Rear brake INTERMITTENT failure!?

[Lucky Phil]

5 hours ago, LaGrasta said:

I actually bought a generic version of this tool over 20 years ago and absolutely love it, and rely on it. I use for both, cars and motos.

It's best to avoid the old pump the pedal and/or lever bleeding process if you can on older vehicles most especially. It's not uncommon for corrosion and contaminants in the system to be at the end of the master cylinder where the piston and seal never get to in normal operation. Then you flush the fluid or bleed the brakes using the old pump the lever/pedal style and the seal is now pushed all the way down to the bottom of the master cylinder bore where it never normally reaches and bingo the seal is damaged. Similar reason for changing the slave cylinders on old drum brakes when you fit new brake shoes. If you don't when the slave piston is pushed all the way back into the cylinder fitting the new shoes it wrecks the seals 90% of the time. Pressure bleeding is better and safer these days and the bleeders are cheap to buy. You also don't get air sucking past the bleed screw threads giving a false reading of bubbles which often happens using a hand pump vacuum bleeder. Clutches don't have the same issue as the master cylinder and slave pistons always move full travel in use.

Phil  

[Gmc28]

18 hours ago, Lucky Phil said:

It's best to avoid the old pump the pedal and/or lever bleeding process if you can on older vehicles most especially. It's not uncommon for corrosion and contaminants in the system to be at the end of the master cylinder where the piston and seal never get to in normal operation. Then you flush the fluid or bleed the brakes using the old pump the lever/pedal style and the seal is now pushed all the way down to the bottom of the master cylinder bore where it never normally reaches and bingo the seal is damaged. Similar reason for changing the slave cylinders on old drum brakes when you fit new brake shoes. If you don't when the slave piston is pushed all the way back into the cylinder fitting the new shoes it wrecks the seals 90% of the time. Pressure bleeding is better and safer these days and the bleeders are cheap to buy. You also don't get air sucking past the bleed screw threads giving a false reading of bubbles which often happens using a hand pump vacuum bleeder. Clutches don't have the same issue as the master cylinder and slave pistons always move full travel in use.

Phil  

which bleeder system do you use?  i’ve got an older bleeder i’ve been using, and its been fine but not loving it. 

[gstallons]

If I were you I would purchase speed bleeders for your calipers. These replace your factory bleeder screws and they have check valves built into them.  You can Google them and see if you want them or whatever you want to do .

[Lucky Phil]

3 hours ago, Gmc28 said:

which bleeder system do you use?  i’ve got an older bleeder i’ve been using, and its been fine but not loving it. 

https://www.motiveproducts.com/collections/brake-bleeder-kits

 

You can buy decent ones now for about half the price of these. I've had mine for 8 years or so.

Phil

[gstallons]

This setup looks a LOT better than the Phoenix stuff I got a long X ago !

[audiomick]

On 7/21/2024 at 9:07 PM, gstallons said:

...speed bleeders for your calipers....You can Google them...

I don't have these, and don't expect to be buying some, but this is the brand that is so dominant here that one could believe that they are the only manufacturer of such systems.

https://www.stahlbus.de/index.php?language=en

[Paul J. Russell]

I had the same problem.  I took apart the master cylinder for the rear brake and found that it was corroded on the inside.  I found a matching master cylinder on a Ducati website and purchased it.  You do have to bleed the rear brakes and it should be a two person job.  The rear calipers must be turned upside down.  However, I found a way to screw the rear calipers to a wooden stool upside down and the bleeding went fine.  Problem solved!!!!!  

[activpop]

@audiomick, those oil drain valves look interesting also.

[gstallons]

Paul , I repaired a front caliper on a Yamaha 4-wheeler a few weeks ago . It was seized from corrosion too. I pressed the piston out w/the front brake and started work on it. It took about 20 mins. and assorted pics to dig out everything from the bore of the dust seal and piston seal bore before I was satisfied . I always use Raybestos brand brake assy. lube going back together.