[Stripes]

In my 69 FB, I am installing a 455 that has 600 hp/600 foot-pounds of torque.

The transmission is an M-23 Muncie style 4 speed, 26 input spline going to a 3:55 rear end.

I was planning to install a McLeod RXT Street Twin Clutch Kits 6921-07 onto my Hays steel flywheel. This clutch is rated at 1200hp. The manufacturer indicates this clutch set up will require less clutch pedal effort than a stock 10.5" clutch with much-improved holding and wear characteristics. It is also supposed to be quiet in operation.

Since I tend to find at least 1/2 the info provided by many manufacturers to be incorrect after my purchase, I would like some feedback. Is anyone running an RXT twin street clutch on their Pontiac? Does it function as described? Regrets?

My previous experience with single plate Zoom and Hays "performance" clutches have not been good with slippage and excessive wear with engines in the 450 foot-pound ratings, slicks, and a youthful driver. Is there another clutch that would be better for my application than the RXT? McLeod does recommend it for my application, but there are many choices out there...I am very curious to know if it drives as smooth as they claim.

[Tom Vaught]

Originally Posted by Stripes

In my 69 FB, I am installing a 455 that has 600 hp/600 foot-pounds of torque.

(1) The transmission is an M-23 Muncie style 4 speed, 26 input spline going to a 3:55 rear end.

(2) I was planning to install a McLeod RXT Street Twin Clutch Kits 6921-07 onto my Hays steel flywheel. This clutch is rated at 1200hp. The manufacturer indicates this clutch set up will require less clutch pedal effort than a stock 10.5" clutch with much-improved holding and wear characteristics. It is also supposed to be quiet in operation.

(3) Since I tend to find at least 1/2 the info provided by many manufacturers to be incorrect after my purchase, I would like some feedback. Is anyone running an RXT twin street clutch on their Pontiac? Does it function as described? Regrets?

(4) My previous experience with single plate Zoom and Hays "performance" clutches have not been good with slippage and excessive wear with engines in the 450 foot-pound ratings, slicks, and a youthful driver. Is there another clutch that would be better for my application than the RXT? McLeod does recommend it for my application, but there are many choices out there...I am very curious to know if it drives as smooth as they claim.

(1) Trans should be a M-21 or M-22 Trans, not aware of a M23 Muncie Transmission. Is the Trans a "Close Ratio" or a "Wide Ratio" Transmission?

(2) McLeod RXT Street Twin Clutch Kits 6921-07 onto my Hays steel flywheel. This clutch is rated at 1200hp. The Clutch gets its rating due to the
design of the parts. A normal Clutch Disc has one side contacting the Flywheel and the other side contacting the Pressure Plate when the Pressure Plate is engaged.

A "Dual Street Twin Clutch Kit" Clutch System has the first Clutch Disc contacting one side of the flywheel and the other side contacting the Floater Plate.
The second disc has one side contacting the Floater Plate and the other side contacting the Pressure Plate when the Pressure Plate is engaged. Twice as much surface area on the clutch system so in theory twice the HP capacity.

(3) Any clutch system will function well if you break-in the clutch disc properly. This means taking the parts and slowly boiling off the excess 'Resin" that bonds the clutch material together so that the Resin DOES NOT CAUSE THE DISC TO SLIP WHEN IT AND THE FLYWHEEL/PRESSURE PLATE COME TOGETHER. If you thermally boil off the excess RESIN and remove it from the flywheel and the Pressure Plate then the disc will be much less likely to "slip". The Manufacturers get blamed for the clutches slipping when the issue is the clutch break-in and removal of the excess resin on the flywheel and pressure plate. If you do this the clutch parts work much better and the disc will last several times longer even under abusive driving. Driver is the issue not the manufacturer.

4) READ #3 ABOVE A FEW TIMES.
My previous experience with single plate Zoom and Hays "performance" clutches have not been good with slippage and excessive wear with engines in the 450 foot-pound ratings, slicks, and a youthful driver.

IF THE CLUTCH PARTS ARE SLIPPING UNDER HIGHER LOAD CONDITIONS, THERE IS A REASON WHY. Remove the excess RESIN from the parts after a break-in period and the parts work much better on the street and strip. Been There, Done That. (That means pulling the clutch down again one more time to do it right so it works for years vs months). I glass bead the friction surface of the disc (both sides) and sandpaper the pressure plate and flywheel surfaces. So you do NOT need to remove the flywheel.

