Quartermaster Clutch Throwout Release Bearing
 

Mazda Motorsports (factory) says that only a radius faced throwout bearing should be used with the Quartermaster clutches. I have been ignoring that and using a stock Mazda throwout bearing on my 7.25" dual disc Quartermaster clutch assembly for the last 3 years. I do have a problem with the clutch not wanting to fully release after a road race. It doesn't bother me on the track since I have a dog ring transmission, but it is a pain on pit road after checking tire temps/pressures. What is your experience with Quartermaster dual disc clutch packs and their throwout bearings?

We've run one of those hydraulic ones that slide over the input shaft and the stock TOB. The only thing we had to do for the stock set-up was to make a new fulcrum for the actuator arm. It needed to be moved out about 3/4" IIRC for the flywheel/clutch combo we have in that car. We have had no problems at all in about the same amount of time as you.

the flat face T/O bearing will wear the clutch prematurely and it may not function very well. I would replace the T/O and inspect the clutch as it maybe damaged. the bearing is not terribly expensive and is a direct replacement for the OEM. You could also remove the OEM bearing from the OEM holder and match a radius face bearing that would fit on the holder(probably what Mazda did). It needs the radius face for the 7.25" and smaller multidisk clutches to work correctly

The Quarter Master catalog lists 2 bearings for the Mazda using the 7.25" 2 disk clutch. One is part number 236520 and the other is 236521. The latter stating that it is designed for a PBS gear box. I assume the bearing retainer snout diameter is different between the stock tranny and the PBS gear box.

The stock Mazda bearing is actually a radius face bearing, although the contact diameter may be larger than what the Quarter Master bearings offer. What might be happening is that the stock bearing is not long enough and that is why your clutch is not fully disengaging. I would try one of the bearing listed above and I bet that will solve your problems.

Andrew

It took me awhile to find the Quartermaster web site. Their name is http://www.racingclutches.com/ I found the nearest distributor was in Nashville, and ordered a 236520 bearing from him. My next race is an SCCA regional Labor Day weekend at Nashville Superspeedway. I will let y'all know how the new release bearing did then.

just sold my Quartermaster setup on Ebay last month. this is a very nice setup and should work good for you.

Curious, how is the engagement of the quartermaster? does it give you progressive engagement? I have been contemplating using this set-up for my autocross turboII. I thought that if it would reduce the rotational mass, it might help me in creating a nationals-competitive TII. My only issue is how I launch. I don't dump the clutch. I slip and that yields the fastests launches for me. I usually see about 2.5lbs of boost as I get off the line.(stock turbo/exhaust minus cats)
Just seeing my options, I wanted to get a lightened flywheel and a smaller diameter clutch that may drop my rotational inertia on the flywheel a bit yielding better power delivery to the ground. Just a thought though. I am not pretending to know it all, thus the questions...

Any info is greatly appreciated.

Anthony Lleras
17SM2
URSCCA(utahscca.com)

It is not very progressive; it is more like an on/off switch; the grab zone is pretty narrow on the clutch pedal stroke. Since we do rolling starts road racing, it is usually not an issue for me. It can be slipped just right with some practice, but I don't think the clutch was designed for that kind of service.

I ran one SCCA level 4 Time Trial hill climb last year at Crow Mountain, Alabama. They use a standing start. I was able to get good, strong launches with some wheelspin of 305mm wide slicks, but I am sure it was pretty hard on the drive train axles.

The new Quartermaster radius faced throwout bearing came in last night.

Thanx for your input speedturn. I may still end up getting this set-up. I will just have to do more research.

if you try to slip this type of clutch it will be overheated and will wear out prematurely. I have seen guys blow these clutches up try to load the car onto the trailer. this clutch needs to be treated like a light switch. rev the motor and step off the pedal. rolling starts are good as well. on a rotary a 2 disk clutch should last a very long time, but overheating it will destroy it quickly. not a street piece.

Make sure you get the 2 disk "rally" as it uses the thicker (.250) friction.

Of course the ultimate would be a 2 dick 7.25" carbon/carbon! It would give great drivability and even lower rotating mass.

Andrew