Originally Posted by FranksCustomTrans

What issue are you having drivability wise? I have been doing this for years with no functional issues. . Line preseure in reverse and forward varies with throttle all operation normal though PRN to Drive a little firmer.

Originally Posted by MaroonMonsterLS1

Up next is Line Bias
This is a very commonly misunderstood valve. And there's lots of guesswork across the net if you go searching.
I hope we can help make some sense of it here.

The line bias valve is very similar in operation to the TV Limit valve...It's just a limiting valve. But in this case, the Line Bias valve is placed between the TV and the Boost valve & accumulator valve.
The line bias valve turns TV oil into MTV oil. MTV oil is what's fed to the boost valve in the pump to control line pressure.
The Line Bias is intended to help give a quick initial line pressure rise, then taper off into a more gradual line pressure rise.
We want the pressure rise to taper after a certain point in stock vehicles because otherwise the shifts at heavy throttle would become unnecessarily firm.
Stock vehicles don't want/like/need to be unnecessarily firm.
BUT...they do need a quick initial rise to be capable of holding the tq the engine is producing.
In stock form, the Line Bias valve allows pressure to rise linearly until about half throttle...then it begins to taper off.

This is because Engine tq is not linear to throttle position. It follows a curve with a steep slope initially that tapers off.
At 50% throttle you might have 75% of max torque.
We want line pressure and shift firmness to follow the engine tq, not the throttle position.
This poses a problem with the Throttle Valve. Remember from above the TV is linear.
So, how do we make sure line pressure rises differently than TV rises? With the Line Bias Valve!

The line bias valve acts like a bouncer at a party.
When the party is empty, the bouncer will just let anybody in the line walk right in.
As the party starts to fill up and the venue is nearing capacity...he has to slow the number of people he can let in.

The line bias valve starts in the open position. It will allow TV oil to freely pass into the MTV circuit. For this stage of Line Bias operation, MTV is equal to TV. This gives the quick
MTV oil is fed to the end of the valve and tries to move the valve against spring pressure.
As TV pressure (and MTV pressure) starts to rise the valve begins to close against the spring. As the valve closes MTV will no longer be equal to TV. It will be less than TV.
This gives the "taper off" effect we're looking for so that the shifts and pressure don't get out of control.



MTV oil acts on the boost valve which controls line pressure
MTV oil also acts on the accumulator valve. This valve is used to control shift firmness. As MTV pressure tapers off...so will the accumulator oil pressure...which will keep the shifts firm but not let them "run away" and get too firm.

Now...how/why might we modify the line bias valve? Anybody that's installed a shift kit and paid attentiion to the instructions will notice that the line bias valve is one of the most commonly modified valves across any and all kits from whichever brand.
Some brands have you install a stiffer spring. Some have you block the valve entirely.
This is done because the line bias valve can limit the maximum achievable line pressure. So increasing the pressure allowed by the line bias valve will increase the max pressure the trans is capable of making.
Increasing the MTV pressure also means accumulator oil pressure can continue to rise for longer which leads to firmer and firmer shifts.
MTV oil is often modified because most performance or heavy duty based kits are OK with having more and more pressure with firmer and firmer shifts as throttle continues to increase. The kits aren't worried about a grandma in her 83 monte carlo complaining about a firm shift on the way to church.

A stiffer spring will allow MTV to match TV pressure for longer. It will also allow max line pressure to be higher.
Some kits have you block the line bias valve entirely. This means that MTV will always equal TV pressure.

I've attached some graphs that demonstrate how different springs can affect the MTV oil pressure vs TV pressure. And how that will affect line pressure in the trans.
These graphs are not gospel truth, TransGo I'm sure has EXACT spring rate charts but I haven't been able to source them, so this is data I gathered weighing and comparing different springs from Kits I've used over the years. There's a little variance for sure, but you'll get the visual which is the real goal.

Stock Form MTV oil raises quickly then tapers off at around half throttle (just like stock engine tq)
Red transgo spring raises quickly then continues to raise for alot longer until it finally starts to taper off. At around 85% throttle.
Blocking the Line Bias valve open means MTV will just track linear with TV oil.

I know that was really long winded...maybe even turned into rambling.
No Magazine editors here to help make sense of my rambling. But I hope somebody can gain something from it.
If anyone has questions or comments please don't hesitate to chime in! Thanks to those above who already have chimed in and shared some good tidbits.

Originally Posted by FranksCustomTrans

Little simple mod I do to allow a bit more adjustability of the TV . Does not seem like alot but as we all know with a 700r4 or even a 200r4 a little with the TV cable is A lot . I do on lathe but can be done several ways, Just gives throttle valve plunger a bit more travel.

Originally Posted by sjsingle1

what exactly are we seeing here ? does this add to the setting of the TV valve?

Originally Posted by sjsingle1

gotcha.....this is the stock valve modified ? do you ever use the trans go valve ?