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97 R1100RT Rear brakes with no pressure


Hotmop

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Bike has 48k miles. I've owned since new.

 

The day I was riding home to yank the rear wheel for a new tire, my rear brake pedal went to full travel with little braking effect. I see no leaks at the caliper or master cylinder so I though 'oh crap, ABS unit'. This lead to removing the tank and at that point I figured I was all in and decided to lube the spline and replace the clutch. Yes, dominos. And, the ABS unit was not leaking. I put braided Galfer brake lines on last year (front and rear). 

 

With the splines lubed and clutch replaced and even final drive pivot bearings replaced with Nushings, I'm back to that rear brake problem.

 

Bleeding results seem kind of odd. I can push to full travel by hand, hold, open bleeder; I get nearly no flow. If I open the bleed valve and just pump, I get a flow of fluid and it drains from the reservoir. I go back to trying to get pressure and bleed, nothing moves.

 

I've removed the master from the bike and short of taking it apart, it looks in good shape. No corrosion or signs of weeping fluid. 

 

I'm reading that the rear master does not usually fail. I was considering a rebuild kit, but maybe that's overkill?

 

Lastly, I'll admit I have a specific dislike of working on brakes and this bike has surely seen far less fluid flushing than it should have. (Though it was done last year with new lines). 

 

What the heck am I missing? 

 

 

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9 minutes ago, Hotmop said:

Bike has 48k miles. I've owned since new.

 

The day I was riding home to yank the rear wheel for a new tire, my rear brake pedal went to full travel with little braking effect. I see no leaks at the caliper or master cylinder so I though 'oh crap, ABS unit'. This lead to removing the tank and at that point I figured I was all in and decided to lube the spline and replace the clutch. Yes, dominos. And, the ABS unit was not leaking. I put braided Galfer brake lines on last year (front and rear). 

 

With the splines lubed and clutch replaced and even final drive pivot bearings replaced with Nushings, I'm back to that rear brake problem.

 

Bleeding results seem kind of odd. I can push to full travel by hand, hold, open bleeder; I get nearly no flow. If I open the bleed valve and just pump, I get a flow of fluid and it drains from the reservoir. I go back to trying to get pressure and bleed, nothing moves.

 

I've removed the master from the bike and short of taking it apart, it looks in good shape. No corrosion or signs of weeping fluid. 

 

I'm reading that the rear master does not usually fail. I was considering a rebuild kit, but maybe that's overkill?

 

Lastly, I'll admit I have a specific dislike of working on brakes and this bike has surely seen far less fluid flushing than it should have. (Though it was done last year with new lines). 

 

What the heck am I missing? 

 

 

 

Afternoon Hotmop

 

Your issue is difficult to diagnose over the internet, as you have found it is not easy to diagnose even when working with it in person.

 

At first thought it sounds like a master cylinder issue with the internal sealing rings.  

 

I have nothing (service bulletin wise) on the 1100RT as far a rear master cylinder not holding pressure goes but your problem mirrors the 1150RT  with the same type problem.  On certain  build number 1150  bikes   there WAS a service bulletin about leaking internal master cylinder sealing rings & the base complaint was very similar to what you are seeing.  

 

If you pump the pedal & have pressure build but no fluid flow then look for a rear hose internal liner problem forming a check valve therefore blocking fluid flow. If you pump the pedal & have NO pressure build & NO fluid flow then look to the master cylinder leaking internally with fluid by-passing the sealing rings.

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The R1100RT rear master cylinder is available used on eBay. Get a syringe or bleed bag filled with brake fluid and back fill the circuit from the caliper bleeder until the master cylinder fills with fluid. With the ABS module being the highest point in the rear circuit, it’s hard to get the rear circuit filled with brake fluid by pumping the lever -  you can’t. If you get the rear circuit filled and then you still can’t get pressure at the lever, then you probably need to replace the master cylinder.

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Morning Hotmop

 

Just keep in mind that your lack of rear brake pressure with the rear master cylinder appeared before you even worked on the bike ("my rear brake pedal went to full travel with little braking effect").

 

Also,  you are getting fluid flow out of the rear caliper bleeder so the fluid it getting to & through the ABS module , you just aren't getting any pressure build when using the rear brake pedal. (" I can push to full travel by hand, hold, open bleeder; I get nearly no flow. If I open the bleed valve and just pump, I get a flow of fluid and it drains from the reservoir"). That draining fluid from the reservoir is going somewhere.

