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The Shop Truck

1971 Chevy C20 with a custom flat bed.
Overview Gallery Discussion
According to the Gearstar website:
  • Billet Direct Drum with 36 Element Oversized Sprag with higher capacity frictions
So I'm just trying to understand exactly what you're talking about so I've snipped the 1-2 shift from my last run.
1788362753183.png
The red line is the gear that is being commanded by the dominator, the blue line is your gear ratio calculation. From the time it commands second until the gear ratio actually starts dropping from the 1st gear ratio of 2.48 is about 1 full second and after the dominator has commanded 3rd. You can see a little bump in the gear ratio line at the 2nd gear ratio of 1.48, but that's about 1.3 seconds after the command, then it drops to the 3rd gear ratio of 1.0.

What makes you think that it was actually in second and slipping while maintaining the 1st gear ratio? To me it seems like if it was actually in second and slipping the effective ratio would go up, not hold at the 1st gear ratio. I don't fully understand automatic transmissions, but to me it looks like it did finally hit second briefly, but took forever to get there. It looks like I'm having a pressure issue and it's just taking forever to apply the pressure to the 2nd gear, but maybe I'm misunderstanding how the transmission actually shifts.

As you mentioned, later in the run, it commands second again for a downshift, .8 seconds later the effective gear ratio starts raising and hits the 1.48 2nd gear ratio almost a full second later and holds until it drops back into 3rd, but it held in second for .5 seconds and the time from the 3rd command to the ratio drop was only .34 seconds and only .4 seconds until it was actually in 3rd again. I'm wondering if the pickup is sucking air and that's what's causing the delayed shifts and converter slipping. I really need that line pressure sensor. I may be able to fix this with a deeper pan, some baffles, or just adding an extra quart of fluid.
1788363324711.png
I need to go datalog a second gear pull, but that's really difficult in the middle of a big city. I wish I was still in Michigan with miles and miles of empty roads everywhere.
I did check my trans fluid on the first day, but never again after that.
 
r3dd0g said:
According to the Gearstar website:
  • Billet Direct Drum with 36 Element Oversized Sprag with higher capacity frictions
Click to expand...

Yeah that one should be good.

r3dd0g said:
So I'm just trying to understand exactly what you're talking about so I've snipped the 1-2 shift from my last run.
View attachment 534364
The red line is the gear that is being commanded by the dominator, the blue line is your gear ratio calculation. From the time it commands second until the gear ratio actually starts dropping from the 1st gear ratio of 2.48 is about 1 full second and after the dominator has commanded 3rd. You can see a little bump in the gear ratio line at the 2nd gear ratio of 1.48, but that's about 1.3 seconds after the command, then it drops to the 3rd gear ratio of 1.0.

What makes you think that it was actually in second and slipping while maintaining the 1st gear ratio? To me it seems like if it was actually in second and slipping the effective ratio would go up, not hold at the 1st gear ratio. I don't fully understand automatic transmissions, but to me it looks like it did finally hit second briefly, but took forever to get there. It looks like I'm having a pressure issue and it's just taking forever to apply the pressure to the 2nd gear, but maybe I'm misunderstanding how the transmission actually shifts.
Click to expand...

Because it shouldn't take that long, something is wrong, whether it be low pressure or too slow of shift circuit I think something is wrong. I think the reason it commanded 3rd is because 2nd did not work. If second does not engage it will still be in 1st gear.

r3dd0g said:
As you mentioned, later in the run, it commands second again for a downshift, .8 seconds later the effective gear ratio starts raising and hits the 1.48 2nd gear ratio almost a full second later and holds until it drops back into 3rd, but it held in second for .5 seconds and the time from the 3rd command to the ratio drop was only .34 seconds and only .4 seconds until it was actually in 3rd again. I'm wondering if the pickup is sucking air and that's what's causing the delayed shifts and converter slipping. I really need that line pressure sensor. I may be able to fix this with a deeper pan, some baffles, or just adding an extra quart of fluid.
Click to expand...

