Cobra brake issue

[mikenstang]

I installed a used set of Cobra PBR dual piston front brakes on my 94GT. and a new set of 13" rotors on the rear with stock calipers in the rear and new pads. The front rotors are Brembro cross drilled. I had the rotors turned and installed new stock 95 Cobra OEM pads up front.

My problem is brake pedal pulsation only on low speed stops at the last few revolutations before a complete stop. I can feel it in the steering wheel so I know it is comming from the front. I checked the rotor runout on the passenger side and I am within 2-3 thou. I still need to double check the dr side.

Also I cannot lock up the brakes. I push as hard as I can and the car will stop and dive the nose but it will not lock the tires or engage the ABS.

My question is do I need different pads to work with cross drilled rotors? I did not rebuild the calipers, could stuck calipers cause the issue? Any other Ideas???

 

[donkey_punch]

the caliper pin has to be greased or the caliper can bind or seize. many people and mechanics forget to do this. as i had calipers seize from not only myself not greasing them but not check after mechanic do the work also. this might be the reason for the pulsing but what first came to mind was warp rotors.

not locking up, i would think the abs was doing its job. but from my experiences when the abs kicks in it feels like the car hits ice and slides on ours cars.

also have the brakes been properly bled?

 

[Mustang5L5]

Rebleed the brakes

 

[mikenstang]

Thanks..I did not know they needed greese, I put my pins in dry , I will grease them later today and I will also double check my rotor runout and re-bleed..

So The stock pads should be good with cross drilled rotors?? I ask because it feels like there is something on the rotor and the pads are being hit by something as the rotor goes around like it is "grabbing the holes" or something.. I know it sounds weird but that is what it feels like in the pedel.

 

[mikenstang]

OK, I blead the brakes and greased the pins. I also checked the runout on the rotors again and the right is about .004 to .005 and the left is .013! So I obtained a few brake alighn shims and got it to about .008.
The brakes can now lock to the point where the ABS kicks in. But my pulsation is still there although it is better. At this point it has to be the rotors.

I will get the left one cut again to see how that worls out. Has anyone had any experiance with the $100 13" rotors on e-bay, Item number: 270379341977 ? Any good??? or Junk?

Thanks for the help.

 

[Mustang5L5]

I think for slightly more, you can get Brembo OEM blanks. I think they are $60 each on Tire Rack - Your performance experts for tires and wheels. Been a while since I checked

 

[donkey_punch]

i personally have no experience with slotted or crossed drill rotors, so i can't say that the pedal feel is going to be different.

but i'm still alittle worried about the brakes pulsing. by an chance when it pulses does the car pull to one side?

 

[Mustang5L5]

Brake pulsing is usually a rotor issue. It's usually due to deposits of friction material on the surface. Usually cutting the rotor eliminates this, but some say you can't cut drilled rotors while others say you can. That may be part of the issue.

 

[donkey_punch]

Brake pulsing is usually a rotor issue. It's usually due to deposits of friction material on the surface. Usually cutting the rotor eliminates this, but some say you can't cut drilled rotors while others say you can. That may be part of the issue.

i thought they couldn't be cut also.

for some reason i'll still thinking the rotor or rotors are warped.

won't cutting warped rotors down make them act less warped, so to say?

just like his pulsing isn't as bad now since he cut the rotors down.

 

[Mustang5L5]

Yes, cutting them should eliminate the pulsation.

But how well they are cut could be a factor.

 

[mikenstang]

Thanks for the input guys. I had the DR side rotor cut and it was out like the Pass side rotor. I just tested it and I still have the pulsation in the pedel on the last few revolultions of the rotors before a light stop. At this point I am going to buy new rotors. Maybe you can't cut cross drilled rotors??? I don't know.. It should not be this difficult.. Brakes a pretty simple.. Wierd..

 

[mikenstang]

Well I finally fixed this problem. After I installed new rotors I still had the pedel pulsing at low speed, light braking. I checked my hub run out and even the rotor run out again with the whees installed. I had less than 0.002 of run out. So I gave in a purchased 2 new calipers. Again no change!

While turning the tire and looking over the brakes in fustration, I noticed one bump on the drivers side reluctor ring for the ABS was slightly pushed in and not as close to the abs sensor as the rest of the ring. I bent it back up and the issue is GONE!

