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With the limiting factor on front brakes being the rear brakes, i always wondered if there was a easier way to upgrade the rear cobra brakes without resorting to the high dollar aftermarket kits.

For example what would it take to install a set of the 93 Cobra/87-88 tbird/93 taurus 42mm varga style calipers in place of the 38mm on the 11.65" rotor? If you could theoretically mount those calipers properly, i wonder how that would affect the bias when running the 13" rotor and ATS brembos. Would it be more favorable?

Again...just thinking out loud. I'll likely keep my brake setup just the way it is
That's how I knew the specs of the OEM calipers of similar Fords, as I posted the caliper piston sizes before. I knew with my large custom brakes on my Explorer mail truck, I wanted a little more for the back also. That's when I discovered the 2003-10 Crown Vic had 1.9" pistons, while the Cobra had 1.5" pistons. I bought the CV brakes before thinking through how they could fit my truck. Thus it's a PITA for my truck to put those one, but it may not be so hard on the cars. The parking brake cable has to go into the back, in stock form it's at the top, which shouldn't interfere with the car's suspension parts. I haven't looked under my Mark VII, which you know has the exact same HO Mustang 8.8 rear. But note the CV pads are not really any bigger than the Mustang pads, or my Explorer rear pads. The rotor diameter and caliper piston size are the big factors.

Here's the new caliper I have to make a bracket for, for my mail truck. This is a Wilwood six pot 5.44 sqin. piston area model, with massive pads.
1053825
 

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With the limiting factor on front brakes being the rear brakes, i always wondered if there was a easier way to upgrade the rear cobra brakes without resorting to the high dollar aftermarket kits.

For example what would it take to install a set of the 93 Cobra/87-88 tbird/93 taurus 42mm varga style calipers in place of the 38mm on the 11.65" rotor? If you could theoretically mount those calipers properly, i wonder how that would affect the bias when running the 13" rotor and ATS brembos. Would it be more favorable?
Baer offers an "upgrade" for the '94-04s to go to 13.25" rear rotors with the stock calipers. Working through the math and making some assumptions about effective rotor diameters, I get:
  • With 13" rotors and PBRs up front (with 38mm pistons), installing the 13.25" rear rotors would shift bias ~14% to the rear. I believe I've seen these larger rear rotors brought up in threads in the past, and it has been pointed out that installing them with stock fronts is not a performance upgrade.
  • With 13" rotors and Caddy Brembos up front (with 42mm pistons) + stock Cobra rears (11.65" rotors, 38mm Vargas), the bias would be shifted ~22% to the front (compared to 13"/38mm PBRs + 11.65"/38mm Vargas), as Jack has said before.
  • With 13" rotors and Caddy Brembos up front (with 42mm pistons) + Baer 13.25" rear rotors (with stock 38mm calipers), the bias would be shifted ~5.5% to the front (compared to 13"/38mm PBRs + 11.65"/38mm Vargas). Significantly better than with stock size rear rotors.
  • With 13" rotors and Caddy Brembos up front (with 42mm pistons) + 42mm Varga rear calipers on 11.65" Cobra rear rotors, the bias would be essentially the same as a stock Cobra setup.
 

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Baer offers an "upgrade" for the '94-04s to go to 13.25" rear rotors with the stock calipers.
This kit i believe.


Only negative about it is that it's a non-vented rotor, and required the GT/V6 axle brackets to mount it.


  • With 13" rotors and Caddy Brembos up front (with 42mm pistons) + 42mm Varga rear calipers on 11.65" Cobra rear rotors, the bias would be essentially the same as a stock Cobra setup.
Now that has me curious as to what it would take to mount the 42mm Varga up on the 11.65 cobra setup safely, and maintain a functional parking brake
 

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There is no such thing as a 42mm Varga caliper. The TC/1993 Mustang Cobra rear calipers are 45mm. They can not be used with an 11.65" rotor due to the curvature in the annulus of the caliper being too small. This makes them useless for adding rear brake bias to the car.

You might be able to use the 43mm TRW caliper from an S197 Mustang. This can be used with a 14" rotor, if it were needed.
 

