front "kick down" servo springs

[chargerdon]

Hi, I am attempting to overhaul my a904 transmission in my 74 Challenger.  GOD HELP ME!!   The challenger originally had a 318 so it is a v8 car and I DO NOT KNOW if the a904 in the car is original or a replacement, or has been previously overhauled.   

My whole question is on the spring(s) in the kickdown (front) servo.

I took it apart to replace the seals in it and found only 1 small in diameter spring.    To disassemble the servo after taking out the snap ring (fairly easy to depress the top piston with my fingers), the pistons inside do not have a place to grap onto to pull out, so I applied air pressure to the servo port to pop it out.   And pop out it did, flying a couple of feet high and then coming down.   It is "possible" that a large spring was in there but flew somewhere and i cant find it...or..it never was in there.   It did not take a lot of pressure  to push down on the top piston guide to allow me to take out the snap ring. 

The Mopar shop manual (74 Dodge SM) for a 94 shows on page 21-117 shows the servo illustration with two springs...  i smaller diameter inner spring and a larger diameter outer spring...the illustration also states that the larger outer spring is NOT USED with 904/6 6cyl engines.   My challenger had a 318 v8 in it so there should have been a large outer spring according to the manual in it.    However, mine didn't... Or did i lose it

I watched a youtube video on rebuilding a a904 and part 8 https://www.youtube.com/watch?v=AXG6OwLpHsI shows it having both an inner and an outer spring.   His a904 was from a 73 dodge dart with 318 engine.  You will notice that in this video to depress the top piston guide he had to use a large c clamp to push it down...   I didnt need the c clamp.

I also watched a different youtube video where an expert was doing an a904 from a 98 jeep, and in it https://www.youtube.com/watch?v=TlSartEcW60 at about the 14 min thru 16 minute the techician removes the assembly and it only has 1 large diameter outer spring.   

WIT transmission shops online manual...  https://www.wittrans.com/parts?type=A904%20(30RH-32RH)%20(Aluminum%20Case)&section=90_case shows only 1 spring for the kickdown servo a large diameter spring...   part number U12906 but unfortunately none available.   Again tho is only 1 spring a larger outer spring...I have only 1 inner spring for mine.

Transtec online parts https://www.transpartsonline.com/TRANS_PARTS_FILE/tpcat.php?TransPartsOnline=904&TransPartsType=904 shows an assembly with only 1 large diameter spring same as WIT and not available to purchase..   either.   Neither the WIT or TRANSTEC web sites differentiate the model year for their A904 transmission diagrams.   

Now I am at the point that I need to put this assembly back together having replaced the three metal seals...and not knowing whether I should try to find a large outer spring or just put it back together the way I think it was, and assume that there was no large outer spring.   Or try to buy one somewhere???   I can tell one thing...The spring(s) are used to push the lower piston back into its bore, to RELEASE the activating rod for the front band.   Not to apply it.   

Anybody have any knowledge here???   

[mopar jack]

The front servo is an area that many transmission shift kits modify. Many kits remove the large spring depending on the band lever ratio. aattached chart from 71 FSM.

[chargerdon]

Well...my story gets better.   First i finally found a way to check my transmissions serial number out, and it turns out that this is an early 68 model transmission.   

I had determined that the front outer spring isnt really supposed to be there.   My 74 manual illustration says "not used on 904/6 cylinder"  I interpreted that as meaning not with the slant six engine.   But, that isnt right...   it actually means that the illustration is showing what is in a 727 not a 904.   The 904 is actually called a 904/6 whereas the 727 is known as a 727/8.   The word cylinder after it threw me off.     I was in a transtec parts depot and the attendant looked at it with me, because they could not find a spring that would work.   He pointed out that the 904 is known as a 904/6.    SO NO OUTER spring.

Then I bought a shift kit, and started to follow its directions.   As soon as i split the VB apart i knew something was amiss..because their diagram as well as my 74 shop manual shows a total of 7 check balls.   However, mine only has 6 !!  The 7'th check ball is supposed to have a spring with it as well...   No spring or checkball in the area shown in the manuals.   After i called Superior shift kit tech...the guy said that the 66-68 models and a 77 doesnt have that ball or spring.   

Thats when i decided to really get serious on identifying my transmission.   Its part number is 2892029Y so I did at his direction a google search for a904 2892029Y  and that gave me a link into Chrysler interchange manual on page 52...it lists 2892029 as being an early 68.   So no check ball.   Sure hope this is the last of these issues...  If anyone knows of other manuals to identify these transmission numbers let me know.   Apparently until you get to a 78 tranny when lockup torque converters where introduced by chrysler there werent a whole lot of changes to the transmission.   Hopefully will finish putting mine together over the next week...   

One last issue, the front kickdown band that came with my kit is a flex band, and my original is a rigid band that appears to be much much better made than the flex band that came in the kit.   Throwing the flex band away, and bought a "relined" original rigid band to put in.   Got it from WIT...   $9.   The big issue with the flex band is that the attachment for the adjuster doesnt fit into it as well as it did for the original so the flex band would have been free to slide around.   I found out no no one is making new rigid bands, thus the reline job.   FYI

[Aracer]

The Mopar shift improver kit for a 904-988-999LA only has you block the accumulator in the down  position towards the oil pan. The blocking is done with a 1/2" tubing x 2 7/8" long.  Leave out both springs. The pistons can be lowered under the car with a bottle jack.
     The other instructions:  Adjust line pressure allen screw counterclockwise to compress the spring until ALMOST all the threads are used. Allow enough threads to completely engage adjustment bracket.


     On the 727 block the acc. piston, with a 2.74" long x .70" tube, and install a solid kickdown piston servo set from any LA904,8,9; and that is the (old) servo upgrade. The new one comes with a rigged up, ( too work solid,) controlled load apply servo. It's done using .185 thick washer instead of small spring. Kit comes with a 2x2" stiffer spring to hold the servo down. It actually helps the band to release quicker. The modified kit apply rod in the servo is fatter then the old style 904 stock stye; so it's 7/16" aluminum tip is rounded and better supported in the servo. It is the same operation but less wiggle. Also wind up the pressure spring too.
              That was $60 worth of Moper Direct Convection info.

[chargerdon]

I used a TransGo shift improver kit.   Its a lot different.  The one I bought doesn't touch the accumulator at all.   Its mostly drilling a couple of holes larger in the flex plate and changing a couple of spring in the VB.   Including both springs in the PR adjustment, and with it you do just the opposite..i.e screw down the pr adjuster until the inside plate is flush with the outside casing.  It also contains a replacement "manual" valve designed to prevent drainback from the Torque Converter when engine not running. 

[chargerdon]

Ok after some investigating ...ran the serial number and turns out my 904 is actually a 1968 model.    Used the 66 Charger SM and there is no large spring in the front servo of that year 904.   Being a 68 explains a lot.