ed, the non-greasefitting approach is finally popping into my ancient mind. The brakeline fitting is a standard thread. In your goody-box you have a bolt with the same thread. Find one. Push grease into the cylinder through the brakeline fitting. Then use the bolt to force more grease into the cylinder. Eventually you'll see the piston start to ease out of the cylinder. This really works. Believe me. Somewhere in my archives I have a photo sequence that shows it. I'll see if I can find it. Bud
Bud Krueger (TD10855)

Here's an image of the grease/bolt technique. The grease gun was used to squirt grease into the fitting. The bolt was then tightened down to force the grease into the cylinder. A few cycles of this and the piston slides right out.

Bud Krueger (TD10855)

Bud, hold that thought! Sounds like a good idea but LaVerne nailed it! 60 seconds in boiling water and those pistons slid right out! Thanks dude!!! No tools needed - just an old pot.

Okay, I've watched some YouTubes showing use of a simple flex honing tool. I'm a little unclear on what the finished product is supposed to look like though -smooth or cross-hatched? "Sand the piston's smooth"? What grit are you talking about here LaVerne? Should the end result between piston and cylinder be a sliding fit, real tight, or loose or what?
efh Haskell

I knew the boiling water would work Ed. I tried the grease, compressed air and the vise and channel locks on the first cylinder I removed on the TF and none of those got the piston loose. The boiling water did the trick. I wound up replacing all the cylinders because the corrosion was too severe.

I'm no expert but I'm just looking to get the walls smooth without any pits. If the pits require you to remove a great deal of wall surface (deep pitting) then you should consider new cylinders or have the old ones sleeved. The bore will become to large for the new seals to work. The piston itself, I'd be looking to get got of the sharp surfaces you put in there with the vice. The motion of sliding back and forth will possibly score the wall and then you have a leaking cylinder. Knock it down with some 220 and finish it out with 400-600 grit. Clean everything spottless when your done. You don't want to leave any grit to wear the bore rubbers.
LaVerne Downey

The cylinder bore picture seems to show a bunch of linear scratches - those must be polished away also. Remember with the single circuit braking system any failure anywhere leads to total brake loss. Also, with the price of shoes, you sure don't want to leak fluid on them. While not cheap, the price of the new front cylinders is about half what it was a few years ago. George
George Butz

ed, i second what george says. i am very conservative about what i judge to be "serviceable" on a single circuit, drum brake system. i had to resort to manual braking one time in traffic..enough to convince me the brake system is no place to take a chance. regards, tom
tom peterson

The surface of the cylinder where the actual seal rides/slides should be polished - not crosshatched like an engine piston cylinder where metal to metal is encountered. If the rubber seal rides on a rough surface it will be useless in no time.

Brain, thanks. That clears that up. Can you or anyone else recommend the correct honing tool? There are lots out there on the web. The one I saw was flixible and expanded to fit any size cylinder and went in your electric drill but I think it produced x-hatching??
efh Haskell

Well, I have progressively worked the surface down to a fair polish by first using a "brake Cylinder hone" as you described then by wrapping progressively finer grit wet-dry sandpapers around the hone stones-and a lubricant like fine, light oil or even water, get the surface down to a say 2,000 grit or finer then use a metal polish or rubbing compound on cloth to finish up. Rinse and clean VERY well- no grit must remain. Repeat as necessary to get a satisfactory polish.

Hones are designed to remove material to get 'through' the pitting...then like any sanding job, you just keep using finer grades until you are at the polishing stage...
gblawson(gordon- TD27667)

This thread was discussed between 20/06/2010 and 22/06/2010

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