 

You could  still have some air trapped in the ABS module and/or upper lines but you should still see 'some' pressure coming out of the rear caliper bleeder after pumping the pedal then holding it down, even if it is mostly air,  or air/fluid mix, or all fluid (pressure 'in' at the master cylinder should equal pressure 'out' at the caliper bleeder).    

 

You already have the rear master cylinder removed so you might clamp it in a soft jawed vise, then plug off the outlet port, then see if you can push on the piston & build any  pressure.  

 

Or, just remove the piston then look to see if the pressure side sealing ring looks worn or damaged.

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@dirtrider,

 

Thanks again for your insights. The primary seal makes perfect sense. I took the master off and disassemble. Everything looked clean and in great shape, nothing i could spot in the bore. Of course the seal could still just be worn and it would be hard to spot. 

 

I remembered having an issue years ago with rear bleeding and someone advised getting the caliper piston pushed back in as one could have air trapped beyond the bleeder. I put it all back together to give another go at bleeding with that in mind. 

 

With bubbles now at the master, I moved a good bit of fluid thru with an open bleeder and eventually saw those bubbles. With a closed bleeder, I get only mush of pressure and not what I call increasing with multiple pumps. I'll give bleeding another go at caliper and ABS.

 

If that does nothing, I'll do the bench test on just the master. @Michaelr11 thanks for the pointer on ebay. I hadn't thought of just replacing with a whole thing with a used unit. They seem pretty affordable. I couldn't find a BMW part number for a rebuild kit, do they even make one? Saw Boneyard had them back in the pre-Magura-mess days. 

 

I'll report back. Thanks again for the advice and consideration. 

 

Best,

Matt

 

BTW, I do have a Mityvac kit, though I've never found it as effective as hoped. If any tricks with applying vac would help, send away. 

 

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32 minutes ago, Hotmop said:

 

 

BTW, I do have a Mityvac kit, though I've never found it as effective as hoped. If any tricks with applying vac would help, send away. 

 

 

Afternoon Hotmop

 

I haven't tried a vacuum bleed on the ABS II in years, I never had much luck doing that on the 1100 rear as it just slowly sucked the fluid under the air in the system. Then when BMW came out with the bulletin on not using vacuum on the ABSII system I quit even trying.

 

Was your rear brake system full of fluid after your last ride where the pedal went all the way down? If so then you most likely don't have a bleeding problem but you DO have whatever failed on your last ride that caused the excess pedal travel & no rear brake.

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On 8/4/2019 at 6:22 AM, dirtrider said:

You already have the rear master cylinder removed so you might clamp it in a soft jawed vise, then plug off the outlet port, then see if you can push on the piston & build any  pressure.  

 

Or, just remove the piston then look to see if the pressure side sealing ring looks worn or damaged.

 

@dirtrider,  

 

Reporting back. I just got the chance to work on the bike again this weekend. I took the hard pipe fitting out of the top of the rear master cylinder and did a simple pressure test. Just holding my finger over the port, I could push the pedal all the way through it's travel. It gave some pressure, but definitely gave the feeling that the pressure seal was just moving thru the fluid.

 

It's off the bike now and under magnification, the seal edges do have a "polished" look to them. 

 

On the crazy side, I started looking for 12mm brake seals from other makes/models. Ever know anyone that compared the seals from this Ducati 12mm service kit?  (Brembo 110436292) That wiper seal look really close to to this one. I've emailed a supplier to see if they might measure it more exactly.

 

Other than that, I guess it's the gamble of a used unit or the $150 for new one. 

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On 8/3/2019 at 3:38 PM, Hotmop said:

Bike has 48k miles. I've owned since new.

 

The day I was riding home to yank the rear wheel for a new tire, my rear brake pedal went to full travel with little braking effect. I see no leaks at the caliper or master cylinder so I though 'oh crap, ABS unit'. This lead to removing the tank and at that point I figured I was all in and decided to lube the spline and replace the clutch. Yes, dominos. And, the ABS unit was not leaking. I put braided Galfer brake lines on last year (front and rear). 

 

With the splines lubed and clutch replaced and even final drive pivot bearings replaced with Nushings, I'm back to that rear brake problem.

 

Bleeding results seem kind of odd. I can push to full travel by hand, hold, open bleeder; I get nearly no flow. If I open the bleed valve and just pump, I get a flow of fluid and it drains from the reservoir. I go back to trying to get pressure and bleed, nothing moves.