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Total brainfart on my behalf on the cobra 45mm vs 42mm thing. Reason being is that i thought i read somewhere that the 93-97 Ford taurus use the same rear caliper. I looked up the specs and it's a 42.8mm caliper

0134E1E3-AA53-4F7A-BABF-E08B4EEEBA1E.jpeg


So i pulled up a stock image of the 93-97 Taurus rear caliper and it looks like a spitting image of the 38mm Varga. The reman shops list it at 42.8mm. It’s stamped 43, like the sn95 38mm units are stamped 38....so 43mm Varga?

Almost temped to grab one at a parts store and see if it does swap with the 38mm Caliper. It looks damn close.

Rotor is 10.1", but my thought it that if the bolt spacing is correct these would bolt right up to the Sn95 style abutment.

Worth looking into at least. no?

If it fits (and that’s if) then the next hurdle is what MC to use with the 42x4 front and 42 rear setup.
 

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That Varga casting looks like the 45mm version, so it probably also uses the caliper hanger with the wider pin spacing. If this caliper and the 45mm version are the same basic casting, then they will both have the same rotor OD limit of around 10.8".
 

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then they will both have the same rotor OD limit of around 10.8".
But isn't that just an assumption? By that logic, the 38mm Varga should not be able to be used on both the 11.65" and 10.5" rotor. However in that case, the rotor offset distance is set by the axle brackets, and not the caliper hanger bracket. Reality is you can toss Cobra rear calipers on a GT, and vice versa (if the GT's abutment slot was wide enough to accomodate the Cobra rotor, which it isn't)

Of course, the only way to know if the 43mm Varga is like the 45mm, or like the 38mm caliper is to go grab one and measure/test it. I'm curious to see if just the caliper portion alone will mount to the Mustang hanger. For this to happen, the bolt spread on the caliper needs to be the same, as well as the position of the cylinder in relation to the center of the brake pad to evenly press the pad. Of course, there's also interference to check for as well.

I'll pick one up next week..just to see. I'm curious after looking at pics of the 43mm vs the 38mm and 45mm.
 

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Mike,

Yes, it is an assumption on my part, but it is based on a lot of years of knowledge dealing with these issues.

I know for certain that the Varga 38mm caliper hanger will not properly fit onto the 45mm Varga caliper.

As Ford already paid for the tooling to build the 45mm caliper, it would be very easy to have Varga change the insert in the casting mold to 43 and machine the piston bore 2mm smaller. This would allow them to use the same hanger bracket. Given this, when the casting mold for the caliper is designed, it is setup for a maximum rotor OD. Unless you are dealing with a truck, back then Ford used very small diameter rear rotors. I'd be very surprised if the 43mm caliper was capable of being used with a rotor larger than 11".

When Ford had Varga build the 38mm caliper, they new that they were going to use it with both 11.65" and 10.5" rotors, so they designed it to be compatible with both.
 

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See the photo linked below.

It is the radius formed by the two flatish areas on the inside of the caliper body in conjunction with the piston location, that determine the maximum rotor OD that can be used with it. The rotor OD can also be limited by the depth of the groove in the hanger.

 

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Sorry Jack, didn't mean to challenge you as i respect your experience in areas I wish i could spend more time researching in. I understand exactly what you are saying in terms of rotor radius and the caliper shape being designed to accommodate it.

I admit that It's wishful thinking on my part to hope this caliper is a 100% bolt on replacement, but i guess i need to pick one up and confirm it works, or doesn't work.

SO i'll update on what i find
 

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i offered mike an '05 rear caliper i have around for testing so now he has the turbo coupe and 05 and just needs a time machine ;)

my concern is the parking brake cables

good reference of different years caliper and rotor sizes here

if we do find a rear combo that works out the balance problem then a more logical brembo caliper option would be the 1st gen cadillac cts-v as they give you pretty much the same area as the ats, don't require any mods to the pads, can be had for $116 brand new, although will require the spindles to be redrilled to accept the gm spacing.

if mike proves the rears i can buy a cts-v caliper and try it on my car since my spindles have been redrilled as i'm running the corvette calipers with GT500 rotors that i cut down (there's a thread on here). my car stops awesome and for me it was more about having 1.25" rotors, so probably wouldn't switch although am happy to help if there's enough interest.
 

