front brake lock up

[doode3005]

hello all, i have an issue with my newish r65 and as i'm just getting into the airhead world i could use some advice. about a month ago i bought a '79 r65. after about 2 weeks of casual riding, i was on my way home at a stoplight and the front brake felt like it was applied (couldnt roll easily under my power). since i was just outside my neighborhood i decided t ride home and not pull off the road but inside my neighborhood the brake was locked bad enough to kill the engine in 2nd gear. i pulled off and shut down. the brake was steaming a bit.

i called my local beemer repair shop and they picked it up (also where i bought it from). they said the master piston wasnt retracting properly and ordered a brake rebuild kit. after a week i got my bike back. the brake seemed loose and wasnt giving me full stopping power. but now its back to its old tricks and is giving me trouble again, i am getting braking power though.

any help would be greatly appreciated. thanks in advance.

[Red_Hen]

I had a similar issue with my K75.  I'd replaced the front master cylinder and bought the part used on Ebay. There was a bunch of dried up brake fluid present and soaking it a can of degreasing fluid (a gallon can from O'Reillys) didn't do the trick.

The culprit was a clogged air relief hole- it's really tiny.  Here's what a friend from MOA said:

 "I really think the relief hole is your problem. How to fix it is the question."  Then he asked me:

"Have you taken the reservoir cap off and watched it? You can see the hole, it's at the end of the round section in the reservoir that is the cylinder outside. When you release the brake, you should see a small spurt of fluid from it (it will show on the surface of the fluid in the reservoir.)"

When I did not see the small spurt of fluid, I took off the front master cylinder and found that the relief hole was clogged with dried up brake fluid.  I used a small and sharp sewing needle to clear the obstruction.
The other option is to buy a ultra sonic machine for Harbor Freight and free up the hole that way.

It's REALLY dangerous to ride your bike like this - trust me!  I was on the freeway when the front brake started engaging - SCARY!!!

I carried a little 11mm box wrench to release the pressure on the caliper but it wouldn't take long for the pressure inside to build up again inside.

I'm almost sure the relief valve is your problem.

Let us know what happens!

[doode3005]

thanks for the quick response. im calling the shop in the morning and will ask if they can check that out. ill let you know what they find.

[bruce_launceston]

 (Cut & pasted from archive) - I can confirm that the below procedure cleared the brake fluid return hole and cured my front brake problems.

front brakes locked on tight22.11.10 at 21:00:43      

Hot here today. I was riding home from work and I noticed that there was almost no freeplay on my front brake lever.
I got to about 500 metres from home and I had to pull over as the free play had all dissapeared and the front brake had locked on tight. I tried to slowly ride onto the footpath but when I got onto the grass the front wheel locked and the back tyre just spun in the dirt.
I walked home and got a 11mm spanner and some tubing and went back and released the bleed nipples on both calipers.
This freed up the brakes and I was able to ride home.

I sucked all the fluid out of the mc reservoir and removed it. The tiny hole in the bottom was blocked solid and it took me 30 or 40 minutes of digging around with a 29 guage hypodermic needle before I got it clear. The hole is tiny, the needle was 0.33 mm so I guess the hole might be only 0.35 mm diameter.

I'm guessing that it has been blocked for a long time as the lever play was varying with the weather temp last summer. Since then I had got rid of some stubborn air bubbles and got the brake lever back to normal so when I rode today in the heat the blocked return hole meant that the brakes eventually locked on, the lever was rock hard.

I'm guessing it will also be a lot easier to bleed the brakes from now on.

Cheers Bruce

[Red_Hen]

Glad you got this cleared up Bruce!  

Brakes locking up at speed can definitely cause an accident!

[suecanada]

I had my front brake lock up once back in 1985....solid as a rock. I was in the city and it locked going very slow after a turn and I had to literary drag the bike to the curb...then the only option was to drain the fluid...had the wrench.... and ride all the rest of the city stoplights and 40 more miles with just the rear brake...from that day on I replace my brake fluid every year! Like taking a bath once a week...whether it needs it or not! Oak always says to change it too!

[doode3005]

okay, after 2 trips to the shop it is finally repaired. the rebuilt the entire front brake system. there were actually a lot of problems like 30 brake lines (just bought the bike). any way it works fine now and im having a blast riding it.

[suecanada]

Good to hear all is well now...going over the handle bars at speed is not a good thing. Try to always replace the brake fluid annually (and manually) I do since my experience in 1985. For $5.95 a bottle of which I throw out the rest after using a bit...it is not worth taking a chance. Brake fluid as you guys all know is hydroscopic and will absorb water and will turn into a real snot-like mess given time. A penny saved in this case is not a penny earned. Penny saved; pound foolish is really where the mistake is made! :-?