3-Door RS Cosworth hub bolt pattern?

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john keefe
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Re: 3-Door RS Cosworth hub bolt pattern?

Post by john keefe » Wed Oct 25, 2017 1:02 pm

whitelx wrote:
Wed Oct 25, 2017 10:51 am
1993 Mustang Cobras use the same rotor and caliper as the turbocoupe. 1994-2004 Cobras use an 11.65" vented rotor with a 38mm piston. The 94-04 GT/V6 use a 10.5" solid rotor with a 38mm piston.
Thanks whitelx. The 11.65" rotors would be nice, and just for looks alone, would give a much better proportion to the front/rears. Kinda' has the Honda boys' "big-front-rotor-with-tiny-stock-rear-drum" setup you see all around here. But besides being 5 lug, it would produce even more braking torque than what I'm pondering with the TC caliper and RS rotor...

Makes sense for the Cobras, since the 1993's were 304lbs. heavier than an XR, and the 1994-2004's were 511lbs. heavier.

Just out of curiosity. The 11.65" Cobras are 0.33" thinner than the TC rotors (0.71" vs. 1.04")... Did the Cobras use a much thicker brake pad, or is there enough safe caliper piston travel to use the TC sized pads?

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whitelx
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Re: 3-Door RS Cosworth hub bolt pattern?

Post by whitelx » Wed Oct 25, 2017 5:00 pm

The caliper is different all together than the turbocoupe caliper. The Cobra and GT/V6 used the same caliper, but had a different caliper mount and axle bracket. In order to account for the rotor thickness, the cobra used a thinner pad vs the GT/V6. I used a GT rear caliper and caliper mount on my 92 Mustang with a cobra (aftermarket) axle mount. In order to use the cobra rotors with the GT/V6 calipers I used a die grinder to open up the slot on the caliper bracket to clear the rotor.

I've been wanting to switch to Tim's rear setup so I can do away with the large turbocoupe caliper and use a 38mm caliper to get back some brake feel. I am using the twin 44mm GT/V6 PBR calipers up front with the T-bird 1 1/16" mastercylinder (which is the same size as the V6 mustang master), but the pedal feel is severely lacking. I have SS braided lines as well. The only thing I can contribute it to is the overly large turbocoupe rear calipers as the V6 Mustang used twin 44mm front, 38mm rear with the 1 1/16" master.

I also hate that my e-brake won't hold on hills (inclined driveways) with the TC calipers.
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timxr8
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Re: 3-Door RS Cosworth hub bolt pattern?

Post by timxr8 » Wed Oct 25, 2017 8:50 pm

john keefe wrote:
Wed Oct 25, 2017 1:27 am
My rear Wilwoods are dual pistons @ 1.25" & 1.0" staggered
Are you planning to try and get rid of those calipers? I may be interested.
john keefe wrote:
Wed Oct 25, 2017 1:27 am
What I calc'd out before was that the combination of Wilwood's front + rear needed 25% more pedal travel to move the pads 0.01" than the stock RS fronts + TC rears (1.77" bore). But, comparing torgue on the WW rears (+RS rotor) vs. TC rear (+TC rotor) was fairly even (1.9% produced by the TC calipers on TC diameter rotors (vs. WWd's on RS diameter rotor).

Recalculating, switching to the TC rears would require 6.4% more pedal travel. Noticeable, but probably not drastic enough to consider going to a different master cylinder bore. But, that combination using the RS rotor on the rear produces 22.1% more rear piston force, and about 14% increase in torque being applied on the rotor at the pad centerline.

That seems like it would be a noticeable difference in rear brake bias. And, not sure if the in-line bias adjuster could dial that out and leave room for further adjustment if needed.

Right now it feels like a really good combination, and a good range of bias using the line-force valve. On the other hand, the Vargas caliper seemed to work fine with heavier Mustang Cobras. Then again, they deal with a smaller diameter rotor than the TC, which requires larger rotors for its greater overall weight, right?

So, now it seems to be a debate of more rear brake bias and a longer pedal travel vs. a parking brake. Hmmm... :? Now I'm confused. Have to think on this one.
Something you need to consider also is the size of the pad and pad compound. I guarantee that the SL pad, both size and compound, makes a much higher torque also. The pad on the TC is tiny, that's compared to every other pad I have seen for these cars (Scorpio/Sierra and the new Focus). That contributes to the lack of holding on the parking brake (unless you rip the handle up) That's from experience.

With a longer travel and larger pistons, there will be more torque, but less modulation. Most race vehicles that I have worked on are significantly "underbraked" by the standards of a road car, but they utilize pad compound and rotor diameter to help compensate. What the small sizes of the pistons affords them is modulation.

Just stuff to think about. If I finally get around to working on the brakes on my car, I'll share that.
Tim Spencer
1988 XR4Ti Duratec project car
2011 Taurus SHO daily driver...not stock.

john keefe
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Re: 3-Door RS Cosworth hub bolt pattern?

