Hard launch in ACR (1.64 60') locks me out of 2nd or 3rd gear!

[FikseGTS]

Took the ACR out to the track last night. When I could get the car to hook hard, the car/clutch would lock me out of 2nd or 3rd gear. The clutch still had pedal pressure, but there is nothing I could do to get it into gear. When coming back in the return lane, the car was noticeably "notchy" to get through the gears.

After the car cooled down, shifting was smooth and back to normal. Any ideas? Could the clutch fluid be toast? I checked it, not super clear.....

Here is a video of the 1.64 60' launch, anytime I would get in the 1.7's or better, the car would not be able to shift into either 2nd or 3rd... Pretty frustrating as those were great launches on the Pilot Cups and would have resulting in some pretty great times for the ACR....

[media]http://www.youtube.com/watch?v=4gLIrDlp4js[/media]

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[Canyon707]

That seems very wrong. I had a 1.49 60' no issues. The clutch fluid is just for a piston and makes no metal contact so I can't imagine it's toast. Maybe the stock linkage is hanging up on power shifts.

 

[FikseGTS]

no powershifting.... 1.49 in what car/setup?

That seems very wrong. I had a 1.49 60' no issues. The clutch fluid is just for a piston and makes no metal contact so I can't imagine it's toast. Maybe the stock linkage is hanging up on power shifts.

 

[ROCKET62]

Any mods to your ACR?

 

[Canyon707]

no powershifting.... 1.49 in what car/setup?

my 04 with MT drag radials 3.73 gears Like I said earlier pretty stock dynoed 480 hp
I think it's all in the launch and the gears. I only ran 12 psi in the drag tires. I have been practicing and practicing broke an axle a few weeks back. now running solid shafts with no groves hooked up to my OS Giken.

 

[utahviper]

Torque management?? Do you have any mods? How about a mopar performance pcm?

Seems like I recall someone adding NOS and his car would go into limp mode in the next gear. So if he hit the nos in 2nd gear it would go into limp mode in 3rd gear. This was before the days of the mopar pcm, so I wonder if that will fix his or your problem.

 

[JonB]

What you are describing is the SKIP SHIFT function at work. When your throttle is less that 30% down, and RPS below ~~3000, it locks you out of 2nd and 3rd. Dumps to 4th. SOMETHING is amiss in skip-shift solenoid or wiring. Do you have a poly trans mount?

Did you (incorrectly?) install a skip-shift eliminator in it? I have NOT seen one work properly with a Gen 4.

 

[FikseGTS]

I have the Mopar ECU, thought that eliminates the skip shift?

What you are describing is the SKIP SHIFT function at work. When your throttle is less that 30% down, and RPS below ~~3000, it locks you out of 2nd and 3rd. Dumps to 4th. SOMETHING is amiss in skip-shift solenoid or wiring. Do you have a poly trans mount?

Did you (incorrectly?) install a skip-shift eliminator in it? I have NOT seen one work properly with a Gen 4.

 

[JonB]

What you are describing is the SKIP SHIFT function at work .....when it should not be.......
So something is amiss with that system

 

[FikseGTS]

looks like the clutch fluid was not working efficienltly when hot, it was contaminated with clutch dust.... here is a before/after fluid change...

Ranger has seen this over and over again with Vettes and Vipers, after a hard launch, the bad fluid can cause shifting issues... we'll see how it goes next time at the track....

 

[bluesrt]

put some high temp fluid in there, the fluid is getting hot and not letting the hydrolics to function correctly.

 

[bmw2nv2000]

Was the Charger actually hanging close to you in that vid????

 

[Art 138]

I had considerable problems with the Belanger exhaust heat....finally Castrol SRF did the trick.....its expensive but worth every dime....

 

[FikseGTS]

I can't recall that run, the car didn't go into either 2nd or 3rd gear, eventually it went into gear and I coasted through at 12.5 @ 75 MPH..... so yea, he might have hung around....

Was the Charger actually hanging close to you in that vid????

 

[jamie furman]

I have the Mopar ECU, thought that eliminates the skip shift?

It sounds like a hot clutch to me and when they get hot they won't let you shift, your fluid doesn't look that bad to me and I wouldn't even change it if it was as clear as yours in the picture.

 

[TrackAire]

It seems that the Z06's really have this problem with clutch dust because it gets past the seal and contaminates the system. Ranger has a very good video on his website of how this occurs.

Do our transmissions have the same style of seal? Is it more of a dust contamination problem or heat problem for those with headers, etc.??

On the Z06's, its a super cheap and easy fix...just replace the fluid on a very reqular basis.

FikseGTS, how many hard runs have you made with the ACR? So far I'm on 12 drag strip runs...more this Sunday if the weather holds out
In addition to the drag stuff, I've got at least 15 autocross runs on the clutch too.

Now on my very last drag run, I did miss getting into 3rd....hhmmm. I thought it was driver error, but I'll have to keep on eye on it and also check my clutch fluid.

Cheers,
George

 

[FikseGTS]

Ranger said he has seen Vipers having the same issues at the track rentals.... you can see in my pic the reservoir had some dust clumps in there.... I have 2900 miles on the car, 15 drag strip passes a few laps around homestead and PBIR.... I'll try again next week at the track....

what kind of times are you running at the track?

