TE/TC TX300 rear brake locking

I put fastway pegs on my bike so I can run them in the low position for better ergos. When I installed them, I adjusted my brake pedal down just slightly below the peg the way I like it. Below the peg and not much free play. About 3mm like the manual says is good.
Anyway, first ride after adjustment, the rear brake locked up. Had to just about triple the free play on the trail to get going again.

Anyway, in cooler temps it seems okay (no lockup), except it has way more free play than I like. But, yesterday it was doing some slow boonie bashing and it started to lock up again. The weather was hotter than any previous ride I've done on this new bike to date. But I've been riding in this area for a while and ridden on much hotter days. Never had a rear brake lock up.

I was reading some threads last night where people had the same thing happen, and some guys mentioned adjusting the reservoir compensation port thingy, but there is only a free play and lever position adjustment on this bike.

Am I missing something? I mean how you can you go from 10mm or more free play to a locked up caliper with no free play?

My dads 2013 KTM 250xc-f is having the same problem. I just ordered a caliper rebuild & new fluids to try and see if that works. First time he was worried he was 'riding' the brake so we adjusted it, he said no way hes riding it so im not sure whats goin on if the fluid is just old & vapor locking itself or what but I figured while I was in there id rebuild it quick.

I think I'm going to put some motul rbf600 in there and maybe a caliper cooler. But I'm not sure I need to rebuild it, it's a 2017 with about 20 or so hours on it.

If you are the original owner talk to your dealer. Husqvarna just did warranty on my low seat that ripped for no reason. Worth a try. On my 17 tc I run a cooler.. And mogul and I needed my pedal super super low as I'm a dragger...so I cut the piece down and now my pedal is low enough if I went any further it would hit the frame. Did it do it before the fastway pegs or? If you've boiled them over I'd get different fluid and flush real well..got to be a simple explanation.. I boiled my 15 over in ten minutes and did a pedal mod etc..then was good..

Have a 17 TX300. Did the same thing til I started running more freeplay.

+1, you have to run enough free play to uncover the small vent port in the master cylinder (front or rear brake) or it will hold pressure in the hose and drag your brake and can pump it up until it locks. I'm not sure how the TX is but on my WR I ground a notch in my rear brake pedal so I could lower the height of the pedal without covering the vent port in the master cylinder.

what fletch said give yourself plenty of free play, be sure to have some air gap in the reservoir as well (don't over fill it) , and use Motul RBF 660. I also use the https://www.fasstco.com/products/rear-brake-return-spring with the OEM return spring too.

along with a ZipTy Racing reservoir extender for more fluid volume. The 17 rear pads seem to be exceptional , I was using EBC red carbon X pads for years, but the new compound pads rock.

http://www.santaclaracycle.com/ziptyraktmbr.html

Nope, however, before the fastway pegs I was riding in much cooler temps. Then I put the fastway pegs on and adjusted the lever at the same time the temps went up 20 degrees. First ride after adjusting, hit a downhill and they locked up. So I added 3 times as much free play. I'm now at the point where when I start riding when the bike is cool, I feel like I have to contort my ankle to engage the brake because there's so much free play. So I ordered the cooler and RBF600 from Slavens (there's another $80 into a brand new bike) and I'll see how that goes. I'll also lower the lever more to make sure I'm not riding it. If it keeps up, I'll go the dealer route.

660? Shoot, I ordered 600. :-(

no worries RBF600 is fine.
but for the future
https://www.motul.com/us/en-US/products/rbf-660-factory-line


Racing Brake Fluid

Stupid point but don't be afraid to try different boots...I had to sell a pair of alpinstars because don't ask me why but even with my pedal lower I was still dragging brakes...you probably need to cut the piece shorter like I did to get pedal lower...I honestly had frustration and was thinking beta for a minute... The 17 pedal is different so my custom lowering piece would not work.and the way it was I was getting irritated badly. I cut it as short as you can and used loctite so I wouldn't have to worry... Made everything fine now railing on this bike..

Good point Fletch, I can only use "shovel toe" boots like my Sidi Cross Fires, the "big toe box boots" boots like Alpinestars style are nogo for me, but thtas not a brake issue its a shift issue. But for sure some have more feel and better fit for each individual.

Ha ha! Last year I ended up switching to the Fox Enduro boots with the lugged soles. I was using Fox motocross boots for years as they fit sooo good -- like slippers. The new ones are pretty good fit. But really a necessity as the non-lugged soles on most other moto boots are no good in the red clay dirt we have up here. Add any moisture and you go sliding around like you're on ice. I can't tell you how many times I've fallen due to my feet slipping when riding with normal moto boots.

Any possibility that there is too much brake fluid in the reservoir or the "weep" hole in the cap is plugged?