Front wheel hop when braking - suspension arm bushes, or... ?? Any help?

[Jetfixer]

I'm working on a friends 2023 RTL that has a severe wheel hop when doing moderate to hard braking. Both front wheels visibly hop very rapidly as if the brakes were grabbing and releasing very rapidly. Here's a list of what I've done and/or checked...

Spyder bought new by current owner. Has 23000 miles.
Two like new Vredestein tires, Centramatic balancers. Both tires running at 18 psi.
Brake pads and rotors are good with no excess runout. Absolutely no pedal pulsation when braking. No binding or pulling. No air in brakes.
No excess play in steering system.
Laser aligned to 3/16" toe-in over the specified 124 inch spread. (Service manual allows between 0 and 5/8").
No shaking in handlebars during the wheel hop. (It just looks like it could throw the fenders off).
No ball joint or tie rod joint wear found.
No wheel bearing play. Wheels mounted properly and nuts torqued to 77 lb/ft.
Spyder still has original anti-sway bar and heim joints. No play or looseness in any of these parts or mounting.
The bike rides very smoothly, does not pull or drift. The problem is only during braking.

I'm beginning to suspect it's the suspension arm bushings. I'd appreciate any help anyone can offer. If I've left something off this list let me know. I've more than likely checked it!

 

[BajaRon]

It's the wheel hop that has me scratching my head. Pulsating, etc., could be warped rotors, worn A-Arm bushings, etc. But for wheel hop, I would remove the Centramatic balancers, torque the front wheels correctly in 2 stages, and give that a try. We've had some wierd front end issues go away by removing the Centramatic balancers.

Check tire pressures while you're at it.

A bit of a shot in the dark. But not hard to do and virtually free.

 

[mecsw500]

I would immediately suspect a problem with the ABS system kicking in, or out, when it shouldn't.

I'd get the dealer to flush the brake fluid AND flush the ABS unit, using the BUDS system. I'd have them check the ABS sensors and rings on the wheels, at the very least clean them or test them for correct signal pulses when the bike is in gear and moving down the road.

Incorrect signals from any of the wheel sensors or contaminants in the brake fluid in the ABS module could be causing issues. Even a faulty ABS module or ECU could be an issue.

Check the connectors from the ABS module to the ECU for corrosion, the same for all three wheel sensors to the ECU harness. Once you have cleaned them all out with electrical connector cleaner and a tooth brush apply a little dielectric grease before re-connection.

I would seriously get the dealer to look at it as the BUDS system will be able to test the sensor operations and allow a full brake fluid change including the ABS unit as well as just the regular parts of the brake lines.

As the Nanny control system relies heavily on correct ABS function, I would treat the issue seriously as you don't want that part of the bikes automatic systems to go wrong when you most need them.

 

[Jetfixer]

Thank you both for your replies. Ron, during a search for this problem you had posted somewhere that the arm bushings should be lubricated. Can you elaborate on that for me? The tires are set at 18 and even from side to side. Wouldn't a failed Centramatic cause vibration all the time? This thing is smooth while riding. It's just the braking that causes the wheel hop. But you're right, it's an easy thing to try. I wish I could get a video of this in action. It truly is unbelievable. It's so violent, I'm not kidding about it trying to throw off the fender.

mecsw500, I have BUDS and started there. No faults in any systems. This bike has the stock exhaust and I don't think the ABS is kicking in; I can't hear it running. I personally did the fluid flush on this bike a year or so ago, so maybe I'll give that a try also.

 

[mecsw500]

Thank you both for your replies. Ron, during a search for this problem you had posted somewhere that the arm bushings should be lubricated. Can you elaborate on that for me? The tires are set at 18 and even from side to side. Wouldn't a failed Centramatic cause vibration all the time? This thing is smooth while riding. It's just the braking that causes the wheel hop. But you're right, it's an easy thing to try. I wish I could get a video of this in action. It truly is unbelievable. It's so violent, I'm not kidding about it trying to throw off the fender.

mecsw500, I have BUDS and started there. No faults in any systems. This bike has the stock exhaust and I don't think the ABS is kicking in; I can't hear it running. I personally did the fluid flush on this bike a year or so ago, so maybe I'll give that a try also.

I'd start with BajaRon's advice first. He's far more expert than me on Spyders. His idea is a far simpler and more likely thing to start with. At the very at least you can rule out another variable for zero cost.

I thought ABS as I did have a problem on a 1997 BMW R1100 RS with the ABS system that made braking a sort of on and off pulsating feeling. It turned out to be an ABS module fault. This was a really difficult problem as BMW no longer made the modules and replacements were almost impossible to find at a price that wasn't absolutely insane even for a used one.

Water from not changing the brake fluid often enough and rubber particles from the brake hoses had scored the pump pistons and made the thing behave really oddly. The ECU kept thinking it needed to operate. By the time I'd figured it all out the pump was beyond repair and there were no service kits available. ABS unit problems were so common after the bikes aged, some folks bypassed the ABS system altogether, but I wasn't that brave. I eventually found a new unit in Germany which was only double the list price of a new one when they were in stock in the US. The electronics one those bikes were not very sophisticated, but the unit never threw a fault.

You are right though, if you listen carefully you should hear it running if it's doing something.

I hope you find the problem out because that would be more than mildly annoying.

 

[Jetfixer]

An update. I tried Ron's advise and removed the front Centramatic balancers. Actually did a 3 step torque on the lug nuts. By hand, then to 40, then to final 77 lb/ft. with a calibrated torque wrench. The problem was marginally improved, but still unacceptable. I believe that whatever is the real cause is happening at such a speed that the balls inside the Centramatics could not react fast enough and could be considered to be compounding the problem. I think I'll try another brake bleed tomorrow...

Any other suggestions would be greatly appreciated.