[TTS]

Originally Posted by screamingchief

That's not exactly how it is according to both my trans manuals...

The only time the low-roller clutch is ineffective in manual low is when the engine is decellerating and the trans is engine braking,then I agree the low-roller de-clutches (ineffective) and over-runs,but as soon as your back on the gas it is indeed effective again,as it is in auto low as well.

If the low band is ON the low roller is INEFFECTIVE. The low band is ON anytime low has been selected, it doesn't change with acceleration or deceleration. The carrier will not turn any direction when held by the band, I don't know how else to explain it. Explain how the carrier can spin through the one way clutch with the band applied .

Originally Posted by screamingchief

Agree with this,and the comments afterwards too,I did'nt mention that difference as it was'nt really relative in the context of my comment,I was discussing the manual power flow thru the trans and gear train,not the hydraulic circuits that activate the elements needed to achieve that power flow.

Understood. I added these comments so someone didn't add to the post that I had left them out. And for general discussion- when all the facts are out there problems are easier to understand.

Originally Posted by screamingchief

That was one of the other dozen or so elements I was refering to in my comments.

So you agree that more than the manual valve is being used in manual low now?

No! Put down the oil circuit diagrams and look at the transmission. There are exactly 3 things that happen directly related to low being selected @ the manual valve.
1. Oil travels to the large spool of the 1-2 shift valve to force a downshift if possible. There is no brake control here, just signal oil to move the shift valve for a 2-1 shift. If the valve can move against modulator oil a shift will happen.

2. Oil travels to the outboard end of the accumulator control valve to position it open for servo control. This is backside oil- an accumulator if you will- to reduce apply area of the oncoming servo. If this valve was stuck in the bore anywhere else along it's travel the band is coming on, just firmer.

3. Oil travels to apply the servo. Oil is going to the servo hell or high water, if there are leaks in the circuit or not. The band may not be able to hold with the reduced
pressure, but if there's enough pressure to move the car there's enough to apply the servo. Low oil travels to the servo if it makes the downshift or not!!! Are you with me? The only thing that keeps it from applying is the presence of D oil on the front side, and the addition of 2nd accumulator oil. Both sides of the servo are equal. Does your book show 2nd gear with low selected?

Originally Posted by screamingchief

I'm not arguing that some of the true relevence of some of those could be considered mostly unimportant in the grand scheme of things here though,just stating that they are other elements involved in the deal...


Looking at the flow path,I agree with these comments completely.

That's why I said there are like a dozen other elements in the hydraulic flow path in manual low.


I could see that,with the TCI V/B kit I used on that TH-400 I mentioned earlier it indeed used a modified 1-2 shift valve,and the kit included a pressed in expansion plug for that hole,so could be that plug was'nt a good fit and it was pushed out by the hydraulic pressure or such.

But that's pretty much like I said earlier,somewhere pressure was being exhausted that should not have been,I just never figured out 100% where that was with that specific trans,I only had some inklings where the issue may have been.

I was just never really worried enough about the loss of engine braking at the time to chase down the root cause of that issue...

If that plug is blown out the forward clutch and reverse band are not going to last long as low range is selected. I don't have any diagrams, you may want to see if that causes a leak in auto as well. I don't plan on leaving the plug out so I'd prefer to not research it .

Originally Posted by screamingchief

More or less were trying to say the same things TTS,just in very,very different ways...

That's part of the problem for those not familiar with the workings of these deals,the confusion factor,even the manuals dont always agree on how best to describe the same things,even terminology varies on certain things,so when the non-tranny guy hears the tranny guy(s) spouting off what's going on,he's often lost as to what those words actually mean.

I like a good transmission discussion, they're hard to come by.