Brake Overhaul - Rear Master Cylinder Leak question

[hampshirehog]

I wouldn't risk it. A pair of stainless rears is only about ?20 and it's job done forever then. And no need to buy the rubber boots either.

 

[scott]

I wouldn't risk it. A pair of stainless rears is only about ?20 and it's job done forever then. And no need to buy the rubber boots either.

I think that would be roughly $32 USD which doesn't sound bad. My rear caliper pistons are roughly 38mm outer diameter by 22 mm high. I tried doing some searching but haven't found any stainless pistons in that size. Is there a UK site that the GS people use to get the appropriate pistons?

It looks like I can get the OEM piston set for around $42 which I think includes the o-rings, boots and the seal between the caliper halves. I would hope even the non-stainless OEM pistons wouldn't start rusting THAT quickly (or would they).

 

[hampshirehog]

Best place to buy them is from this guy:

http://www.ebay.co.uk/itm/Suzuki-gs...74?pt=UK_Motorcycle_Parts&hash=item5ae3b7b35a

(yes, those pistons are identical to the ones you have, just in stainless).

He does them without the groove for the dust boot and they are fine as well (no need to fit that boot when you go stainless).

 

[TooManyToys]

......He does them without the groove for the dust boot and they are fine as well (no need to fit that boot when you go stainless).

That's really a bad idea.

 

[1_v8_merc]

I've sanded down pistons worse than those...never had a leak.
But i'm dirt cheap, I'll take the chances with my Rear Brakes....never my fronts!

I'm not telling you what to do, if you have any doubts, get new ones, or get some cheap calipers off ebay.

 

[hampshirehog]

That's really a bad idea.

Why? They're stainless.

Loads of bikes run without the dust boots from the factory and if the dust boots worked then the things wouldn't rust in the first place. The only downside is when you pop in new pads it's best to tear the calipers down to remove all the gunge on the exposed part of the piston. Not a bad thing though as a full caliper service gives me peace of mind anyway. I must have 50+k miles on my 750 on stainless exposed pistons (fronts and rears) and when they're clean they look like new. All my bikes are bootless - and on wet, salty UK roads.....

 

[TooManyToys]

What bikes come from the factory without boots? Just would like to know.

 

[scott]

I got my shipments of brake parts. I was able to assemble the rear master cylinder without too much trouble although I haven't tested it yet. I ordered the OEM rear piston set (couldn't figure out how to order from Ebay UK to get the stainless pistons).

The pistons are REALLY tight in the calipers.

I'm having issues with the piston / piston boot installation. I've read the various suggestions but haven't had much luck. I've already ripped both boots that came with the pistons.

Here is half of my caliper.

The inner groove A (this pic was taken before I scraped that gunk out) is where I put the seal/o-ring. I used a qtip to put clean brake fluid in the caliper bore and on the seal. I understand that part of boot fits on the ridge on the piston itself. On the caliper, I assume the outer part of the boot should wrap around the outer ridge/lip C. Is this true? I assume B is just formed for the boot to sit in.

For the suggestion where people put the boot on the bottom part of the piston, I don't really understand why the boot should extend beyond the piston. I tried this on my first attempt but couldn't push the piston - I think it was my forcing that ripped the boot.

On my second attempt (and second boot), I put the boot just above the bottom of the piston and seemed to get further until trying to get the outer part of the boot around ridge C when the boot ripped. Also, since I was able to get the piston pretty much all the way into the bore, I am unable to get the piston back out (it's that tight).

Any thoughts on where I went wrong? I'm planning to try my front caliper and see if I rip that boot before I place an order for more boots.

 

[hampshirehog]

What bikes come from the factory without boots? Just would like to know.

Bikes I've worked on that I can remember:
GSXR - various
RGV250
SV650 / GSF 600
400 / 600 / 900 Divi
Deauville
VFR400
Aprilia (various)
Triumph (various)

And loads more. There was a debate back in the day that the boots kept moisture in and thus promoted rusting rather than the other way round. Of course that was with chrome plated pistons. Stainless don't rust.

 

[TooManyToys]

Those Nissin calipers still had a dirt seal, although now I realize you differentiating between a dust sliding seal vs. an accordion boot. If a sliding seal was the perfect answer they would not still be using the accordion boots in vehicle production. I have no issue with the sliding seal.

The problem I have is in message 41 where you said not to use any protection and discard the boot. The majority of brake calipers use a pressure sealing o-ring that is slightly narrower then the groove that is cut into caliper housing, which also mostly is a tangential groove, tighter at the outer end. This allows the square-cut o-ring to become a tighter seal as the piston moves outward, and provides some elastic roll back of the piston as the hydraulic pressure is being released. Any debris that gets into the o-ring bore groove alters the performance of the brake caliper. This is why even though Nissin did not use an accordion boot, still had a seal.

