Rear Brake Issue


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Elmobile
Posts: 86
Joined: Sat Aug 22, 2015 8:35 pm
Location: Bridgewater, Nova Scotia, Canada
Motorcycle: 1990 GL1500SE

Rear Brake Issue

Post by Elmobile » Mon May 13, 2019 2:27 pm



I started talking about my rear brake ceasing in the "88 GL500 sticking clutch" post.

Well my rear brake is still ceasing...
I have a sidecar attached to my 1500SE and I just recently completed some work started over a year ago. I coupled the 2 front disks caliper to the front master cylinder. I rebuilt the rear master cylinder and the rear caliper. I polished the 2 pistons which are still not the best but seems to slide OK. I also replaced the OEM brakes lines with SS lines. The rear caliper is now connected to the open port of the master cylinder while the sidecar brake is connected to the pressure controlled port...
During my first road test the rear brake locked up the wheel solid, after about 10 kms. The disk on the rear wheel was very hot and could not be touched. What I did was to disconnect the sidecar at the quick connect and relief the pressure in the line right at the quick connect. I made it home but had to repeat relieving the pressure one more time!
Next morning I checked how the pedal felt. Seems OK: The brake would grab the wheel and release it as if all was normal. Went for a quick ride without touching the rear brake and again feel like I could have kept ongoing for ever. On the return way, I pressed the pedal just once, not hard and while cruising, and shortly after that like a couple of minutes, lost of power. I stopped aside the road. The brake is holding the wheel and the disk is very hot. I relieved the pressure in the line and the brake let go immediately. Made it home without any problems but without touching the rear brake pedals.
I can't see myself forgetting to clear the small pressure relief hole in the master when I rebuilt it and I have new seals in the calipers!
So long story short, I am looking at ideas/suggestions as to could be wrong?
Cheers...



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PedroTQ
Posts: 192
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Location: Perth, Western Australia
Motorcycle: Motorcycles on the road;
1976 GL-1000 DJP outfit
1988 GL-1500 HRD outfit
1998 Valkyrie

Re: Rear Brake Issue

Post by PedroTQ » Mon May 13, 2019 4:03 pm

G'day "Elmobile",

I did the same thing except I added a pressure control valve midway so I could lessen the braking force to the sidecar wheel just in case it grabbed too much, my set-up works just fine.

The only thing that I can think of is your brake pedal is not returning all the way up? maybe your pedal spline is one tooth out and still holding the master cylinder piston just in?.

Best of luck, Peter.
Attachments

Brake line going to the chair.
Brake line going to the chair.


As above.
As above.


Pressure reducing valve.
Pressure reducing valve.


Sidecar brake set-up.
Sidecar brake set-up.

#1 - 1975 GL-1000 - showroom
#2 - 1976 GL-1000 -DJP sidecar fitted
#3 - 1978 GL-1000 - RIP
#4 - 1975 GL-1000 - RIP
#5 - 1978 GL-1000 - RIP
#6 - 1988 GL-1500 - HRD sidecar fitted
#7 - 1998 GL-1500C - Valkyrie
#8 - 1990 GL-1500 SE - Naked 90

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Elmobile
Posts: 86
Joined: Sat Aug 22, 2015 8:35 pm
Location: Bridgewater, Nova Scotia, Canada
Motorcycle: 1990 GL1500SE

Re: Rear Brake Issue

Post by Elmobile » Fri Sep 27, 2019 7:35 pm

Well here I am with the same issue. This time I took the rear master cylinder apart again for another in depth cleaning. Needless to say that the relief hole is clear and clean. Below is a picture of what I found when I remove the plastic connector of the top of the master cylinder where the hose from the reservoir does connect. Not very obvious on the picture but it was full of a translucide jelly like residue. Not sure where it was coming from but I did remove every bit of it.

Jelly like residue above the relief hole.
Jelly like residue above the relief hole.

That is the only thing wrong that I could see. I also made sure that the pedal did not bind or get stuck anywhere. I finally put every thing back together yesterday and went for a test drive today...
Sadly I must report that after 25 kms the rear brake ceased again. The pedal was rock hard and the line was under pressure. After releasing the pressure, I again made it home with no problem making sure I was not touching the rear pedal.
I am at a lost to understand why the pressure gets locked in the line. Obviously, it looks like the pedal does not return all the way and keep the relief hole closed. However there is enough pressure in the line that you would think it would push it back all the way!
Again looking for suggestions as to why this is happening. Everything felt OK when I tested it in my shop before going for my test drive...

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Sadanorakman
Posts: 192
Joined: Tue Sep 19, 2017 1:42 pm
Location: Leicester, ENGLAND
Motorcycle: 1991 GL1500 SE

Re: Rear Brake Issue

Post by Sadanorakman » Sat Sep 28, 2019 12:23 am

So the Jelly is the elephant in the room.

I get that you had rebuilt the master cylinder, so the fluid was new, but what about the sidecar caliper and piping?

The Jelly has to come from somewhrte, and it is likely the result of water contamination of the fluid. You've not used a mixture of dot 5 fluid with dot 3 or dot 4 have you?