So I assume that the abs was activating at low speends and grabbing and releasig the brake giving me the pulse. The ABS was "seeing the wheel as stoping" as the lowered ring bump passed the sensor.

Sorry about reviving this old thread but I thought I would put in the fix incase anyone else ran across a similar issue.

 

[SVT32VDOHC]

You need a Cobra master cylinder. The booster is the same, but the master is different. My 13" brakes SUCKED the big one on my 95GT. Mushy, pulsation, wouldn't stop for anything. I never installed the Cobra master, but I have read on SN in tons of posts that you need a Cobra master.

 

[Chythar]

SVT32VDOHC has a good point, although I've also read that some folks like the pedal feel with the GT master cylinder and the Cobra brakes; they report a firmer brake pedal rather than a mushy one. A Cobra master cylinder will return the brake pedal feel back to the GT level.

I had a mushy pedal on my old V6, never found the cause. But after my 2-Cylinder snake upgrade (Cobra conversion), the brakes are nice and firm. I did install the brake booster, master cylinder and proportioning valve from the Cobra donor car, so it's possible one of them was failing. Brake pressure is about the same between my GT's and the Cobra clone, although the Cobra clone does stop faster with the larger brakes.

 

[Mustang5L5]

It also depends on which calipers you use, the 94-98's or the 99-04's.

I have a 94-95 GT MC on my 5.0 with SN95 rear disks and 03-04 Mach 1 calipers...and I like the feel of the pedal.

 

[mikenstang]

I'd say my pedel is firmer, I have not tried to brake hard yet B/C is has been raining here for a week
If I decided to change to the Cobra MC, would I need to change anything else? or just the MC.

 

[Chythar]

I'd say my pedel is firmer, I have not tried to brake hard yet B/C is has been raining here for a week
If I decided to change to the Cobra MC, would I need to change anything else? or just the MC.

The proportioning valve (the block below the master cylinder) is different for the Cobras. The two ports coming in from the master cylinder are reversed. This was probably done so the assembly line workers wouldn't install the wrong master cylinder in the wrong car. You can do one of a few things:

1. Bend your existing hard lines around so they will fit. You can also make new brake lines if you have the tools. However, this changes the front & rear bias on the brakes.

2. Cut the ends off of the current brake lines, swap the connectors and re-flare them.

3. Get a Cobra proportioning valve. Only resource I know of is a junkyard, it's been long discontinued.

A bit of research came up with a fourth option:

4. Buy a 93 Cobra master cylinder. Info is in this thread:

94-95 cobra brake upgrade + proportioning valve tech. - Corral Forums

Supposedly the 93 Cobra master cylinder has the same threaded holes to the proportioning valve as do the 94-95 GT's. Read the thread for more info.

 

[Bosko5.0]

You do not need a cobra master clyinder.

I am running stock gt master cylinder with cobra brakes and my pedal is nice and firm. I can lock them up real easily, but I don't need too. And I also have cobra rears, and I use dot3 brake fluid,

If your fluid is dark, or unclear you need to flush it, also there might be air still in the system if its mushy.


If you have badly worn out tires the abs will not work properly I would know, I had bald tires and they would shake like crazy, when locked up due too lack of gripp. I now have 1 bald(Damn pothole) and 1 newer tire and I can lock up the bald one, while my newer holds ground.

 

[SVT32VDOHC]

SVT32VDOHC has a good point, although I've also read that some folks like the pedal feel with the GT master cylinder and the Cobra brakes; they report a firmer brake pedal rather than a mushy one. A Cobra master cylinder will return the brake pedal feel back to the GT level.

I had a mushy pedal on my old V6, never found the cause. But after my 2-Cylinder snake upgrade (Cobra conversion), the brakes are nice and firm. I did install the brake booster, master cylinder and proportioning valve from the Cobra donor car, so it's possible one of them was failing. Brake pressure is about the same between my GT's and the Cobra clone, although the Cobra clone does stop faster with the larger brakes.

Thanks for agreeing and seeing my point. I had a firmer pedal as well after the swap of the calipers....BUT....the car wouldn't stop. You could ease into the brakes or just stomp on them and the car wouldn't stop. If someone pulled out in front of you even at 20MPH....I would have been doomed.