lt170chevelle

iTrader: (2)

hey guys,im at it again with another rebuild and having a 4th gear issue.

First off, i forgot that the 2/4 band can stretch a little and had initially ground the servo pin to give me 3/16" travel , but after a few days of driving i noticed i now have almost a 1/4"of servo cover travel.

Fourth gear almost feels like it is slipping and dont know if its related to the extra travel the servo pin now has!?!

Also i have no 4th engagement when im not giving it gas.Like no engine braking at all ,just goes to idle.

Is all this related to just the servo pin or is there another culprit?

I just rebuilt this thing over the weekend and have only driven it 30 minutes one way to work and back today and yesterday?!?

zgp

How does the 1-2 shift feel? Is it long?

lt170chevelle

iTrader: (2)

1-2 shift is perfect and firm even with the stall. Which is why im curious about allowable band travel..This is also with the super billet servos aswell.

lt170chevelle

iTrader: (2)

superior billet servos

Vince B

iTrader: (1)

Personally with a new band I think your setting the band clearance to loose. When I build a unit I set all of this before the pump is installed and with the trans standing in an upright position. I make sure I can turn the drum in both directions. IMO if you can wiggle the band then its to loose! Normally I can barely move the band side to side on the drum and that works fine for me. I honestly have not used one of those 4Th servo's in about 10 years but if I remember correctly you should have a washer between the 4Th servo piston and the "E" clip on the servo pin. If you don't this could be your issue as to why second feels fine and you have an issue with 4Th. Hope this helps. Vince

performabuilt

iTrader: (25)

Note also that if you are in the 4th gear position and the band is not applied there will be no overun or "Braking" as the inout sprag is free wheeling.

lt170chevelle

iTrader: (2)

Well i know the washer is there between the piston and clip..I guess i need to lengthen that pin then maybe?
And i really cant go by just the servo cover travel past the clip?
I just want to make sure my method is correct

Also I noticed today that when i let off the throttle in 4th in lockup it takes a second and can feel the engine braking but instantle goes to idle and when i get back on the gas it jerks like its almost just catching when back at that rpm it stopped braking at.
Could just a leaking seal on that piston be a possibillity? i did not see a seal that would fit the billet 4th in my rebuild kit and is probally the only one i did not replace this time around...its one of those slash cut square ones..

lt170chevelle

iTrader: (2)

Thanks vince and performabuilt you guys always steer me in the right direction.Well i took the servo assy out and legnthend the pin so i have just about the clipdiameter of travel in past clip..which is 3/16" i believe? Which is what i had set it up at during the rebuild.
I did double check all washers , stackup, and seal orientation and all was correct besides the stinkin pin length. I am still concerned if this will remedy my problem but will take it for a test drive in a bit to see if it did.

98 4X4 burban

iTrader: (1)

I am having almost the exact same problem with my transmission and my build is simular to yours with the billet servos and wide band. but with mine i am not getting lock up with the shifter in the 3rd position. and in the 4th/od position it will not up shift but will give me a 3rd lock up. did yours do this?

lt170chevelle

iTrader: (2)

UPDATE: I lengthened the servo pin and so far 4th feels much better than it did. But i still have no engine braking (overrun) in 4th with converter locked or unlocked.
I did notice it if i just barely give it gas just off idle , it was engine braking(overrun)
TPS maybe?
To Burban, I have the converter locking up early in 3rd and 4th on mine, before i did that , i think 3rd doesnt lockup from the factory or it does it late in 3rd.
Now im still having issues with taking off in 3rd and have to manually shift it down to take off in 1st.
But if i am in P N or R then go to OD and take off from a stop , then it upshifts from 1st but if i slow again it will not downshift itself . If that makes sense.

Predator T/A

iTrader: (7)

still sounds like under low pressure theband is not able to hold allowing it to fall out of gear a freewheel

lt170chevelle

iTrader: (2)

Well i have more overrun(engine braking) in my tune . Also the way i have my tune the 0tps and right off idle pressure tables arent much different.
When i get right off idle just pressing the gas enough to move the pedal in it felt like it should as far as the engine braking is concerned.
Does this simply sound like an enternal leak maybe causing low apply pressure in idle?
maybe 4th aply piston leaking? The seal looked perfect when i had it removed the other day to lengthen the pin.

Predator T/A

iTrader: (7)

thats what i was getting at is possibly there isnt enough apply pressure on the band aty lower pressure maybe due to a leak in the servo or the pin still not long enough hard to say but if the trans is not staying coupled to the engine when you let off the throttle then I would say the band is not being held on for some reason. how much servo travel do you have right now. as rule of thumb for a beginner the travel should be no more that the thickness of the sanp ring on the servo I usually have about .030 travel in my setups the servo travel has more to do wit hthe 2-3 shift than a 1-2 shift but if its too short it can not apply....how does the 3-4 shift feel when it engages... there could also be a problem with the billet servo..try putting a stock 4th piston and cover on ans see what happens.

lt170chevelle

iTrader: (2)

Yeah when i rebuilt it a week ago i set the servo cover travel at just the snap ring diameter passed the actual ring. Then after a day or so of driving i rechecked it to find it had almost doubled.
Im thinking the band just stretched or maybe wasnt seated all the way when i intially set the pin length.
So I lengthened the pin to get the same travel again.
The 3-4 feels like its shifting correctly and seems to be holding under partial and half throttle. I will look into getting a new seal for the 4th servo and double check the clearance between the pin diameter and the 4th servo bore just in case its leaking there.

Predator T/A

iTrader: (7)

as rule of thumb as long as you can turn the output shaft backwards with resistance the band isnt locking down and you shoudnt be able to turn it at all with the servo cover applied thats how i set them.

lt170chevelle

iTrader: (2)

So if i push the servo cover in then the output shaft shouldnt be able to spin? If it does , then my pin length still isnt long enough ? or something else?

Predator T/A

iTrader: (7)

yes wit hthe servo cover pushed in you shouldnt be able to spin the output shaft backwards even with a pair of vise grips