Losing rear brake after a good bleed.

MikeinNZ

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Hi all,

Just picked up my 2010 ten and the rear brake pedal keeps turning to mush.
We are 400ks into our 1200k trip home so not ideal. I called into an auto shop and grabbed some wire/fluid/one man bleed kit and after about 6 cycles of the ABS, alternating bleeding of the rear brake I managed to get a solid normal feeling pedal with new oil coming through bubble free.
It will hold pressure and still feels good overnight...until it gets ridden and the front brake is used. I have a horrible feeling the ABS pump is pumping air when the interconnect side of the brakes is operated. I have Bled it as above another 3 times now with the same end result.
I have researched the site and found a few threads but am low on Data so hoping there is a brake Guru that could help explain?
Is it worth bleeding the front brake at the same time? As I’m not sure if the fluid from the front brake transfers to the rear during interconnection. No ABS lights on and the pump does as it should and sounds ok during the bleed procedure.
 

2daMax

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Regardless of number of times you bleed, as long as the abs pump is not actuated, air is still trapped inside the pump and will give you that missing feeling. The procedure for the S10 for bleeding is to bleed first for the front and rear, then cycle the abs pump using a procedure mentioned in the service guide (or go to the Brake section of this forum and there is a sticky on it), and then do a final bleed. If you do observe bubbles at the Final bleed, it means there are still air in the pump. Repeat until there is no more air bubbles. This can take multiple cycling of the pump to completely remove the air. So dun give up easily.
 

MikeinNZ

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Thanks for the comments 2damax, I have been cycling the abs pump and then bleeding and cycling then bleeding per the thread procedure multiple times and on multiple days now. I get it to being near perfect and at the end of the days ride it has no rear brake.
It’s sucking air from somewhere. There’s no leaks from anywhere and has me stumped. I would have thought if it had a bad seal in the master cylinder it would leak on the ground or not produce pressure.
I have tried to buy a master cylinder kit and a master cylinder here in NZ but there are none here or Australia. Guess I’ll have to sort this one when I get it home.
 

2daMax

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There is plenty of air inside the pump is all I can say. Not a leak for sure. IF there is any leak, the high pressure of the fluids would jet out and leave signs of a leak.
 

MikeinNZ

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I have ridden another 500ks today and have found if I bleed the rear brake and then ride it and not use the front brake I still have a rear brake after a day of riding. As soon as I use the front only and it does it’s interconnect thing the rear gets full of air. Looks like I’m looking for a new ABS pump
 

EricV

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I very much doubt you need a new ABS pump. And they are expensive! Are you bleeding the front calipers? You only mention the rear. The entire system needs to be bled, regardless of what end you feel has issues. Bleed the entire system until you feel it's firm on both ends, then tie the brake lever to the grip overnight and if it feels soft in the morning, bleed the entire system again.

Unless you have a master cylinder leak, (possible), that should get all the air out of the system. Don't throw parts at it when you get home, find the failure point.
 

MikeinNZ

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I have bled both systems multiple times now over the past week and can get both feeling normal.
I am hoping the UBS operation is sucking air past a bad rear master cylinder seal otherwise I’ll be broke.
I rode another 400ks today on a good rear brake right up till I used the front first to brake during a corner if I do that a few times the rear brake is next to useless and full of air.
I will pull the rear master cylinder apart tomorrow and have a look at the bore and seals.
 

MikeinNZ

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you cant fix what is not broken, a nw master cylinder is cheap and can be R&R in 20 mins

Unfortunately there are none available in New Zealand or Australia so it’ll have to come on a slow boat from somewhere? The good news is I have 320ks to go today and I’ll be home.
Here’s some pickys of our trip so far Auckland to Picton. 2132607C-FB6D-4586-80A3-0251A52E2DED.jpegB87AE095-FFD3-438B-A89B-D90648781062.jpeg0A76F3B4-9E33-4D38-B27E-7D56AB01E22B.jpeg83981424-10C9-4A18-A2D4-EAA58E28751D.jpeg
 

MikeinNZ

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Update: Fitted a master cylinder kit to the rear and bled everything x10 and then once more for good luck. Went for a ride into town and did some unified braking and lost my brake pedal in about 5 minutes :(
Bled the rear again which was full of bubbles.

Pulled the ABS unit out of the bike, took it to work and pulled it apart. The Brain side unscrews from the valve side. It has 6 seals, some contacts and a connector for the pump motor.
I couldn’t believe how much dirt had made it’s way into the cavity. The ECU side has drain vents on the lower side which were totally blocked with dirt.
Anyway, Spent an hour cleaning and have put it back together with Fuel tank sealant added to the seals and have sealed up all of the external valve block pressings.
I will put it back in the bike and try it but not holding my breath.... here’s a photo if anyone’s interested.
824562CF-FE89-4725-83B4-51D0B922ACE8.jpeg
 

patrickg450

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I hope you get it fixed, I have not had any success finding anyone who can or will service the unit.
 

MikeinNZ

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I rode 500ks yesterday and still had a rear brake at the end of it.... I bled it last night and still had a small amount of air that came through so I’m not saying I have fixed it yet. I will ride it this week and see if I can get an air free bleed.
 

MikeinNZ

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I Just wrote to Yamaha Australasia with this...

Hi, I have recently bought a 2010 Super Tenere and am having issues with the brakes.
I have fitted a rear master cylinder repair kit. bled the brakes including cycling the ABS unit many many times now and every time I use the front brake first (unified braking mode) the rear brake lines fill with air and the pedal goes soft.
I am an aircraft engineer and so a capable mechanic but this has me stumped. There are no leaks and I have even had the ABS unit out and vacuum and pressure leak checked all the lines.
The ABS unit has no faults and cycles perfectly on loose gravel.
I have studied the workshop manual diagrams of the ABS unit and apart from the master cylinders/ reservoirs can’t see how air can get into the system.
Have Yamaha ever seen an ABS unit cause this ? The bike has done 67,000ks so it’s far from new but I love it all the same.
Could you please give me some direction regarding this issue as I am reluctant to buy an ABS unit if it is an unlikely cause.
Thank you so much for your time and look forward to your reply.

Regards Mike

Will update if I get a reply
 

MikeinNZ

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Got a reply.......

Thank you for your contact.

  • Completely bleed the system as per the attached instruction explained in the service manual extract. Re-evaluate the performance.
  • Present and demonstrate the issue to a dealer for confirmation and comment. The dealer will either recheck the bleeding procedures or consult with Yamaha for diagnosis assistance.
 

EricV

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I rode 500ks yesterday and still had a rear brake at the end of it.... I bled it last night and still had a small amount of air that came through so I’m not saying I have fixed it yet. I will ride it this week and see if I can get an air free bleed.
I curious as to what method you are using to bleed the system? Vacuum bleeder?

Probably something you are aware of already, but when vacuum bleeding you will suck air from around the bleed nipple threads. Bubbles in the fluid don't necessarily mean air in the system in that case. It may only be coming from the loosened thread connection. This can still happen in pressure bleeding when you have a nose on the bleed nipple to watch for air in the fluid, but it's less common since the pressure tends to push fluid out around the threads.

Pretty much the standard response from Yamaha. It's normal to want local eyes on the problem before they start suggesting upper level solutions for what could be a minor issue.
 
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