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Extreme Veteran
Posts: 323
Location: New Orleans-ish | Torqueflite experts:
I have a '65 TF I am eventually going to install in a car. I am wanting to swap the valve body with one from a '62 TF along with the '62 drain pan to have the best of all worlds in a 727.
My question concerns the large spring that lives above the valve body. The spring from the '62 is almost an inch longer than the one from the '65. Why would one be longer and does it matter which one I use?
Thanks!
Brian |
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Extreme Veteran
Posts: 444
Location: North of the 49th | Hi
The spring you are referring to is the accumulator spring which will affect shift quality as its in the 1-2 servo(Kickdown band) apply circuit and the rear clutch apply circuit. With some High performance transmission mods this spring is left out but for stock street use the trans should have one . I can't give you a firm answer on the spring lengths as I've never done a side by side full parts comparison of the early 727's ; suffice to say that Chrysler did change the shift calibration throughout the production run of the 727 and since '62 was the first year the spring length would have been their "engineered" selection for production. The accumulator piston moves up and down in its bore either with the spring assist (up) for Kickdown band apply or down against spring pressure for the Rear clutch apply all of this in accordance with applied line pressure so its kind of a balancing act. Generally it can be said that the longer spring would have a more variable spring rate (increasing as it compressed and visa-versa )so personally I would be inclined to select that one for street use, but prior to that I would actually measure the rates by compressing the springs against a scale to see what was what as the rates would vary with spring wire diameter and so on. The stronger spring would provide a delayed or softer rear clutch apply and perhaps a firmer 1-2 shift and a weaker spring would give a firmer rear clutch apply and a softer 1-2. That's the way I see it.... |
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Expert
Posts: 3775
  
Location: NorCal |
There are lots of myths surrounding the accumulator spring and most center around the spring's part in the 1-2 upshift i.e. the myth that "the spring cushions the 1-2 upshift and should therefore be omitted for a firmer shift".
In reality, the only time the accumulator piston travels toward the spring is when the trans is initially placed in a forward gear...the spring cushions the application of the rear clutch. On the 1-2 upshift the piston travels away from the spring therefore the spring cushions nothing on an upshift.
As to the OP's question, all '62-'70 727's used a longer spring than 'most '71 and later and this is because the operation of the accumulator was modified starting in '71. In a pre-'71 I would use the longest spring to take advantage of its cushioning ability...there is no downside to using the longer spring. |
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Expert
Posts: 3393
Location: Chestertown, NY ( near Lake George) | To the best of my knowledge,the acc. comes into play on the 1-2 shift and the 2-3 shift, reverse and drive engagement, no. |
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Expert
Posts: 3775
Location: NorCal |
There is no pressure to the accumulator in Park, Reverse or Neutral.
While the accumulator DOES cushion the 1-2 upshift it does it strictly by hydraulics, the spring plays no part in any upshift. On the 2-3 upshift the accumulator piston remains in the same position it was after the completion of the 1-2 shift...IOW, no movement. |
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Expert
Posts: 3393
Location: Chestertown, NY ( near Lake George) | If we are looking at the same hydraulic circuit diagram, you will see application pressure is routed to the 2cnd gear band servo as well as the direct clutch pak, when commanded, as well as the the accumulator agreed?
obviously not reverse, neutral and park. |
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Expert
Posts: 2312
Location: Arizona | If you are familiar with water hammer in house plumbing, and the use of air filled "T's" to prevent it, my understanding of the accumulator in an AT is for the same purpose.. it's stops a hydraulic BANG from taking place when the circuit is closed, such as to apply the bands or clutches. Given the same diameter accumulator, a "stiffer" spring in it will allow less cushioning to happen and the band/clutch will apply faster. So a high performance AT will have a stiffer spring to provide firmer shifts. |
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Expert
Posts: 3393
Location: Chestertown, NY ( near Lake George) | The all out racing TF in my old 64 Maxwedge car had no spring in the acc., shifts would knock your socks off, not for street use for sure! |
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Expert
Posts: 3775
Location: NorCal | Shep - 2014-07-20 3:14 PM
If we are looking at the same hydraulic circuit diagram, you will see application pressure is routed to the 2cnd gear band servo as well as the direct clutch pak, when commanded, as well as the the accumulator agreed?.
Yes, but notice that the accumulator piston is in the same position in 2nd gear as it is in 3rd (at the end of its bore in the case)...no piston movement means the accumulator provided no action on the 2-3 upshift.
