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727 front clutch # springs vs front clutch restrictor size #3061577
07/22/22 10:21 AM
07/22/22 10:21 AM
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Posts: 1,072
Loudoun County, VA
Brad_Haak Offline OP
super stock
Brad_Haak  Offline OP
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727 front clutch # springs vs front clutch restrictor size?

My trans as built has 12 springs in the front clutch setup, but the RMVB I have for it recommends 15. I'm not clear on the relationship between how the number of springs affects the 2-3 shift overlap vs the use of (or not using) a restrictor in the front clutch apply passage. The RMVB is supposed to not require any restrictor, FWIW.

Maybe it's a dumba$$ question, but I'll own it. grin

EDIT: It's got a 4.2 lever

Last edited by Brad_Haak; 07/22/22 11:44 AM.

2021 Challenger 6.4L Scat Pack 1320 (2022)
100% stock: 1.680, 11.894 at 113.75 (DA 175 ft)
wheels, tires, air filter: 1.714, 11.833 at 115.80 (DA 310 ft)

1973 Challenger 452 ci street/strip (2008)
pump gas, DOT radials: 1.454, 10.523 at 126.44 (DA 514 ft)
Re: 727 front clutch # springs vs front clutch restrictor size [Re: Brad_Haak] #3061589
07/22/22 11:13 AM
07/22/22 11:13 AM
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fredericksburg,va
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cudaman1969 Offline
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This is one thing I’m interested in too, mine would drag or overlap a lot till I cycled it thru a couple of times, especially the trans brake. It wouldn’t hold on the line unless I did that. I’m thinking I had too many springs?

Re: 727 front clutch # springs vs front clutch restrictor size [Re: Brad_Haak] #3061615
07/22/22 12:15 PM
07/22/22 12:15 PM
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Portsmouth, VA
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DusterW2 Offline
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Typically a restrictor in the front clutch apply passage
is used with a stock pressure valve body like the Trans
Go kits. They use around 9 springs in the front clutch
The restrictor along with nine springs helps eliminate
the overlap. A purpose built RMVB with higher pressure
does not call out a restrictor but uses 12-15 springs
Also two springs in the front servo to help unload the
kick down band faster. Along with a 3.8 or 4.2 band lever
to allow a clean 2-3 shift. This would be for a VB with
no low band apply in 1st. If you have band apply in 1st
you might need a higher rate spring in the low/rev servo
to allow a clean 1-2 shift. Griner VB uses enlarged
low/rev servo passage to help unload servo upon
release. In a Transbrake application, the 15 springs
help release the direct clutch faster when you release
the button to prevent the direct clutches from dragging
during launch. When the line pressure is 180-200,
typically have to reduce the band lever ratio to 3.2 or
2.9 so the kick down band strut will not deform. A lot
of testing is needed to fine tune combination. I know
Randy who sells many parts on the board has done
a lot of testing.

Re: 727 front clutch # springs vs front clutch restrictor size [Re: Brad_Haak] #3061645
07/22/22 02:52 PM
07/22/22 02:52 PM
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Rio Linda, CA
John_Kunkel Offline
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Originally Posted by Brad_Haak
The RMVB is supposed to not require any restrictor, FWIW.


The restrictor doesn't have to be in the case, it can be within the VB separator plate.


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Re: 727 front clutch # springs vs front clutch restrictor size [Re: Brad_Haak] #3061702
07/22/22 08:02 PM
07/22/22 08:02 PM
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Benton, IL.
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DaveRS23 Offline
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I use Dorman #555-115 3/8" mini freeze plugs. Dorman calls them cup expansion plugs. Press one into the passage with a .090" hole and go from there. .090" is usually too small and allows a flair up. But is a good starting point. It usually ends up close to .100". When I am lazy I just put grease on the next size drill bit and drill it in place if it needs opened up. Of course the better way is to screw a sheet metal screw into the restriction and pull it out with a claw hammer.

