When the brakes are applied normally (not hard enough to envoke the rear antilocks)the pedal pulsates and there is a vibration in the steering wheel on my '91 Aerostar. I checked the rotor thickness and runout and both are well within tolerance. Rear shoes, pads, caliper slides have all been replaced. I can't feel any play in the suspension or wheel bearings. What is the likely or typical cause? What should I check next?

 

Hello,

I have had a '91 Aerostar and had the same thing. I checked the runout with a dial indicator, checked the wheel bearings, nothing seemed wrong. Finally I changed the pads, and everything seemed OK. For about a thousand miles. Then I had the shaking feeling when stopping. Finally someone suggested that I change the calipers. I did, and the problem went away. It seems that sometimes the caliper piston will **** slightly in the caliper bore, and the caliper doesn't release all the way. This will allow the pads to really notice any run-out in the rotor... Anyway, on my wifes new (well '88 Aerostar), when we got it, it did the same thing, so I immediatly replaced the calipers, the pads and had the rotors turned to as close to zero run-out that the machinist could get. So far 25,000 miles no shimmy or shake. Also, I have discovered that some of the problems in the front brakes on the '91 was due to the rear brakes not self-adjusting as Ford advertised, causing the front brakes to work harder than they should. So now on the '88 I periodically check the rear brake adjustment. And the brakes do work pretty darn good.

Oh, and if you wonder why I went backwards replacing the '91 with an '88, it's simple. The '91 had EVERY toy and gadget. At about 170K it started to have expensive electrical failures. The 4x4, the ABS computer, the digital dash. I dumped it and my wife insisted on a kid mover, ideally another Aerostar, so I found a nice '88 with manual everything (except it has A/C)...

Good luck with the brakes.

 

The pads, rotors, and wheel bearing were replaced and the calipers were rebuilt. I checked the run-out with a dial indicator and it is under .001". Rear brake cylinders and shoes were replaced and I adjusted the shoes last night. I still have a pulsating pedal and a shaking steering wheel when the brakes are applied. Any Ideas?

 

Worn tie rod ends will elicit similar symptoms. You mentioned checking for suspension play, did this include the tie rods as well? Do you have this pulsation when the rotors are cold as well as hot?

 

Tie rod ends where recently replaced and have no play in them. The vibration and pulsating pedal is always there, but it does get worse when the brakes are hot, i.e. after several stops from high speed or down a long hill.

 

I reviewed your original post and was not sure if this problem existed before you replaced the rotors or the problem arose after you replaced the rotors, bearings, etc. Get a buddy to assist you and raise the front end. Spin the tires, one at a time, by hand as fast as you can and have the helper gently apply the brakes. See which side causes the steering wheel to shudder. If you can isolate one side as being the problem, then reinspect everything on that side-bearings for proper load, tie rod to ensure it is not loose either in the coupling or mounting bolt, the upper and lower ball joints. One thing to consider is how the runout is performed. Do you pull the wheel and then re-mount the rotor or do you do the runout with the wheel attached? If you remove the wheel and reattach the rotor with minimal pressure from the lug nuts, this would disguise a damaged/bent wheel or hub causing distortion on the rotor when the lug nuts are torqued down. Do a runout on the hub alone to see if all is correct there. Then attach the rotor and torque the lug nuts to specs and take a runout of the rotor/hub. If all still well, attach the wheel and see if you can obtain a reading on both the wheel and rotor. Let us know what you find.

 

Good idea on rotating the wheels individually to isolate the problem to a side. Not sure I can make it shudder by spinning the wheel by hand, but I will give it a try.

I'm not sure I followed your comments on the run out procedure, although I understand over-torquing of the lug nuts or a bent wheel may distort the rotor and cause the shudder. I tested the run out by removing the wheel and placing the dial indicator on the face of the rotor. The hub and rotor is one piece on my Aerostar. I don't think there is sufficient access to check the rotor run-out with the wheel installed. I have always torqued the lug nuts to 90 ft-lbs and the wheels do not appear to be damaged.

The shudder developed after a front brake hose bursted and I replaced the front hoses, rebuilt the calipers, and installed new pads. The rotors, wheel bearings, and new tie-rod ends had been replaced about 10K miles earlier and the brakes did not cause a shudder at that time.

 

Sorry, the rotors on the AWD are independent of the hub, ignore that portion. Still try and isolate one side if you can. When you say the steering wheel moves in conjuction with the brake pulsation, does the steering wheel actually move in a small arc (i.e. back & forth type of movement) or does the wheel/column vibrate or shudder as an in-and-out motion/feel in time with the brake pulsation? Also, when braking now, is there any pulling to one side or the other that was not evident previously? You've got me really curious about what is going on now.

 

During light braking the steering wheel moves back and forth a few degrees in an arcing motion, i.e, in the same pattern if you were turning left then right over and over again. When you apply the brakes coming down a hill (moderate braking) the steering wheel and column seems to move up and down. This could be a very fast back and forth motion that is just causing an overall vibration in the steering column.

I'm not getting any pull to one side when braking.

I will try to isolate the problem to a side this weekend.

 

Couldn't isolate the problem to one side by rotating one wheel at a time by hand. It either wouldn't pulsate or the wheel would just stop. Changed the calipers, they were only $12 each, it didn't help. Decided to change the rotors even though the run-out was only .001". The new rotors completely eliminated the pulsation and vibration. I believe the spec for run out is less than .003". Its hard to believe the brakes would pulsate this bad with a run out of .001".

 

Glad you solved the problem. Your post should be required reading for anyone experiencing similar symptoms. 95% of the time such symptoms are either rotors or tie rods. Nothing else gives that peculiar motion to the steering wheel. Thanks for sharing your findings with all of us.