rjheard

I just replaced the front rotors on my 98 GS400 for the second time in three months. I replaced the first time with Brembo blanks because the old ones seemed to be warped. Three months later and the Brembos are pulsing too. I'm concerned that the new ones are going to do the same thing. I noticed that the passenger side was dragging in spot and the drivers side seemed to drag a little on the whole disk. By "dragging" I don't mean so much that it's difficult to turn the hub by hand without the wheel on. It also seems to pulsate slightly when stopping during the test drive. Am I wrong to be concerned.?

mitsuguy

iTrader: (2)

you need to mount the rotor on the hub, and measure the runout of the rotor itself... you should have less than .002" of runout... Variances in the hub, a dirty or corroded hub, and sometimes even not tightening lug nuts properly can all cause this issue... you should also check the wheel bearing for play, as this can cause that as well...

rjheard

That's what I was afraid of. I'll have to try and find a reasonable dial gauge today. Assuming I confirm this is the problem and changing the position of the disc does not fix it have you ever used shims for this situation?

PureDrifter

iTrader: (10)

did you change the pads out/bed them in properly?

rjheard

I did change the pads out too. I'm not sure bedding would affect this problem. Opinions vary but what is yours on proper bedding?

mitsuguy

iTrader: (2)

the only part of bedding in pads and rotors that could affect this is if you were using a very aggressive bedding procedure, and they weren't allowed to cool properly...

certain bedding procedures call for rotor temps high enough to make the rotors glow, if you were to stop the car using the brakes and leave the brake pedal depressed in one position once stopped, it could cause a high/low spot...

other than that, shouldn't matter..

rjheard

I checked the runout and it's right on the .02 tolerance. I'm beginning to wonder if it could be ABS related or maybe the rears.

mitsuguy

iTrader: (2)

if it's .02, then it's wayyyyy high...

the spec is .002

rjheard

Oops.... .002 is what I meant.

mitsuguy

iTrader: (2)

I highly doubt it's ABS related...

try having the rotors turned on the car, see what happens... I almost bet, even though you currently don't have much runout, that it gets better / is fixed...

if it's not the rotors, and it's only when you brake, the only thing else it could be would be like ball joints, severely loose tie rods, etc...

Have you checked the rears? It is possible for them to produce a pulsation as well...