SG model caliper rebuild

[DominicM]

Brakes are dragging bad on the front. I have to compress the piston everytime I need to move it. I didn't realize how bad they were sticking until I could hardly push it around. When I took it around the block, it won't coast to a stop so I end up stopping at least 6ft from where I want to be. It doesn't help that the clutch is so far out either.

When I compress the piston with it off the disc, it's hard to push in too. I haven't pulled it completely apart but the pistons probably pitted and I've heard you shouldn't sand it down and pop it back in. Has anyone done that or should I just get a new piston and seals?

I can't find a piston that says it's for this exact model but one of them has to work. Would this one work? I read on here that people used it on their bikes but I think theirs was a different model (http://www.xs400.com/forum/showthread.php?t=8719&highlight=caliper+piston). The manual doesn't have measurements of the piston either

http://www.mikesxs.net/product/29-0516.html

I also switched bars from the buckhorns to rd400 stock bars. This makes the MC angled down. How should I go about bleeding the system without all the fluid falling out?

Does anyone know if a new piston and seals will solve the problem or do I basically need to replace most of the brake system (brake line, bleeder, fluid, MC parts, etc) since it's probably all original?

 

[bcware]

New piston, new seals. No sanding. Don't ghetto rig your brakes. The piston and seal is available and not very expensive.

I'm sorry, but what's an SG model? SOHC? DOHC? Maxim? Seca?

I don't know what rd400 bars look like, but you should be able to loosen the master cylinder/brake lever clamping bolt and or handlebar clamps so that the bars/MC can be rotated in such a way that the MC is level.

You should also replace the brake line and pads. Pretty much everything else just needs to be cleaned. Just replace the parts that are malfunctioning or leaking.

 

[DominicM]

its a 1980 or 81 xs 400 special SOHC. SG is different than sh or se, etc etc, and I remember it being identified somewhere as that (probably in the manual).

do you or anyone else know if that xs650 piston will work with this model?

What about one of these:
http://yambits.co.uk/xs400-brake-caliper-piston-stainless-steel-p-32644.html

http://yambits.co.uk/xs400se-brake-caliper-piston-front-p-32642.html

I have new pads ready to be put in when i fix this. I also plan on flushing the brake fluid because it's probably never been changed and most likely contributed to this problem. How much would a SS line put me back?

 

[xschris]

You can measure your piston and see if it the same size as the xs650. Mikesxs lists the size of the ones they sell.

 

[angrybuddha]

Based upon part numbers, of the seal kits as the parts diagram don't list the pistons seperately, I deduce that the pistons are the same diameter, I imagine they are 47mm.

Most xs650's from 77-81 the xs750 D, 2D, E (various years) and xs400 77 -79 all have part number 1J3-W0047-00

80-81 xs400's (except SJ Heritage models) have 2G2-W0047-00

I presume the W0047-00 is the important bit specifying diameter of piston to which the seal fits?

I have a box of xs750 and xs400 caliper bit somewhere so could potentially measure and compare the diameter and depth of piston if you can't?

 

[DominicM]

I can measure it. I was trying to avoid pulling it apart before I had all the parts but it doesn't matter. Just wanted to see if anyone knew from experience.

Does anyone think that a MC rebuild will help? I think I'll at least get the top seal

Thanks to all the replies in helping me sort this out

 

[angrybuddha]

It cant hurt to strip the master cylinder and clean out any gunk. Just be careful not to damage anything and only apply suitable grease, if anything, while rebuilding.

Not sure what you mean by top seal so cant comment?

Do you know the trick about annealing the copper washers on the banjo bolt connections?

 

[motoTrooper]

I rebuilt my calipers with new pistons and seals and it was easy. As far as bleeding it with the different bars, put it on the sidestand and turn the bars left or right and you should be close to level.

 

[DominicM]

angrybuddha,
i mean the diaphragm (the black piece that goes between the cap and the reservoir)

no, i dont know that trick

 

[16VGTIDave]

Find a local shop that can make you a custom braided stainless steel brake line. They should also provide new banjo bolts and copper washers for around $40. Your choice of black or silver fittings, and various colours for the line. I chose all black for my bike.

Take a look at this site for ideas.

 

[angrybuddha]

Ahh ok, if ever re-using a copper washer for either banjo bolts, fuel lines, or sump plugs then you should really anneal them. i.e. make the copper soft again as it goes hard over time and work hardens under compression.

Its really easy to do, just heat them up till they glow red hot, with a blow torch or on a gas cooker hob if you havent anything else, then the important bit is to let them cool them slowly. Do not quench them in water as this hardens them. Just pop them on a block of scrap wood and leave them to cool naturally.

This process is call annealing and makes them soft as new so when you tighten them up they deform as they should and make a good seal.

Many sump plug threads have been ripped out because the copper washer has been re-used, and is old and hard, and so is then over-tightened to stop it leaking and then the threads are stripped.

Sorry for the essay

 

[xschris]

This is good info to have

 

[DominicM]

16VGTIDave,

I will probably get one from Dime City Cycles. They have ones where you pick the length and then get fittings that screw on.

angrybuddha,

This is useful information. I will keep this in mind for the future even if I get new washers. I actually was reading about this in Cafe Racer magazine earlier. They had a head gasket leak on a Norton Commando after a fresh rebuild. The paper gasket got stretched on the studs two times in a row. So the mechanic re-used a copper gasket and had to anneal it first before he could put it on the engine.