97 F150 Flareside, 4.2L, 2WD, front disc/rear drum with ABS... new rotors/pads/caliper slides/noise suppression hardware on front; rear shoes not replaced...problem I have is the rear seems to start hopping or rocking front-to-rear when making a normal (or gentle) stop from 40 to 50 mph. It seems to hit a natural resonance frequency like that described in the TSB about the pavement joints causing bounce. If you make a hard stop it doesn't happen. The hop rate is similar to what warped rotors feel like except its all in the seat; none in the steering wheel. Anybody have a clue what might be causing this? Disproportionate braking between front & rear wheels? Some malfunction of the ABS that makes it think a wheel lost traction?

Anybody know where the diagnostic connector for the ABS is located? Chilton/Haynes/AllData just say "... momentarily ground the orange/black wire of the ABS diagnostic connector to initiate the ABS light blinking to read codes"... but nobody tells where the connector is.

Thanks for all your help in this forum with all the problems I have had with this truck.
Paul

 

if it was an ABS issue it would light the light automatically, so I don't think that's it.

I'd check the lugnuts to make sure theyy're tight, sometimes if a lugnut is crossthreaded or not tightened properly it can do what you're describing. Then the rear brakes. You say the rears were not replaced. Did you check them, disassemble them, or adjust them? they might just be out of adjustment. Also could you have swapped the sides on the drums? Your post sounds a lot like a drum out of round.

good luck!


EDIT: the preceding post is assuming that this is a NEW issue, which happened since you did the front brakes. If this is NOT new and has been going for a while I'd look first at the Ujoints, then at the driveshaft, maybe take it down and have it balanced.

 

Since my initial post I have taken the drums off both rear wheels and checked shoe lining and drum wear. Shoes are excellent with no glaze. Drums are smooth and not out of round. I cleaned everything, regreased the shoe bearing points on the backing plate, and put it all back together. Lugs and lug nuts are in good shape. I torqued them per Ford's TSB; 100 ft-lb+1/8-turn in proper sequence. However, these lug nuts are the original two-piece nuts, not the replacement nuts of Recall 98V095000. (We, for some reason, never got the recall letter). The first time stopped when I drove it after inspecting the shoes it stopped smooth and straight. After that is was back to hoppin'...

I do not know if this condition existed prior to me beginning to work on this truck. It belongs to my stepdaughter. I have replaced to engine and transmission so I doubt it is U-Joints or driveshaft balance causing this. Also, I have replaced the shocks all around and replaced all 4 ball joints. My next test is to lay a couple of bags of gravel in the bed behind the rear wheels to see if the bounce is dampened. Otherwise I am befuddled...

I will let you all know how the extra ballast reacts... thanks...