Need help identifying and locating rear rotor for Spridget

M

mg_john

Well-known member
My HP Spridget has rear discs which have been on the car for some time. They were on the car when I bought it.

It is Kenny Purgeson's old #29 car which I believe ran at the Runoffs years ago. The log book starts in 1977.

While looking over the car in anticipation of going to Sebring Thanksgiving weekend, I found a crack in the right rear rotor. Picture attached. Crack is at 12:00.

Anybody have one or know what car it came from originally or where I might get one?

Rotor dimensions are: 8 1/8 " OD. 4 3/4" ID. Depth of "hat" 2". Looks like original rotor thickness is .300". Of course it might have been machined some for the Spridget rear application.

It might be Fiat X1/9 or Fiat 124.

Any help would be greatly appreciated.
 
I've got similar disks which I thought were Winner Circle's. Mine are used with Wilwood single piston calipers. The hats are 2 3/8" on the dish side and about 2" high on the raised side. I haven't called WC but does anyone know if they are still available? If not any more spares out there? Neither of mine are cracked at this time but I have been concerened that one may crack with no spare.
 
These disc brake conversions were done by Winners Circle. It used a special size disc for the H cars at the time because we hadn't been given the big brake conversion that the G and F cars had, so we needed a smaller disc so that the rear was no bigger than the front, which was the rule at the time. I don't know whether there were any other changes besides the size of the disc.

Anyway, check with Winners Circle.
 
A stock Honda 1200 rear disc (I think) can be machined to work on the rear of the sprite (thin the rotor thickness, drill new mounting holes, machine the ID of the hub a bit). This one fits over a stock rear hub and has the proper offset to make the caliper anchor plate EZ to bolt up to the stock drum brake axle mounting flanges. This is what I used on my H car.
 
Per the rules, this would have to be a solid disc. Matt's kind effort appears to be a vented rotor but is decribed as solid...?
FWIW, some of us in the SouthEast have disc conversions figured out by racers Tony Drum (Sports Car Salvage and/or Mike Miller (Comptune). However, these rotors bolted to the aftermarket hubs on the inside (did NOT slide over the studs from the outside.) The rotors had to be drilled & counterbored for bolts and also machined to fit the hub and reduce the OD to the HP limit. This might help some of you looking for spares to know which setup you have... Joel
 
When I made my rear disk conversion for the F car, I looked at the WC stuff...those rotors had a very deep hat. Was told that they were "specials"/not readily available.

A buddy with a Jabro had a Sprite axle housing...he discovered that the Ford Fiesta rotors on his son's car were pretty close to working. He fabbed up some caliper brackets and made those work. They had a 4 on 4.25 or 4.5 bc...had to index and redrill. Those rotors were dirt cheap. I bought 6 new off ebay for $12. each. I used a Wilwood caliper.

When I got to making everything go together, I had problems with offsets. The Fiesta rotor when put over the studs, forced the caliper too close to wheel spokes to clear, and the bracket became more complex. My car had "std" double brg. hubs. I then bored out the center of the rotors to slide over the hubs from the back....redrilled them for the 4 on 4 pattern, mounted the studs thru the rotor then hubs, and added 4, 1/4 AN cap screws to bolt the rotor to the back of the hub flange, these were safety wired two on two.. This made the mount bracket for the caliper easier out of a flat plate, bolted to 3 of the 4 backplate mounts.
All this to fit the offset in the hat and clear the spokes on the wheels.

However, the plus is, you don't have to mess with the brakes to change rear gear or axles...all stays in place.

My biggest regret was not having a rotary table to make the holes and everything else "repeatable" from side to side... in my case each was "custom fitted" (hand fitted with ham hands?) and any replacement rotors will need to be machined to fit a non-standard mounting.... Geezzz hate doing things like that...but...

Think the Fiesta solid rotors were 78-80 or 82 range... I could go back and look for notes if some one is really interested...tried to attach a photo, but my files too big..have to go work on that if you

Wait, wait... got a photo shrunk!!!!

Forgot to mention, went to WC and got longer studs, too. I'm using 3/8"...if 7/16", will have issue with heads and hole size being too large when you bore out center of rotor to slide over back of hub...have to do something different there...

Hope this helps a bit.

Bob L.
 
My conversion sandwiched between the stock axle and the wheel......just like a stock drum. No hub machining monkey business. Offset worked perfectly also with a flat plate anchor plate. When complete they met the old rule of no larger diameter and thickness than the front rotor. Honda 1200 like Malley used to drive.
 
And by the way, if anybody thinks WC has access to "special", not available to the general public rear rotors............you must be smoking something. Tooling a special rotor is big $......WC is just trying to maximize their revenues by not telling you what car it came from. That's their SOP.
 
I have found that Auto Zone has the best information for looking at brake rotors. They have a photo of each with some critical dimensions listed either on the photo or below on a chart and if you find one that you think will work they are pretty cooperative with ordering it in and letting you measure it. If it doesn't turn out to be what you want they give you the money back without a hassle.
 
Gee Jay....

I don't smoke...where'd that come from?

So:
If a simple production item: How about saying which mfgr/model/year those "old" WC rear rotors fit? What mods are required? Are they the "Malley" 1200 Honda's that you used? (I looked for those earlier, and couldn't source quickly/low cost...too old/not stocked I was told.)

I'm sure there are other inquiring minds. Heck, I would like to know, if only for future reference.

Okie
 
Just another tidbit.. Rockauto often has dimensions listed when you go through the drill-down menu to a particular car. i.e. 1980 for Fiesta shows measurements from Brembo and another brand of rotor all the way down to hat thickness and offset.

Again not much help for a specific one, but you can at least search online for cars that might have a proper size rotor and then go from there.

One other shot is to check Coleman Racing. They will do custom rotors and such, but very often have a rotor on the shelf they can modify to fit your needs. it may be ridiculously expensive compared to other options, but it could work as a last resort.
 
Okie, I will post the Honda rotor number once I get a chance to dig it out. Jay

It's an EZ modification
 
The Winners circle rotors were made by Colman and were a special order just for WC. Winners Circle wouldn't even sell you a rotor unless you could prove you or the previous owner had bought the kit from them. Colman will make you anything you want but they aren't cheap. They are a big supplier for circle track and hot rods.

I ended up building my own rear disk brake kit for my Spridget using a fiat front rotor (All X19's, 124, etc all used the same rotor). I also used the Willwood calipers. Great set-up and rotors are cheap but do require a new wheel pattern to be drilled on them. Also depending on your DB rear hubs, I have had to have a slight machining on the inside of the rotor hat.

Peter
 
Peter beat me to it. All the rear disk kits I built for the spitfires had Fiat X19 rotors and used wilwood calipers. Same setup we used for the GRM Rospit. I still have a box of front and rear setups that fit GT6'S, Lotus, and spits if anyone needs them cheap.
 
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