View Full Version : Reducing 2-3 shift overlap
02-04-2003, 10:04 PM
How can you effectively reduce the 2-3 shift overlap on a 727? There is a definate lag from 2nd gear to 3rd in my 727. Could be costing me a 10th or 2.
The over lap really has many causes, but basicly it is the clutch applying before the band is released.
Is there a shift kit in it? If not are you planning one?
If it is going to be rebuilt soon let us know.
I would, if all of the above aswers are no, just try to loosen the front band a 1/2 turn at a time until you get a flair-up then tighten it 1/4 to 1/2 turn.
02-05-2003, 10:18 PM
thanks, I kinda know whats causing it, I am wondering if there is some kind of adjustment (like you have mentioned), or if it has to be taken apart and some modifications made. I did instal a B & M shift improver kit, you know, the one that anybody can instal in a short time. It came with a different seperator plate and some adjustment info. Not a really involved kit. I will probably get a Trans-Go kit but before I do was wondering if there was something else I could do to improve the 2-3 overlap. One other thing, the B & M kit said to toss the accumulator spring and there was no mention of installing a blocker rod. Would that have an effect on the 2-3 shift? I do have the blocker rod now but haven't installed it yet.
02-06-2003, 12:29 AM
Some kits use a blocker rod, some don't, I think it just depends on the kit.
The 2-3 shift overlap is a bear to get rid of. I had a 5.0:1 front band lever and replaced it with a 3.8:1.
I also reduced the number of clutch springs in the front clutch pack.
If you used the B&M transpack where you install a restrictor in the transmission case fluid passage, remove the restrictor.
451 MOPAR, are you sure that less springs is right?
Also, the restrictor also should slow the clutch apply same as the more springs.
02-06-2003, 03:38 PM
The 2-3 shift has to release the front band (acumulator) and apply the front clutches.
The more springs you run in the front clutch, the softer the clutches apply. I run nine springs on my street car, and I have seen racers use six springs in the front clutch pack.
02-06-2003, 05:35 PM
The accumulator plays no part in the 2-3 upshift, tossing the spring as B&M advocates does nothing to improve shifts but blocking the piston will firm up the 1-2 upshift.
The B&M Shift Improver is a poor shift kit, for best results I'd recommend a reprogramming kit like the B&M Transpack or the TransGo TF-2.
02-07-2003, 09:04 PM
Yes, the B&M kit is a no-brainer John. I just did a quick instal to see how it would react. I will go with the Trans-Go kit. Maybe I have too much line pressure. Maybe the adjustment with the B&M kit is too much. That may cause the overlap to increase, or maybe not?
02-07-2003, 11:05 PM
MANY years ago, I had a stock '66 Charger with a Hemi and a Torqueflite. That trans had serious overlap. I felt at the time it was due to the 5.0 lever. In a conversation with a B&M rep. he said that the lever was not the problem, that it was the Chrysler valve body. He wanted me to buy their manual shift body and insisted that the problem would go away. I never did, but I built many race TF's after that, some with 5.0 levers and some with 4.2 levers. All of those transmissions had home brewed Chrysler manual valve bodies and there never was an overlap problem. There was a slight overlap with the 5.0 lever. I preferred the 4.2 lever but I couldn't get them after a while. I don't know if this is of any help, but more info is always good (I think).
02-08-2003, 08:09 PM
The valve body, itself, has only limited control over the overlap period. When the valve body commands the 2-3 upshift, fluid is routed to the kickdown servo to release the band and fluid is simultaneously routed to apply the front clutch.
If the kickdown band is properly adjusted, a known quantity of fluid is needed to release the band but, because the clearance in the clutch can vary widely (and isn't adjustable externally), the quantity of fluid required to engage the clutch can also vary widely.
If the front clutch clearance is at its tightest allowable factory tolerance (.025"), a mere 7 CC's of fluid is required to engage the clutch while 27 CC's are needed to fully release the band. As one can see, with this much discrepancy in fluid quantity, the clutch will tend to apply before the band can release; big time overlap.
If the clutch clearance is at its maximum allowable factory
tolerance (.125"), 34 CC's of fluid are required to engage the clutch. This discrepancy in fluid quantity would tend to make the band release too soon before the clutch can engage and you have engine RPM flareup. (Since the trans is technically back in 1st gear)
Additional factors that can influence the overlap are the size of restrictor orifices in the fluid circuits that limit the velocity of fluid flow and the configuration of the return springs in the servo/clutch.
If one is assembling the transmission, the proper choice of clearances and spring combinations goes a long way to attaining the proper overlap, but if one is working with an assembled unit , already in service, adjustments are limited.
