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Discussion Starter · #1 ·
I just rebuilt the rear master cylinder on my 88 1500. I cannot get any brakes. I have bled the front left & rear calipers several times, and I still have no brakes. I continue to get air in lines. When rebuilding, is there any technique needed to bleed properly. I am using a Mighty Vac & about a quart of brake fluid so far.
 

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Did you precharge the lines after installing the new master cylinder??? It can take a lot of bleeding to remove all the air if you don't "precharge or prefill" the lines and master when reinstalling - I expect that is your problem assuming you have no visible leaks...

Les
 

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You might try tying or laying something on the brake pedal overnight and see if that helps. Sometimes holding the pedal down will get the air out of lines. Can't hurt.
Did you bench bleed the master before hooking it back up?
 

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Discussion Starter · #4 ·
No to both questions. I did not bench bleed or precharge the lines. I did not see anything in the Clymer Manual about doing that. I did tie the brake pedal down over night.
So, it sounds like I just need to keep on bleeding till all lines are purged?
 

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I just rebuilt the rear master cylinder on my 88 1500. I cannot get any brakes. I have bled the front left & rear calipers several times, and I still have no brakes. I continue to get air in lines. When rebuilding, is there any technique needed to bleed properly. I am using a Mighty Vac & about a quart of brake fluid so far.
Steps:
1) Bleed front left caliper, using Mighty Vac
2) Bleed rear caliper, using Mighty Vac
3) Hang a weight on the rear brake pedal overnight --A full paint can works good.

There's no need to pre-fill the brake lines or master cylinder.
 

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Discussion Starter · #6 ·
GL 1500 rear brake bleed

Thanks for your help. I have done all the above, starting to think I have an air leak somewhere. Going to replace all banjo washers & put some teflon tape on that front brake connector hook-up. Hope that fixes it!!
 

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All master cylinders have to be bench bled after rebuilding them. You can hold finger on the outlet holes as you pump so air doesn't get sucked back in the holes.

Now that you have it mounted, pump up pedal/lever and hold, open banjo/flare nut at master to bleed air, close banjo /nut and repeat till you have flow of fluid at banjo bolt/flare nut, then rebleed the system normally.
I had to rebuild my 1500 rear m/cyl and bench bleeding on the bike is a royal PIA.

As to leaks, did your battery overflow? If so check the metal lines coming off the m/cyl. Battery acid eats the brake lines.
 

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Thanks for your help. I have done all the above, starting to think I have an air leak somewhere. Going to replace all banjo washers & put some teflon tape on that front brake connector hook-up. Hope that fixes it!!
IMHO: If there is no wetness there then you don't need the tape. If there is wetness there, you should find out why before using a band-aid. There is a reason why brake systems are made to work fine without using tapes and sealers.

I have also done a couple of systems that no matter what I did I could not get it to bleed, but a few days of leaving it alone it would bleed out and be fine.



Bill
 

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Discussion Starter · #9 ·
Thanks guys for the input. Newday, the lines look real good, no acid damage that I can see. And Pinto, no wetness anywhere, thought if it is sucking air then there might not be any wetness?? Anyway, will try again. I bought this bike last winter & had to rebuild all of the calibers, front & back. I never could get real good brakes on the foot pedal, you really had to stand on the pedal to get the bike to stop quick. I thought I would rebuild the master cylinder this year just in case that was the problem. I had a heck of a time last year getting the brakes bled, I think the linked brakes are what is giving me fits.
More brake fluid & more patience & I will try again.
Thanks for all the input.
 

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When you use your MigthyWac , somethimes you will such air in throug the thread off the bleeders and that makes it ineffective.
In that case ,use a LITTLE teflon tape on the bleeders , - on the thread only !
 

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When you use your MigthyWac , somethimes you will such air in throug the thread off the bleeders and that makes it ineffective.
In that case ,use a LITTLE teflon tape on the bleeders , - on the thread only !
+1... It also helps to put some Grease on the threads of the bleed nipple, so as to prevent any air entering at that point.

Also, did you use New Crush Washers everywhere? ...If you recycled the old ones, then you might also be getting air into the system that way.
 

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Uhh ohh....

I have done several brake Master Cylinder rebuilds already and have only had a problem like this once...

It was on a GL1100...
I somehow installed one of the rubber bits inside the MC backwards...And while it would draw fluid just fine through the MityVac it would never hold pressure enough to get the brake working...

IF you did a rebuild of the MC then I suspect you may be getting some practice in removing and checking your assembly method...



If this looks like the parts you replaced...be sure the rubber bit on the plunger (above) is facing the correct way....

Just soemthing else to look for...:?
 

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After doing a master cylinder rebuild on my 96SE and all the calipers. I started bleeding with a vacuum bleeder. Left front then rear. Lots of air. pulled out bleeders and applied a very small amount of liquid teflon thread sealer. This was applied with a Q tip being extra careful not to plug the hole in the bleed valve. After at least a dozen times bleeding the front then the back, I finally had all the air out of the front then started getting some brake pedal. It took a while and kept the reservoir full with the fluid collected in the vacuum bottle but after an hour or so it was all good! Hung all the plastic back on and away I went. A mile down the road the rear brake dragged me to a stop. Popped the bleeder to release the brake and went back home. Turns out my brake pedal was set too tight and I had to move it down one spline so the fluid could flow and return. Problem solved and no issues since. It can be a trying experience!
 
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