XR4ti Front Brakes

I had heard from someone (I am not naming names to protect the innocent) that I could put RX7 Front brake calipers on my XR for better brakes. I have an oval asphalt track race car and the wheel size we are limited to is a 13" wheel. The stock brakes leave a lot to be desired...along with the limited selection of good race pads. I have upgraded the rears to discs, but when trying to fit the RX7 calipers onto the XR rotor and spindle, pushing the cliper down on the rotor, by the time the caliper hits the mounting tabs for the caliper (I will have to build an adapter bracket) the pad is still not all the way on the rotor-its about 1/8" to 1/4" hanging over.

Has anyone actually done this? Is the pad not being fully on the rotor going to cause problems or cause the stopping issues not to really be resolved. The RX7 aluminum 4 piston calipers look very trick, but ultimately it is about stopping and possibly shaving some weight.

Jason

I pioneered the using on RX7 calipers onto Volvos maybe 10 years ago... But of course that's on a 280mm disc and 15" wheels..
Then, a lotta guys did the conversion, slimy parasites took the dimensions for the adaptor I published (1 1/2 bar of aluminum spot faced to 3/8" for the step---and 4 holes drilled, 2 tapped) and began selling the $5 worth of aluminum for $125 and THEN when we were able to run the car harder ---and I must stress: we were usassisted----we found they simply weren't strong enough un-boosted and that was that.

Here's the deal: when the mounting ears on the knuckle are 3.5" c-c and the caliper mounts are 3.5" c-c, its always a bitch.
In that respect the RX7 calipers are good with that wide spacing.

The question becomes: do you have a booster?
And: howsa booster work in a cammed low vacuum at idle motor?

That 13" tire thing really causes problems.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

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I dont have a booster, I took all that off and just run the brake pedal shaft right into the Master Cylinder.
The stock brakes from the XR fit, and the come with 14" rims and I believe the RX7's came with 14" rims, so that part of it should work, the biggest issue is trying to figure out how to mount them so that the brake caliper fits all the way down on the rotor properly and allows the spindle to still sit properly.

So curious if anyone has done this.

Jason

How about a slightly larger rotor? Many cars out there with 4x108.....

How big of a rotor? I've got a few randoms on the shelf.

As big as I can get to fit rotor, RX7 4 piston caliper on a XR4 spindle inside a 13" rim.....

On the stock XR rotor, the pad is hanging off the rotor approx 1/8-1/4"

Does the XR rotor and caliper fit under a 13" wheel?
The rules really require 13" wheels max? That's crazy.
Not sure how they would do in your application, but Porterfield R4's are available for the stock Merkur stuff.

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Grant Hughes

Quote
NoCoast

The rules really require 13" wheels max? That's crazy.

No tire choice does.
He can use a small diameter thing, or some HUGE fat monster thing if he goes 15".
We've talked and he is in a pickle.

Wonder if he's looked at the outside of caliper to wheel clearance?
Those RX7 calipers have a lot of caliper outboard and then the bump---the fluid transfer passage sticks out a bit more...

Really a shame he can't use like a tarmac tire at 60cm

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I just built some 260 mm brakes for a friend's historic racecar. Same type of rules, gotta run 13" wheels. I had to offset the rotor far back from the hub face to get the calipers inside the wheels, but it all fits. Could have probably even fit 10.5" rotors (266 mm).

I wanted to stick RX7 calipers in there, but they were a bit too long and the caliper corners hit the wheels.

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Opel is a 4-letter word...
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Edited 1 time(s). Last edit at 05/07/2012 03:01PM by Ascona73.

Jason, there are 3 or 4 different diameter Focus rotors, Saab has some 4x108 stuff, Early t-birds, and some other Ford FWD stuff. If you go on to rock auto, alot of the rotor diminsions are listed. Measure your stock rotor, and find something 1/4" bigger or so. See whats in stock at Napa and go compare offsets and stuff.

Are you mandated to those diamond racing style wheels? Can you try to find a wheel with more clearance inside for brakes? (I've only seen the inside of a diamond racing wheel once, and that was a LONG time ago).

What about an aftermarket caliper setup?

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Welcome to the cult of JVL drink the koolaid or be banned.

Thanks for all the help guys. Couple things:

1. How did you offset rotor from hub face?
2. After looking at RX7 calipers, yes, they actually do stick out quite a bit...hmmm whoever gave me this advice may have been a little forgetful on what this is going to take.

May have to space wheel from rotor...

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Jason.Gotz
Thanks for all the help guys. Couple things:

1. How did you offset rotor from hub face?

I did a custom spacer, countersunk bolts, etc. I used a FWD rotor from another car for my fitment. Calipers are inexpensive Wilwoods, but they're compact.

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Opel is a 4-letter word...
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Edited 1 time(s). Last edit at 05/07/2012 08:03PM by Ascona73.

What is the rotor and the other item off of? That looks pretty trick.

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Jason.Gotz
What is the rotor and the other item off of? That looks pretty trick.

Well, the car is an Opel vintage race car. I am using the stock Opel hubs with new ARP studs. I had the aluminum adapter custom made to my specs. The rotor is a 1984 Dodge Daytona turbo rotor (24 mm thick x 260 mm OD). Rotor cost was only $19 each.

I used generic steel caliper brackets which I cut and drilled to fit the caliper to the stock spindle. Total investment is around $600...that's everything, even the new hardware.

They fit steel circle track wheels with room to spare, and they fit inside Panasport 13 x 8's with no problem either. A huge improvement over the stock non-vented rotors that are 240 mm. Calipers have four 1.375" pistons, which are only about 6% larger than the stock 2-piston 45 mm iron calipers in terms of piston area, so the M/C remained as is.

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Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/