I think my brakes locked on causing a crash.

[Asher]

So the weather here on Wednesday was beautiful so i decided to go for a blast through the hills with a few friends.
Unfortunately coming through a sweeping uphill right corner at medium pace it tucked the front which put me into a drain smashing up the back of the bike and doing a number on my back (thank god for back protectors).
Straight away i was confused as to why i crashed as i wasnt riding hard, the road was in good condition and i crashed on the exit of an uphill corner so the front tyre wasnt loaded.
After i got my bike back to my house the front brake was locked on, i undid the banjo bolt at the master cylinder which made no difference, i then undid the banjo bolt at the brake caliper which also made no difference. Only just no have i gone to look at the bike thinking maybe the factory hadnt greased the wheel bearing causing them to seize but i removed the caliper and the wheel spun freely.

So for some reason the caliper has locked on, has any one here experienced anything similar?

Now i cant be certain the brakes caused the crash or the crash has damaged the brakes but there is no visible damage to them.

Any advice on what i do next?

Notes: The bike has done 2000kms, had its 1st service completed at 1000kms by the dealership, the dealership is picking it up on Monday to give a repair quote to my insurance.

 

[aj@x]

After market or stock levers on the bike?

 

[Asher]

Ebay specials, but like i said brakes were still locked on with the MC disconnected.

 

[aj@x]

I also use Ebay specials. The reason i asked was i read recently of a case where another rider was using ebay levers, they fitted up fine and had been in use with no issues and without warning he had a crash very similar in description to yours. It turned out the levers were not letting the master cyclinder piston all the way back out slightly somehow and pressure slowly built up into the system eventually causing the front caliper to clamp on unexpectedly and lock the brakes...he low sided.

If your brakes were still locked on without the MC connected that doesn't make mechanical sense as the system needs pressure to do so. Sounds like a machining tolerance issue with the piston and bore it sits in.

 

[Asher]

I have also heard of the same issue of ebay levers locking on, but people said that caused the brakes to lock up slowly not suddenly like my case, and my ABS was turned on so that should have prevented the brakes locking up too.
While this is all guess work it points to an issue with the caliper, and if this turns out to be a manufacturing fault then it is very serious for KTM.

 

[psych0hans]

I also use Ebay specials. The reason i asked was i read recently of a case where another rider was using ebay levers, they fitted up fine and had been in use with no issues and without warning he had a crash very similar in description to yours. It turned out the levers were not letting the master cyclinder piston all the way back out slightly somehow and pressure slowly built up into the system eventually causing the front caliper to clamp on unexpectedly and lock the brakes...he low sided.

If your brakes were still locked on without the MC connected that doesn't make mechanical sense as the system needs pressure to do so. Sounds like a machining tolerance issue with the piston and bore it sits in.

I've had this issue as well, I just drilled out the part that pushes the piston to give it more clearance will update with results later in the evening.

 

[aj@x]

I've had this issue as well, I just drilled out the part that pushes the piston to give it more clearance will update with results later in the evening.

I've not had the issue with my second set as they are much better quality in regards to tolerances, they were bought from an Australian seller. The first levers i bought from Ebay were chinese (not that it matters much) and they were from the same seller that was recommended here in the levers thread, they were very poor fitting and very sloppy in the pivot. I thought to myself if they can't get the basic movement in the lever correct then the rest is probably off as well so i removed them as i didn't trust them. The second set from the Australian seller are better fitting that OEM and i've not had any issues at all using them for the last month and half, the best part is he sells the same design in full and shorty lengths

Btw Asher, glad to hear your relatively ok injury wise, bike wise well she's mean't to be ridden hard so a few bumps and scratches gives character

As far as ABS goes, yes it is supposed to stop wheel lockup however it can only do it's job with a fully functional braking system in place, yours isn't at the moment for whatever reason that may be. I am very interested in finding out the cause if your able to, i'm really hoping it's not a problem with the caliper itself because that would be a world of shite for all us including ktm.

 

[guzz46]

I have also heard of the same issue of ebay levers locking on, but people said that caused the brakes to lock up slowly not suddenly like my case, and my ABS was turned on so that should have prevented the brakes locking up too.
While this is all guess work it points to an issue with the caliper, and if this turns out to be a manufacturing fault then it is very serious for KTM.

