Miata Mailing List: December 1999, Message #484

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Ralph
Your scenario does seem to fit the best.  The second part about the brake
piston could be what is happening.  I've never done my own brakes so I'm
not sure how it was done.

I mentioned the directional pirellis (I normally just rotate front to back
keeping them on the correct side) and how I attempted to rotate left to
right only to rule out the tires as the source.  Switching left to right
still left a pull to the left.

The question that bugs me is why the problem is intermittant and doesn't
seem to occur with my summer tires/alloys.  Would the pressence of air
blowing through the alloys keep the rotors cooler?.  I think I'm on the
right track now.

Any more thoughts gang?

Thanks again
Paul Cartwright
& Hakuna 94brg

At 12:35 PM 12/4/99 -0500, Ralph Alder wrote:
>Paul,
>
>I have two suggestions for solutions.
>
>My brother had some snow tires on his VW Rabbit that pulled to one side all
>the time.  Switching the tires side to side shifted the pull.  A tire
>dealer, the one who sold him the tires, diagnosed the problem as a bad tire,
>which was replace and solved the problem.  Something with the belt made it
>have more drag than the other tire.  You could easily swap tires side to
>side to see of that solves the problem.
>
>The other problem of pulling under initial braking *I* had to deal with.
>When first applying brakes after driving on the freeway, for instance, the
>car would initially dart to one side just slightly, then stop normally with
>no pull.  When doing threshold braking stops, the left tire would always
>lockup first.  Since it was time to replace the brake pads and since it was
>to be the third set of pads I decided it was time to have the rotors cut.  I
>asked the guy at the machine shop if he knew of any reason for the brake
>problems I described.  He looked at the rotors laying on the counter,
>pointed to one and said that *this* one was from the side that pulled.
>Since I had marked them and he was correct, I said yes.  Closer inspection
>revealed that one  rotor had a slight bluish tinge to it.  He described a
>scenario where the person who did the last brake pad replacement took the
>easy way out and just pushed the piston back into the caliper and fitted the
>new pads, and that the problem with that is that dirt and debris accumulates
>in the bottom of the cylinder and obstructs the free movement of the piston.
>I knew the first part to be true because I had done all brake
>repairs/replacement since the car was new (it had somewhere around
>80,000miles at the time).  Furthermore, when I later popped the piston out I
>found a bunch of mungy stuff in the cylinder despite flushing out and
>replacing the brake fluid about every other year.
>
>To sum up, the car lost its darty nature and stops straight and true.  I
>seems that the left piston would not retract off the rotor surface like the
>right side would, keeping the left side rotor/pads at a higher temp all the
>time giving the left side better bite until the right side pads had made
>several rotations against the rotor and heated up as well...causing the car
>to dart to the left side momentarily.  The situation was not dangerous and
>didn't require any heroics to stop but was just a bit irritating to someone
>who appreciates that mechanical things are supposed to work properly and is
>bothered when they don't.
>
>Very closely check the rotors...probably need to be side by side on a bench
>to see the difference in color.  Then do a cylinder rebuild with new seals
>and dust boots and new fluid into newly cleaned cylinders.  I'll bet it will
>solve your problem.
>
>Ralph Alder
>Tustin, CA
>'90 Classic Red w/Yellow Stripes
>Team  Aerodyne
>
>
>-----Original Message-----
>From: Paul Cartwright <p.cartwright@home.com>
>To: Multiple recipients of list <miata@list.miata.net>
>Date: Friday, December 03, 1999 22:22
>Subject: Possessed car
>
>
>>Hey all
>>
>>Its not really possessed but I thought it would get your attention.
>>I'm having a real strange intermittent behavior from my 94 miata.
>>
>>It only seems to occur with my snow tires on.  Pirelli ice performance
>>tires (directional) mounted on steel rims.  While I notice a slight pull to
>>the left (none with the summer tires/alloys) the worst part is a strong
>>yank to the left on hard braking... BUT NOT ALWAYS!!!!.  This is
>>frustrating as hell.  I can be cruising along and apply fairly strong brake
>>action and the car stops straight.  The very next strong braking action
>>results in a extreme pull to the left and then the next brake is normal.
>>
>>Questions:  Why does this problem only show up when the winter tires are
>>on.  I've tried rotating the tires, even swapped left to right... same
>result.
>>Cold or hot doesn't seem to affect it.  Maybe the problem is there always
>>but only noticable with the heavier wheels.
>>
>>I'm begining to suspect the brakes.  Can the slider pins on the left front
>>cause it to lock to early.  Or am I experiencing occasional loss of brake
>>pressure on the right side causing the pull to the left.  Could crap in the
>>brake fluid cause that?
>>
>>The overall feel of the front end is loose and the tires tend to tramline a
>>bit.
>>
>>I call out to wisdom of the list, surely someone has seen this phenomenom.
>>
>>
>>Thanks in advance
>>
>>Paul Cartwright
>>& HAKUNA 94BRG
>>Calgary, Alberta
>>
>>
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