New Rider
Currently Offline
Posts: 26
Likes: 0
Joined: Apr 22, 2013 19:57:11 GMT -5
|
Post by chris9183 on Apr 22, 2013 20:08:23 GMT -5
Hello!
The last couple of days I've been trying to replace my brake fluid in my rear brakes. I bled the old fluid out, and I'm certain there's no air in the system. I am doing the steps in the usual order while keeping the reservoir filled: pump the lever 3 times, hold it in, open and close the caliper screw down by the wheel, and I can repeat this step infinitely and the lever never has any pressure behind it. I even tried closing the caliper screw and just pumping the lever over and over again to try to build pressure...nothing.
I'm not so sure that the master cylinder could be damaged...it's doing everything properly, it's moving fluid and not leaking any. When I pump the lever there is clearly fluid moving through the clear tube I use to bleed the DOT3. But for some dadgum reason, the lever stays squishy and won't pressurize one bit.
I'm not convinced that I'm not just doing something wrong here. Is my method above incorrect? If so, could someone go over the method I need to follow to pressurize the brake? Otherwise, what could be going on here?
I really appreciate any help.
|
|
|
|
Post by alleyoop on Apr 22, 2013 20:28:03 GMT -5
|
|
New Rider
Currently Offline
Posts: 26
Likes: 0
Joined: Apr 22, 2013 19:57:11 GMT -5
|
Post by chris9183 on Apr 22, 2013 23:56:37 GMT -5
Well that's an informative video, but he didn't go into any detail about re-pressurizing the brakes unfortunately.
Is it possible my master cylinder is broken, even though it seems to be doing its job pushing fluid through the tubes?
|
|
|
|
Post by alleyoop on Apr 23, 2013 0:34:24 GMT -5
|
|
New Rider
Currently Offline
Posts: 46
Likes: 1
Joined: Mar 2, 2013 18:43:48 GMT -5
|
Post by oldbikerider on Apr 23, 2013 4:06:01 GMT -5
By chance do you have the two piston caliper? I know this sounds odd but someone else here on the board had a similar issue with a two piston caliper that was solved by putting in new pads and using the old pads as a shim. Something about the pistons got to a certain point and refused to go any further, no breaking power and the lever was spongy, and it refused to be bled even though it was moving fluid. If someone else doesn't find that thread, I will later this afternoon.
|
|
New Rider
Currently Offline
Posts: 26
Likes: 0
Joined: Apr 22, 2013 19:57:11 GMT -5
|
Post by chris9183 on Apr 23, 2013 7:44:35 GMT -5
Yes it's a two piston caliper. Sounds a lot like my problem.
|
|
|
|
Post by jeepsteve92xj on Apr 23, 2013 7:58:23 GMT -5
|
|
|
|
Post by RapidJim on Apr 23, 2013 8:44:37 GMT -5
Usually the reverse proceedure works quite well. You may have a master cylinder problem where it is pushing fluid but as Alley said it may be pushing back past the seals.
Take the line off the master and hold your finger over the outlet hole and gently squeeze the handle a few times to see if the master will build pressure and hold.
Jim
|
|
|
|
Post by rockynv on Apr 23, 2013 12:06:22 GMT -5
I use a vaccuum bleeder now and don't have these issues any more. Look for a sale and they are not that expensive.
|
|
|
|
Post by jeepsteve92xj on Apr 23, 2013 12:12:21 GMT -5
|
|
|
|
Post by urbanmadness on Apr 23, 2013 12:42:29 GMT -5
Here's what I do to get fluid down... Open the bleeder, and just keep pumping it, it will get some fluid down there. Then bleed as normal.
|
|
|
|
Post by oldchopperguy on Apr 23, 2013 14:01:40 GMT -5
Hey, Chris9183,
Yup, I'm the old geezer with the EXACT same problem!!! Now all scoots are different, BUT I'm betting you're experiencing the same problem I had on my Xingyue Eagle. After trying EVERYTHING from the lever back, I finally bought a new rear 2-piston caliper. When placing it over the disk, I found the gap between pads was DOUBLE the thickness of the thin disk. (The old caliper showed the pistons to be WAY out from their normal position). You can inspect for THAT by looking at the exposed pistons from the rear, while the caliper is still on the scooter. (Removing/replacing the caliper is SUPER-EASY!) Just two bolts.
I'm guessing these calipers are used in different applications, on disks up to 1/4" thick... I took a pad from the original caliper, ground off all the friction material and used it for a spacer BEHIND the new inner (moving) pad. PROBLEM SOLVED!!!
After again back-flushing and filling as/per Alleyoop's great video post (I got a cheap animal feeder/syringe off eBay. You might find one at a farm supply store.) The brake now performs fine.
