1998 F150 3-Dr 4.6 2wd Auto...

I can not figure out why my truck has a slight hop from the rear while braking from above 40 mph as it slows down thru the 40 mph range ? I got new brakes all around, new shocks all around, good tires, etc, etc, etc.... The u-joints are not loose .... This is only during light braking as if approaching a red light you have a lot of time to slow down for ? During moderate to heavy braking, I don't feel that hop thru the seat of my pants....never ever feel it in the brake pedal ? I thought maybe the torque converter might be lazy to disengage, but, my 1988 did the same thing with a standard tranyy ?

 

Did you replace or turn the rear rotors? Warped rear rotors have this effect on F150s for some reason.

 

found this TSB...now you might not experiences all the noise....but seem to be a simple procedure and couldn't hurt on a maintenance level.
04-1-6***NOISE - DRIVELINE CLUNKING/GRUNTING NOISE OR SHUDDER SENSATION DURING LIGHT TO MODERATE ACCELERATION AND/OR BRAKING***TRANSMISSION - DRIVELINE CLUNKING/GRUNTING NOISE OR SHUDDER SENSATION DURING LIGHT TO MODERATE ACCELERATION AND/OR BRAKING

 

One of the things that should have been noted is if one side rear pads or lining was wore more than the other side.
This would indicate brake drag.
Heating the disk or drum on one side causing a warp.
I have this on one side and is a caliper not releasing.
Remember that braking removes/transfers weight from the rear to the front making the rear able to react more to any issue that would cause vibration.
Good luck.

 

I guess some people may call it a "vibration" but it really isn't...it's a "hop" effect as I noted... the damb'est thing...I'm stumped big time...I might try new rear shackle bushings and eye bushings next ?

 

You may go on and replace the U-joints. I had a needle bearing go bad in mine and that can cause a vibration during both acc/decel. It may seem tight and with no play, but it is very possibly your issue. Replace them both while ya got it out.

 

I would have the rotors checked to see if there warped!

 

This can also happen if the linings for the drum are mixed and a Left-right lining is installed on one side and a Right-left lining installed on the other. Yes, it is possible to do this. This causes one side to drag more than the other and also shows up when you start the vehicle forward. The one brake is pushing against the drum and the other is free.

 

What do you mean by you "had the rear brakes done"? I.E. what was replaced?

I'm assuming you have rear drum brakes? Or are they disc? I had the same problem with the hopping in my '98 (but 4x4), and I had the rear brakes completely re-done (drums, shoes, springs, wheel cylinders, and adjuster) and all is well now. You can test this by coming to a stop from the freeway off ramp and lightly pushing in the emergency brake (if you have drums). Mine hopped like crazy with the e-brake and the guy at the shop measured the drums in front of me and you could see on the gauge how warped they were.

 

yep everything was redone ...completely..nothing skipped...i would never just throw shoes in there...had drums turned as well...the guy at o'reilly said it took one pass to true up and another minor pass for good measures...

 

That is exactly what I was thinking. All four of the shoes look very similar. Each side gets a long shoe and a short shoe. The long shoe goes toward the back always. When braking the long shoes contacts the drum, then the "roll" of the assembly pushes the front shoe against the drum. This is why when you leave the park brake on you can back up, but it is hard to go forward. f you slam them on does it have any drift to one side or the other?

 

Last time I tried to backup forgetting to release the parking brake, the truck didn't move at all.

 

Can you pull forward though?

If the brakes are right you can back up, just not forward. I'm not saying you can back up like there is no brakes on, but it is a ton easier than going the other way.

 

Nope. Just had the rear drum brakes re-done, as mentioned before, no movement forward or backwards with the parking brake applied. Your conclusion seems absurd to me, considering I park my truck on my driveway, that is considerably sloped, and apply the parking brake before putting the truck into 'Park'. This eliminates the necessity for me to yank the tranny into 'Reverse' before pulling out the next time, it shifts to 'R' with 1 finger. No movement backwards whatsoever. Maybe yours aren't operating properly if you can move backwards. Do you just avoid parking on a hill with the rear facing downwards?

Sorry to steal the post from the 'hopping at 40mph' subject, but does anyone else have any comments about this?

 

Like I said, it is not like you don't have any brakes, just moves that direction a lot easier than the other. It is the way drum brakes have worked for decades, that is nothing new, look up the theory of operation on them.