I'm having an issue with my rear brake. I took a 30 minute ride last night on the freeway, consistent 65 mph, and when I got off the freeway I noticed my brake pedal was very stiff and my rear brake was slightly applied. These are the stock style hydraulic drum brakes. About a year ago I replaced the shoes, wheel cylinder and master cylinder. When I got back on the bike several hours later the brake had loosened up and was back to normal but it was stiff again one I got home. Any Ideas on what could cause this? I wasnt doing any braking on the ride there or back except from when I got off the freeway.
Post by panache on Jul 16, 2006, 8:43pm
Here's a guess -- you might have a wee bit of brake drag. After a bit of riding, either the shoes expand a bit from the heating or some moisture in your brake fluid vaporizes from the heating and locks up your brakes. The heating might also be caused from rear axle bolts being too tight overheating your wheel bearings. I'd check the rear wheel bearings for correct side play (just lifting the rear wheel and pushing/pulling sideways), re-adjust the rear drums and change the brake fluid. I'm sure others on this board will have other suggestions -- like checks for the brake backing plate or master cylinder plunger settings... Hope this helps.
Post by 108 on Jul 16, 2006, 10:11pm
xnohax, Make sure you have some free-play at the master cyl. pushrod and that the piston is returning completely. There might also be a problem with the residual pressure valve in the bottom of the bore and pressure is building up from the heat , holding the brake on.
Post by sleeper on Jul 17, 2006, 7:39am
I've been switching older bikes to "Dot 5" brake fluid. it's synthetic & ya just don't have the headaches from condensation & rust as w/Dot 3
However it does require a extremely thorough clean out of ALL existing parts & hoses..FWIW
Post by xnoahx on Jul 17, 2006, 7:46am
What is the best way to go about switching to dot 5 fluid? Could I run a mild solvent through the brake system or should I just drain the old stuff and start running the dot 5 through it?
Post by PanPal on Jul 17, 2006, 4:27pm
Something I have seen in the past also is a bad brake hose. The inside can start to scale so presuure to the wheel cylinder can be applied, but the scaling acts as a check valve when fluid tries to return to the master cylinder. FWIW.
Post by xnoahx on Jul 18, 2006, 3:33am
I should probably replace that brake hose anyhow. Its looking pretty crappy on the outside
Post by sleeper on Jul 18, 2006, 6:41am
I use de-natured alcohol for cleaning & then rebuild the clys & masters... (+ new hoses never hurt either...)
Works fer me...
Post by caschnd1 on Jul 18, 2006, 4:49pm
If you get water mixed in with your brake fluid it can cause exactly the symptoms you are describing. As you ride and use the brakes the water in the line expands from the heat and applies the brake. When you stop and it cools off, the water contracts and the brake frees up.
I'd recommend purging the brake lines with the correct brake fluid.
Post by xnoahx on Jul 19, 2006, 8:29am
Thanks for all the replies, I think im going to purge the lines with DOT 3 and see how that goes, I will probably also replace the rear hose and if that doesnt help me out I will try DOT5
Post by sleeper on Jul 20, 2006, 6:17am
Dot 3 seems to create moisture.. For this reason it is a good practice to *flush* the system perhaps yearly depending on the machine's use, or lack there of.. ..
I do the Dot 5 flushes every 5 yrs !!! ;D
Post by jellero on Aug 4, 2006, 5:14am
dot 3 absorbs moisture from the air, so every time you open anything up you get more water in there. that is why you are suppose to use only a new, unopened can to refill. not that i do that but i do change it out once a year. it was my understanding that dot 4-5 have higher boiling temps so are used in the newer machines like superbikes in races where you have to use the brakes much more than pans. i've had my brakes fail due to watery, dirty fluid and it is not a good feeling. j