47/48re 2nd gear servo question.

[Kodiak24V]

trying to up my trans knowledge and figure out what effect different spring rates have on 2nd gear servo operation. 
 

There a 3 holes in the front servo bore. 
 

im assuming the oil comes in through the top hole and pushes down on the top of the piston pushing against spring tension causing the center pin to push down on the band strut  and causing the band to tighten. 
 

question is where does the oil come from? where does it go?

from there what causes the servo to release tension and what are the 2 bottom holes for?

I’m assuming a stiffer spring would cause a reduction in pressure on the servo center pin…

 

or does a spring that has to much tension make the servo release the band faster causing a potential flare 2-3 shift?

[Mopar1973Man]

1 hour ago, Kodiak24V said:

 

question is where does the oil come from?

From the supply pump at the head of the transmission. 

 

1 hour ago, Kodiak24V said:

where does it go?

Most of it just returned to the pan. Oil that is flowing to the torque converter is passed through the cooler before returning. 

 

As for the other questions I'm not sure of. I've only owned one 46RE transmission (1996 Dodge Ram 1500 - Lil Red). I've worked on more manuals than autos sorry to say. 

[Kodiak24V]

57 minutes ago, Mopar1973Man said:

From the supply pump at the head of the transmission. 

 

Most of it just returned to the pan. Oil that is flowing to the torque converter is passed through the cooler before returning. 

 

As for the other questions I'm not sure of. I've only owned one 46RE transmission (1996 Dodge Ram 1500 - Lil Red). I've worked on more manuals than autos sorry to say. 

hey thanks

Does the oil go straight from the pump to the 2nd gear piston or is there other stuff that the oil sees before it makes it to the piston?
 

I looked but couldn’t find a video with a cutaway of the transmission in operation as it’s being shifted and a short explanation of how it works. 

[Mopar1973Man]

Might try hitting the download area and grabbing a factory service manual and it will explain the flow for all the gears. 

[Great work!]

The servo gets applied by the 1-2 shift valve and the 2-3 in the valve body, but its complicated the other holes go more valves and the direct clutch (that's the first clutch nearest the pump end). There is a balancing act that goes on The direct clutch engaged for 3rd and reverse. Pressure gets increased to the clutch at the same time pressure gets decreased  at the servo via the extra holes. Both band and clutch drag for a moment so that there is no flare up in RPM during the 2-3 shift. The process is reversed for down shift.

[Kodiak24V]

21 minutes ago, Great work! said:

The servo gets applied by the 1-2 shift valve and the 2-3 in the valve body, but its complicated the other holes go more valves and the direct clutch (that's the first clutch nearest the pump end). There is a balancing act that goes on The direct clutch engaged for 3rd and reverse. Pressure gets increased to the clutch at the same time pressure gets decreased  at the servo via the extra holes. Both band and clutch drag for a moment so that there is no flare up in RPM during the 2-3 shift. The process is reversed for down shift.

thanks for the knowledge.

 

In order for me to build/fix something I like to know how it works. 
 

So the servo releasing that oil causes it to go back up with spring pressure?
 

the oil that 1st originally forced the servo down is the same oil being released while the piston is in the down position? Just trying to visualize where in the piston stroke the oil is released. 

 

would a spring with to much resistance cause a lack of servo out flow at the lower drains? 
 

I think the “white”heavier spring from a reprogram kit was installed in my trans.

 

my belief is it’s causing issues with the way the oil flows through 

 

Even the high horsepower builds I see on YouTube have a stock appearing spring. 
 

I can’t find a stock spring for sale anywhere so I can try it. 

[Great work!]

The clutch apply pressure shows up on the servo un- apply side. Once that builds up enough to overcome the pressure on the apply side the servo starts to release the band and a valve is tripped that allows fast release of the servo. It's a well orchestrated dance. The springs and orifices in the separator plate time it all. The usual tinkering methods involve changing the band apply lever for more or less leverage. So to answer one of questions it's more than just spring pressure the forces the servo back. 

