Some more brake questions

[matthewr87]

I recently installed my new solid rotors. Now I find that the front wheels tend to not spin as freely as before when off the ground. The RH side is a bit worse than the LH side. I can spin them with one hand and they spin for a couple of revolutions, but they seem to "stick" at one particular point in the spin and eventually stop at that point. Is this normal? I can't recall this happening with the drilled rotors.

Possibly related to this is a weird squeaking noise coming from the RH side when I just lightly touch the brakes. Sounds like a chipmunk squeaking. Frequency changes with speed when braking. If I hit the brakes hard there is no squeak.

Also, I flushed the brake fluid using the Motive bleeder. I filled the bleeder with fluid, raised the pressure to 15 PSI, and just bled inside/outside on the RR, LR, FR, LF. The reservoir never ran dry and I did not notice any air bubbles coming about of the bleeder valves. Now however my brake pedal is a bit spongier than before and I have to depress it further to engage the brakes. Should I bleed and flush again? No idea how air would have been introduced, but obviously I have air in the lines.

I will say that despite all of this the car still brakes just fine...

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[pilotgore]

I recently installed my new solid rotors. Now I find that the front wheels tend to not spin as freely as before when off the ground. The RH side is a bit worse than the LH side. I can spin them with one hand and they spin for a couple of revolutions, but they seem to "stick" at one particular point in the spin and eventually stop at that point. Is this normal? I can't recall this happening with the drilled rotors.

Possibly related to this is a weird squeaking noise coming from the RH side when I just lightly touch the brakes. Sounds like a chipmunk squeaking. Frequency changes with speed when braking. If I hit the brakes hard there is no squeak.

Also, I flushed the brake fluid using the Motive bleeder. I filled the bleeder with fluid, raised the pressure to 15 PSI, and just bled inside/outside on the RR, LR, FR, LF. The reservoir never ran dry and I did not notice any air bubbles coming about of the bleeder valves. Now however my brake pedal is a bit spongier than before and I have to depress it further to engage the brakes. Should I bleed and flush again? No idea how air would have been introduced, but obviously I have air in the lines.

I will say that despite all of this the car still brakes just fine...

As long as the rotors are installed correctly, they should act the exact same as the drilled ones.

What type of brake fluid did you use when bleeding and just curious how much you used. Did you use an anti-siphoning bleeder bottle? (Not required, just curious). Certain types of fluids can give you a slightly different pedal feel. I switched to Castro SRF in my mini track car and fully bled the system 3 times in a row thinking I had air in the lines each time. . . and SRF is expensive as sheot! I even swapped the brake booster (because I’m an idiot) trying to track down the problem. Out of desperation I switched to motul rbf 600, which I use in the mustang and corvette. Problem solved. After that drama, I read others saying different fluids can produce a different pedal feel.

After all that you’re probably going to say you used stock motorcraft fluid, and if that’s the case sorry for wasting your time with that rant

 

[BierGut]

As Pilotgore mentioned-- it's not the rotor if flat against the hub. What I might look at is whether you have a sticky caliper piston... just slightly gummed up with crap depending on how long you've tracked them and condition of the dust boots. I'd start there.

 

[matthewr87]

Hmmmmm....guess I'll take the rotor off and try to reseat it. Not sure what I could do differently than last time though. Is there some kind of trick to ensuring the rotor is flat against the hub?

Also I haven't detected any vibrations (up to 150 mph). Would I feel something if the rotors were not seated properly?

When you guys have the car up in the air do your front wheels spin freely? Or is there some resistance which eventually stops the wheel after a few revolutions?

 

[matthewr87]

And to answer the question about the fluid, yes just the stock Motorcraft pentosin crap

 

[pilotgore]

And to answer the question about the fluid, yes just the stock Motorcraft pentosin crap

On advice from the track attack mechanics, I use 25psi in the pressure bleeder (but your 15 should have been plenty). You may want to think about upgrading to something higher temp like rbf 600 or SRF as you pick up pace on track and start getting more heat into the brakes. My first solo on track was in my z06. I boiled the stock fluid as I picked up pace and went off track at 144mph….. now I use better fluid and bleed brakes before every single track event.

When you spin the wheel, does it sounds like it’s dragging against the brake pads? Maybe the pads aren’t properly seated/moving freely? The rotors are held in place by wheel pressure, so unless you have a pebble stuck between the rotor surface and hub, you’re probably good. It never helps to pull everything, inspect, and reinstall.

 

[shogun32]

use steel wool on the exposed piston face and outer piston bores (lightly). fully recess your pistons before you re-install the caliper. check the pliability of the seals. And on your first stop, give if a good 3-4 hard pumps to make sure all the pistons move to engage. take the wheels off or use a borescope and try fit a shim between piston and pad backing plate. Look for any 'twisted' seals.

pads skim the rotors at all times so you won't get free-wheeling like you get if there were no brake pads installed.

I would take a wire brush to the hub and knock off any rust, dirt, high points. And make sure the backside of your rotor hat is clean as well.

 

[DCShelby]

Buy some brake clean aerosol and squirt a good amount of it into the calipers, you will be amazed at how much gunk comes out. That’s the actual brand name Brake clean. Also as others said, RBF600 is the way to go.

 

[matthewr87]

Thanks guys. I'll get it up on the Quickjack this weekend and clean and reinstall all the brake hardware. I also have 1.5 L of the PM-20 fluid left over so I will flush and bleed with that to see if I can get the brake pedal feel back to what it was before. If I am successful I will switch out to a better fluid later.

The car still performed well at VIR the last couple of days, so hopefully these are all just minor issues.

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