I have a powerglide that has a 300-400 Rpm spike at the shift. I have done a lot of reading and have tried everything I’ve read so far with no change at all. I have pulled it down 4 times trying something different with no luck. So far I’ve changed band adjustment from 2 1/2 to 5 rounds out from 72 inch lbs. I’ve pulled it down to a bare case and air checked rear piston seal and it was good. I’ve changed the rings on servo from steel to teflon and 1 of each. I’ve changed high gear clutch clearance from .060-.100. I’ve changed all seals at least 2 times.
I have changed the valve body from cast to billet aluminum. I have changed the rooster and everything with shift linkage. New servo tube and tried 2 different converters(both the same spike).
The only thing I haven’t changed is the pump, input shaft, and case. What am I missing.

Any help will be very much appreciated.

Thanks Justin Allbritton

I can say from personal experience that a shift flare is more prevalent in high HP applications.
Bottom line is the band is releasing before the hi clutch's are fully applied.

Increasing your high clutch clearance was defiantly a move in the wrong direction, same with increasing your band adjustment

What is your combo? HP, car type, weight etc.
What is your line pressure?
How many clutch's?
What servo are you using?

1980 lbs 4link dragster
1200hp
190psi at servo at idle
8 clutch drum
Hughes dual ring servo

What is the pressure going down the track?
Can you post a run graph showing the flare?
Mine was 5-600 rpm with 10 clutch drum with my 2000hp blown TD.
I fought this for a while and was able to bring it down to about 300 RPM with some adjustments

It is most likely internal and Big Steve's suggestions are good ones.... As another possibility to consider is the Shifter Cable,
Usually on a Dragster that cable has to make a few bends to get to the Trans Linkage...It doesn't take much drag in that cable to impact the shift..The Shifter gates and the Trans detents are adjusted to make sure they are in synch so there isn't any ovelap between gears. That adjustment is done statically but that doesn't insure that the operation is smooth or that the chassis isnt flexing ot something external isn't affecting the shift..

I do not record pressure. Just checked it at servo with a manual guage. I tried posting pic of graph but I wasn’t successful.
Shifting at 7400 it completes the shift at 7750.

justin the spring and the line pressure have to match.go to sonnax and do so research really good reading there .i hope yall are doing well,long time no see

190 psi at idle seems really low to me. I would be curious what its at going down the track. Maybe put it on the trans brake and see what it is on the manual gauge. 250psi should be good.
I ran mine high with the TD in the 280psi range using a Sonnax boost valve in a cast iron VB.
You said you had a billet VB, those have external pressure regulators so you can adjust the pressure without using shims like on a internal boost valve
I also found that if I set the clutch pack clearance at .050 with new clutch's that after a few runs the clearance was at .060 which is perfect in my experience, this was with 10 clutch's, having 8 shouldn't make a difference.
As far as the band adjustment, 72 inch lbs then back off 3-3.5 turns should be just fine. I set mine to 3 turns with new band and after a few runs it will loosen up some, reset it again and its stays put.

Like I said in my first post, the issue is the band is releasing before the cavity behind the forward clutch piston fills and fully applies the clutch's, this is a timing issue and what causes the flare.
If you follow the hyd path from the pump into the case, the passage has a tee where it goes to the band release side of the servo and forward clutch piston at the same time.
For what its worth I run the black cover Sonnax servo with the green spring, there is some shims in the kit based on the pressure you are running that you install behind the spring.
I tried running that Sonnax blue cover smart tech ratio servo, but after burning up 2 bands I took it out but I know many who swear by it, I just didnt have any luck for some reason.
I have something you can try but would prefer to take it offline. if your interested send me a PM

This message has been edited. Last edited by: Big Steve,

quote:

justin the spring and the line pressure have to match.go to sonnax and do so research really good reading there

This. It's an issue with the servo spring and line pressure. Talk to Marco Abruzzi

quote:

Originally posted by DragRaceResults:

quote:

justin the spring and the line pressure have to match.go to sonnax and do so research really good reading there

This. It's an issue with the servo spring and line pressure. Talk to Marco Abruzzi

First thing Marco will ask is what the line pressure is going down the track, he does not have that info. That is why I suggested checking the pressure while on the TB/Chip with the manual gauge, that should be close.
With the Sonnax servo, you need that info to determine what shim goes under the spring.
The servo spring can defiantly be contributing but may not be a fix all, it wasn't on my TD but I had a whole lot more power and accelerating allot faster

I've had a bad check ball in the high gear drum cause a flair on the shift.

Have you air checked the drum it was apart? Like Dennis said a leaky check ball will delay the clutch lockup. Also air check the high gear drum when its back together while the valve body is off. I cut a seal one time putting my trans together. Caught it with an air check. When I switched to the sonnax servo kit it was the best money I ever spent on a trans part. Like Big Steve said shim it for the line pressure. I run 225 PSI. Stock case, 6 clutch high drum with 65 70 thou clearance. Cant ask for a better shifting trans.