 

[TooManyToys]

....... The pistons are REALLY tight in the calipers.

I'm having issues with the piston / piston boot installation. I've read the various suggestions but haven't had much luck. I've already ripped both boots that came with the pistons.

Here is half of my caliper.

The inner groove A (this pic was taken before I scraped that gunk out) is where I put the seal/o-ring. I used a qtip to put clean brake fluid in the caliper bore and on the seal. I understand that part of boot fits on the ridge on the piston itself. On the caliper, I assume the outer part of the boot should wrap around the outer ridge/lip C. Is this true? I assume B is just formed for the boot to sit in.

For the suggestion where people put the boot on the bottom part of the piston, I don't really understand why the boot should extend beyond the piston. I tried this on my first attempt but couldn't push the piston - I think it was my forcing that ripped the boot.

On my second attempt (and second boot), I put the boot just above the bottom of the piston and seemed to get further until trying to get the outer part of the boot around ridge C when the boot ripped. Also, since I was able to get the piston pretty much all the way into the bore, I am unable to get the piston back out (it's that tight).

Any thoughts on where I went wrong? I'm planning to try my front caliper and see if I rip that boot before I place an order for more boots.

Your analysis of A, B and C are correct. First you have to make sure all of the debris and corrosion are removed from groove A where the o-ring resides. Any excessive material here will cause the o-ring to be tighter against the piston making it hard to go in.

Second I really would recommend you go to an auto parts store and get some brake assembly fluid. It is silicone based and provides more lubrication for getting this all back together. Glycol based brake fluid tends to be a little "grippy". Another advantage of using the silicone fluid is that it is not hygroscopic like brake fluid is. The combination of brake fluid under the exterior boot and poor sealing lips due to the housing corrosion pits is what causes the fast development of rust / oxidation within that area.

Groove C also needs to be free of any corrosion that would hang up the boot lip. And you can use the assembly fluid to get these installed as well.

This caliper design uses external boot lips on both ends. You should be grateful. The harder project is when the caliper housing boot lip is located on the inside so you have to slide the piston past both the boot lip and o-ring.

The way I rebuild calipers designed like this one is to first install the o-ring, then use a dowel rod fitted into the piston bore and force the o-ring 360? into the groove just to be sure it's fully seated. Next with the piston end wetted down with assembly fluid and the o-ring also re-lubricated (you first wet the o-ring and caliper bore before any assembly) you should be able to push the piston past the o-ring and about 1/2 way into the housing.

Next I install the boot into the pistons groove and finally into the housings lip.

Not sure if you have anything like these:

http://enginemechanics.tpub.com/14105/css/14105_120.htm

Here is the OTC set I have:

http://ins.sears.com/otc-o-ring-pick-set-display-of-10-7103-order/p-00971318000P

I picked the Sears site as it allows you magnify the tools, especially the ends. These are dangerous as you can see three of the ends have a point, especially considering you punctured two boots already.

I modified the one flat end of the one tool with a file to make it round and less prove to puncture thin boot skin. But you don't have to spend the $10-20 to buy them, they can be made with coat hanger wire and some needle-noise pliers. I would make up a hook tool then try using it to install the torn boot into the housing lip while waiting for your new boots. Remember - rounded end.

 

[scott]

Your analysis of A, B and C are correct. First you have to make sure all of the debris and corrosion are removed from groove A where the o-ring resides. Any excessive material here will cause the o-ring to be tighter against the piston making it hard to go in.

Second I really would recommend you go to an auto parts store and get some brake assembly fluid. It is silicone based and provides more lubrication for getting this all back together. Glycol based brake fluid tends to be a little "grippy". Another advantage of using the silicone fluid is that it is not hygroscopic like brake fluid is. The combination of brake fluid under the exterior boot and poor sealing lips due to the housing corrosion pits is what causes the fast development of rust / oxidation within that area.

Groove C also needs to be free of any corrosion that would hang up the boot lip. And you can use the assembly fluid to get these installed as well.

This caliper design uses external boot lips on both ends. You should be grateful. The harder project is when the caliper housing boot lip is located on the inside so you have to slide the piston past both the boot lip and o-ring.

The way I rebuild calipers designed like this one is to first install the o-ring, then use a dowel rod fitted into the piston bore and force the o-ring 360? into the groove just to be sure it's fully seated. Next with the piston end wetted down with assembly fluid and the o-ring also re-lubricated (you first wet the o-ring and caliper bore before any assembly) you should be able to push the piston past the o-ring and about 1/2 way into the housing.

Next I install the boot into the pistons groove and finally into the housings lip.