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i offered mike an '05 rear caliper i have around for testing so now he has the turbo coupe and 05 and just needs a time machine ;)

my concern is the parking brake cables

good reference of different years caliper and rotor sizes here

if we do find a rear combo that works out the balance problem then a more logical brembo caliper option would be the 1st gen cadillac cts-v as they give you pretty much the same area as the ats, don't require any mods to the pads, can be had for $116 brand new, although will require the spindles to be redrilled to accept the gm spacing.

if mike proves the rears i can buy a cts-v caliper and try it on my car since my spindles have been redrilled as i'm running the corvette calipers with GT500 rotors that i cut down (there's a thread on here). my car stops awesome and for me it was more about having 1.25" rotors, so probably wouldn't switch although am happy to help if there's enough interest.
Interesting. What was the piston size on those early CTS-V rear calipers? I actually had a pair in hand that might have been those. I got them from eBay to try, but one had a stripped hole and I sent it back. They were nice looking calipers, but a small pad I thought. This was in 2006;

1053912
 

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Since we are talking hypothetically,

Even if some of these larger calipers do fit, the larger piston sizes do create an issue with MC selection. I haven’t crunched the numbers but I don’t believe there is a factory option that can accommodate the hypothetical ATS/taurus 43mm setup.

I haven’t looked aftermarket yet. I won’t bother unless there is a rear Caliper that fits.


As for the CTS-V, I thought that Caliper used a completely different offset and bolt spacing?

To get the ATS brembos on, I designed and machined an offset bushings to compensate for the 128mm vs 130mm bolt spacing. I didn’t want to modify my spindle. My later revision dropped the Caliper down 3mm to clear 17” rims.

AE54E868-BCC6-4B04-B6FC-A284A8EBEE2E.jpeg
2CB972F8-8AB5-400B-BC89-B0139A7ED25F.jpeg


Then you run in the same issues as with 00 Brembos. From clearance to the spokes. 98 Cobras clear fine, but other 17x8 will need a spacer

CC202432-8DF7-4997-B4F0-8B774A872211.jpeg
 

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Just so happens the 986 master is 25mm, the rotors are similar sizes and the cars weight is in the ballpark. They are radial mount calipers so an adapter might be tough.
 

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The problem will likey be that the 986 has about 10% more rear weight bias than a Mustang. The rear calipers will be too large and the fronts too small.
 

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Interesting. What was the piston size on those early CTS-V rear calipers? I actually had a pair in hand that might have been those. I got them from eBay to try, but one had a stripped hole and I sent it back. They were nice looking calipers, but a small pad I thought.
The 1st gen ('04-07) CTS-V rear calipers are the same family as the '00 Cobra R front calipers, and are smaller calipers than the ATS/XTS calipers, hence the smaller pads. The V rear / Cobra R front calipers use FMSI D592/D1053 pads, respectively, which are ~110x69mm (according to Hawk's catalog; they designate them as pad shape HB194). The Cobra R pads are thicker than the V pads, which I believe is why the FMSI numbers are different.

The ATS/XTS use the larger FMSI D1001 (132x77mm), which is a very common pad shape used on all sorts of Brembo cars in the past 15 years or so (STIs, EVOs, SRT8s, Mustangs, Camaros, CTS-V front, and on and on).

I have an '05 CTS-V, and have the original calipers (D1001 front and D592 rear) on hand if anyone wants any measurements. I believe I also have piston sizing info at home.
 

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the piston size of the rear cts-v brembos is significantly smaller at 28 and 32mm

i'm more than happy to test fit that front cts-v caliper on my car if you want to ship it over
(can't see your location with this new bs update... i'm in marlborough mass)
 

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WHat's the spindle mount bolt spacing on the CTS-V caliper? 128MM using M14 bolts?
 
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