Drag racing launching question/problem

[Pocket]

This happened on my old tunes from Jody. With the A/D counts on the throttle at 504 and higher, the 1st gear TC lockup speed was set at 16 mph. Anything below 504 was raised all the way up to 127.5 mph.

If the TC locked up, then it would make sense as to why it lurched forward like it did. So did it shift into 2nd and then lock, or do you think it locked the TC in first while I was spooling up?

I'm still going to try changing that table to see what happens. I might do it on my old tune to see if it makes a difference. I know how to duplicate the launch problem... just hold 1800+ RPM for longer than about 5-6 seconds.

[cleatus12r]

Originally Posted by Pocket

This happened on my old tunes from Jody. With the A/D counts on the throttle at 504 and higher, the 1st gear TC lockup speed was set at 16 mph. Anything below 504 was raised all the way up to 127.5 mph.

If the TC locked up, then it would make sense as to why it lurched forward like it did. So did it shift into 2nd and then lock, or do you think it locked the TC in first while I was spooling up?

I'm still going to try changing that table to see what happens. I might do it on my old tune to see if it makes a difference. I know how to duplicate the launch problem... just hold 1800+ RPM for longer than about 5-6 seconds.

Curtis,

It's impossible to say what is actually going on...and it can even be so stupid as a mechanical transmission issue where the pump isn't supplying enough fluid under that load (since it's raised to such a high pressure under WOT in 1st) to hold the torque converter clutch off of the backing plate.

I'd put a scanner on it and see what is being commanded.

[Pocket]

Thanks Cody. I'll see what I find. Still gotta figure out how to quit blowing my intercooler boots off every time I attempt a shake-down run.

[GTS]

I actually have some input on this. I've had this exact thing happen to me and it is not your transmission shifting. When it happened to me I described it exactly as you did initially thinking the transmission was shifting but it is not. While it does seem to make sense that if it shifted it would want to lurch however to the contrary it actually doesn't matter what gear the transmission is in. If the transmision sin't spinning (you moving forward) the gear is irrelevent and all that is going on in before the stationary input shaft which means what is going on is all in the TC.

I actually destroyed a TC doing this. When I talked to Brian at BTS he said what's happening is it's sucking the oil pan dry of oil then something in the TC wants to lock up. I don't think it's the clutch locking and I didn't understand what all it was but I've had this same thing happen when I was doing a tranny service and tried to put the transmission in gear before it had a chance to get the fluid flowing completely through the transmission.

You might want to call your tranny builder for a better explanation of whats going on but it's not the transmission shifting.

When I busted the TC doing this it sounded like a tin can with a bunch of bolts in it and it also locked up solid so as soon as I put it in gear the truck was rolling and if you hit the brakes to stop it it would kill the engine.

I suggest not spooling up so quick. Watch the other driver and as soon as he lights up the 2nd set of staging light start spooling. when I did this I would roll into the first set of lights, start spooling it then roll into the 2nd set of lights. This was just to much spool up time and caused the issue.

[Power Hungry]

I wonder if a deep sump pan may also help this. You're probably already running one, so that would make the previous statement false.

Another thought is that the TFT is elevating during staging and causing the trans to shift into the default failure gear... 2nd. Any idea what the TFT is rising to?

Anyway, this is a complete mystery to me. I've never heard of this before so we'll need to have some more input in order to come to a resolution.

[GTS]

Bill I have wondered if a deep pan would help it as well. Brian at BTS doesn't feel deep pans are beneficial as if you get the tranny hot it takes a lot longer to cool it back down with those pans. So I'm running a stock pan.

As I mentioned above about it shifting it really doesn't matter what gear it's in. If the tranny is not spinning it's not spinning so I don't think it's trying to shift into a default gear. When mine as doing it I don't recall the TFT getting all that hot. I mean it was climbing due to loading the TC but not out of range. And I have my temp sensor in the line to the cooler so that's right when it comes out of the TC and at it's hottest point.

BTW what are you doing on the furms while you are on vaca? I mean I love to see you post but man go take vacation!

[Power Hungry]

The reason I mention the shifting thing is that the transmission internals don't have to be moving for the transmission to actually change gears. All the ECM has to do is detect a fault somewhere and it will electronically shift into 2nd. This is not all that dissimilar to putting the shift selector in "L". One way to really help identify what's happening is to datalog the Current Gear PID and see what the ECM is actually requesting for gear. That would definitely eliminate whether the ECM is causing a problem of if the problem may be mechanical.

As for vacation... I have to do something in the morning while Corey is still asleep.