Not sure if you have anything like these:

http://enginemechanics.tpub.com/14105/css/14105_120.htm

Here is the OTC set I have:

http://ins.sears.com/otc-o-ring-pick-set-display-of-10-7103-order/p-00971318000P

I picked the Sears site as it allows you magnify the tools, especially the ends. These are dangerous as you can see three of the ends have a point, especially considering you punctured two boots already.

I modified the one flat end of the one tool with a file to make it round and less prove to puncture thin boot skin. But you don't have to spend the $10-20 to buy them, they can be made with coat hanger wire and some needle-noise pliers. I would make up a hook tool then try using it to install the torn boot into the housing lip while waiting for your new boots. Remember - rounded end.

Thanks for this info - it's very helpful. I'll look for some brake assembly fluid. I have some picks that I can try to file down. So far, I've managed to rip the boots without using the picks though!

 

[scott]

Second I really would recommend you go to an auto parts store and get some brake assembly fluid. It is silicone based and provides more lubrication for getting this all back together. Glycol based brake fluid tends to be a little "grippy". Another advantage of using the silicone fluid is that it is not hygroscopic like brake fluid is. The combination of brake fluid under the exterior boot and poor sealing lips due to the housing corrosion pits is what causes the fast development of rust / oxidation within that area.

I went to the local NAPA and they directed me to a tube of CRC Sta-Lube Brake Caliper Synthetic Grease.

http://www.crcindustries.com/ei/content/prod_detail.aspx?PN=SL3301&S=Y

I don't see anything problematic at the CRC web site (url above).

However, after I got home I read the back of the tube more closely and found this:

Do not use on internal piston parts; use brake fluid for internal piston assembly.

Is this referring to the master cylinder or should I not use this on the caliper bore / seal / piston? Did I get the wrong thing? This makes it sound like it won't play nice with brake fluid.

 

[hampshirehog]

That grease is for external use only - don't get it anywhere near the insides of your calipers or your MC. The only stuff allowed on the inside is brake fluid.

 

[TooManyToys]

That's brake caliper SLIDE grease. For exterior parts of the brake caliper that slide, such as pins or anchor brackets. Although it has been mentioned on web locations, it is not the proper item for hydraulic parts rebuilding.

NAPA does have the product as we used to get it from them both in a bottle and in little red capsules that also used to come in United wheel cylinder kits. It's buried deep within their United Brake Parts catalog. I think the darth of wheel cylinder and brake caliper rebuilding has led to a loss of knowledge in the service industry. I just don't have the part number for that and the NAPA on-line site is abysmal.

Raybestos sells it as BAF12 assembly Fluid.

Wildwood sells it as:

http://www.google.com/products/cata...=X&ei=YkOwT4O4JYbw6AHp1b2KCQ&ved=0CJ4BEPMCMAA

Centric has it too:

http://mibearings.com/brake-parts-c...ntric-brake-assembly-lube-805890131489-p-7692

While many parts guys and on-line sites talk about using brake fluid as an assembly fluid, it's just not right as you don't want a hygroscopic fluid outside of the sealed fluid system to accelerate oxidation.

 

[scott]

Wildwood sells it as:

http://www.google.com/products/cata...=X&ei=YkOwT4O4JYbw6AHp1b2KCQ&ved=0CJ4BEPMCMAA

I ordered the Wilwood Brake Assembly Lubricant online - it does seem more slick than brake fluid and the bottle specifically says it's compatible with brake fluid:

You should be grateful. The harder project is when the caliper housing boot lip is located on the inside so you have to slide the piston past both the boot lip and o-ring.

I tried to do my front caliper before ordering new boots for the rear. My front caliper is like you describe above - the boot lip goes inside the bore. I guess it's a good thing I waited because I ripped that one too. I tried all tips I've read:

1. Put boot on bottom of piston, insert and push piston down
   This tip is in one of the brake overhaul guides on BikeCliff's site and I've seen it recommended on various threads here. I don't think this applies to my boots/calipers. My front boot does not look like the pictures I've seen with this suggestion and my rear caliper boots install differently.
2. Install boot on the caliper, tip piston into the back of the boot and use paper clip or other tool to work boot around as you straighten the piston
   This was in the other brake overhaul guide on BikeCliff's site. I enlisted my wife for an extra pair of hands but I couldn't get this to work.
3. Install boot on the caliper, use compressed air to "inflate" boot while installing piston
   I saw a youtube video of this. I tried it but I think I need a real air compressor (I was using my small tire air compressor as opposed to a shop air compressor). I think the boot may have been ripped at this point so maybe I should try this when I get new boots.

I placed an order for 3 new boots (1 front, 2 rear). I'm considering taking the calipers/piston/boots to a shop and see if they can install it for me.