caliper reassembly

Hi XJer's.

Well, have had to order new brake pistons, seals and pads etc.
Just for the practise though, I've been attempting reassembly of the unit. As per, doing it all for the first time.

I'm finding there's a surprising amount of play ie the body is sort of rocking around the bolt that clamps it to the bracket. I'm pretty sure that the bolt is tight. I notice on the bracket the paint has rubbed away over time.

Should there be play, or should body and bracket be a solid unit on the wheel ?

Does the single little screw with the tapered end pass through the eye of the brake pad, or push up the anti-rattle spring from underneath ? Would either situation make a difference to the play in the body ?

thanks as usual

Yepper

 

There are several different styles of calipers but they all need to be free to either slide or rotate on the mounting bolt to stay centered on the disc as the pads wear. If it isn't free to move without sticking the pad on one side will wear out while the other one doesn't wear at all.

 

Hi Steve, thanks for that. Still not sure though.

The motion is more like perpendicular to the disc, not sliding, but with the bolt more as a fulcrum - kinda difficult to explain.

Can you tell me what exactly is going on between that screw and the pads ?

Sorry if these are idiot questions

 

Are you talking about the bolt that mounts the caliper to the fork? The caliper should be free to rotate around that bolt (within limit of disc and pads of course). If not the brakes/rotor will not wear evenly and braking will be impropper.

 

We really need ot know which bike you have. The calipers are different on some models.

 

I think the "Bolt" he's referring to is the traveler on 82-83 vintage bikes. The Traveler post is supposed to be solidly mounted. The unexposed end has an Allen inside hex for tightening that post to the caliper's brace.

That post is also a major contributing factor to binding front brakes on bikes with that style front brakes. Generally, the post does become loose, but rather ... contaminated ... causing the "Floating Assembly" to be slow ... both in braking and releasing. An examination of your front pads will tell the story. Uneven wear on the pads indicates that the post has either become loose (rare) or, run dry and needs to be lubricated. Despite being protected by a tight fitting dust seal ... the seal only keeps out dust ... NOT moisture ... which contaminates the grease and causes the binding.

Solution:

Remove floating caliper from the post.
Remove post and clean it.
Reinstall post using thread locking compound.
Grease with synthetic, waterproof grease.

The waterproof grease and the anti-friction o-ring guides causes the air in the travelers cylinder to compress making re-assembly difficult; unless you "exercise" the caliper on and off to allow that trapped air to escape.

 

Sorry, should have said at the outset - '81 650 Seca - the caliper is shown in the Haynes as UK650.

I'm at work now so will try to describe this from memory -

If I look FROM THE FRONT of the bike, I can grab the top of the caliper body and it will move anticlockwise as I am looking at it - ie perpendicular to the wheel's direction of travel. NOT moving in unison back along the bolt, but more gap appearing at the top of the body. The bolt I'm talking about is the single bolt that clamps the body of the caliper to the bracket. The bracket in turn is mounted to the fork.

It's about five mil of play, but I wasn't expecting it at all. It's really that I don't know the underlying principles of the system I guess.

By the way, a question has been asked in the past about removing a seized piston. I found that I could use a pinion puller in the groove of the piston and the forcing screw pushing into a small block of wood. A little bit tricky as you're holding it all together by hand. Maybe not ideal on a serviceable piston :?: but mine was shot.

 

that play you see=normal -/+.

how about putting yor bike in your signiture!

 

Thanks HooNz, that's excellent news !

Well, I first have to learn how to do the bike/signature thingy... and to say that the bike is cosmetically challenged is putting it mildly

It's an import, so a 750 engine in a 650 body (one big headlight, two chrome clocks, Seca tank)

Will give it a go - no laughing though :!:

 

Ok yepper , twill be good to see some pics when you can....

 

So how would I tell if my XJ650R has these style calipers?

The reason I ask is because I found out that my previous "on the hill" problem was actually my front brakes. I didn't see it on level ground until just recently.

Thus I need to most likely re-build my front brakes because they aren't releasing properly. But if cleaning it might solve the problem I'd rather not have to pull the pistons.

 

nimitz , see if the calipers are free first then go from there , is there enough freeplay in the front brake lever adjustment? for starters.....

 

The freeplay adjustment was fine.

Turned out I had uneven wear on the one outside pad and that caliper wasn't releasing. Cleaned the whole thing up and lubed as necessary and now it works like a charm!

Did the same to the other side as well just on general principle.

 

nimitz , good one...