During the 2-3 upshift the exact same hydraulic pressure is applied to the valve body side of the accumulator and to both sides of the kickdown servo piston...even though there is the same pressure on both sides of the piston the piston moves to release the band because of the difference in surface area of the two sides of the piston: IOW, the side of the piston with the largest surface area overrides the side with the smaller surface area. (basic hydraulic theory) |
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Expert
Posts: 3775
Location: NorCal | jimntempe - 2014-07-20 8:48 PM
If you are familiar with water hammer in house plumbing, and the use of air filled "T's" to prevent it, my understanding of the accumulator in an AT is for the same purpose.. it's stops a hydraulic BANG from taking place when the circuit is closed, such as to apply the bands or clutches. Given the same diameter accumulator, a "stiffer" spring in it will allow less cushioning to happen and the band/clutch will apply faster. So a high performance AT will have a stiffer spring to provide firmer shifts.
Once again, THE OUTER ACCUMULATOR SPRING PLAYS NO PART IN ANY UPSHIFT and, therefore, does not affect the firmness of any upshift; the sole purpose of the accumulator spring is to cushion the application of the rear clutch which occurs when the car is at or near a dead standstill.
To understand the accumulator's cushioning effect on the 1-2 upshift one must understand basic hydraulic theory i.e. hydraulic pressure is always expressed in relation to surface area; in the U.S. it is expressed as pounds per square inch. Since the accumulator piston has three different surface areas to which pressure can be applied, the larger surface will always override the same pressure on a smaller surface and move the piston toward the side with smallest area.
So, in 1st gear with line pressure applied only to the case side of the accumulator piston (small area), the piston will be forced against the spring until the spring is fully compressed (it takes only 37 psi to fully compress the stiffest accumulator spring) then, on the 1-2 upshift, line pressure is applied to the valve body side (largest area) of the piston and the piston moves away from the spring. As the piston moves away from the spring it must displace the pressurized fluid in its path and this action of displacing the pressurized fluid provides a hydraulic cushioning effect to the application of the kickdown band. The upshift cushioning affect of the accumulator is strictly hydraulic, the spring plays no part.
Once the 1-2 upshift is complete and pressure stabilizes on both sides of the accumulator piston, the piston remains bottomed out in its bore in the case and remains there throughout the 2-3 upshift...the only time it leaves the bottom of its bore is if the trans drops into 1st gear (or Neutral Reverse).
Edited by 57chizler 2014-07-21 2:47 PM
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Expert
Posts: 3775
Location: NorCal | Shep - 2014-07-21 4:18 AM
The all out racing TF in my old 64 Maxwedge car had no spring in the acc., shifts would knock your socks off, not for street use for sure!
Then somebody removed it. All '62-'65 727's left the factory with an accumulator spring. |
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Expert
Posts: 3393
Location: Chestertown, NY ( near Lake George) | Correct, as stated the trans was modified to operate with 550 hp, and all out 1/4 mile drag racing. |
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Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
Location: bishop, ca | Ran this thread by "FuryJim", who is a well known trannie rebuilder; his transmission upgrades include this advise:
the 1-2 accumulator, as its named, cushions the "water hammer" of hydraulic pressure when second gear applies. I remove the spring and add a specific length of 1/2" copper pipe to keep the piston bottomed out in the case. folks who leave the spring out are killing the case as it flies in each direction, full travel, with every shift into drive, second, and back to rest at 3rd... jamming it in one spot is the best. doing this with no other mods is almost undetected, other than second gear feels firm, it wont cause a chirp or notably uncomfortable shifts.
Same goes for GM TH350- the easiest one to do, as you don't even drain the trans fluid [that much] pull off a snap ring and cover from the side of the case, loose the spring, add a jam rod, bam- firmer 1-2 shift for towing or racing.
Jim can be reached at : jrawa@aol.com
Edited by d500neil 2014-07-23 3:18 PM
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Expert
Posts: 3775
Location: NorCal | Like many builders, your buddy Jim knows how to build a stiff-shifting trans but doesn't know why, has no idea how the trans works.
Simply removing the spring is one thing but removing the spring AND adding a piston blocker is an entirely different thing; as I've repeated several times here, simply removing the spring has no affect on upshifts because the hydraulic cushioning function still works, but blocking the piston completely eliminates all cushioning and will result in a thunderous 1-2 upshift (which often results in busted parts). BTW, adding the 1/2" pipe as a blocker doesn't bottom the piston in the case, it pushes the piston all the way against the valve body.
Fury Jim's statement that "killing the case as it flies in each direction" proves he's a dufus and you can tell him I said that. He's equally ignorant of the TH350 intermediate accumulator function which works exactly like the TF i.e. spring only cushions initial application of a clutch.
The full-color hydraulic diagrams in the FSM prove my assertions, in both the 727 and 350 the accumulator piston is seen moving AWAY from the spring on the 1-2 upshift.
Edited by 57chizler 2014-07-23 4:11 PM
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Aluminum TF valve body differences
