Whatusp everybody. I'm having some serious issues at WOT. The car won't shift from second to third at the track. It hits the rev limiter like 3 times before it actually shifts. The 1 > 2 shift is set a 6200 and it shifts fine. When the car is about to shift again from 2 > 3 it won't do it without hitting the rev limiter a couple of times. I've tried setting the shift to 5500 using Tuner Cats and still I have the same problem. Shifted it manually and still I had the same problem.

Driving around town and highway cruising is fine, but when I'm at the track this crap happens. Anybody know what could be happening? I had the tranny rebuilt like a year ago.

 

Are you running the same tires and or the same size tires when running at the track? I ask this because it is important when tuning is an issue. I have seen a 3-4 clutch starting to fail cause what you talking about. Also in some cases I have had guy's lower the shift for the 2-3 even lower than you have it now. You said it only happens at the track, is this when the trans is hot, cold, warm, or doesn't matter? Did you have this problem when the trans was rebuilt? Also have you done anything to the car that could be causing this problem recently?

 

yeah im running mickey thompson e/t streets at the track and the street. the problems happen whether the car is hot or cold. however when the car is fully cold it is not as bad. im running a trans cooler. i have had this problem since the tranny was rebuilt but i thought it was a tuning issues since my gear ratio and tire sizewas out of wack. it used to hit the rev limiter on the highway due to that. i calibrated my rear end gear ratio and tire size and the problem was fixed. unfortunately at the track im still bouncing off the limiter. its killing my 1/4 times.

 

Do you run the same tire pressure on the street and at the track? The reason I ask is I wonder if this could be effecting your tire height under wide open throttle on a nice sticky track. This might effect the overall ratio for the rear end. However you did say that when it was cold it did not seem as bad. Not sure what the problem is but I would have to say it is a tuning issue. I know a very good tuner here in Chicago, when I get a chance I want to ask him some of these questions to see what his thoughts are. Maybe I'm way out there so to speak but I have read dozens of threads like this and would like to know more about the tuning in your car's. I am by trade a builder and a machinist please bear with me. I'm definitely am not a tuner.

 

i've ran with the same pressure and less pressure at the track. that doesn't seem to have any different effect. on run about 20 lbs of pressure at the tack. tir height doesn't change all that much. what does it feel like when the 3-4 clutch pack is giving way?

 

I had the same problem in my TA. Under WOT, (track or street) she smacked the rev limiter. I drove it for about a year like that. After that the transmission died. Would'nt shift from first to second or enything else until darn near the redline. I believe track outings actually compounded the transmission issues. Did a stock rebuild. (Warranty of course) And no more problems.

 

Well, when the 3/4 clutches are giving it up they usually go pretty quick, especially at the track with a sticky tire. If the fluid condition is still good it probably is not the issue as the fluid is the 1st indicator... it will smell burnt before it changes color. We watched the fluid in our test mule like a hawk, daily in fact because we hammered on it every single day, every chance we had... many times we would see symptoms of clutch failure prior to actually seeing the fluid become discolored. But the fluid would have the distinct odor of clutches failing / burnt.

And like Vince states tire size vs gear ratio is critical. The '98 & '99 PCM's cannot accomodate some combinations mathmatically. We fought that on the test mule last year.

We have a client who runs a 5.3l Truck who has 26' tires in the back... bad idea right. Well he just stepped up to a 150 shot and now he is hitting the limiter at 1/2 and 2/3. I told him start with 28's in the back and let's see what happens. I'll let you guys know how that goes... he's a good guy and we help him alot when are at the track.

One alternative is to take it full manual. But for a DD/strip car that can get annoying.

We found that the tune, the hydraulics and the 3/4 clutch setup is crucial, when we solved those issues we for the most part quit having 2/3 shift timing issues on the bottle. But when they have a 1/2 and 2/3 shift issue that typically is combination and tune related.

Remember, the controller can only do so much. On the bottle things happen much faster.

g

 

funny thing is even when i shift the car manually the same thing happens. even if i shift it early.

