Monthly Archives: October 2009

Question:

I need the position of the rotor caps. I assumed they were indexed and did not note position upon removal twice. 1987 Porsche 928 S4 32v V8 (2) rotors on end of camshafts.

Answer:

I dont have a specific procedure for your vehicle, but its pretty
much the same for any car. You first need to bring the engine to TDC
(top dead center) TDC is when cylinder #1 is at the top of the
compression stroke and the spark plug is ready to fire. You can pull
the spark plug from cylinder one, feel for compression by placing your
finger over the spark plug hole and turn the engine until the timing
mark comes up to TDC. The timing mark should be close to the
crankshaft pulley and is usually cast into the front cover. If you
dont feel air escaping the spark plug hole, you are coming up to the
top of the exhaust stroke, rotate the engine another 360 degrees and
you should then feel the compression.

Once you know you are at TDC, you can align the rotor so that it
points towards cylinder #1s plug wire. As for the other rotor cap,
you would need your firing order to determine which other cylinder is
firing at TDC.

Check out the following site for some specific instructions...
http://jenniskens.livedsl.nl/Technical/Tips/Files/pirtle_tbelt.pdf

Question: I have an 03 Ford Expedition and I have been experiencing pulsating in the steering wheel, I have turned the front rotors twice and in no time they are back the same way. So, I replaced both the front rotors and calibers, and its still not right. When I was bleeding the whole brake system, I noticed that the rear did not bleed like the front did, the pedal did not go all the way down. My question is what determines the amount of pressure that goes to the front verses the rear? I think that my problem is that the rear brakes are not being applied enough, thus causing the front to work harder and get hotter than normal, causing them to warp easier.

Answer:

There is a proportioning valve ( or sometimes called a modulator valve
) which in modern vehicles is usually combined with the ABS functions.
It should be located immediately after the master cylinder and is
usually an aluminum block. Your brake system should apply more
pressure to the front brakes, which is where most of the braking
occurs. You can test function of the proportioning valve by doing a
low speed panic test and see if the front or rear brakes lock up
first. Do it in an empty parking lot and have someone watch from a
distance to see which wheels lock up. With ABS, it wont be easy to
see. I would say 20 - 30mph would be all the faster you would want to
go. Again, be careful, make sure the parking lot is empty.

When you replaced your rotors, did you tighten the lug nuts with a
torque wrench? Improper torquing of the lug nuts can cause rotor
warpage over time.