Transmission Line Presure

Can someone explane what transmission Line Pressure is? What does it do? How can it get out of specs?

Does a 97 lesabre have line pressure?

Thank you,
Chris.

Main line pressure applies clutches, bands, this is the heart of any auto trans function, to put it simply.

Does the 97 have it? One camp says it doesn't. It's totally controlled by the computer.

Chris.

Every auto trans has main line pressure from the pump or it is a no go, on older vehicles the tv cable usually modulated the pressure along with a vacuum modulator, from about 91 up most GM cars were pcm controlled by analog engine/speed inputs and solenoids in the valve body. You seem to have a specific issue in mind, what is it?

After I put a new(er) motor in, since then when I accelerate, the first part of the throttle it accelerates fine. When I push the last bit, like to pass, the RPM's go way up, but I don't go like I used to.

Doesn't feel like trans slip, no code ether. I was thinking it might not be shifting right. On the freeway at 60, If I floor it, I don't accelerate very fast but the RPM's go up. Like in stead of going from 4th to 3rd, it goes into 2nd. My macanic says to check the line pressure. The DS at the trans shop says this model doesn't have line pressure, it's all controlled by the computer.

Dont know what to look for,


Chris.

You need to have someone who knows what they are doing drive the car for a diagnosis.

I agree maxwedge..

Happy....... You have a 4T60E, The line pressure is controlled with the Vac Modulator, the line pressure in this trans is in no way controlled electronically... All 4T60E's are the same way( All of them from 91-99 )....

The 4T65E does have Electronically controlled line pressure( all of them 97 to Current )... 97 was a Mixed year for the 4T65E and mostly in the Supercharged Models... all the rest had the 4T60E

I agree the Trans needs a real diagnosis...

Chris, when you replaced the motor, are you sure you reconnected the trans modulator vacuum line to the right place. The latest description of your problem, sounds like the tranny is "pressure shifting" rather than modulating pressure. Do you have a vacuum digram on your radiator support, similar to the one below? This one is for an L36, but not very clear. The second picture is an actual shot of my L67 vacuum ports (modified) but in original locations. The modulator vacuum line goes to the bottom throttle body port "T" fitting and the other side of the "T" goes to the fuel pressure regulator (FPR). Track yours down & let us know where it is connected. A few pics would help.

http://img517.imageshack.us/img517/8376/l36vaccumdiag.jpg

http://img411.imageshack.us/img411/5710/vacredo.jpg

You need to have someone who knows what they are doing drive the car for a diagnosis.The guy who knows what they are doing said mine doesn't use 'Line Pressure', its totally controlled by the computer. :runaround:

I think mine is hooked up right. I saw one rubber piece was cracked, so when I replaced it, I looked at the diagram. I will take a picture.

Hope I can get this figured out, the gas mileage is killing me during the rescission. Plus I've been in a few close calls because I couldn't accelerate out of it.


Chris.

The vacuum connection appears to be right @ the TB, just be sure the other end goes to the modulator. Have you removed the vacuum line from the modulator and checked for the presence of trans fluid?

No, don't know what the transmission modulator is.

Aren't you going to explane it more?

This is a Modulator, located on the front of the trans.

http://info.rockauto.com/getimage/getimage.php?imagekey=55864&imageurl=http%3A//info.rockauto.com/Honeywell/FM2333_031006.jpg

I think mine had a hose coming off it, then a black piece. The guy at the trans shop took it off, then blew into it. It was clogged. He said it was not a big deal. When I got home, I took it off and blew it out.

Chris.

I think mine had a hose coming off it, then a black piece. The guy at the trans shop took it off, then blew into it. It was clogged. He said it was not a big deal. When I got home, I took it off and blew it out.

Chris.

I hope the opposite end of the line was removed from the modulator when the tech blew through it.

The pressure test port is on top of the trans just rearward and slightly right of the case vent fitting. Remove the plug and connect a 350 PSI test gauge to the port. With the engine running at about 1200-1300 RPM and NO vacuum applied to the modulator the pressure should be 250-320 PSIG in Park, Rev, and N ranges and about 160-210 PSIG in all other ranges.

At the same engine speed and with normal idle vacuum of 18" Hg applied to the modulator the pressure should be 75-100 PSIG in all ranges except L1. In L1 the pressure should be about 155-175 PSIG with 18" vacuum applied.

The piece he took off he blew through with his mouth.