The reason I ask is that dot 3 and 4 absorb water, and distribute that moisture throughout the system. Dot 5 is silicon based and does not absorb water.ive not experienced the effects myself, but have heard that If dot 5 is used when reminants of dot 3 or 4 are in the system along with moisture, the moisture and dot 3/5 mix will gather in one place as opposed to remain distributed, and turn glue-like.

Would be great to get to the bottom of this.
Every day's a school day....What have you learned today?

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terryt
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Motorcycle: 1979 gl1000 trike
1989 gl1500 trike

Re: Rear Brake Issue

Post by terryt » Sat Sep 28, 2019 12:35 am

When you refitted the brake master cylinder did you fit the heat deflector plate between the cylinder and exhaust pipe. the fluid is getting hot and expanding causing the callipers to close. also check the front one as there linked it may be binding causing the same effect.

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Elmobile
Posts: 86
Joined: Sat Aug 22, 2015 8:35 pm
Location: Bridgewater, Nova Scotia, Canada
Motorcycle: 1990 GL1500SE

Re: Rear Brake Issue

Post by Elmobile » Sun Sep 29, 2019 8:32 am

Thank you for your comments,
Terry,
The heat protector plates are all in place and I have disconnected the front and rear brakes. The bike is committed to the sidecar hence why the 2 front discs now work together.
Sadano,
Agreed, the jelly like stuff that I found is more than likely water contamination. The first time around, I rebuilt the master cylinder, meaning a generous amount of DOT4 for "lubrication" during assembly, but it then sat around for a year (all winter in an unheated shop) before I had time to put it back together. I only found this contamination on the top of the master but nothing inside. So I doubt it is the issue here. The 2ND time, I clean, reassemble and test drive within a week. It is DOT4 and new fluid.
My line of thinking is that the relief hole does not open and I need to find out why. The rebuilt kit I've used is not an OEM. I bought a K&L from Cyclemax, so it should fit? I am in to take the master cylinder apart one more time. I will check the length of the piston just to make sure, I still have the original one... but I can't see it being wrong.
I need to see if I can put a bit more tension on the recall spring for the pedal as it seemed kind of too easy to put back in. But again you would think that there is enough pressure in the line to push everything back home and relief the pressure.
Anyway if or rather when I find what's wrong I'll be posting my findings... We may all learn something :D

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Sadanorakman
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Location: Leicester, ENGLAND
Motorcycle: 1991 GL1500 SE

Re: Rear Brake Issue

Post by Sadanorakman » Tue Oct 01, 2019 6:12 am

seems plausible that either the piston is a little long, or the piston is not returning fully if the spring is weak, and therefore not uncovering the pressure relief hole. The pads stay in contact, the pads heat-up by an uncomfortable amount, conducting the heat through to the pots, which causes the fluid to heat and expand a little, increasing the bind further. Please let us know what you find.
Every day's a school day....What have you learned today?

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Elmobile
Posts: 86
Joined: Sat Aug 22, 2015 8:35 pm
Location: Bridgewater, Nova Scotia, Canada
Motorcycle: 1990 GL1500SE

Re: Rear Brake Issue

Post by Elmobile » Tue Oct 01, 2019 9:03 am

Small update to my brake problem...
This really bother me as you can imagine! I was sorting through my invoices and found the one for the rear master cylinder kit. It is indeed an OEM kit, part # 43520-MG9-305. So I will take it apart again but I doubt very much that the piston would be too long. As for the spring being weak, I checked the pedal before relieving the pressure in the line and it was all the way up solid, no play what so ever in it...
Right now the pedal feel completely normal. Goes up and down as it should. Good progression in the braking depending on the pressure put on the pedal. So before taking the master apart, I will pressurize the brake line from the caliper end to see if the relief hole is opened or not.
Cheers

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Elmobile
Posts: 86
Joined: Sat Aug 22, 2015 8:35 pm
Location: Bridgewater, Nova Scotia, Canada
Motorcycle: 1990 GL1500SE

Re: Rear Brake Issue

Post by Elmobile » Thu Oct 10, 2019 7:23 pm

Well I think this will be the closing update for this problem.
Indeed the relief hole was not opening, not at all for some incorrect part but for my own mistake when I rebuilt the master cylinder.
Interestingly enough, neither my official maintenance book nor my Clymer show how to put it back together correctly so this finding could be of interest to whom ever rebuilt a rear master cylinder...
First of all I pressurized the line before taking any thing apart to confirm that the relief hole was closed. I was able to put 80 psi in the line (see picture below) and I had no return in the reservoir. Time to take the master cylinder out again and find out what was going on.

Was able to put 80psi
Was able to put 80psi

There is a pressure plate to close it held in place by a circlip. That plate has a little dimple on it and which can be facing toward the piston OR toward the circlip. If like I did it does face the inside, it will reduce the stroke of the piston enough that the piston will not clear the relief hole. There is no obvious way to see which side is right. Have a look at the picture below.

Wrong way
Wrong way


Proper orientation
Proper orientation

I have road tested it and all seems to be working as it should not, at least the brakes... Couple of others problems but I'll open others posts for them...

Hope this can help someone...



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