Tom V.

[70GS455]

Originally Posted by Tom Vaught

(1) Trans should be a M-21 or M-22 Trans, not aware of a M23 Muncie Transmission. Is the Trans a "Close Ratio" or a "Wide Ratio" Transmission?

(2) McLeod RXT Street Twin Clutch Kits 6921-07 onto my Hays steel flywheel. This clutch is rated at 1200hp. The Clutch gets its rating due to the
design of the parts. A normal Clutch Disc has one side contacting the Flywheel and the other side contacting the Pressure Plate when the Pressure Plate is engaged.

A "Dual Street Twin Clutch Kit" Clutch System has the first Clutch Disc contacting one side of the flywheel and the other side contacting the Floater Plate.
The second disc has one side contacting the Floater Plate and the other side contacting the Pressure Plate when the Pressure Plate is engaged. Twice as much surface area on the clutch system so in theory twice the HP capacity.

(3) Any clutch system will function well if you break-in the clutch disc properly. This means taking the parts and slowly boiling off the excess 'Resin" that bonds the clutch material together so that the Resin DOES NOT CAUSE THE DISC TO SLIP WHEN IT AND THE FLYWHEEL/PRESSURE PLATE COME TOGETHER. If you thermally boil off the excess RESIN and remove it from the flywheel and the Pressure Plate then the disc will be much less likely to "slip". The Manufacturers get blamed for the clutches slipping when the issue is the clutch break-in and removal of the excess resin on the flywheel and pressure plate. If you do this the clutch parts work much better and the disc will last several times longer even under abusive driving. Driver is the issue not the manufacturer.

4) READ #3 ABOVE A FEW TIMES.
My previous experience with single plate Zoom and Hays "performance" clutches have not been good with slippage and excessive wear with engines in the 450 foot-pound ratings, slicks, and a youthful driver.

IF THE CLUTCH PARTS ARE SLIPPING UNDER HIGHER LOAD CONDITIONS, THERE IS A REASON WHY. Remove the excess RESIN from the parts after a break-in period and the parts work much better on the street and strip. Been There, Done That. (That means pulling the clutch down again one more time to do it right so it works for years vs months). I glass bead the friction surface of the disc (both sides) and sandpaper the pressure plate and flywheel surfaces. So you do NOT need to remove the flywheel.

Tom V.

I have the same M23

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[455-4+1]

For more "spirited" driving you could also look at the McLeod soft lok. As Tom states, increasing the load capacity can be done by increasing the amount of friction surfaces, and lessing PP load so less pedal effort. Another is to increase the friction coeff of the disk matetial and substantially reduce the PP load at low rpm (when your foot is on the pedal) and use weighted levers to lock up at high RPM.
I can see the haters now, but it is a very viable / surprisingly drivable, reliable set up for spirited street driving. After smoking the latest "Kevlar' disc from other companies, i finally went with an old Hayes 12 post slider with ONLY 1200 to 1400 lb on the the pressure plate (adjustable through hole in scattersheild) and a solid hub sintered iron disk, lever weights for lock up above 3-4000 rpm.
The soft lok is just a more modern version of this setup. Mine had great pedal {1200 lb Vs over 3000 for a stock disc) and no chatter, it was actually easier to drive with low PP load at low Rpm and will help your trans live should you ever hook up on the street or track

[Skip Fix]

I think most of the Stocker and Super Stocker stick car use a "slipper" style clutch that is adjustable centrifical assist.

[Tom Vaught]

70GS455, as I said I was not aware of the M23 Trans. Is it built off of the M-22 HD design or something new like a Liberty or a Nash/Leonard Long type transmission?

Many many Racing Transmissions have used multi-disc clutch systems with high HP applications. The Pressure Plate on some of these applications can be quite small.

You should give the McLeod RXT Street Twin Clutch Kits 6921-07 if it is in your budget.
That being said the resin removal from the surface of the disc sides makes a massive difference in durability.

Tom V.