 

[TrackAire]

I've gotten to 11.66 @ 124 mph. That was on my 11th run ever down a track, stock 2009 with PS2's at around 24 psi. What is killing me is my 60' times, I ran a 1.87 second 60' time on that run. Working on launching it better...the prepped track is pretty damn sticky.

Now here is the problem...I too have around 2300 miles on the car, about the same runs as you, etc. Most of the autocrosses I ran were in the 50 second per lap range, I'm guessing maybe more clutch dust generated with the multitudes of tight corners and takeoffs per lap than one drag race. This might be something the Gen IV cars have to keep on eye on. Does the dual disk clutch emit more dust by design? I'm just not an expert on clutches (especially the new style in the Gen IV's) so any info people in the know can pass along would be appreciated.

Ok, now for you drag racing experts, if I knock another tenth off my 60' time, what would that equate to in final ET on a Gen IV? I'm thinking it might be worth more than a tenth, am I right?

Since these are organized bracket races, I run into a problem if I go below 11.50 ET without the safety equipment required.

Cheers,
George

 

[FikseGTS]

If the track is sticking, keep raising the launch RPM's, I'm leaving at just over 5k RPM's and the car still bogs a little, 1st gear is just too tall.... each 1/10th off the 60' will about 2/10's off your final ET.....

seems like high RPM shifts and launching causes the dust, check your fluid and report back...

 

[Camfab]

It'll be interesting to see if it's a fluid problem. 5K is really ******* the clutch (two in your case right). I wonder if the dual disc design is part of the issue, as Jamie suggested a hot clutch can cause shifting issues, two clutches may increase that potential. Your 60 ft times are amazing and like I've said in the past the Sport Cups are great tires.

 

[Gary Weeks]

It's not dust getting in the fluid that's making it dark it's the heat from the clutch slipping that's burning it. If the fluid boils it's like having air in the system and you can't build any pressure on the clutch servo when you depress the pedal so it's like shifting without a clutch. Changing the fluid will insure that it doesn't have any moisture in it and has a high boiling temp. That is why the dot 4 or dot 5 rating

 

[TrackAire]

Ok, quick clutch fluid question. Art 138 mentioned that Castrol SRF was what works well for him.

Is the Castrol stuff best or is something out there that is even better?

Thanks,
George

 

[Viper X]

Sounds like clutches getting hot.

Fluid doesn't look that bad but I'd change it too. Motul 600 RBF works pretty well - just change it frequently.

Dan

 

[bmw2nv2000]

I can't recall that run, the car didn't go into either 2nd or 3rd gear, eventually it went into gear and I coasted through at 12.5 @ 75 MPH..... so yea, he might have hung around....

OH that makes sense Just a note I could flush the clutch fluid to be perfectly clean on my C6Z and make 1 run hitting 4 gears and the fluid would be very contaminated too. I flushed the clutch fluid every time I filled up with gas

 

[Tom F&L GoR]

I don't have the magic bullet yet, but two comments:

If the fluid got hot, it will darken, but would not create the black dust that settles to the bottom. I think that is something else, perhaps also caused by heat.

Crackle test. If you think the fluid has accumulated water and is boiling, try this: Make a small "pan" out of aluminum foil and put a drop of the brake fluid on it. Light a match under it and listen. If there is water in the brake/clutch fluid it will crackle and spit as the water boils off. If there is no water, it won't do anything or eventually just smell. This is a quickie "field test" for fleet operators checking engine oils. Obviously, take proper safety measures.

 

[Viperless]

looks like the clutch fluid was not working efficienltly when hot, it was contaminated with clutch dust.... here is a before/after fluid change...

Ranger has seen this over and over again with Vettes and Vipers, after a hard launch, the bad fluid can cause shifting issues... we'll see how it goes next time at the track....

What does that have to do with how hard you launch? You said you only had problems if you had a 1.7 or better 60'. Wouldn't the fluid affect clutch operation across the board??

 

[Newport Viper]

I change mine very couple of years...

 

[FikseGTS]

fluid change worked, car was shifting fine last night.... ended up running 11.08 @ 132.7 MPH.....

2008 Dodge Viper ACR 1/4 mile

don't have that run on video, but here is a video running against a GT-R....


Viper ACR vs Nissan GT-R Video


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[Greg-TT]

Great run and awesome 60ft time!!

Fikse, did you by any chance short shift 1-2 and cross the 1/4

in 3rd gear?

I was just quick comparing with my time slip and I've noticed

that your 1/8 trap speed is about 2mph slower at 98.75mph

but gained a whopping 33.95mph in back half.

When I crossed the 1/4 mark, I did hit the rev limiter in 3rd

gear but I'm not 100% sure whether I hit the limiter before

or after crossing the line.

As I'm trying to improve my drag racing skill I'd like to know

what am I doing wrong here. I believe our cars have about

same mods and HP/TQ

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[FikseGTS]

I'm not short shifting and I'm going through the traps in 3rd gear hitting the rev limiter, I was running 132.x all night, but if I shifted into 4th the traps would drop to 129 MPH..... the car is bad for drag racing, 1st gear is WAY to long, and the car bogs even with a 1.7x short time....

one of my runs I hit a 1.65 short time, but I was "slightly" out of the groove and the car broke loose half way into 2nd gear....

what RPM are you launching at?