 

i went over my trans log. if i leave the car id overdrive and take it down the track this is what happens (keep in mind all my rpm kickdown points are set at 6200 and my rev limiter is at 6700):

1>2 shift at 36 mph 5014 rpm
this leads me to believe that the car shifts at whatever comes first the mph table or the rpm table

2nd gear: rpms keep rising from 5014 to 5944 before they drop to 4746

2>3 shift at 73mph 5423 rpm
again this tells me the car shifts at whatever comes first mph or rpm

3rd gear: rpms keep going rising until they smack the revlimiter (6700 rpm) a couple of times. the rpms finally settle down to about 4024.

to get the car to shift at 6200 do I set the mph tables very high? also what would I have to do to keep the car from hitting the limiter on the 2>3 shift? do i remove the limiter or could that ruin the tranny?

 

It is my understanding that you need to lower the mph along the rpm. I'm not sure that raising the rev limiter is a good idea unless you want to loose a motor. I have heard of it being done for testing but what is safe I'm personally not sure of. You might want to try posting in the tuning section for that information. Vince

 

Yeah, that couldn't hurt. Thanks.

 

Yeah do not raise you engine rpm limiter. You might be dissapointed if you do!!!!!!

What is the time it takes to complete the shift?

WHen it hits is it firm or not?

I am pretty sure the MPH is normally going to have the highest range of authority when the PCM is determining upshifts. But... TPS, MAF and a host of other inputs are relevan to the upshift event timing.

Send me your .bin files if you like and I'll look at them as soon as I get a chance.

Good Luck.

g

 

sent it to your gilbert email addy. thanks. i just want the damn thing to shift at 6200. i was worried that if i lowered the moh the car would shift according to the lower mph which was still way to early. i have to see what the actual shift time was and the shifts are fairly smooth not too crazy. i did modify my shift time tables though to have the car shift quicker.

 

I am gonna go with Slipping 2-3 shift, time for a rebuild...

 

I hope not i just had it rebuilt like a year ago. thank goodness for the warranty.

 

E-Mail sent.

g

 

well i found something out that might be helpful. my cousin who has an LS1 has his car shifting at 6200rpm. he's not having the problem I am with my LT1 so I asked him what his mph was set at here is what i found out:
Mine His
1>2 36 45
2>3 77 88

So I have increased my mph to see what happens. It makes the most sense to raise the my mph since it looks like the car is shifting according to mph anyway which is too early. The 2>3 shift kept smacking the limiter so I don't know if raising the mph will fix that but we'll see. I think the problem with the 2-3 shift is that the mph and rpm settings are conflicting with eachother and freaking out the transmission.

 

Raising the MPH will likely cause more problems then it will fix. Especially If there's any slippage occuring it will take more RPMs to hit a higher MPH target, causing you to smack that limiter even easier.

The safest thing for you to do would be to drop your MPH tables further.
The PCM requires BOTH targets (MPH/RPM) to be met before a shift occurs.
Having a lower MPH and set your RPM to where you want it to shift.

I have my car shifting at 6400RPM.

When I had the MPH for 1-2 at 44ish mph, it would hit the limiter. When I lowered it to 34mph, and kept it at 6400, it would shift when I wanted it to. (about 45mph) It does this because it meets the mph requirement early, then waits for the RPM requirement.
VS hitting the RPM requirement, and waiting for MPH, possibly smacking the limiter in the process.

 

Very well stated! Sometimes it takes a few adjustments before you get it right. Make sure that your gear ratio and tire size are entered correctly.

Lot's of times at the track when dialing in a new combination we will set the mph to shift very low and the rpm's low as well. We anticipate a "stack shift", sometimes we see that and sometimes we don't. From there we walk both up and settle on settings that work for that given combination.

Indeed the PCM needs to see that both the MPH and RPM meet the required threshold in order to shift. One condition you could be fighting though is if there is exscessive clearance in the 3/4 clutches there can be a flare shift or an excessively long shift time once the shift solenoids are opened / closed. When this occurs the clutches are building heat because they are slipping. Also, we modify the 3 gear accumulation circuits in order to speed up the shift, not necessarily make it shift harder as some would like. Also, it is for that reason that we set the 3/4 clutches up very tight in assembly.

I think with a little time you will get it to shift like you want, be patient. But also, be careful as again in our experience it is those units that we allowed to hit the rev limiter with that we lost the 3/4 clutches much sooner than those that we dialed in very quickly.

Good Luck.

g

 

okay so it seems like the consensus is lower my mph. so i will since it is probably the safest thing to do. i'll definitely lower my mph tables and then take baby steps from there. i just need to get this problem fixed. i went to the track on friday and put a whooping on a 2007 vette up until i smacked the limiter at the 1/8th and he passed by me. if the car would have shifted properly i would have beaten him by at least a car.