2002 FX4 Scab - Strange Bounce while braking as truck slows down through 42-41 MPH...I thought it was an out-o- round tire, but just put new Nitto's on last week and it's still there. Before the new tires it would bounce without braking at 42-41 MPH, now not so much - Any Ideas? Bent Rim? Warped Rotor?

 

the only thought I have is actually transmission... does it downshift when you cross that speed and the transmission is making it hop?

Maybe repost this in that forum and see what they say.

There is nothing I can think of in the brake system (except maybe an ABS fault, but highly unlikely) that would be speed dependent like that.

 

Torque converter locking/unlocking? Fuel shutting on/off?

What does the tach do at that exact point in time? Does it jump or drop at all?

 

no down shift occurs and tach is steady and normal - but thanks for the comments - I'm still just guessing its a rotor or wheel thing...

 

tested the torque converter theory by accelerating up to 50 mph, shifted to neutral, and braking through ~42 mph...it still bounced.

 

What do you mean by hop? Sound like a drive line issue, maybe drive shaft?

 

Mine feels like it hopes when Im slowing down but I think mine might be due to new 10ply tires and the air pressure I am running them at. What psi are your tires at and whats the max?

 

Its like the truck is riding on "basketballs", for maybe 2 seconds when I brake, and only as it slows down from around 43 to 41 mph, then all is normal. In other words if I'm traveling at say 55 mph and begin braking, all is normal until the truck slows thru the 43 to 41 mph range, then the truck bounces until it slows below 41 mph, then as I continue to brake, its back to normal as the truck slows from 40 mph on down to 0. The 43 to 41 mph bounce while braking occurs no matter how hard I brake, only the duration of the bounce changes with how hard I brake - its so stinking weird.

 

That is a strange one. Wonder if it could be in the drive shaft or ujoint.

 

Bluejay - it occurs while in drive or neutral, so I would assume that would most likely rule out the drive shaft, u-joint & torque converter...it also has new tires, front end aliment, new upper control arms, and new sway links.

 

Even if in neutral, the shaft and ujoint are turning, but it does sound as if it has to be suspension or frame related.