Yes this is why I don't think it's your sprag or it would have zero holding power. But its also much easier to hold for a moment on a downshift during acceleration. The pressure sensor would help yes. If its just a slow shift for 2nd only the transbrake valve body will probably fix that. If the pressure is low then you may need to fix or replace the filter or pump. I've had a 4L80E filter go bad and lose pressure before but when pressure loss happens its usually every gear not just 2nd.


r3dd0g said:
I need to go datalog a second gear pull, but that's really difficult in the middle of a big city. I wish I was still in Michigan with miles and miles of empty roads everywhere.
I did check my trans fluid on the first day, but never again after that.
Click to expand...

Yes that would help too, even at 50% throttle to see if it holds on an upshift or even if it holds when it's already in 2nd gear.
 
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folkenheath said:
If its just a slow shift for 2nd only the transbrake valve body will probably fix that.
Click to expand...
The Rossler kit does not replace the valve body. http://www.rosslertrans.com/online-store.html#!/4L80E-Trans-Brake-Kit/p/80029817
folkenheath said:
If the pressure is low then you may need to fix or replace the filter or pump. I've had a 4L80E filter go bad and lose pressure before but when pressure loss happens its usually every gear not just 2nd.
Click to expand...
It took 1 full second from when it commanded 2nd the first time to get into 2nd and .8 seconds from the first time it commanded 3rd to get into 3rd. It was happening in every gear, but once the acceleration was reduced it only took .9 seconds for the 3-2 shift and .4 seconds for the 2-3 shift. I'm thinking it's a pan/baffle issue.
 
You are wondering how it works, here is a chart to explain from a sheet that came with some parts I purchased a while back. I realize hard to visualize if you haven't seen/assembled the parts. I can see all these parts in my head having rebuilt some 4L80E trans.

So when in D, if the computer commands 2nd, Sol A shuts off, which applies the intermediate clutch, which causes the intermediate sprag to hold and the low roller clutch (actually more like a sprag) to overrun. A sprag works like a one way bearing, it grabs one direction and free spins the other. Every gear shift just over runs a one way bearing so if the new shift doesn't happen, it's still in the same gear.

So either the circuit that feeds the intermediate clutch is too restricted, or the pressure is too low. The factory restricts the feed with orifices, checkballs, and accumulators (spring loaded pistons that take time to fill up to pressure). All those can be modified, and the checkball and acumulator can even be removed, as long as the orifice isn't too big, that can cause extremely harsh parts breaking shifts. This is parts of mechanical transmission tuning. Too large of orifice can cause the trans to shift too hard, and you can't turn the pressure down or then you lose holding power, as the pressure keeps the clutch applied, less pressure means slower shift, but also less holding power. There is a balance. I keep full pressure and just size the orifice for a nice firm but not harsh shift at full WOT pressure.




PXL_20260902_162121868~2.jpg

r3dd0g said:
The Rossler kit does not replace the valve body. http://www.rosslertrans.com/online-store.html#!/4L80E-Trans-Brake-Kit/p/80029817
Click to expand...

It does replace the orifice plate, boost valve, and several springs. I haven't personaly used that exact brake but Rossler has a good reputation. It appears that goes under the PSM and requires a deep pan.

FYI, those springs in the bottom center of the picture are the springs I was referring too that probably go in the direct drum, and it says it requires trans disassembly. So hopefully they already did what I mentioned for those and the bleed hole.

r3dd0g said:
It took 1 full second from when it commanded 2nd the first time to get into 2nd and .8 seconds from the first time it commanded 3rd to get into 3rd. It was happening in every gear, but once the acceleration was reduced it only took .9 seconds for the 3-2 shift and .4 seconds for the 2-3 shift. I'm thinking it's a pan/baffle issue.
Click to expand...

