Transmisson Shifting Question

[nborton]

For anyone that has read any of my other posts, my truck is finally back on the road and doing well for the most part.

I have a quick question about tuning the transmission.

When driving, if I am in 3rd (regardless of if Im in D or OD) and I give it more than say 10% throttle, the truck downshifts. If I am in OD, the truck downshifts to D.

My problem (maybe) is that it seems to cycle from OD to D too much. After a WOT from 0 - 95 or so, if I maintain WOT I will stay in OD, but if I let off slightly at that high of speed, it feels like it has fallen back into D and seems to spin frictionless.

I hope that makes sense, is it just a TV adjustment? How can I do that?

thanks

 

[George Blake]

Re: Transmisson Shifting Question

It's been my experience that at WOT on stock setup, it doesn't shift into 4th until about 99 MPH. Torque converter lockup at WOT seems to happen at about 70-72 MPH. What you are feeling is most likely the torque converter locking and unlocking, not a gear change. Your ECM controls TCC lockup based on MANY factors. When you have the shift selector in OD, the overrun piston does NOT apply and the sprag is in overrun when you are in 4th. The ONLY thing moving you forward in fourth is the 3-4 clutches, the forwards are HOLDING but they are being overrun by the sprag. This is why the 3-4 clutches burn up in ours so often. Whatever you do, do NOT shift from OD to D at WOT at 99+MPH, you WILL blow the sprag apart or damage the piston seal.

 

[nborton]

Re: Transmisson Shifting Question

THX - Deffinately no shifting being done at WOT, I don't even like manually shifting the truck because the engine brake scares me from 3-2.

I played with it some more, and think you are absolutely right, it is the TC. I changed from the stock to a 2800 stall, and think the slipping I experience is the TC waiting for more RPM's? I'm not terribly clear on how the TC works =(

My engine must need new wires (I did cap/rotor + plugs) but when the RPM changes from 2700 (waiting to have enough torque?) to 3500 instantly when it lets go, My tach has a wild flutter. bounces +/- 1500 RPM's a few times ~ unless there is anything else anyone can think of? (I know this is drivetrain only).

Atleast it's really fast again

 

[nightdiver]

Re: Transmisson Shifting Question

with a looser converter i would also use a .5 pressure regulator valve
George ?

 

[nborton]

Re: Transmisson Shifting Question

They put a .5 in it on the build. They also replaced one set of the clutches to a 9 piece design?

I had to go in for the routine 300 mile checkup, and got the green light for the 1 year warranty, so now I'm just going to drive it.

The sensation I'm feeling is the Torque Converter not unlocking, which I can live with, since it may actually make the stop and go commute softer, and when I put my foot in it, it unlocks. I was just accustomed to not being able to build 5+ lbs of boost with it still locked. Is that normal?

I really wish I knew more about how a transmission works, because something just doesn't seem right. The 1-2 shift after the build was a firm kick, but already that has gone and now it just shifts into second without any notice (yawn). The Corvette servo was used. Under WOT the transition takes 1 to 1.5 seconds. Also in OD it seems to slip as well at higher speeds. Again WOT at speed it is great, but if I let off I assume it's going back into OD and slipping (though at this point I could just be paranoid?) I see on huryde that the 2-4 band is applied in 4th and 2nd. Could I be having issues with this band? does the band rotate like the clutches, or is it more like a drum brake setup?

Thanks all

 

[jwaller]

Re: Transmisson Shifting Question

They put a .5 in it on the build. They also replaced one set of the clutches to a 9 piece design?

I had to go in for the routine 300 mile checkup, and got the green light for the 1 year warranty, so now I'm just going to drive it.

The sensation I'm feeling is the Torque Converter not unlocking, which I can live with, since it may actually make the stop and go commute softer, and when I put my foot in it, it unlocks. I was just accustomed to not being able to build 5+ lbs of boost with it still locked. Is that normal?

I really wish I knew more about how a transmission works, because something just doesn't seem right. The 1-2 shift after the build was a firm kick, but already that has gone and now it just shifts into second without any notice (yawn). The Corvette servo was used. Under WOT the transition takes 1 to 1.5 seconds. Also in OD it seems to slip as well at higher speeds. Again WOT at speed it is great, but if I let off I assume it's going back into OD and slipping (though at this point I could just be paranoid?) I see on huryde that the 2-4 band is applied in 4th and 2nd. Could I be having issues with this band? does the band rotate like the clutches, or is it more like a drum brake setup?

Thanks all

if the conv isnt unlocking you wont get a good pull from a roll(above the 32mph part throttle lockup speed). it will be hard to build boost from a roll. the lock up function should have no affect on the launch from a stop. a stock turbo truck should still build boost very quickly locked or unlocked.


if you are losing shift feel something is going away. stock syty trannies came with the corvette 2nd gear servo. it should not take anywhere near 1-1.5 sec to shift. the band is just that a big band that wraps around a drum. and yes it's used for 2nd and 4th gears but so are several other clutches. if your having problems with 2nd and 4th as you describe though you very well could be having a band issue. it might be too loose or could be you have already burnt it from slipping it in OD. either way it's not good and you will prob soon start to slip 2nd as well.

 

[nborton]

Re: Transmisson Shifting Question

Update:

The truck lost 2nd gear and had to go back to the shop. The diagnosis was a cracked input Drum =(.

They had put a larger width fiber band on, and honed the old drum to create a smooth surface. From what I've read out there on the net, a new drum is often mated with a new band during a rebuild.

Would smoothing out the drum weaken it that much or did something else go on?

Atleast I get it back tomorrow, and since they had to clean out some shavings from the drum, it should be in top shape (I hope).. to be updated I am sure..

-n

 

[jwaller]

Re: Transmisson Shifting Question

smoothing or honing the drum is a big mistake, it doesn't fix the out of round condition that the "ears" have. honing only smooths the surface the band rides on. always replace with new.

the band rides on the reverse input drum not the input drum. those are 2 different components. if they input drum broke then it has nothing to do with honing the old one. those are different thing.

 

[nborton]

Re: Transmisson Shifting Question

I didn't realize the difference. It was definately the input drum that had a crack. From what I gather, the 3-4 clutches then got wet, burned, warped, and lost their adhesion which caused the 2-4 band to burn as well. I saw the drum that cracked, and I could barely see the crack even when it was pointed out. Amazing something that small can turn it to poop. Hartman always told me I could rebuild one myself, but after seeing that, I don't know... seems best to leave to peopel that see them everyday.

I got it back and will drive it carefully for a few days, but hopefully everything is up to par. They replaced the reverse drum for good measure since the burnt band smoothed it out more.

Wish me luck!

-n

 

[George Blake]

Re: Transmisson Shifting Question

They most likely found the crack on an air check of the input drum. While everything is still in it, you apply air to the feed holes in the shaft. If there's a crack, even one you can't see, it'll show up immediately with a little trans fluid. You could do it, just have to be ready to put some time into it. It's easier to update one the didn't fail than one that has already failed. Let us know when everything comes out ok.

 

[nightdiver]

Re: Transmisson Shifting Question

when my input drum broke the crack was big. 3-4s went and the TCC burned also. If i remember right the overruns were also burned