Boost + hard launch + RXT Twin disk = problem

[Sam@Coastal]

UPDATE - I spoke with McLeod today and they seemed a little surprised about shifting in the 6,600 - 6,800 RPM range. Anyway, they did not use that as any type of excuse and after listening to me fully describe the problem they stated that it sounds like some type of hydraulic issue, not a problem with their clutch. They recommended using their p/n 14-301 hydraulic TOB and also switching to Wilwood EXP 600 High Temp Dot 4 brake fluid. I'm going to try switching to the EXP 600 and see if that helps. If not, I'll pull the clutch and inspect it and take pics, and I might try switching to their TOB.

try the TOB and let us know if that helps, i do find it a bit funny that they always have the same response to the sticking issue. trust me your not the first person to contact them about it.

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[Sam@Coastal]

N2MB makes the 2 step and has the no lift feature. I have it and works great. if needed I have the wire pins and locations for installing on the 15. The owner has not updated the site for the 15 yet.

post up what you have for the wiring pin out, that would be a great help to everyone wanting to try this.

 

[sonic]

 

[rainmaker]

Do you have any pics or quick vid of your install? And maybe a demo video (just Rev without launch)? Does it trigger any DTC codes that you have to clear with your X4? Thanks! My wiring and soldering skills are avg at best.

 

[phunk]

I didnt spend much time with my RXT before installing it, but I cannot currently imagine where a centrifugal force acting on it would cause it to release or stick in a released position.

So I have a hard time imagining that its directly related to only RPM. I would just have to believe that either it doesnt have enough coefficient of friction to handle the load and temperatures its seeing, or something hydraulic.

What could cause the hydraulic to not let go of pressure immediately? Maybe some sort of restriction in the plumbing slowing the transfer? Maybe the helper spring on the pedal is resisting the rapid release on the master cylinder side?

 

[Derek@Lethal]

Only way to know for sure if you have to duplicate the shifting scenario, meaning hit the higher RPM you were hitting when it was sticking before removing the clutch pedal assist spring. We had the same issue in 2011 with our Mustang GT that everyone is pretty well aware of, but this was with the stock clutch. We installed a GT500 pedal assembly (no assist spring as is) and installed the RXT and the pedal sticking never happened again. We have used the RXT in our Boss 302 making well over 800 rwhp with a Vortech JT and spinning near 8k, it never had a pedal sticking issue. So, it's my opinion that it may be the assist spring. Not sure it can be hydraulic as the slave cylinders are the same in the 15-16 as the 11-14 and I don't recall anyone ever having an issue with them.

 

[rainmaker]

I have 12 - 15 passes now since removing the clutch pedal assist spring and have not had any issues with the RXT "sticking." The clutch has been great and I have had many 1.52 to 1.62 60' times on the 19" MT DRs. My biggest problems now have been inconsistent launch RPMs (just ordered the MSD 2-step) and missing 3rd gear and hitting 5th gear instead. I know the car is running strong when I can miss 3rd and hit 5th gear, downshift and run 3rd gear out, and then bang 4th and complete the pass and still run 11.8s :frusty:

On the street I would say it is impossible to miss 3rd and hit 5th gear, but on the track with the stock shifter and under high load and high rpm it has been a frequent nuisance. I'll most likely add a MGW over the winter since the season is basically over here in Chicagoland + drivermod and see how that works.

Also it was great meeting RBS550 (NA with CJ intake) & olaosunt (Hellion twin turbo kit) at the track, all three cars DIB . Weather permitting I'll be back this weekend, lets get some more S550's out at US41 !!

 

[sonic]

Are the DR your running on stock PP rims?

 

[rainmaker]

Are the DR your running on stock PP rims?

AM 19x10 PP replicas with stock lug nuts.

 

[Mikeyd56]

I almost went to 41 Sunday with my whipple stang! But I'm on the stock clutch half shafts and street tired so I didn't want to break anything. Can't wait to see you next year!

 

[Travis@boostworks]

It's the clutch.. Namely, the pressure plate. We had the same problem with our original shop car last year. The high rpm makes the diaphragm start to flatten out on it's own due to centrifugal force at that rpm. The trick is to lighten up the diaphragm by going to a 3 or 5 finger setup. McLeod is always hit or miss when trying to spin over 7k rpm. I've had them work in other cars to 7800rpm, no problem. But, it's not always that way. We currently have the same issue with Jeff's high hp 2015 mile car. We can't rev it over 7200 or so, because it'll start to disengage the clutch on it's own.

 

[mustang_guy]

It's the clutch.. Namely, the pressure plate. We had the same problem with our original shop car last year. The high rpm makes the diaphragm start to flatten out on it's own due to centrifugal force at that rpm. The trick is to lighten up the diaphragm by going to a 3 or 5 finger setup. McLeod is always hit or miss when trying to spin over 7k rpm. I've had them work in other cars to 7800rpm, no problem. But, it's not always that way. We currently have the same issue with Jeff's high hp 2015 mile car. We can't rev it over 7200 or so, because it'll start to disengage the clutch on it's own.

what clutch do you use instead? Comp or spec? Ive always had great luck with both. Im nervous to try mccleod. After what i saw the gt500 owners go through sometimes its been enough to make me leery every since.

 

[evo8904]

I have always used ACT without any issues. I have also bought clutches that were closely matched to my torque output.

 

[mustang_guy]

I have always used ACT without any issues. I have also bought clutches that were closely matched to my torque output.

Ive had issues with act and exedy for high hp applications. Ive had great luck with os gikens twin and triple discs, tiltons, spec and comp.

 

[z06psi]

So I got my RXT broken in. With the TC off I was able to go up to 7750 r.p.m. through the first 4 gears with no issues.

I even think I should redyno at this point.

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