 

I've removed the master from the bike and short of taking it apart, it looks in good shape. No corrosion or signs of weeping fluid. 

 

I'm reading that the rear master does not usually fail. I was considering a rebuild kit, but maybe that's overkill?

 

Lastly, I'll admit I have a specific dislike of working on brakes and this bike has surely seen far less fluid flushing than it should have. (Though it was done last year with new lines). 

 

What the heck am I missing? 

 

 

 

I had the same issue with the rear master cylinder on my '96 R1100RT.

 

I found it illogical that I could buy a rebuild kit for the front, but not the rear.  If I remember correctly, there was even a rebuild kit for the rear MC on older K bikes -- which appear to have a very similar (albeit not identical) design.

 

I bought a used one on Ebay and it didn't hold pressure either.  In hindsight, that was a bad decision.  Why would the 20 year old rubber seals in someone else's master cylinder be any better than the 20 year old rubber seals in mine?

 

Like you, I poked around online to see if I could find replacement seals from anther application.  I think there was a Guzzi part that looked promising, but I never pursued it.  

 

In the end I bit the bullet and paid the Bevarian overlords their $150 and went on my way.

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Promising news!

 

The Ducati Brembo kit measures up to be identical. Just received last night and haven’t reassembled the rear master yet for a full test.  I’ll take pics and post full details shortly. 

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  • 5 months later...

I started to have this problem today. Local BMW shop replaced brake lines with ss lines last month. Rode yesterday and had no problems, left today and no rear pressure. What was your end result with the Ducati kit? Have a 96 RT with 43,000 miles. 

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I am going to try a fluid bleed from abs unit first.  I do not think bleeding from rear caliper will work, my understanding is that fluid travels from reservoir to abs unit to caliper. Am I correct? Reviewing ibmwr maintenance manual also recommends to bleed from abs. 

Looking at videos from Illinoisbmwriders I see the location of abs unit but I have not found which side is rear. I am not very mechanically inclined, but will have someone who is looking over my shoulder to make sure I do not blow things up.  

Looking for advice on where to look for more info, please. I want to learn how to do more maintenance myself. 

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The failed seal feels quite different from air bubbles. Bubbles make the lever feel soft, but with some measure of increasing pressure. A failed seal will go all the way down with a feel of some dampening, but never builds any pressure. The seal and piston are just "passing through" the brake fluid.

 

Once you have the fuel tank off the bike to reach the ABS unit, you can visually trace the line from the rear reservoir up to the ABS fittings. Not much in your way at that point. 

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12 hours ago, evilkevin said:

I am going to try a fluid bleed from abs unit first.  I do not think bleeding from rear caliper will work, my understanding is that fluid travels from reservoir to abs unit to caliper. Am I correct? Reviewing ibmwr maintenance manual also recommends to bleed from abs. 

Looking at videos from Illinoisbmwriders I see the location of abs unit but I have not found which side is rear. I am not very mechanically inclined, but will have someone who is looking over my shoulder to make sure I do not blow things up.  

Looking for advice on where to look for more info, please. I want to learn how to do more maintenance myself. 

 

Hi evilkevin.

Can you tell us what bike you are dealing with.

This would be a lot cleaner if you started a new thread.

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19 hours ago, evilkevin said:

I am going to try a fluid bleed from abs unit first.  I do not think bleeding from rear caliper will work, my understanding is that fluid travels from reservoir to abs unit to caliper. Am I correct? Reviewing ibmwr maintenance manual also recommends to bleed from abs. 

Looking at videos from Illinoisbmwriders I see the location of abs unit but I have not found which side is rear. I am not very mechanically inclined, but will have someone who is looking over my shoulder to make sure I do not blow things up.  

Looking for advice on where to look for more info, please. I want to learn how to do more maintenance myself. 

 

Evening  evilkevin

 

Before getting too involved with bleeding the ABS make sure that you have fluid IN the bottom of the rear master cylinder reservoir. 

 

There is a rubber bladder in the rear reservoir, sometimes people will put the fluid on TOP of that bladder so the reservoir looks full but there is no actual fluid in the bottom of the reservoir getting to the master cylinder.

 

If you are not getting ANY  rear pressure from the brake pedal then that sounds like more than just an air in the system problem as even with air  in the ABS module you can usually pump the pedal a few times quickly & get s-o-m-e pedal pressure. 

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