[Stripes]

I bought a wide ratio m-23. This re-engineered transmission has a super case, and upgraded internals and gear sets rated to handle 800 hp. Severe Duty M23 gearboxes feature enlarged steel ‘thrust button’ case assembled modular countershaft clusters with ground drive gears, unit cage needle bearings, integral countershaft spacer tubes and carbonitrided oversized synchronizer hubs. Slick Shift 18 spline hardened sliders. Small pad Crowned Steel Forks. Welded Shift Shafts. Forged Brass blocker rings. Main drive oil seal input shaft and bearing retainer. 34 tooth 1st super strong 1st gear (stronger than the M22 1st gear). C355 Forged Aluminum mid plate. Lightened main shaft for less rotating mass. The M23 is the strongest Muncie style 4-speed available.

While it is certainly important to properly break in a clutch, the issues I was referring to with prior single plate clutches were their lack of holding capacity and high leg pressure required.
The Hays classic street clutch is only rated for 442hp. Zoom are single disc also.
I haven't driven a double disc clutch set up and I am looking for someone who has to tell me it drives ok around town, and not just great at the drag strip. Or suggest a better clutch option entirely.

I do know both the Zoom and the Hays versions I purchased many years ago did not last long with slicks and 4:10 gears and a healthy Pontiac. I'm looking to improve my results and I'm sure someone is out there trashing on one and they
know what will last with 600 hp.

[Tom Vaught]

Stock Clutch Discs have a "spring hub" that helps dampen shock loads on the drivetrain during engagement. The McLeod RXT Street Twin Clutch Kits 6921-07 uses a 'Unsprung" clutch disc design which you may not like for normal street driving. Just a comment.

Tom V.

ps thanks for the additional info on the Latest Muncie design transmission capabilities.

Tom V.

[Stripes]

That's a good point and I bet those springs help smooth out engagement. McLeod says its a street clutch. Its certainly a double disc unit with a doubled up price.

I thought it was interesting McLeod said their 800 hp rated RST clutch kit would not hold up to 600 foot-pounds of torque. I'm not sure how you get 800 hp and less than 600 foot-pounds of torque, maybe a chevy? :-)

[Tom Vaught]

Once you have it engaged it probably would allow you to drive it at typical street speeds IF you had it in the right gear for that driving mode. The issue would be not 35-40 mph steady city street driving but a lot of 25 mph to 45 mph heavy city traffic type gear change driving. Rush Hour driving I do not think would be a good experience.

Tom V.

[Stripes]

I suspect you are correct. Fortunately it's not a daily driver...

[Tom Vaught]

Then you should be good to go once you get used to the clutch and how it operates without the springs to cushion the initial engagement.

Trans Am cars run very small diameter pressure plates with multiple clutch discs for the hp capability and make hundreds of shifts in a typical race. Your deal would be fine for what you say you are doing. Lots of Torque/HP capacity and some extra $$$ required.

Tom V.

[GOAT WHORE]

I run the RXT in my 70 with a TKO 600 and an engine with 600+ ft/lbs and it is great. I have many street miles on it and no issues.

[gtofreek]

Originally Posted by Stripes

That's a good point and I bet those springs help smooth out engagement. McLeod says its a street clutch. Its certainly a double disc unit with a doubled up price.

I thought it was interesting McLeod said their 800 hp rated RST clutch kit would not hold up to 600 foot-pounds of torque. I'm not sure how you get 800 hp and less than 600 foot-pounds of torque, maybe a chevy? :-)

494 ft. lbs. at 8500 RPM = 800 HP. When the RPM's are there, it doesn't take a lot of torque to make the HP.

[Bob's GTO]

I also run the RXT in my 69 with a Legend 5 speed. I like it too, it's very smooth.

[Stripes]

Did those running the RXT set up have any issues needing an adjustable clutch fork ball or an adjustable throw out bearing? I was planning on a short throw out bearing and maybe a Lakewood adjustable ball.

[Bob's GTO]

I'm using new stock replacement parts.

[Stripes]

perfect!

[stickboy]

McLeod RXT solid hub (2) 9.5" ceramic discs EASY pressure plate, pedal feels stock. At first you will think you did the wrong thing, but let it break in for some miles and it gets way better. It feels like a normal clutch now, but it takes a 4000 launch with some slip and will not heat up and get glazed.