Posted By: willard
727 shifting pattern help - 07/25/12 07:44 AM
70 challenger, mild 383, stock 11" tc, 3.23 rear 26,5" tires, new cheetach standard automatic VB, 5400 rpm governor, proper throttle linkage, set as per FSM, holley carb with dedicated bracket, billet rear servo, 4.2 KD lever,
Symptoms:
- WOT shifts at 3000 rpm and 3300 rpm
- 3-2 downshift only below 40 mph, no manual downshift either!
- 2-1 only below 10 mph, no manual downshift either - should be 1 at any speedwith this valve body.
- governor pressure verified and ok.
- line pressure 55-60 at 1000rpm in 3rd (measured at front servo), when throttle lever pushed climbs to 70 and then downshifts to 2nd and pressure drops to 0psi.
- when operated manually acts ok, shifts are firm but wont downshift manually to 2nd above 40mph and to 1st above 10mph.
closed throttle upshifts are like with stock VB.
I guess line pressure should be higher with that valve body? What part aside VB produces the line pressure?
Over last year I replaced the VB (before had a stock with TF2) and governor, and performance changes are very small. Before, WOT upshifts were even lower at 2500 rpm and no 2-1 kickdown until car stopped.
Posted By: 340SHORTY
Re: 727 shifting pattern help - 07/25/12 08:22 AM
The pump makes the pressuse.. The pressure is adjusted by a screw in the valve body..
Posted By: willard
Re: 727 shifting pattern help - 07/25/12 06:40 PM
Damn... pulling the tranny out is not my favourite job ;/ I guess you're right... Is replacing the pump rotors enough? Or there is something else in the pump body?
Posted By: Dodgem
Re: 727 shifting pattern help - 07/25/12 09:19 PM
Sounds like the kickdown lever needs to adjusted farther back!
Posted By: willard
Re: 727 shifting pattern help - 07/25/12 09:26 PM
I swapped the old stock VB for brand new cheetach and the problem was not cured.
The KD rod is adjusted properly, at WOT the tranny lever cant be pushed further.
I guess the line pressure should be around 100 psi with that VB, right?
Posted By: JohnRR
Re: 727 shifting pattern help - 07/26/12 06:32 PM
What carb do you have and do you have all the proper linkage and adapters required if the carb is an aftermarket ?
The linkage doesn't necessarily need to be full back , 1/8" to 1/16" from all the way back is ok.
My thought an aftermarket VB should have more pressure than that at idle , start up the car with your pressure gauge attach and at idle manually move the kickdown lever fully to the rear, what is the pressure ?
Posted By: willard
Re: 727 shifting pattern help - 07/29/12 04:12 PM
Shall I check the throttle pressure at idle in N or 3rd?
Holley 770 street avenger with holley bracket for mopars. Linkage is 3 piece stock set.
Posted By: John_Kunkel
Re: 727 shifting pattern help - 07/29/12 10:27 PM
There is no way to check the actual throttle pressure; for later shifts just adjust the linkage so that the transmission lever is further back for any given throttle setting (lengthen the linkage). BTW, line presure is measured at the accumulator (center tap) not the front servo which is servo release pressure.
Also, be sure that WOT under the hood is the same as WOT at the pedal. Misadjusted throttle cable will prevent the carb from going WO when the pedal is matted.
Posted By: willard
Re: 727 shifting pattern help - 07/30/12 06:55 AM
The turboaction manual says to measure the line pressure at the front servo, not the accumulator port... I guess this VB doesnt use the accumulator? I already checked everything you write about...
Maybe it is the pump itself or the sealing rings on the pump shaft?
Posted By: fishy68
Re: 727 shifting pattern help - 08/01/12 06:11 AM
Pressure is definetly quite a bit low. I generally see close to (sometimes over) 100 psi. with a valve body like that or a stock vb with a trans-go kit. The sealing rings on the pump stator won't affect pressure in 1st or 2nd as their job is to seal oil pressure going to the front clutch pack. They'd affect it in 3rd gear or reverse only. Since it did this with 2 different valve bodies my guess is the pump is worn out.
Posted By: willard
Re: 727 shifting pattern help - 08/01/12 03:03 PM
That's the answer I wanted. I didnt know the pump rings are sealing only 3rd and R. 1-2 shift is definately stronger thank 2-3 but theres no slipping, flare up etc. I guess I'd change the pump after the season.
Thanks everyone.