Attaining the perfect overlap period with all of the possible variables is akin to choreography; this is what the reprogramming kits attempt to do, to balance the action of the valve body and the existing hydro/mechanical components it controls.
02-09-2003, 02:10 AM
John: Certainly sounds reasonable to me! Great post.
02-09-2003, 01:47 PM
Not trying to hijack the thread, but another question. How about this, 727 trans with a Turboaction manual valve body and a 5.0 kickdown lever. The 2-3 shift is so fast, that I think the trans may be in two gears at once? When shifted 2-3, it shifts very fast but the car actually "brakes" for a split second. I'm not too familiar with the trans internals, but the trans builder felt like the clutch pack did not have enough clearance?
02-09-2003, 05:32 PM
You guys brought up some good points. I have a B&M shift kit in my 727 440 Cuda and I'm not happy with it. I want to go with TransGo but which one? They have a Performance Shift kit TFOD518 for 1966-2002 at Summit and I see a Shift reprograming kit at there web site TF1, TF2, TF3. I don't want a manual valve body, just want it to shift firm with no over lap. I have a lot in 2-3 shifts. I have the trans out, so now is the time to change over. But to which one? Thanks
02-09-2003, 05:34 PM
The perception that the brakes are applied momentarily on the 2-3 upshift is an example of severe overlap, the clutch is being applied before the band releases.
Loosening the band adjustment and adding springs to the servo might help, as will opening the clutch clearance or adding springs to the clutch.
Playing with the clutch clearance/springs requires removal and partial disassembly. Another way to slow down the clutch application is to add an orifice to the clutch apply hydraulic circuit. This can be done by removing the valve body and inserting a small cupped soft plug, into which a small hole has been drilled, into the clutch feed passage in the case. Such an orifice plug is provided in most reprogramming kits, the orifice used by B&M and Transgo is .140" (#27 drill).
I prefer to tap the passage in the case 1/8" NPT and use a socket head pipe plug with the orifice drilled in it. This makes it easier to change orifice size if needed.
The TransGo TF-2 is an excellent reprogramming kit.
02-09-2003, 05:52 PM
Excellent post guys, now we are getting somewhere. John, what is it that you do for a living? Transmission repair? You sure seem to know your stuff about the 727. Good to have you around! Looks like you may just be the "Go To Guy" for transmission problems. Anything else that you would like to add?, I'm about to print this info.
02-13-2003, 08:02 PM
John, do you have any experience with the Hughes performance shift kit part #HP1205? I see only one listing for the Mopar 727. Are they any good?
02-14-2003, 08:55 PM
John, what is it that you do for a living? Transmission repair?
I'm a retired aircraft mechanic. I never did transmission repair for a living, I just started building my own when I raced and eventually made a side business of it specializing in the 727.
02-15-2003, 04:43 PM
Thats great, you just picked up on the 727 as you needed. Whats the take on the hughes transmission stuff, I really don't know much about them.
02-15-2003, 05:28 PM
Sorry, I don't have any first hand experience with Hughes stuff, I've heard good things about their converters.
02-15-2003, 05:41 PM
Thanks John, it looks like I will go with the Transgo T2 kit then. If a product isn't well known to guys who specialize on trannys then I won't gamble on it.
02-15-2003, 10:45 PM
Back in 1969 ,we ran a C/A Corvette with a 4Spd. and bought a Clutchflite from B&M . It put the 4Spd. to shame but after about 20 runs it stared laying down from 2-3 . As B&M was a small outfit back then and you could talk to some body that knew something , they suggested a new valve body they had just come up with . They sent us the valve body, a different lever and a set of new clutches for $150 . Cured the problem . I wonder what the same stuff would cost today ?
02-16-2003, 03:52 AM
I can give you the perspective of how this is solved with a Ford 4R70W transmission. The individual who worked as a powertrain developmental engineer respnsible for the 4R70W trans development at Ford built my trans. This trans has a similar problem with the 3->4 upshift. When running a high power engine with gears, the factory calbration does not release the forward clutch fast enough and the overdrive band engages too slow. To avoid going into neutral, Ford ends up momentarily overlapping the too events so the OD band applies before the clutch releases. This gives an 'eat the wheel' feeling and is called tie-up. The way to eliminate this on the Ford trans is to drill the forward clutch exhaust port in the valve body larger so it will release faster. A lower tension OD band servo is used to quicken the band application. For someone with a lot of experience, you will know how to calibrate the valve body for a given application. In your case, I guess you would have to do some experimentation with the valve body to get it right. But the solution is a similar one. You have to make the 2nd gear band release faster while making the clutch apply faster without neutral or tie-up. This should be very specific to each application because the shift timing is governed by how quickly the engine builds RPM and this depends on many variables.
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