Be sure to check the shift at the temp that you usually run because the fluid temp can affect the amount of flair or overlap. It is hard to get perfect through a variety of temps. You may have to make a choice towards a slight flair of slight overlap.


Master, again and still
Re: 727 front clutch # springs vs front clutch restrictor size [Re: DaveRS23] #3061789
07/23/22 09:12 AM
07/23/22 09:12 AM
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Loudoun County, VA
Brad_Haak Offline OP
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I did a good bit of reading up on the relationship between line pressure, kickdown lever ratio, number of springs in front clutch, and restricting the front clutch apply circuit. I am pleased to say that I am less ignorant today than I was yesterday. grin


2021 Challenger 6.4L Scat Pack 1320 (2022)
100% stock: 1.680, 11.894 at 113.75 (DA 175 ft)
wheels, tires, air filter: 1.714, 11.833 at 115.80 (DA 310 ft)

1973 Challenger 452 ci street/strip (2008)
pump gas, DOT radials: 1.454, 10.523 at 126.44 (DA 514 ft)
Re: 727 front clutch # springs vs front clutch restrictor size [Re: Brad_Haak] #3061838
07/23/22 12:36 PM
07/23/22 12:36 PM
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fredericksburg,va
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cudaman1969 Offline
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Looking up my other question n another post and saw this. Maybe the reverse valve bodies use these different. But this diagram shows the front clutch only engaged in drive-low? And rear clutch all the time in forward gears. What gives here?

image.jpg
Last edited by cudaman1969; 07/23/22 12:37 PM.
Re: 727 front clutch # springs vs front clutch restrictor size [Re: cudaman1969] #3061839
07/23/22 12:42 PM
07/23/22 12:42 PM
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fredericksburg,va
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cudaman1969 Offline
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Then looking at the oil circuits with drive it shows the front clutch engaged? Misprint?

Re: 727 front clutch # springs vs front clutch restrictor size [Re: cudaman1969] #3061854
07/23/22 01:48 PM
07/23/22 01:48 PM
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Rio Linda, CA
John_Kunkel Offline
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Originally Posted by cudaman1969
But this diagram shows the front clutch only engaged in drive-low? And rear clutch all the time in forward gears. What gives here?


You're misreading the chart. Drive has three modes, Breakaway (1st gear with no rear band apply), Second and Direct. The front clutch is only engaged in Reverse and Direct. Yes, the rear clutch is applied in all forward gears.


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Re: 727 front clutch # springs vs front clutch restrictor size [Re: cudaman1969] #3061855
07/23/22 01:49 PM
07/23/22 01:49 PM
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Fulton County, PA
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CMcAllister Offline
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Originally Posted by cudaman1969
Looking up my other question n another post and saw this. Maybe the reverse valve bodies use these different. But this diagram shows the front clutch only engaged in drive-low? And rear clutch all the time in forward gears. What gives here?


That is correct. Front (direct or high) clutch only applied in reverse and high gear. And to apply the transbrake.


Misread the question. The answer is accurate otherwise,

Last edited by CMcAllister; 07/23/22 06:58 PM.

If the results don't match the theory, change the theory.
Re: 727 front clutch # springs vs front clutch restrictor size [Re: CMcAllister] #3061859
07/23/22 02:00 PM
07/23/22 02:00 PM
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Fulton County, PA
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CMcAllister Offline
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Just as with the suspension, springs and the energy stored in them affect how fast things happen. In the past, I've used a balance between the spring load in the front servo and the front clutch to get to 2-3 shift where I wanted it. Mostly in the servo, since it's easier to deal with. Unless it was a transbrake deal. Different deal.

As with most of this stuff, data logging, rather than just listening to it, is invaluable.


If the results don't match the theory, change the theory.
Re: 727 front clutch # springs vs front clutch restrictor size [Re: John_Kunkel] #3061883
07/23/22 04:10 PM
07/23/22 04:10 PM
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fredericksburg,va
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cudaman1969 Offline
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Originally Posted by John_Kunkel
Originally Posted by cudaman1969
But this diagram shows the front clutch only engaged in drive-low? And rear clutch all the time in forward gears. What gives here?


