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How to improve brakes? (Warning: rambling)

DAMN maintenance and repair thread; including Farkle Fests! :boohoo:
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smdub
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How to improve brakes? (Warning: rambling)

Post by smdub »

Disclaimer: Having raced cars and ridden a lot of mountain biking, along w/ being an engineer, I am a brake snob. They should have little travel to the engagement point then be very firm to be force modulated. Squishy pedals and levers suck IMO.

Ok, so on to my main question: I have some play bikes to teach wife/friends. XR100 w/ drums on both ends. Those that suck as bad as those old 70's era bikes w/ drums you'd borrow from a college friend and hoon around on (They honestly suck.) The TTR125LE is another one: Disc front and drum rear. The disc works 'ok' but the rear drum still sucks. Definitely not Brembo Ducati/KTM level but they are cheap toys so what can I honestly expect right? Enter the TTR125L (w/ 150cc BBK) project I bought this winter. Exact same year and bike as my LE except no e-start. It has AMAZING brakes front AND rear. As good feel as the Brembo KTMs. WTF?

I'll discuss the front disc first:
LE: works well but once engagement starts the lever can be pulled back almost to the bar for good stopping force. Its just squishy.
L: about the same amount of initial movement but goes super firm once pads engage. Pulling really hard will not let the lever go to the bar.
So I stare at these for a while and think - bleed the LE front brakes again, must have an air bubble. No improvement. So I stare some more - the L might have an aftermarket hose on it and that could be the difference. Braided cables make a big difference in feel in a car. That must be it! $50 and a Russel braided brake line later I was disappointed to find it didn't make much difference. I know pad material plays a big role in how much force you need to apply to get good stopping power but they shouldn't affect how firm the lever is with the bike stopped. What gives (literally)? Does the LE master cyl need a rebuild? Do I need to take the whole system off but intact, hang it vertically and bleed again? (is there an air bubble in there somewhere I can't get out?) FWIW, I've reverse bled it using syringes and that typically works great getting bubbles out. How does one make a play bike brake feel so awesome? I will slowly replace every part one by one until I can make the LE feel as good as the L if thats what it takes (or finally give up and swap the brakes between the bikes :lol2: )

Now the rear drum:
I've never ridden drum brakes that works very well. There is a reason bikes uses discs today. But I'm sure they can be tuned for racing and such and work much better than your never-adjusted-or-serviced mini bike drum. So what do you do to them? I'm too young to know these speed secrets. I put new aftermarket front shoes in the XR100 and its 'better' but not great. There are no adjustments in there. I've seen inside the TTR LE drum and no adjustments in there either. So you need to space out the end contact points so the shoes fit closer to the drums? Do you machine the shoes to better match the drum radius? What are the old-school racing drum secrets? I haven't taken the TTR L rear apart yet to see if there is 'special stuff' in there.

And while I'm discussing brake problems: The kid's SurRon rear brakes have a ton of travel until the pads contact the rotor. I know disc brakes have square seals that are used to retract the pads slightly. His seem to retract a LOT. Seems stiction may be causing the pistons to be stuck to the (cheap) seals? I'm wondering if I can lift the caliper up up off the rotor, and squeeze the lever a LITTLE and try to move the pads to a closer static location. He has small hands so has to run the levers fairly close to the bars. Coupling close levers w/ a lot of free play puts the levers into the grips by the time good braking kicks in. Not very easy to use or confidence inspiring.
Stephen (not Steve) - '08 Monster S2R1000 / '20 Husky 701LR / KTM '20 500 EXC / '17 150 XC-W / '21 E-XC / '21 890R / '19 Sherco 300FST / Sur-Ron LBX / Segway X160 / Sur-Ron Ultra Bee
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Laoch
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Re: How to improve brakes? (Warning: rambling)

Post by Laoch »

On my Freeride I replaced the pistons with stainless steel, I think. The oem were plastic. I also drilled out the hole in the banjo. Big improvement.

I’ve heard folks machine the drums for a “better shape”?

I keep mine clean. Spread them a bit and play with cables. They work good enough for old trials bikes.


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Bruce
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BigBird
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Re: How to improve brakes? (Warning: rambling)

Post by BigBird »

Re: The LE you said "Do I need to take the whole system off but intact, hang it vertically and bleed again? (is there an air bubble in there somewhere I can't get out?)"

I'd say there probably is an air bubble and hanging it vertically would probably work - BUT you can often position the bike in a way that sort of replicates the "vertical hang" with all or most of the stuff still attached. Also tieing the brake lever down so the system is pressurized and leaving it that way for a while before reverse bleeding often helps - and repeatedly pulling the lever in then letting it pop/snap out seems to move the bubbles along toward the MC.

Good Luck!
Sam Jones - Frederick MD
GL1800 DCT TRIO Tilting Trike - KTM 525 EXC - KTM 200 XCW - 2 KTM Freeride 250Rs - TRS 300 Xtrack Trials
Lots of E-Bikes/MCs
Polaris RZR 800
Lots of MTBs and Road Bikes and a BamBuk Recumbant Tandem Trike eBike
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juddspaintballs
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Re: How to improve brakes? (Warning: rambling)

Post by juddspaintballs »

Skip housed the CRF I now own in my garage for a year or two a few years ago. During that time, we wrestled with a front brake problem on it for a while. They just didn't grab all that well and you could take the lever all the way to the bar. We bled, reverse bled, hung the whole system overnight, etc. to no avail. We rebuilt the master cylinder. We rebuilt the caliper. It had a braided stainless line on it already, but we replaced it anyways. Bled, rebleed, reverse bleed, tie the lever back overnight, hang the whole system overnight, etc. again didn't do anything. Brand new HH pads didn't even help much. What in the world!


I don't know how Skip ever noticed, but he eventually found the problem to be the lever itself. It had an adjustable pin on it that let you position the lever closer or further to the bars but engage the master cylinder with the same amount of travel...like most dirt and street bikes have. Well, somehow that adjustable pin portion was stripped out in the aluminum lever and would move deeper into the lever as you applied the brake, but would come back out as the lever was released due to the rubber boot acting like a spring. Quite perplexing, but I'm glad we eventually figured that one out.
Jed Gregory
1090 Adventure R
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