727 front clutch # springs vs front clutch restrictor size

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.

EDIT: It's got a 4.2 lever

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?

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.

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

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.

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.

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?

Then looking at the oil circuits with drive it shows the front clutch engaged? Misprint?

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.

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,

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.

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

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.

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

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.

Yep, not used to the term break away.

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.

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 ?

Check my earlier post for an easier way to make the restriction.

i saw that Dave.

A drilled cup plug certainly works, but a screw-in part makes more sense to me if the size is still to be worked out.

Why?

Same reason it's a better idea to have replaceable screw-in carburetor jets than a fixed-size metering plate that you have to plug and/or re-drill every time you need to make a change. Surprised you even asked...

the nice thing about using a 1/8 npt female hex pipe plug, is the case hole size is perfect as is. just needs tapped for the plug.

I'm surprised you are trying to make that particular connection.

I do my share of carb tuning. And have done my share of this with the trannies. I don't see the association you are trying to make between the two, but if you somehow see some kind of advantage to tapping the case, more power to ya.

Good luck.

The advantage of a threaded socket-head plug to a cupped plug is ease of removal. If you need to experiment with different sized orifices, the advantage of a plug that can simply be unscrewed will be apparent.

To remove the plug I simply screw a sheet metal screw in it and pull it with a claw hammer. Not everyone has taps, but most people have a claw hammer. Either way gets the job done.

How about this; if you have the tap, then tap it. If not, use the plug?