It's clear that even new, the internal pistons in the caliper must travel farther than they should, just to get the inner pad to meet the disk. Then, after a couple of seasons, the pads wear just a teensy bit, and suddenly the pistons are fully-extended and you have NO brake!
Lacking a used pad, you could easily cut a "biscuit" from aluminum, brass or steel flat-bar-stock, using a pad for a pattern. I'm NOT sure however, that pushing the pistons in the original caliper BACK into their original position to allow for the spacer is a good idea. Corrosion and general old "schmootz" might make them sticky, or leak. Even though money is awfully tight, I would still suggest replacing the rear caliper. They seem to run around $50 shipping included depending on where you get it. (Alleyoop, please chime in here... You know more about this than I do!)
One final note... I found that while back-flushing/re-filling, like in the video, I could easily squeeze the syringe and watch the fluid enter the master-cylinder at the same time. Then, I could keep the syringe "pressured" gently, while reaching down and closing the bleeder. This absolutely prevents any air from sneaking in... LOL!
The dual-piston REAR brake definitely has a slightly longer "squeeze" on the lever than the single-piston FRONT unit. Since they use the same lever/master-cylinder assembly, this must be due to the itty-bitty reservoir having to push the 2 pistons at the disk. Even though the front piston is larger, the dual-piston rear still uses a tad more juice to push them. But now, mine works fine.
I'm betting yours will too!
Hope this helps!
Most sincerely,
Leo in Texas
|
|
New Rider
Currently Offline
Posts: 26
Likes: 0
Joined: Apr 22, 2013 19:57:11 GMT -5
|
Post by chris9183 on Apr 24, 2013 14:24:23 GMT -5
Thank you for your very detailed reply. Unfortunately I now have a new problem. One of the screws holding the lid on the reservoir has been stripped bare...I've tried every method to get it out, short of welding a nut to the top of it...so, I just went ahead and ordered a whole new master cylinder off ebay. Kinda had to.
If this new master cylinder doesn't solve the problem, I'll know for sure it's the caliper, and then I'll replace that (or if it's a problem similar to yours, I'll do what you recommended).
Thank you very much!
|
|
|
|
Post by oldchopperguy on Apr 25, 2013 7:59:22 GMT -5
Thank you for your very detailed reply. Unfortunately I now have a new problem. One of the screws holding the lid on the reservoir has been stripped bare...I've tried every method to get it out, short of welding a nut to the top of it...so, I just went ahead and ordered a whole new master cylinder off ebay. Kinda had to. If this new master cylinder doesn't solve the problem, I'll know for sure it's the caliper, and then I'll replace that (or if it's a problem similar to yours, I'll do what you recommended). Thank you very much!
And you must have my scooter's twin brother... LOL! My first "fix" was also to check out the master cylinder. It actually WAS bad, as it was not pumping much through the line. It would still apply the brake though, but weak. It looked like it came out of a Chinese dumpster, and sat in the weather for a year... Probably it was. The FRONT master-cylinder assembly was shiny and nice... Go figger... When removing the cover, one of the screws broke off, but at least I could see that the fluid was passing by the piston, so I too ordered a new assembly from eBay. I put it on, figuring THAT would fix it... NOPE! However, it was now properly pushing fluid to the rear caliper, and would give a solid "squirt" out the bleeder. But still NO brake action.Since the line was not leaking, that left ONLY the caliper itself as the culprit. After examining the original caliper, and seeing the pistons were overly extended, I placed the new caliper on the disk and saw it too would require the pistons to extend FAR more than I was comfortable with. That led me to make the spacer from the old inner pad. The new caliper might work OK, but I didn't chance it. I figured that after a little wear to the pads, it too would suddenly fail due to the pistons reaching their maximum-possible extension, and I didn't want to experience that while riding, OR go through all the hassle of repair again... Even if it was a couple of years down the road... LOL!You won't regret replacing the master cylinder for sure. It might even fix the problem, but I'll bet the Chinese farm that it's still your rear caliper experiencing "full-extension" of the pistons, at which point the fluid just blows by them. I'm surely no expert on these often "marginally" engineered scoots, but I'm getting pretty savvy on the brakes... If I can be of any advice, feel free to PM me any time. Wishing you the very BEST with this irritating problem,Leo in Texs |
|
|
|
Post by jeepsteve92xj on Apr 25, 2013 8:11:20 GMT -5
For the screws - I use a Dremel with the thin cut off wheel, usually I use a worn down one for the smaller radius to cut a slot for a straight blade screw driver. Then replace the screws with an Allen style.
Even if you have a working reservoir window, undoing the screws and redoing them a few times a year saves the grief. Don't over torque them. A tiny amount of anti-seize my help too - don't get it into the fluid. Just enough to prevent the galvanic reaction.
|
|
..BAD TO THE BONE..
