i have a 98 f150 4.6 4x2. when i break the back end shakes . it has new brakes and drums in the back and new pads in the front. is there somthing i am missing.

 

Were the new parts from autozone, advance or o reilly? Did you have the new rotors/drums turned? Are they OEM parts?? More than likely you have a warped front rotors or rear drums and they need to be turned. Even new rotors/drums can be warped.

 

Out of round drums...................Have them turned....

 

i would assume the from discs are warped since those are the only lold parts... new parts COULD be bad, but i doubt it.

 

Back drums are not round. Easy to check as long as the shoes are taken up so you can feel the drag in part of the rotation
Front discs, if they have hard spots will feel like motion pulsing as brakeing is applied.
Pedal pulsing is front discs have a difference of thickness as they rotate past the caliper pads forcing them apart and you feel the motion feedback on the pedal..
Good luck.

 

I tink I'll try turning the drums. Since that seem to be the most likely.I did get them from auto zone and have been having a lot of bad luck with them lately. The front rotors I have not changed. But did put new pads on

 

Did you put the rear shoes on correctly? Shoes with shorter lining material go towards front of vehicle. Shoes with longer lining go to the rear.

 

i never thought about that, the shoes came with the ebrake cable pin preinstalled so i installed the shoes on the side the pin needed to be. Im removeing the drum and having them turned today. ill also check the shoes.

 

shoes are installed the right way. the drums are being turned, i was told they are having to be turned more than normal because they are so far out of round. brand new, 300 miles on them. autozone is ticking me off. now on to another issue. i think i am getting more pressure to the back than the front. is it possible my proportioning valve has gone out. the master cylinder is new, also for autozone. wouldnt supprize me if i need to change that again for the 3rd time.

 

Not that it helps any but all these vendors get parts from Mexico or China and are inferior.
Low cost of these items is the price you pay in the end for problems.
Coils are another problem.
You don't know where they come from and don't have the reliability over the long term unless you happen to have luck.
I am, right now, going through a hassle with a vendor over a miss assembled cat converter the mfger (an American co. )knew had a bad run of but as luck would go I got one.
They are offering to replace or refund but problem is the replacement has caused other issues that put the truck in a shop so I cannot get to take it off and hold up the truck even longer than it is now.
The word to the wise is use OEM parts as much as you can because very often the after market parts are cheaper for a reason.
The vendors don't make them so you are at the mercy of there policies.
Btw, I had Ranger with your same issue that was rear ended accident repaired at a dealer. The truck shook when driven. Finally I had to look at it. Jacked up the rear so the axle hung free off the ground and spun the wheels in 1st gear only to have the rear practically shake the whole truck. Found the drums way out of round.
Good luck.

 

turned out the drum need 5 passed to resurface. rides good so far. the shaking has gone away. i think im going to change the master cylinder again with a motocraft one from rock auto. On another note i have gone threw 5 alternators for my wife focus, in the last year. i may end up paying ford the 500 for a motorcraft one. napa autozone and oreilys is killing me.

 

On your Focus maybe you need some diagnostics of the system to see if there is anything wrong before spending Ford money and losing the new one as well.
Good luck.

 

any suggestions. these alternators are lasting about 4-6 months. Also the battery light never comes on.

 

If you haven't changed out the battery since this problem started I would have the specific gravity checked in each battery cell and then have it load tested properly. I don't always trust the electronic handheld battery testers. Alternators aren't designed to charge dead or extremly low charged batteries. They are designed to maintain a batteries charge.

 

i got a new battery evertime i changed the alt. might not help that it is a autozone battery.