I decided against using the ebay levers for this reason, assuming this was the reason, I went with the official power parts lever instead, some people have said they felt drag before the brake locked up, so depending on how much lean angle you had, drag could have caused the front to wash out before the the front brake actually locked on, I don't know why they would still be locked on with the master cylinder disconnected.

 

[aj@x]

Nothing wrong with using Ebay levers as long as you do one thing, check the depth of the bore hole that cups the MC piston with a set of verniers. Check the measurement against your oem lever, if it's deeper all good if not then use either a drill or a dremel with appropriate bit to take out material till the bore is same depth as oem. I steered clear of the power parts levers because they are cast just like the brittle oem ones, i've also heard some guys snapping the lever off because the pivot mid lever didn't work, if you have them it might be worth loosening that pivot off a tiny bit so they do infact do their job before snappage.

Most of the ktm cast parts are brittle and nasty due to cheap casting, this is evident due to the high silica content within the casting metal (when i snapped a lever it was sort of white and very powdery) . The exact same reason the gear selector and rear brake levers on the rear sets snap off so easy instead of bending like the should so your not left stranded if you have a little off in the country. (i've broken a gear lever too, white and powdery just like the brake lever i broke)

 

[Asher]

Just checked my levers, the after market ones are 0.5mm shallower. Thats a bit of variance but i still dont think its the cause.

 

[OldVet]

Bummer Asher I hope you didn't bend the frame...

 

[Asher]

The sub frame is bent as the bike slid backwards into a bank, im thinking its a write off.

 

[OldVet]

Yeah good chance, that's sad...

 

[psych0hans]

Just an update, I drilled out the hole by 1.5mm and it's made all the difference. Used an 8mm drill bit on a drill press and just pushed the lever into it. Made 5-6 cuts, measuring with a vernier each time.

 

[Treachery]

Nothing wrong with using Ebay levers as long as you do one thing, check the depth of the bore hole that cups the MC piston with a set of verniers. Check the measurement against your oem lever, if it's deeper all good if not then use either a drill or a dremel with appropriate bit to take out material till the bore is same depth as oem. I steered clear of the power parts levers because they are cast just like the brittle oem ones, i've also heard some guys snapping the lever off because the pivot mid lever didn't work, if you have them it might be worth loosening that pivot off a tiny bit so they do infact do their job before snappage.

Just checked my levers, the after market ones are 0.5mm shallower. Thats a bit of variance but i still dont think its the cause.

Appreciate the information, but I'm having a problem visualizing what you're speaking of. IIRC, there is a small hemispherical pocket that engages the MC piston rod. Am I remembering correctly? Can you post up pix of what you're describing and where you were measuring? Thx much.

 

[Asher]

You would be correct, im measuring the top of the 'cup' to the deepest part with the depth gauge on my verniers

 

[ryandalling]

I've heard of this happening with overfilled fluid. When things heat up it expands and locks the brakes. Either way this sucks.

 

[Diploman]

Are there any scrape marks on the lower side of your brake lever end? That would indicate that the lever touched down when you low-sided. If the brake lever did touch down, even momentarily, that would put a sudden, enormous load on the brake system, possibly causing/contributing to the brake lockup.

 

[fs1ephil]

I cant wait to upgrade to the racing disc setup, my original front rotor has warped with only 2234 miles on the clock.

By the way whats the chances of your front brake locking on its own during a corner, sucks but at least you wasn't flat out on the highway, you probably wouldn't be around to let us all no what happened. I am glad your ok and hope you get the rc sorted soon.

I was wondering about the ktm 390 cup race bikes, do they get to change their front brake caliper or do they only get to use the race rotor and spacers to refit the original caliper?
If they use the original caliper then they don't seem to be having problems so whats up there?

 

[Asher]

Update: I only dropped the bike off at the dealer a few days ago but a good point the mechanic made was if the forks were twisted the disc could be twisted causing it to drag on on the caliper. It wasn't a frontal impact but it's a good theory.