Rear Brake Hung Up

[stixx3969]

Hi gang.
Had a nice day in Mid Missouri so I drug the ol' Roketa out of the shed. Got her fired up and went for a little ride. A few blocks from the house after using the rear brake it hung up and started bogging me down but it didn't lock up. I limped back to the house slowly in first gear because that's all that would pull it. I didn't really overheat too bad but I need to know what to do now if it's still hung after everything cools down. I figure sitting all winter is the culprit and the piston is gooey. New Fluid? , Bleeding?
Ideas.

[blimpman]

Happened to me too. I just opened the bleed valve and let the pressure out... Been OK since then. I would recommend that the fluid be replaced with known good quality DOT 4 fluid. I have done this to my front brake and the rear brake is next.

[ob1]

Seems like someone said the reservoir was overfilled. this reduced the area for the brake fluid to expand as it heated, forcing the brake caliper to absorb the expansion, dragging the brake.

[msRandi]

one check the vent and brake fluid, can,t be over full. open bleeder and move the piston back, close the bleeder and hit the brake. see if wheel speens? if the piston keeps sticking. you need to rebild or replace it.

[stixx3969]

Thanx for the tips. It loosened up after I let it sit for a little while. Think I'll crack the bleeder and check the fluid. I think it'll be ok. Thanx again!

[red2003]

Seems like someone said the reservoir was overfilled. this reduced the area for the brake fluid to expand as it heated, forcing the brake caliper to absorb the expansion, dragging the brake.

Yup, that's more then likely the culprit. All good advice. Let us know what you find out :D .

[fatboy250]

Ok, Dad and I have figured out the deal on this. If you look at the bottom of your rear break master cylinder (not the slave at the wheel) you will see where the armature pushing in has two linkages with a bolt and two nuts for adjustment. Well, even with the nuts in the lowest setting where the linkages are both resting on the top nut, the master cylinder armature is still being pushed into the master cylinder creating some pressure. So, you will need to permanantly remove the nut between the two linkages and shorten the bolt (a grinding wheel may work well) so that the two linkages are touching. This will allow the master cylinder armature to release all the way out. We believe it's not necessarily a design flaw, but more of where the weld ended up for the bracket that holds both the rear foot peg bracket and the master cylinder. If this bracket weld had been about 1/2" higher the master cylinder armature would be allowed to extend all the way out with the stock bolt and nuts adjustment. I will try to get a picture of this to show more when I do mine. Dad is in the middle of getting his taken care of. So far this has been the only "problem" that was not a result of hard riding. There's no dissatisfaction with these, but he and I are both relieved to finally figure this out.

Jason

[liverchip]

Good find there Jason!

[mdsuave13]

any recommend a specific fluid? i used prestone dot 4 fluid.. it seems to be working fine, so far no braking issues whatsoever except for when my front caliper almost fell off because a bolt fell out while riding (managed to back track and find it in the road!)

[ambassador]

Prestone dot 4 here...

[fatboy250]

Dot 3 or 4 is fine. I had 4 when I bled mine so that's what I replaced it with.

Yeah, VFRFlyer had his hang up twice when we were out a couple of weeks ago. The fix is pretty straight forward, but I figure 20-30min and mine should be done. I just have to set aside the time to do it. Kind of low priority since mine never hung up as much as Dad's did.

Jason

[mdsuave13]

hey jason, how are your tires working out for you? you still like them?

you have the cheng shin's correct? i've been considering getting a spare set of wheels with a set of them so i can have street tires for commuting, and the knobbies for when i play on unpaved roads (even tho they are pretty terrible tires)

[fatboy250]

Ride is fantastic. just don't expect to do any serious mud riding. They also have better side wall rigidity for cornering. These bikes will get down if you want to corner. I worn a pretty good place on my right shoe from when I touch from time to time (exit ramps)

[cycleway4]

Hi Jason.........I did your fix to my rear master cylinder linkeage today....
I had ridden the bike around the property here short trips,..but went out on first road trip today...brake began to drag within a few minutes...
so came back and found the problem to be just as you say....no free play in the linkeage........................took out the jamb nut [in between]..all ok now............

[fatboy250]

Yeah our bolt had to be shortened because the two linkages would not touch otherwise. Only the cotter pin in the top and the one nut at the bottom. Both ours are working great now and Dad is finally happy! :lol:

[cycleway4]

same here...had to shorten the bolt

..........I cant believe more havent had to go this route....it must be a common problem in need of a similar fix

[fatboy250]

Some may just be content to crack the bleeder valve every time it happens. Well, I was at one time, but that got old pretty quick having to stop in some of the least desirable places (side of the interstate, back road with very little shoulder, etc.) Glad to have it fixed finally and glad you were able too!

Jason

[deputygene]

Ok, I think I know what you are talking about by shortening the bolt. My brake pedal has a bolt stop adjustment that should solve this problem, I have adjusted it and adjusted it, still it feels like there is air in the system and if it heats up it eventuually locks up. Then I have to get my 8mm wrench and crack open the bleeder valve. Doesn't have anything to do with amount of brake fluid in it, it locks up with the reservoir almost empty.
A couple questions, is filling the brake fluid reservoir and pushing on the brake while opening the bleeder enough to bleed the system? I don't seem to get any bubbles. I didn't notice this at all riding dirt, but I wasn't going as fast or far between stops.
My son's Lifan QP 100 has a disc front brake, when put together it rolled kinda hard, noticed that one side of the brake was dragging. Fixed it by installing a washer between brake and fork, a way to kind of shim it, no more problems. I am wondering if the same thing is wrong with our bikes. Is the brake a little off-center, causing one side to rub, heating up the works causing the fluid to expand?
If I take the bolt out, how much to grind off? Any pictures for the mechanically challenged?

[fatboy250]

A couple questions, is filling the brake fluid reservoir and pushing on the brake while opening the bleeder enough to bleed the system?

Is the brake a little off-center, causing one side to rub, heating up the works causing the fluid to expand?

If I take the bolt out, how much to grind off? Any pictures for the mechanically challenged?

1)Yes
2)Ours weren't, but yours may be
3)About a 1/4-3/8". You can put it back in after you remove the nut and see you would need to grind away about the width of the nut.

Check out my gallery http://www.chinariders.net/gallery2/main.php?g2_itemId=1336

I added some pics of the shortened bolt and how the linkages look afterwards.

Jason

[molypod]

My Rear Brake has always locked up going down hill in the dirt but then most bikes I've had did that. I use alot of front braking and low gear to go down steep hills. I never thought to check the linkage.

FatBoy250,
I see you've also added a spring to your Clutch what difference can you feel?

[red2003]

Molypod, they mean the rear brake hangs up. Like it is ALWAYS on, even when the brakes aren't being applied. The only fix is to remove all the pressure the pedal is putting on the brake linkage. With the pedal adjuster all the way loose, it still will hang. The fix is as Fatboy has suggested. Cut off that bolt, and remove the nut. On mine, this STILL wasn't enough to totally remove all the pressure on the master cylinder, so I redrilled the mounting holes and moved the master cylinder up and out of the way. Problem solved!

[molypod]

thanx Red,
sounds like that would be a real drag.. (pun intended)

[fatboy250]

FatBoy250,
I see you've also added a spring to your Clutch what difference can you feel?

Performance none. Clutch lever feel great. No slop/slack in the lever and it completely disengages back to the stop when released.