You're misreading the chart. Drive has three modes, Breakaway (1st gear with no rear band apply), Second and Direct. The front clutch is only engaged in Reverse and Direct. Yes, the rear clutch is applied in all forward gears.

Hard to misread ‘disengaged’ right across from drive (breakaway)

Re: 727 front clutch # springs vs front clutch restrictor size [Re: cudaman1969] #3062098
07/24/22 02:14 PM
07/24/22 02:14 PM
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Rio Linda, CA
John_Kunkel Offline
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Like I said, there are three modes in the Drive box. Breakaway (where it's disengaged) is 1st gear, Direct (where it's engaged) is 3rd gear.


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Re: 727 front clutch # springs vs front clutch restrictor size [Re: John_Kunkel] #3062301
07/25/22 08:22 AM
07/25/22 08:22 AM
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Ontario Canada
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Hutch Offline
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Neat question and a good one for sure. Is this question in regards to using an auto shift vb or a reverse manual type vb? In an auto shift or forward manual shift, there are so many variables, rocker ratio, vb year, hole dill sizes, vb channel casting sizes, shift kit modifications being made etc to determine a combination that works well and provides clean shifts.


Hutch

Re: 727 front clutch # springs vs front clutch restrictor size [Re: Hutch] #3062317
07/25/22 09:27 AM
07/25/22 09:27 AM
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jwb123 Offline
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I think the big question is when using a restrictor or not is who engineered the valvebody or shift kit. Timing of the 2/3 shift is the weak point of a 727, several things mentioned affect it, What I have seen is that many of these 727's have been is service for what well over 30 years? How many different times have they been built and modified, and how many people can recognize when rebuilding one what modifications have been done before? Plus a lot of aftermarket orifice plates have no markings on them to tell you if they are modified. So just to be careful any discussion on what number of springs to use depends a lot on whose components you are using and how many times has somebody before you drilled or restricted a passage, and how. I have fixed several problems transmissions, that the root cause of the failures were modifications done over the top of modifications.

Re: 727 front clutch # springs vs front clutch restrictor size [Re: John_Kunkel] #3062324
07/25/22 09:51 AM
07/25/22 09:51 AM
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fredericksburg,va
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cudaman1969 Offline
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Originally Posted by John_Kunkel
Like I said, there are three modes in the Drive box. Breakaway (where it's disengaged) is 1st gear, Direct (where it's engaged) is 3rd gear.

Yep, not used to the term break away.

Re: 727 front clutch # springs vs front clutch restrictor size [Re: cudaman1969] #3062393
07/25/22 12:57 PM
07/25/22 12:57 PM
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Rio Linda, CA
John_Kunkel Offline
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They use the term breakaway to differentiate between 1st gear in Drive and 1st gear in manual low (1). Only difference is the rear band applies in manual low to provide deceleration braking.


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Re: 727 front clutch # springs vs front clutch restrictor size [Re: John_Kunkel] #3062481
07/25/22 03:38 PM
07/25/22 03:38 PM
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north of coder
moparx Offline
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i remember somewhere you could tap the case for 1/8" npt. the hole size in the case was already the size needed for the tap.
then use a female hex pipe plug, drill the plug for the restriction size you wanted, then screw in the plug, keeping it slightly below the case surface so the valve body would bolt up flush.
anyone ever try this ?
beer

Re: 727 front clutch # springs vs front clutch restrictor size [Re: moparx] #3062556
07/25/22 07:42 PM
07/25/22 07:42 PM
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DaveRS23 Offline
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Check my earlier post for an easier way to make the restriction.


Master, again and still
Re: 727 front clutch # springs vs front clutch restrictor size [Re: DaveRS23] #3062957
07/27/22 10:08 AM
07/27/22 10:08 AM
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north of coder
moparx Offline
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i saw that Dave. up
beer

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