Hard to roll when cold. Brake pistion?

[happydaze]

Hi all,

I'm experiencing a phenomenon whereby my XS650H becomes hard to roll when it's cold. I took it for a short ride on Thursday and I could feel the resistance. I put it up on the center stand and spun the back wheel, which seemed to rotate freely, so I assume the drag is happening at the front wheel, which makes me assume the front brake caliper piston is getting stuck when it's cold.

Does that seem like a logical assumption? The problem is intermittent, which is what makes me think it's the brake hanging up. I rolled it out of the garage today and it rolled freely.

I ordered new brake pads, the Caliper Piston Detaching Tool, and the Brake Caliper Rebuild Kit from MikesXS. Mikes does not seem to sell the actual piston.

Thanks for any guidance.

 

[happydaze]

The pin the caliper slides on needs cleaning and lube.

Thanks I will check it out. I figured I may as well change the brake pads while I have it apart, so I'll wait for the parts to come before doing anything.

 

[happydaze]

The pin the caliper slides on needs cleaning and lube.

I'm looking at the Clymer manual and it doesn't show the caliper sliding on anything. It seems to be bolted in place.

 

[retiredgentleman]

I'm looking at the Clymer manual and it doesn't show the caliper sliding on anything. It seems to be bolted in place.

Your front caliper is of the same design that most cars and trucks have used for many years. The piston only acts on one side, with the other side simply holding the pad in place. As the pads wear down there are sliding surfaces that allow the wear difference to be taken up. Take the caliper off the bike and you will soon see what is meant by sliding surfaces.

In fact you should have removed the caliper and piston from the bike for a thorough inspection, before you ordered any parts. That way you know what you are working with.

The actual part that retracts the piston, when the hydraulic pressure is removed, is the piston rubber seal ring. Your seal ring is likely very old and has turned hard, so it does not pull back the piston. The kit you ordered will have a new seal ring that is soft and pliable as compared to the old one.

The groove that holds the piston seal ring likely has dirt/crud/rust etc. in it. You must remove every little bit of that bad stuff, until the groove is surgically clean. If the piston is not badly corroded, it can be re-used.

 

[happydaze]

Thank you @retiredgentleman. I'll post what I find after I pull it apart. This is something that has probably never been serviced on this bike, so I figured it was pretty safe to order the parts.

 

[XSLeo]

If you look at your caliper Right below the round part of the caliper you will see a bolt. This bolt goes through a steel sleeve inside a rubber boot then into the caliper bracket.
The caliper slides on this steel sleeve.
There are two bolts that hold the bracket on the fork.
In the Clymer book you need to look in the back half of the book for the 78 and later bikes. Page 209 has a rough drawing of the brake caliper and bracket, pic #81. On page 211, pic #86 you will see a better pic of just the caliper.
In that pic it shows the bolt, sleeve and rubber boot.
Leo

 

[happydaze]

Thanks @XSLeo. I was looking at page 172 (periodic maintenance in the 1978 & later info) and didn't realize that there was more information.

 

[gggGary]

You might find this thread useful.

http://www.xs650.com/forum/showthread.php?t=41676

 

[gggGary]

PS from mikes XS; there is also a german e-bayer that sells nicely machined caliper pistons, reasonable even with shipping but they take a bit to get here.
Caliper Piston - Front or Rear 1977-84 XS650
Caliper Piston - Front or Rear 1977-84 XS650 Photo Brake Caliper Piston - Fits: Front or Rear Caliper on 1977-84 650's.
Replace if pitted or scored or air will seep into the brake system.
Length = 41.3mm
Bottom Width = 38.15mm
Top Width = 27.26mm
inside dementions = 5.5mm
Part #29-0516 $28.00 USD Ea.

 

[happydaze]

I have the caliper off. The piston was stuck and caked with old brake fluid and grease.

What should I use to lube the pin that the caliper slides on? Lithium grease?

 

[gggGary]

Best is synthetic brake grease. just because brake rubber is fussy about petro products. don't go overboard, don't want any getting out.

 

[happydaze]

Ok thanks. I will have to buy some.

 

[gggGary]

Did you remove the square shape piston seal and get the gunk out from behind it?

 

[happydaze]

I got the piston out by loosening it with those special caliper pliers from Mikes XS and then a little squirt of compressed air in the hole where the banjo bolt goes (note: leave the zerk in or you will just spray brake fluid out of the zerk hole. Don't ask me how I know this). If you do this, wrap the caliper in a rag and point the piston away from you. It comes out with quite a pop. Now time to pull the inner seal and clean it up.

 

[happydaze]

p.s. My piston does have some pits but I can't do anything about that today.

 

[happydaze]

And that wire ring just goes around the base of the outer seal, correct?

 

[gggGary]

leave the zerk in or you will just spray brake fluid out of the zerk hole.

Oh yeah!
Um.... In spite of the beliefs of a PO or two, that is a bleeder NOT a zerk!

 

[happydaze]

Here's a pic.

 

[gggGary]

Yes, it's bit fumbly to get the dust boot and ring back on, the good news is it's almost impossible to tear the rubber. If the dust boot rubber is "too loose" it has absorbed fork oil and is useless, needs to be replaced.

 

[gggGary]

Looks good!