My drivetrain does some funky stuff when casually upshifting. If I start and gradually go from 0 - 50 mph, it feels like a 5 speed automatic. There are 4 distinct "jolts" if you will, that feel like shifts.

Now, I can narrow it down a bit. It usually happens as I approach 25 mph. I clearly feel my 1-2 upshift, then shortly after I feel another jolt which is usually associated with a bang and a minor loss of power (By loss of power I mean it feels like I let off the throttle a bit but I didnt) and then I can feel my 2-3 upshift a bit after that. However, the extra jolt feels a lot like a shift. It is often VERY hard to differentiate my 2-3 upshift and the extra jolt which is obviously not a real shift. Sometimes I dont even feel the 2-3 shift and sometimes I dont feel the extra "jolt" so this makes it hard to tell what I felt and what I didnt. My 700R4 goes into OD at 40 just like any other and all the funny business has finished by the time I hit 40 anyway. Sometimes I cannot even tell which comes first, the 2-3 shift or this extra jolt. The jolt could be happening after my 2-3 shift for all I know.

I figure this has something to do with the TCC - but what? What is this extra jolt I am getting between shifts? Why is there usually a pretty distinct bang associated with it? The bang for sure is coming from the transmission area.

 

Everything is normal except for the jolt. If this is happening on the 2-3 shift there is a timing issue in the transmission. Can disable the TCC to help narrow it down. Disabling the TCC can be done in the eprom or by disconnecting it (at the brake switch or un plug it at the trans).

If the jolt is from the 2-3 shift it needs to be fixed. One of two things happen when the timing is off. Either the 2-3 shift flairs, or it binds.

It sounds like your trans is binding. This causes a short stop in acceleration, followed by the bang. The bang is the driveline slack being taken back up.

The actual cause of the bind is that the 3/4 clutch pack is engaging before the 2/4 band is pushed off. So the trans is in 2 gears at once. This is torture on the 3/4 clutch pack.

If the trans has a 'super servo' in it that can cause the problem. Change to a 093 (Vette) servo. It can also be the check ball capsule in the servo bore is leaking. Or a leak or bad seal elsewhere.

RBob.

 

Its not happening ON one of the shifts....its happening between the shifts while in steady gear. There is an extra jolt with a bang that happens while in 2nd gear or seemingly sometimes while in 3rd gear. Looking at the TCC lockup parameters in the .bin, the CTS OK To Lock setting is at 41*C. After seeing that I am reminded that the car doesnt do this while cold. Here are my TCC settings - do they look normal?

http://img244.imageshack.us/img244/5332/1ne5.jpg

http://img515.imageshack.us/img515/1676/2jh8.jpg

 

Can I raise the minimum TCC lockup speed and safely drive around? Its set at 26, is it OK to play with this and see what effects it has? What about driving around with TCC disabled?

 

Can set the TCC minimum CTS threshold to a high value (150c). This way the TCC won't lock up at all. For testing & checking this is OK. Only thing to avoid are long highway trips, best to have lockup for that.

As far as TCC lock setup, I usually use a lower MPH lock point for the low gears. Then a higher MPH lock point for high gear (4th). If the high & low tables act reversed, then flip the option word bit that defines the high gear polarity. GM switched around the high gear pressure switch. Some are NC while others are NO.

RBob.

 

I wired up a switch to the (pink?) wire under the dash connected to the brake pedal. I just flip the switch and trick the 'puter into thinking I'm on the brake, thus never allowing lock-up.

When I swapped gears and put in a stall I noticed lockup around town that I never noticed before, so this little mod helped out a bit. Of course, on the highway, I'll leave it on so it'll lock.

 

Will it ever lock up while on the brake and decelerating? Because it sure seems like it is. I havent had time to try any of these solutions yet, but it sure seems like when I am slowing down, especially right before I come to a stop I hear a big bang-crash coming from under the car that I can FEEL in the seat of my pants. It sounds like drivetrain stress being relieved or something, because it becomes somewhat easier to stop the car once the bang has occured.

Is this a sign that my tables might be switched and I should flip that bit? When cruising at exactly 40mph, I can do that test of tapping the brake and seeing my RPMs go up for a second then go back down - so lockup seems to be working properly. I just dont know if its doing it at the wrong times...or what.

 

It shouldn't ever lock upon braking or decelerating. Like you said, maybe it ISN'T unlocking, and maybe that's your problem.

 

I just drove around with it disabled. Wow, it drives so much better. All the knocks were gone, if I floor it from any speed it goes so much smoother, and if I do a panic stop and quickly slow down it is so much smoother. How do you recomend I set my TCC settings in the PROM so it drives smooth like this all the time, but gives me TCC lockup while cruising?

 

Almost sounds like the tranny mount is broken. Double check it by pushing up on the tailhousing of the tranny. If it separates it is bad.

Or, maybe the TCC soleniod is sticking.

I'll email you a set of TCC tables that I use. Not the same engine but should be a good starting point.

RBob.