[Kodiak24V]

55 minutes ago, Great work! said:

The clutch apply pressure shows up on the servo un- apply side. Once that builds up enough to overcome the pressure on the apply side the servo starts to release the band and a valve is tripped that allows fast release of the servo. It's a well orchestrated dance. The springs and orifices in the separator plate time it all. The usual tinkering methods involve changing the band apply lever for more or less leverage. So to answer one of questions it's more than just spring pressure the forces the servo back. 

in my head it seems like the stiffer spring in addition to the full oil dump would cause the band to release early? Causing the flare? 
 

when it happens the harder the throttle the more of a delay between when the band releases and when the clutch engages. I’m assuming or is that backwards? 
 

Does the 1/reverse band have to come off too while all this taking place?

 

Could a poor band  adjustment cause this? 
 

[Great work!]

Yes band adjustment can cause flare up or the opposite bind up. Not to mention band slipping and drum wear while towing heavily in second gear.

 

I'm speculating the heavier spring compensates for the significant increase in line pressure that all built trannys have. Not sure though. The servo shift timing is more about relative pressure differential than absolute. I'm not familiar with all the kits out there.

 

The band anchor thingy called a wedge is a weak link too but causes loss of second.

 

First in drive has no hold back ability because a one way clutch in the back takes over but is useless in reverse so the rear band has to hold the rear drum. It doubles as the hold back element in low range.

[Kodiak24V]

19 hours ago, Great work! said:

Yes band adjustment can cause flare up or the opposite bind up. Not to mention band slipping and drum wear while towing heavily in second gear.

 

I'm speculating the heavier spring compensates for the significant increase in line pressure that all built trannys have. Not sure though. The servo shift timing is more about relative pressure differential than absolute. I'm not familiar with all the kits out there.

 

The band anchor thingy called a wedge is a weak link too but causes loss of second.

 

First in drive has no hold back ability because a one way clutch in the back takes over but is useless in reverse so the rear band has to hold the rear drum. It doubles as the hold back element in low range.

Thanks for all the info!

 

im thinking it could be also be to much space in the clutch. 

 

it has TCS front and accumulator servo. billet triple disc, billet input shaft, billet wedge and brace. Built valve body. 150psi line pressure. 

 

Before all that It would tach the engine out full power 2-3 shift. It was slipping the clutch and ended up killing the frictions I’m assuming. 
 

I was ignorant and trusted the local trans builder. I told them I wanted a 600hp trans.
 

they put a VB kit in it. Left all the stock servos, band strut, ect…  

 

Once I started educating myself bought a pressure gauge and checked line pressure it was 90ish PSI max. the damage to the clutches was already done though. 
 

Now with 150psi it’ll hold tune 4 on the quadzilla with 63/68 turbo, 7x.010 injectors fine. Turn it up to level 6, 150psi line pressure and the clutches will slip when not locked. 
 

I put a different built VB, the band strut/wedge in and adjusted the bands at the same time and that’s when the flare started. 

 The front band is Borg Warner without the holes. I have it adjusted with a 1/4” Allen between the pin and the strut. I may try loosening. I then put TCI front servo and accumulator to see if it was that as it still had the plastic loose garbage in there. just wasn’t sure on the thicker front servo spring because all the performance builds I’ve watched on YT still have the stock spring. 

 

I believe the band is adjusted properly so I’m thinking it may be loose clearance in the direct or forward clutch. I may play with the front band as it didn’t do it before adjusting the band.
The pan had friction material before adjusting the band and it didn’t flare. 

 

I know it needs to come out and I plan to myself when I do the commonrail swap but it would be nice if it didn’t flare 2-3 as it drives/shifts fine up to quadzilla level 4. 

[Great work!]

Try adjusting the band, did your kit or builder have any instructions?

 

Let us know what you find out.

Too tight causes a constant, subtle and almost undetectable drag that will cook your band and drum.

 

If you want to know how it works 

Search the web for Simpson planetary gear transmission. That's the guy behind virtually all the vintage 3 speed automatic transmissions. 

[Mopar1973Man]

 

 

[Kodiak24V]

3 hours ago, Mopar1973Man said:

 

 

Thanks you guys!

 

I’ve got the ATSG book ordered up. GreatWork!’s explainations helped visualize what is happening. 

 

when I get some time I’ll mess with the band adjustment some.

[Mopar1973Man]

Just thinking I might have that book in the download section.