If it was a pan baffle issue it would probably be all the gears, not just 2nd. Second might be too restricted.
 
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OK, it seems to be shifting fine when I'm traction limited. I did a few pulls driving around trying to keep the tire spin to a minimum. The first pull was a waste, it was in 1st and didn't get into second until I let off the throttle because I was spinning too much (90% throttle). The second pull it was already in second, rolled to 80% and backed off a bit to control the spin. It did the 2-1 in .5 seconds and the 1-2 shift .4 seconds.
Green-TPS
Blue-Gear Ratio
Yellow-input shaft speed
darker green-speed
1788374255382.png

Third pull was on a more major road so I was doing my best to keep the wheels from spinning. I got it all the way up to 88% throttle in 2nd. 2-1 shift took .48 seconds, 1-2 shift took .4 seconds again.
1788374562352.png
On the final pull I finally figured out how much I could push it without spinning. I only got it up to about 70% throttle, but the 2-1 shift was good at .42 seconds and the 1-2 shift took .5.
1788374936509.png
I can trim these files and send them to you if you want to look at them closer @folkenheath .
 
The middle one is a tiny bit strange but the other two look fine.

Was this with the old or modified shift speed tune?
 
This was with the old shift speed tune, I didn't change anything there yet. You can see I was modulating the throttle heavily on the second one, which is probably why it looks a little weird.
 
r3dd0g said:
This was with the old shift speed tune, I didn't change anything there yet. You can see I was modulating the throttle heavily on the second one, which is probably why it looks a little weird.
Click to expand...

Yeah but that shouldn't matter, the clutch should still hold the throttle modulations, the ratio should not change.

Babaganoosh said:
Doubt this is the reason it's doing it but I did some messing around on google, I'm bored at work and found this interesting.

https://www.holley.com/blog/post/deep_dive_a_look_at_the_latest_upgrades_in_holley_efi_v6_software/

Look under the shift power management and specifically at what they call Inactive Time After Shift
Click to expand...

That's only for the racing trans control method, that's not applicable for the 4L80E tune files.
 
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Babaganoosh said:
Doubt this is the reason it's doing it but I did some messing around on google, I'm bored at work and found this interesting.

https://www.holley.com/blog/post/deep_dive_a_look_at_the_latest_upgrades_in_holley_efi_v6_software/

Look under the shift power management and specifically at what they call Inactive Time After Shift
Click to expand...
I'm currently using Holleys 4l80E ICF to run the transmission. I'd have to switch that to the race transmission ICF and figure out how to do all the other things that Holley did for me already in the ICF I'm using. It would give me more control of the transmission, but I think what I have will be fine as long as we can figure out what's causing the slow shifts or slipping.
 
r3dd0g said:
I'm currently using Holleys 4l80E ICF to run the transmission. I'd have to switch that to the race transmission ICF and figure out how to do all the other things that Holley did for me already in the ICF I'm using. It would give me more control of the transmission, but I think what I have will be fine as long as we can figure out what's causing the slow shifts or slipping.
Click to expand...

I agree that shouldn't be necessary. I did add a single output I labelled TC Clutch. This enabled me to have another "ground" output that I also hooked to the TC clutch wire. With that I can engage the TC Clutch based on speed, TPS, race mode switch, nitrous enable, etc.

The TC clutch is still controlled by the 4L80E ICF as well using the regular controls.

Below is my current configuration for that race output.

If you have a triple disc lockup it will likely help your top end, particularly for 1/4 mile. You just need to find a speed to turn it on for your runs.

You could also turn it on above a certain boost level and speed if you want, doesn't have to be nitrous.

If you don't have a triple disc this will just burn up your converter clutch.

1788377580934.png
 
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I was planning on doing some of that after I got more runs in and got consistent with the truck. I'm not sure of the specs on the Yank torque converter, I don't seem to have any paperwork on it as it was preinstalled on the transmission.
 
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