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New Fork has caused "ABS" braking in front wheel

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saidrick

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Discussion starter · #1 ·
Hi there,
I recently bought a Marz' AM SL 1 ( 07) and really like how it rides, despite the forums views on the subject. But a weird thing happens when I hit the brakes hard, the rear locks up and the front goes into an ABS-car brake style and wont lock up. I run full downhill compression on the ETA knob and the rebound is set at 25% from full rebound. The travel is at full extenison ( 160mm) and the brakes are Avid Juicy seven's. The rotors are 6", which I suspect is the problem. I wouldn't mine upgrading the rotor to a 7" or 8" , because I like how the fork performs with its current settings. Any thoughts would be great, thanks.

Cedric

P.S. the bike is a Ventana EL Chamuco, I run the factory recommeded air pressures.
 
#3 ·
I run the Jucy5s. Once I swapped frames to my Heckler with Fox36 Talas I found I needed more breaking power than the 6'' rotors. By upgrading to the 203mm front rotor not only did the braking power increase (as was expected) but the brakes became more progressive in feel. The power was more evenly distributed than before, something that used to cause intermittent fork dive at high speeds, a lot like your "ABS" feel.
 
#4 ·
If the front end braking is pulsing, then your suspension set up is not doing its job properly, regardless of the rotor size. I would continue to tweak the rebound adjustments. Stick to the Downhill setting as you make the rebound changes.

Also, are you sure your brakes are free of contamination and the pads are properly bedded in.
 
#6 ·
bleed your brake? when you installed the fork, did you change the line to accomodate a different crown/axle length? and then not properly bleed the system?

if you didn't change the line, didn't disturb the system, might still have had an air bubble in there that migrated from the lever to the caliper?

if you didn't change the line and the new fork is longer, could it be stretching, deforming the line? causing a leak?

is the brake squealing too? loose mounting bolts? uneven mounting surface?

contamination in the caliper from changing the parts? grease/oil on the rotor from overspray?
 
#7 ·
I think drunkle & flipnidaho have got the idea, by ABS braking you basically mean loss of power? I don't think that it should have anything to do with the fork, could have been caused by installing a new fork though. I would follow flipnidaho's suggestions/questions. Also I noticed that when going to bigger fork that is run too soft, the brakes will feel less powerful as the fork will dive excessively which takes some time before the the wheel will lock up.
Have the brakes actually become less powerful or do you just notice the lack of power more on the forks?

Tim
 
#8 ·
It sounds like you are getting more grip out of the front tire, assuming you haven't contaminated or otherwise altered the braking systems as others have mentioned. You are probably getting more weight (always) and load transfer in that more of the weight is actually rotating forward with your chassis and unloading the rear too much. A bigger rotor in the front will have more mechanical leverage (translates into brake torque) and better heat dissipation, but I have to wonder if it will help or aggrivate your dive issue even more (although I love 203mm/185mm rotor combos).

How much rebound control do you have on the rear? Can you lessen it and see if the rear holds longer? If it's too stiff, your weight transfer will unload the contact patch (tire to ground) before the rebound will let the wheel extend. Might be worth a shot.
 
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Discussion starter · #9 ·
Update/ answers to your questions,
I did not do the install, my LBS did the install. The brake lines are plenty long, and the brakes did not make much noise so i suspect that there is no rotor/pad contamination. I am still going to wipe down the rotors with rubbing alcohol, just to rule it out.

As for the pads, they worked great on the old fork ( Minute 3-130mm). The tires are big time grippers- Nevegal 2.35'ers.

I talked to my buddy "Downieville Dan" about the problem and thought that the problem is in the physics of the new rotor placement. Meaning that the front rotor is now offset( as opposed to the old "trail" fork) more and thus, has more distance from the rider's weight/center of gravity, so the brake is less powerful because the rider's weight is more on biased on the rear and the front end is lighter. What do you think now?
Thanks

Cedric
 
#10 ·
Wouldn't it be if the front end is lighter it would have less grip on ground and be easier to lock up? Mind you those nevegals are hard to lock up with the amount of traction they have. I've got a 2.5" and still find it hard to lock up with a 8" rotor and K18's. But that's a good thing as it stops me instead!
 
#11 ·
If your brakes worked better before the new fork, your LBS got some grease or oil on the disc while doing the fork install. Just wiping the rotor may not be enough. I would remove the pads and rinse them a few times well with alcohol as well (put a bit of alcohol in jar with pads..let sit for 10min, throw out the alcohol and repeat..). Your pads will not work again until all the alcohol had been burned off, and you have re-bedded the pads. Do a few medium hard front brake slow-downs (dont completely stop with the pads on the rotors!) until you get brake grab again.

Do not touch the rotor or pads after cleaning!!!!!

Fork length, compression settings, and rebound setting have absolutely nothing to do with brake function.

Air in the lines would cause the lever to be soft or 'spongy' feeling. It would not impart any kind of pulsation or change in coefficient of friction between the pads and rotors.
 
#13 ·
Yeah, the caliper position shouldn't have anything to do with braking power unless it's mis-aligned and you aren't getting all of the pad on the braking surface of the rotor. I agree with contaminated pads if it just isn't braking as hard as it used to. I highly recommend going to a bigger rotor though, it makes it much easier on the hands during extended downhills. I started with 6" rotors and outgrew them, went to a 7" front rotor, outgrew that and I'm now at a 8"/7" front and rear setup and lovin it!
 
#14 ·
NZSpokes said:
Sounds just like contaminated pads and rotor. Take it back and get them to sort it out.
Click to expand...
I would say this is the case, too. I few weeks ago I ran through one little puddle, only to then notice a parked car leaking tranny fluid big time. Guess where all that transmission fluid was pooling up??? The puddle. My front brake went from full power to no power, even with a full fistful on the lever. No squealing, either. I soaked the pads in alcohol as davep recommends and then rebedded them. Back to full power.
 
Discussion starter · #15 ·
Newest update.

Ok, so I take the bike out to ride for its second ride on the new fork and there is 25PSI missing/lost from the top chamber and 40PSI from the bottom chamber. I know that the the correct pressures were in it when I rode last week because I checked them myself. So I took into my "other" LBS, which doesn't sell Marzocchi, and having him( shop manager who actually reads the maintance manuals) fix the issues with the brakes( he thinks the pads are either contaminated and/or worn out) and the ATA knob winding down, and having him check out the air pressure problem.

I did take the bike down a grassy hill and laid into the front brake only; the result was that the bike started to nose ride/ slash wheelie on the front wheel, but still no lock up.

Cedric
 
Discussion starter · #16 ·
Problem is fixed and will be improved even more after I have the brakes bled. I had the LBS throw on another set of pads( Avid organic) and the front wheel can lock up, but it takes a little while. The whole fork was sent back to the factory and had new internals installed, under warranty. The shock pump, turned out to be another factor in the air loss. I have since switched to a Buzzy's Pollinator, it seems to be much more accurate and has much less air loss from pump detachment. The new brake pads work sweet.

Thanks for all the advice.

Cedric
 
#17 ·
Glad all is sorted. Good luck with the All Mountain fork, mine never worked properly and I'm now considering a RC2 cart conversion (TST suuuuuuucks!!!!!). Hopefully the factory treated you better than they have me.
 
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Clutchman83
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