[screamingchief]

Originally Posted by TTS

It's getting old being the only one to bring facts to the discussion.

No offense intended,but that comes off sounding kinda arrogant on your part,,,what brought that out???

This has been friendly enough,I'm not looking for a dust up,and if that's where this is going I'll be outta here as I really dont need the grief either.

Originally Posted by TTS

No, the higher pressures do not effect anything other than apply.

I sorta disagree with this,pressure affects how many things operate.

If not then why change it?
Why not just keep the pressure the same everywhere all the time???
Does not shift timing change with more pressure?
Does not shift firmness change?

Or do you include those in that "apply" comment??

And then why do we also often change certain springs when we bump up the line pressures?

Originally Posted by TTS

I need a circuit diagram to tell you how pressure is increased in low range, would assume through the detent regulator valve. Instead of speculation maybe you could research that since you have a diagram.

Originally Posted by TTS

For those who may be interested, the boost valve signal is from the manual valve in L or 2. It's routed from the 2 position that's active in both ranges.

Yep,intermediate oil is indeed responsible for the line pressure boost in low ranges,the actual boost happens at the pressure regulator valve,that intermediate oil applys line pressure to the boost valve inside the pressure regulator assembly and that increases the boost springs tension and that inturn bumps up the line pressure.

The boost pistons diameter is pretty small so the effect is controlled somewhat.

Pretty much the same as shimming the spring or a stiffer spring raises the line pressure.

Sure the intermediate oil starts at the manual valve,I'll readily admit that,but that's not the only link in that chain,the fluid path for that intermedaite oil circuit also goes to the 2-3 mod valve,where it has other circuits fighting to tell that valve what to do.

If there were a leak in the intermediate oil circuit at any point after the manual valve or the pressure regulator/boost valve,or some other ailment has occured like a stuck valve or such,it's entirely possible that no line pressure boost will occur,thus the manual valve alone is not the sole controling feature of that flow path.

In hydraulic systems pressure is exerted equally thru-out the entire circuit,that is Pascal's law,look it up,if pressure is lost anywhere in a hydraulic circuit,it is lost equally thru-out that entire circuit,so if a given hydraulic circuit extends past a given valve or such,there lies the possibillity for a leak in another area that may not be directly related to that given point one is looking at.

That's been my point from the start here,TTS you seem to suggest these circuits begin and end with the manual valve,I just disagree with that narrow view,I feel the manual valve just tries to tell the rest of the valves what to do,and then they get to work fighting with all these other forces trying to be sure they are doing the right thing at the right time.

A circuit leak can happen most anywhere,but we cleared that point up already I believe.

I'd post the hydraulic circuit diagrams here for all to see if I could find a way,but they just are'nt readable when I shrink them down enough to fit the forum size posting limits.

I'll keep trying though.

BTW,,,those hydraulic circuit charts in the Ron Sessions book,,,they're from GM,,,I trust their accuracy...

Originally Posted by TTS

So, if the RS 400 book does not show oil at the low servo apply side in L2, he failed to color that passage in.

See above,,,your saying GM failed to do that???

It does'nt show low apply oil at the servo because there is none L2 (or S2 as you seem to prefer that terminology) because there is no need anymore,the trans does'nt want the low-reverse band to apply in manual second,that low oil path has been lost at the valve body,by that all powerful manual valve of yours.

Originally Posted by screamingchief

Then please do explain to us laymen how the trans prevents a high speed band apply when the trans is shifted into L1

That was meant as a rhetorical question,but seeing as it was taken outta context and used here we'll run with it.

Originally Posted by TTS

Happily! Starting with the shift lever in S2, with a stock 1-2 shift valve; In front of the servo there is 2nd accumulator oil and there is second oil between the accumulator and the servo. The entire front side of the servo is pressurized. When the shift lever is moved to L1, regardless of the 1-2 shift valve position, the apply side of the servo will be pressurized via the manual valve. If the shift valve has not moved for a 2-1 downshift nothing will happen because 2nd oil is still present and the servo cannot move forward. As soon as the shift valve moves, second oil is vented, and the servo moves forward applying the band.

This I agree with,never tried to say otherwise,my problem was with the statement that there was low apply oil behind the low-reverse band apply servo in S2 (L2) when the diagram clearly shows there is none.

I agree there may be some low oil trying to apply the servo momentarily while the car is still in S2 (L2) after the initial downshift to L1 at the manual valve,this charges the servo to prepare for the band apply,meanwhile the valvebody is sorting out what exactly to do based on the govenor input to the 1-2 shift valve and such,but that low oil does'nt stay there long if the manual valve is moved back to the S2 (L2) position as it will vent the circuit to the pan via the manual valves relative position.

What would be the purpose of having low oil trying to apply low-reverse band servo in S2 (L2)?

It's not gonna affect the operation of the accumulator much at all.

And where is this low apply oil coming from if the manual valve has "dropped" that circuit completely when the shifter was moved to S2 (L2).

At times I feel were saying the same things,just in very different ways.

Ask me this is getting to be like a "who's on first" routine...

Here's how I see S2 (L2) as it concerns the servo/accumulator,there is 1-2 oil on the one side of the accumulator piston trying to push the accumulator piston to the bottom of it's bore's (one bore also happens to be the inner bore of the servo apply piston),when it gets there it also will try to push the servo to full release as well (as long as there is no low apply oil fighting it),when the range selector was moved to S2 (L2) that opened up an exhaust path for the low oil circuit,the action of the the 1-2 apply oil on the accumulator piston bottomed out in it's bore just pushes the low-reverse servo to full release and exhausts that low oil circuit.

The delay caused by that process (ie. exhausting the low oil) is how the accumulator has slowed the apply of that circuit (1-2) and cushions the apply of that circuit,during that process it is also "charging" the 1-2 accumulator in preperation for it's continued shift timing duties.

Meanwhile the intermediate oil has begun pushing on the other side of the servo trying to push that accumulator piston back up the bores (this also happens to be filling the inside chamber of the servo piston),but it also has to be pushing against a heavy spring as well,and seeing as it can necessarily "beat" the 1-2 apply oil and that spring it will in essence just "cushion" the apply of that circuit as that action just delays the apply of full pressure momentarily.

Those two circuits time the apply of the intermediate clutch and band dependant on input from the remainder of the valves in those circuits.

I can see zero reason for any low-reverse servo "apply" action in S2 (L2).

Likely that's why there is none show in the diagrams as well.

Originally Posted by TTS

Your turn. Using the RS book, you tell me how it says low braking is achieved. And more importantly in L2 where is this magical apply oil? If it works better for you, just come up with your own tale of how it happens. Maybe I'm off my rocker, show me some facts.

Engine braking in L2 (S2) is from the intermediate band,not the low-reverse band,entirely different servo from the low-reverse servo...

The low-reverse band is not applied in L2 (S2).

Low-reverse oil controls the low-reverse (rear) servo.

Intermediate (cl) oil controls the intermediate band (front) servo.

We must not be on the same page with this whole L1-L2-S2 deal or something???

Again I expect a lot of the back and forth is more about terminology and reading comprehension and writing composition on both our parts,and this forum is not the ideal place for straightening out the differing issues of such at times.

But I dont expect that will end anything here...

I'm not sure how much more I feel like going on on about this topic here.

It seems like the language/terminology differences alone could take a lifetime to work out,some times two different fellas just cant get on the same page even when they both know what's going on,that barrier is often just too high to climb,and neither side seems to want to bother to work that deal out.

I'm pretty much done with this...

I'm gonna go have a beer or two!