GS700 rear brake master cylinder

[markn]

Hello - I have a problem with my 1985 GS 700ES. Initially the rear brake caliper was stuck so I completely rebuilt the rear caliper. When I went to bleed the system I had zero pressure in the foot break lever. I tried numerous times trying to bleed the air out of the system, but I can’t pump any fluid through the brake line. I verify this by removing the banjo bolt from the master cylinder, but I was unable to get any fluid to pass from the reservoir through the cylinder and out of the discharge hole of the master cylinder . A pal thinks all I need is a speed bleeder to rapidly get the air out and the fluid flowing, but I’m not feeling so good about it. I have no problem purchasing a new rear master cylinder, but according to the shop service manual, I have to remove the rear wheel, swing-arm, rear shock and other items, just to replace the master cylinder. I was shocked ! (I’m not much of a mechanic) Has anyone replaced a rear master cylinder on a GS 700/750 without removing the swing arm and rear shock? Thanks in advance for any help you can provide me ! markn.

[dorkburger]

Hey Mark.
you say that you're not much of a mechanic. Not trying to be an arse, but did you bleed the brakes properly, as in pump the pedal, hold it down, then crack open the bleeder?
Speed bleeders are handy, but personally, I do it the lazy way when possible - fill the M/C, open the bleeder, then let gravity work. Once fluid makes its way down to the caliper, then I'll pump / bleed to get any remaining air out. Another thing to look out for is the M/C while doing the bleeding. They are small and empty out quickly sending you back to square one. Sometines air gets trapped in the M/C and tapping on it can free it up.

All that said, if the caliper was loaded up with grimy brake fluid, the M/C may be in bad shape as well.

[Rich82GS750TZ]

I had a quick look at the 700 Supplement on BikeCliff's website. It does look like Suzuki tucked the rear MC way in there on the mono-shock models. I do believe you'd have to take off all that they say in order to get the MC out to rebuild it, if it comes to that. That said, I have no experience here.

[Nessism]

I'd bite the bullet and pull the wheel and swingarm like the manual states. That way you can properly clean the master cylinder and replace the brake line. No doubt there is sludge in both (pay attention to the tiny fluid return hole.) You can also grease the swingarm pivot bearings at the same time.

[markn]

I was able to remove the rear master cylinder by unbolting the reservoir from the frame, then merely unscrewing the threaded shaft from the pivot section attached to the swing-arm. I have no clue why the shop manual says the swing-arm, rear shock, and rear wheel has to be removed.
Unfortunately, the master cylinder is so bad, after removing the spring-clip,I’m unable to pull the piston out of housing. I’ve tried every thing imaginable to remove the piston, but it’s fused into place.
I’ve been unable to find a replacement master cylinder for a GS700E, but I understand the 1980 to 1984 GS750 is the same….Can anyone confirm this?
I’m hoping to locate a master cylinder that will fit my frame (new or used) then attach the the linkage from my GS700ES. Does anyone know where I can purchase a rear master cylinder that will fit on my 700ES, and use my current shaft and linkage?

[Grimly]

Partzilla's x-ref has it on the GS750E of 83 as well as yours.
No mention of earlier years, but it might be a fit anyway. The part number of a complete assembly changes even if the physical change is something minor that wouldn't prevent fitting.

https://www.partzilla.com/product/suzuki/69600-31300?ref=ebbe8075722db82e24c581d08815c1fb8a0e652a

[markn]

Partzilla's x-ref has it on the GS750E of 83 as well as yours.
No mention of earlier years, but it might be a fit anyway. The part number of a complete assembly changes even if the physical change is something minor that wouldn't prevent fitting.

https://www.partzilla.com/product/su...15c1fb8a0e652a

Hi Dave - thanks for the info - Partszilla is showing it as unavailable, but now I know what part numbers to cross reference vs. GS model. markn