My front end shimmys violently when braking only above 40MPH. Below that it brakes fine. I have about 55K miles on a 2000 f150 supercab, 2wd w ABS. The brakes were redone by the PO, but I am not sure what was done or where or when. I suspect front rotors, but my previous experience with warped rotors is that warped rotors can be felt at any speed. Any other ideas? My search of the archives leads me to believe rotors, but have not found this exact hi speed only sympton.

In my search for new rotors I am asked what size lug bolts do I have. 12mm or 14 mm. The service manual only says "12mm should be torqued to 100 Ftlbs and the 14mm 150 FTlbs". This leads me to believe I have the 12 mm. Any easy way to identify them? What application would have the 14mm?

Thanks,
Mike

 

It should say on the lugnut slip washer. Mine say 130lb/ft and I have 14mm.

I would check for worn front end parts like ball joints and tie-rod ends for the shimmy.

 

i agree with LX. jack one wheel a couple inches off the ground, by lifting under the A frame. put a 4 ft bar or 2 x 4 under tire and lift up and down. see how much play is in the lower ball joint. next grab the tire on the outside and wiggle it in and out as if it was turning. have someone look under the truck behind the radiator area and see if the tie rod ends or frame anchor joint are wiggling excessive. - i agree, rotors will act up at any speed, not just above 40.

 

12 mm studs use 19 mm nuts
14 mm studs use 21 mm nuts

 

It appears they are 14 mm. The nut size is 21mm(Thanks AzBlueWolf). It also is stamped "14mm insert" on the wheel) I will check the slip washer to see what the torque value should be.

I will also check the front suspension as Steve suggested.

Thanks,
Mike

 

[QUOTE=steve(ill)]i agree with LX. jack one wheel a couple inches off the ground, by lifting under the A frame. put a 4 ft bar or 2 x 4 under tire and lift up and down. see how much play is in the lower ball joint.

You are correct. The test revealed that the lower left ball joint is "as loose as a goose". Now I have to figure out how to replace it. Thanks for your help!

Mike

 

new ball joints are $20-50 each depending on the brand. look for the ones that have greasable zerks installed. If you got enough tools, you can change out each joint in about 3 hours, but you need lots of tools and this is not a job for the meek at heart. Dealer will charge about $300.