Post by john keefe » Thu Oct 26, 2017 2:44 am

whitelx wrote:
Wed Oct 25, 2017 5:00 pm
The caliper is different all together than the turbocoupe caliper. The Cobra and GT/V6 used the same caliper, but had a different caliper mount and axle bracket. In order to account for the rotor thickness, the cobra used a thinner pad vs the GT/V6. I used a GT rear caliper and caliper mount on my 92 Mustang with a cobra (aftermarket) axle mount. In order to use the cobra rotors with the GT/V6 calipers I used a die grinder to open up the slot on the caliper bracket to clear the rotor.

I've been wanting to switch to Tim's rear setup so I can do away with the large turbocoupe caliper and use a 38mm caliper to get back some brake feel. I am using the twin 44mm GT/V6 PBR calipers up front with the T-bird 1 1/16" mastercylinder (which is the same size as the V6 mustang master), but the pedal feel is severely lacking. I have SS braided lines as well. The only thing I can contribute it to is the overly large turbocoupe rear calipers as the V6 Mustang used twin 44mm front, 38mm rear with the 1 1/16" master.

I also hate that my e-brake won't hold on hills (inclined driveways) with the TC calipers.
Didn't know that the TC e-brake was that weak. With a 1-1/16" MC, that should be plenty of bore to give you a fairly high pedal, and feel...

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Re: 3-Door RS Cosworth hub bolt pattern?

Post by john keefe » Thu Oct 26, 2017 2:54 am

timxr8 wrote:
Wed Oct 25, 2017 8:50 pm
john keefe wrote:
Wed Oct 25, 2017 1:27 am
My rear Wilwoods are dual pistons @ 1.25" & 1.0" staggered

Something you need to consider also is the size of the pad and pad compound. I guarantee that the SL pad, both size and compound, makes a much higher torque also. The pad on the TC is tiny, that's compared to every other pad I have seen for these cars (Scorpio/Sierra and the new Focus). That contributes to the lack of holding on the parking brake (unless you rip the handle up) That's from experience.

With a longer travel and larger pistons, there will be more torque, but less modulation. Most race vehicles that I have worked on are significantly "underbraked" by the standards of a road car, but they utilize pad compound and rotor diameter to help compensate. What the small sizes of the pistons affords them is modulation.

Just stuff to think about. If I finally get around to working on the brakes on my car, I'll share that.
The Wilwood pads are sizeable. When I did my calcs, I factored in for the overall pad area, guestimated a CF for Hawk pads vs. semi-met "performance" TC pads, and calc'd torque from the radial centerline of the pads from the hub center. The large TC piston's bore puts its center of pressure a lot lower on the rotor than the smaller Wilwood pistons, which are designed to be higher up on the rotor (e.g., for use w/ rotors with hats).

Gotta' think on what the extra travel will do to pedal force. I much prefer a hard pedal. One of the things I don't like with ABS is the softer pedal.

On the race cars' brakes being undersized, I'd think that with passenger cars, nobody wants a squealing hard compound, but something nice and quiet, so the compensation from car makers is larger diameter rotors to get more consistent torque over repeated applications where the softer pads might fade more quickly.

john keefe
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Re: 3-Door RS Cosworth hub bolt pattern?

Post by john keefe » Thu Oct 26, 2017 1:27 pm

timxr8 wrote:
Wed Oct 25, 2017 8:50 pm
Are you planning to try and get rid of those calipers? I may be interested.
OK. But... dunno. Would have to do a back-to-back comparison first. Then, if I ever do get the time to finish this car and take it out for a track day or two, I think I'd trust the Wilwoods more than the TC's. Always thought you should be checking/bleeding the brakes beforehand anyway, and its not a whole lot more work to swap setups if you have all the parts. It would be a PITA, though, to have to swap back.

Guess it boils down to the argument I still can't finish after all this time... Track car, or a high-performance street car. Sure, it rides harsh at times, but doing the roll cage, gutting the interior, et al is a one-time commitment, at least for me with not a lot of spare time to convert it back if it turns out a track setup is not for me.

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Re: 3-Door RS Cosworth hub bolt pattern?

Post by john keefe » Tue Oct 31, 2017 2:40 pm

Thinking about the TC rear caliper setup I had a long time ago, one thing that I forgot about which might solve some of the "weak parking brake" experiences is that I had to resort to using a small diameter electrical conduit tubing between the clip on the STA, and the e-brake cable "catch" or receiver on the caliper.

Don't know if this makes a difference for everyone else' experience , but I used the stock XR e-brake cable, and there was just way too much slack to be taken up. Engaging the e-brake took up the slack (i.e., pulled straight), and the cable wouldn't really activate the brake lever until the very end of travel. By bending the conduit, the cable take the line of least resistance (straight), but had to maintain the inside curve of the conduit. So... got immediate actuation on the e-brake caliper lever, and never had a problem with those brakes holding on an incline. KInda' like adding a small chrome tube on a road-bike's scissor brakes.

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