75 gl1000 front brake master cylinder rebuild (help)

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pjlogue
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#16

Post by pjlogue »

Make sure your MC body is real clean. From the pic of the piston you probably have a lot of crud inside the piston bore. Light honing of the bore is a good idea. You can use 400 grit wet/dry and use a thin wooden dowel with a slit in the end and an electric drill. Put the sandpaper in the slit and spool it onto the dowel and hone away. Check the bore for pits. If it is badly pitted you will need a new MC. Be sure to clean the small hole (pressure release hole) in the bottom of the resivior and make sure everything is real clean before reassembly.

-P.
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Sidecar Bob
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#17

Post by Sidecar Bob »

Re painting the reservoir: Keep in mind that the brake fluid level is the easiest indicator of pad wear (if the fluid is at the upper mark when the pads are new it should be close to the lower mark when the pads need to be replaced) so if you paint it you won't be able to tell easily.
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pidjones
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#18

Post by pidjones »

Sidecar Bob wrote:Re painting the reservoir: Keep in mind that the brake fluid level is the easiest indicator of pad wear (if the fluid is at the upper mark when the pads are new it should be close to the lower mark when the pads need to be replaced) so if you paint it you won't be able to tell easily.
I change my fluid a lot more frequently than pads - even on the GL1800 (more weight, more pad wear).
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Sidecar Bob
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#19

Post by Sidecar Bob »

With rubber lines you should change the fluid every couple of years and the lines every 2-3 fluid changes. With stainless braided lines you can easily double the fluid life so you shouldn't need to replace it more often than the pads.
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
Corey_wicks
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#20

Post by Corey_wicks »

Sidecar Bob wrote:With rubber lines you should change the fluid every couple of years and the lines every 2-3 fluid changes. With stainless braided lines you can easily double the fluid life so you shouldn't need to replace it more often than the pads.
That's good to know
I was probably going to go stainless down the road. Mainly for the benefit of having stainless that and I plan on going to more of a streetbike style bars
Corey_wicks
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#21

Post by Corey_wicks »

pjlogue wrote:Make sure your MC body is real clean. From the pic of the piston you probably have a lot of crud inside the piston bore. Light honing of the bore is a good idea. You can use 400 grit wet/dry and use a thin wooden dowel with a slit in the end and an electric drill. Put the sandpaper in the slit and spool it onto the dowel and hone away. Check the bore for pits. If it is badly pitted you will need a new MC. Be sure to clean the small hole (pressure release hole) in the bottom of the resivior and make sure everything is real clean before reassembly.

It's the inside of the mc is really nice for the most part. It looked as if some residual stuff from the brake lines themselves actually backbled into the mc it's self. I soaked the mc in some mineral spirits for a few days and spreyed everything out. It came out a lot cleaner than I expected for sure. It doesn't look like it's a 45 year old part that's for sure! I was excited when I pulled it out
-P.
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#22

Post by digschopper »

Goldwing parts. Com has the reservoir for around $35, same for the rebuild kit, which has everything but the reservoir and its o ring. Im rebuilding mine right now. A used complete MC can be had for about $20 used online, id go smaller bore as well. I believe CB900C is a good replacement MC.
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Sidecar Bob
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#23

Post by Sidecar Bob »

But not too small. If you go too small the lever might reach the handlegrip before the brake locks.
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
redglbx
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Re: 75 gl1000 front brake master cylinder rebuild (help)

#24

Post by redglbx »

If you use braided stainless brake lines a 14mm bore m/c is about as small as you can go, if you use the oe rubber lines then the 14mm bore m/c is marginal for enough displacement to keep the lever from bottoming.

I think but am not sure that the oe m/c 16 or 16.4mm bore. If you are able to rebuild & reuse the oe, just the addition of braided stainless brake lines will reduce the wooden feel significantly and provide much improved braking. I just did my 76 earlier this year and was completely amazed at how much better the braking is ! Very happy with the results.

Edit : 9-28-22,, the OE front m/c bore size is 17.5mm.
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