Front brake pull?

[KIMMER]

Anyone else have a bad pull on their mustang. Sometimes it stops fine, sometimes there is a pull left. Doesn't always do it and I know it is not hanging up on anything.

 

[Hawgman]

Only time I have ever noticed a pull is if I am on a surface that is not flat, or is "humped" in the middle. It will dive pretty badly to the side that has the slope.

 

[don_w]

Kim... how wide are your front tires?

 

[KIMMER]

9" but it's done this stock to...acts like the valve isn't giving the same pressure to both sides.

 

[SoundGuyDave]

Kim,

Just for giggles, try lubricating the slides on the right side caliper, and make sure that there isn't something that could bind up intermittantly, like a line-lock hose, or other gak. If the car pulls to the left (driver's side), then the problem is on the right, where it's not getting sufficient clamping force. Dumb question, but are you high mileage on your brakes? If the pads are worn sufficiently thin, and your rotors are worn sufficiently thin, you MAY be getting one or more of the pistons cocking in the caliper bores, and not applying properly. If the right is worn, and the left is not worn as much, this could also be a sign of caliper bind at the slides. The caliper would apply, but not release properly (due to slide binding) and wear out the outer pad.

For there to be a pressure differential from side to side, it would have to be a malfunctioning master cylinder (I believe that the S197 has a standard 2-chamber master, with each chamber feeding one front brake and the opposing rear brake), or a malfunctioning ABS module. The ABS module would be a REALLY bizarre failure, since the solenoid controlling the R/F caliper would have to stick closed, preventing pressure buildup. If it was the master, the left-rear brake would also be affected, but you wouldn't notice much, since the majority of the braking effort (~80%) is from the fronts.

This is intermittant, right? Do you only get the brake pull under light braking, but with moderate pedal force it'll track straight? Or is it fine under light but goes wonky when you stab the brakes? Or is it completely random? More info might help...

 

[MrClean]

9" but it's done this stock to...acts like the valve isn't giving the same pressure to both sides.

I had that exact problem on my F-150...I'm guessing you're probably right, or there an obstruction in the line to the side that isn't pulling...and hence getting less pressure applied to the caliper.

 

[KIMMER]

My car only has 2500 miles on it, so there is no excessive wear. It is intermittent but normally under light pressure. If I stab the brakes it stays straight. I've taken the calipers off and checked everything and it still does it. Its more of an annoyance than anything.

 

[ClassJ]

Try lubing the caliper pins or slides.

 

[MikeVistaBlue06]

Be sure it is not leaking grease on that side. Believe it or not a leaky hub putting grease on the rotor will cause it to grab quicker. Same thing for drum brakes as well.

Hope this helps.

Mike

 

[SoundGuyDave]

My car only has 2500 miles on it, so there is no excessive wear. It is intermittent but normally under light pressure. If I stab the brakes it stays straight. I've taken the calipers off and checked everything and it still does it. Its more of an annoyance than anything.

Any issue with your brake system is more than an annoyance... The light pressure thing is REALLY aiming me towards your caliper slides. This is also fairly common on low-mileage vehicles, as the slides can start corroding slightly while the car is just sitting.

Mike's hypothesis of grease contamination is also a possibility, but I would expect that to still exhibit pull in moderate braking conditions as well.

If you've checked the basics, slide function, pad and rotor condition (glazing), fluid levels, etc., and you're still under warranty, I would take it to the stealer, ahem, dealer, and let them suss it out.

If you really want to tear into it yourself, I would start by doing pressure measurements on the braking system. With a known weight on the pedal (like a 20lb sandbag), measure the static pressure developed at the master cylinder, and also at the caliper inlets on both sides. If they differ, then start back-tracing the low-pressure side, up to the outlet of the ABS module, then at the inlet, etc. It's a LOT of work, considering that you have to bleed the brakes each time you move your pressure gauge.

If it's not slides, personally, I would take a flyer and buy a set of take-off front calipers from Roush or Saleen, and see if that just doesn't fix the issue. Could be just a burr in the caliper bore that's causing one of the pistons to hang just a bit.

Either way, you need to get to the bottom of it, because brakes are one place not to screw around...