'83 GS850GL - Rear Caliper rebuild struggles

[Wingsconsin]

Any secrets / tips / tricks to offer ?
I struggle getting the boots ON and 'hooked' to the pistons
This one is 2 sided but I can NOT get it apart ...I have the pistons out and it's all cleaned up
I am waiting now for the kit from Z1 ---
Then I will tackle it

WHY does it need it ..?
The rear brake was dragging (hard) especially on the inside of the rotor.
It was HOT and causing the bike to slow noticeably...
When I removed it the rubber boot was mangled and ripped and ..bad
The by product of me doing a poor job a few years ago so I am trying to do it perfectly now.

SS brake lines already on the bike

So -- re-build , bleed with my mityvac , and ride again...

Thanks for your contributions

 

[Wingsconsin]

First time I think I stumped the hive mind here


No body have any tips or tricks to share ...?

LOL

 

[1978GS750E]

When I do them, I lube the rubber boot real good with silicone spray, enough so that it will rotate on the piston and the caliper. Seems to make it easier to get it hooked onto the caliper if you can rotate it as you go???
The silicone and a lot of patience seem to work!
Hope this helps!

 

[Nessism]

Did you order OEM seals and dust boots? Don't use K&L, they suck.

Dragging typically means the small return port in the master could be clogged.

When installing the piston I slide the dust boot onto the piston and position it at the very bottom. Then get the lip into the groove on the caliper and once it's in, slide the piston into the caliper.

 

[Wingsconsin]

Thank you for the advice --
My struggle right now is getting the 2 halves apart on the rear caliper --
The return port through the Master cylinder is clear - I have checked that already -
As I disassembled the caliper I found that one dust boot had ripped and was jammed in the space around the piston -
No matter how well the MC was working it wasn't going back in-- The importance of getting the rubber on properly is illustrated by this issue -
SO - Back to getting those 2 bolts OUT to split the caliper -- I am going to try to bolt them back onto the bike and get some leverage -
Perhaps my pneumatic impact can loosen them (I have them soaking PB blaster right now) And then a dip into the ultrasonic cleaner -
So many challenges - Always working on 'Kaizen'

 

[Grimly]

Given you're replacing all the rubber parts, hit the caliper body where the threaded portion is with a propane torch.

Heat, heat, and heat again.

 

[Wingsconsin]

Given you're replacing all the rubber parts, hit the caliper body where the threaded portion is with a propane torch.

Heat, heat, and heat again.

I have a heat gun --- ?
The paint on the caliper is remarkably good and I would like to keep it nice if I can without a repaint --
I will try the heat gun and some effort after the PB blaster soak --
It is truly stuck --- my impact didn't budge it - but it was in my hand so not all the energy was transferred to the bolt I suspect...(cushioned by my hand) ?

 

[Grimly]

You're up against 40 years of corrosion, happening in a place that's out of sight, out of mind, and subject to various corrosive substances ranging from road salt to alkaline cleaners and all of those aiding and abetting the dissimilar material corrosive tendency in the bolt holes.
Fi to the paint - heat the b'std.

 

[Wingsconsin]

You're up against 40 years of corrosion, happening in a place that's out of sight, out of mind, and subject to various corrosive substances ranging from road salt to alkaline cleaners and all of those aiding and abetting the dissimilar material corrosive tendency in the bolt holes.
Fi to the paint - heat the b'std.

HEAT IT IS ! !

Caliper Bolts ? You shall be mine !

 

[salty_monk]

A proper impact or a long breaker bar will get them out if you bolt the caliper into a big vice.. otherwise you need the heat. They are always tight.

 

[bwringer]

Yep, I've always used an impact on these bolts. Not worth messing with anything else. You gotta get it apart to do it right.

FWIW, the impact hex bit set at Harbor Freight is the bee's knees, the arthropod's ankles, and the cat's patoot for this sort of work. Weirdly high quality stuff.
https://www.harborfreight.com/12-in-drive-metric-impact-hex-socket-set-8-pc-67895.html
Great for those pesky fork damper rod bolts, too.



As far as getting the boots in... I don't know what to tell you here. It's always a trial and error thing that takes a few minutes. I've gotten much faster at it, but I couldn't begin to tell you how to teach your fingers this skill.

I can say two things:

1) You should NEVER use any substance besides brake fluid as a lubricant.

2) You should NEVER use a tool. Great way to poke a hole.

Also, the grooves have to be IMMACULATE. Any microscopic bits of crud in the corners of the seal or boot grooves will cause failure. Get something pointy and clean every millimeter of the grooves, paying special attention to the corners.

 

[Wingsconsin]

I was able to break loose the bolts holding the 2 halves together --

I bolted the caliper back on the bike -
Used my 1/2" ratchet with a 12" extension and applied leverage -- POP !

After getting the halves apart I sent them through my Ultrasonic cleaner a few times -
Then I cleaned all the grooves SUPER well --
Using only brake fluid as lube and fingers as tools I was able to (after some time) get those DAMN boots back on --

I then put it all back together and on the bike - Bleeding the brake lines (stainless steel) with my MityVac and lots of fluid I felt I was able to get a nice air free line

After a 20ish mile test ride I was dismayed to find the rotor quite hot and the brakes still not working well...

SO - I ordered the Master Cylinder REAR brake rebuild kit and will try that too... (my cheaping out has cost me again- when will I learn to do it right the first time?)

If that isn't the answer -- then MAYBE new pistons -- but they SEEM to work fine with compressed air -- so it has to be the MC -- RIGHT ??

I will let you know eventually

Continual Improvement -- "KaiZen"

 

[Grimly]

Sounds like the tiny return port in the m/c might be partially blocked. Be as well to re-seal it anyway given the age of it.

 

[Wingsconsin]

OKAY - MC rebuild kit arrived -
Now I need some time to play and get it done -
But the weather here has turned and he cooler mornings deters me riding the smaller bike anyway (commuting)
So -- maybe this weekend --
And then to Time Sert the one lower stator cover fastener to end the leaking (dripping)

 

[Wingsconsin]

UPDATE on REAR BRAKES

UPDATE on REAR BRAKES

I rebuilt the Master Cylinder last night -
Got all back together after a good cleaning and new rubber bits
Primed the MC and then started bleeding the brakes out the caliper with my Mity-Vac pump.
It seemed to work well and I went for a ride -
25 miles later I came back home and the rear rotor still felt pretty warm and there seems to be a little bit of 'rubbing' -
I think I will bleed MORE fluid through the system trying to remove any & all air -

Any other tips and tricks to share ? -

The advice I have received thus far has been spot on (of course)

 

[Rich82GS750TZ]

Bear in mind my 82 750 T has a rear drum, not disc. So just thinking out-loud. When we bleed the front brakes, it's often helpful to tie the lever to the grip and leave it overnight. Untying the lever in the morning, it will often regain a better, less squishy pull. Can you do the same with the rear? Wedge something between the right peg and brake pedal to depress the pedal overnight or for a few hours and see if it helps?

 

[Wingsconsin]

Bear in mind my 82 750 T has a rear drum, not disc. So just thinking out-loud. When we bleed the front brakes, it's often helpful to tie the lever to the grip and leave it overnight. Untying the lever in the morning, it will often regain a better, less squishy pull. Can you do the same with the rear? Wedge something between the right peg and brake pedal to depress the pedal overnight or for a few hours and see if it helps?

Worth a try - thanks for the thought :encouragement: