Trans Probs

STRACER

New Member
What exactly does line pressure do in a trans? Does it control when and how a trans shifts or what. I am having a problem with my car shifting very high and acting like it is slipping. Someone told me it could either be too much line pressure or just a slipping trans that needs fixing or replacing. When you get into in first it bounces off the rev limiter and won't shift under normal driving until around 3200.

Driving in traffic is a B!@#h.

If anyone can help, please do I am ready to get this thing running right.
 
Line pressure is the terminology used to describe the clutch/band apply pressure. It is designed to follow the engine torque through the rpm band. On the 200-4R the TV cable tells the transmission where your right foot is. Older automatics used vacuum modulators for that purpose.

The valve body takes this input signal and modulates it for various fluid circuits like a hydro-mechanical computer.

Your particular malfuctions sound more like a possible lack of line pressure if anything. Reduced pressure can result in slipping. I would recommend three things at this point.
  1. Take it easy on the transmission until you straighten it out.
  2. Check your TV cable adjustment to be sure it is correct.
  3. Have a line pressure check performed on the transmission as that is a good diagnostic procedure.
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Where should the TV cable be set at?

What should line pressure be?

I am planning on checking it out this weekend.
 
To adjust the TV Cable skip the book method and do this: Press the 'D' shaped lock button on the adjuster and loosen the cable setting (The black housing that the metal cable is in will move forward). Now, have someone floor the gas pedal while you check to see if the throttle plate is open all the way. Usually they are off a little and will wiggle. Do whatever you have to do to get it open solid. Now, with the pedal still floored, press the 'D' button and pull the cable casing (the black tube) back as hard as you can (putting maximum tension on the metal cable) and release the button. You now have the engine, tranny and gas pedal all in sync at WOT. Mark the cable casing so if for some reason it gets moved you can know where to put it again. The problem with the 'self adjust method' is that it bends things and puts them permanently out of whack. It is also the full TV setting, which is theoretically what the GM method does.

Line pressure will depend on what has been done to it and what tranny is in the car (not always original). In O/D and D you should see a minimum line pressure of @70 (again, depending on what is in it, it could be lower or higher) and when you stall it or pull the TV cable it should at least double, but expect 160- 170 but as high as 200+ to 250 with oversized boost valves. D2 and D1 should stay steady at a max pressure but depends on boost valve but at least 160-170. Reverse will be higher at minimum and max than the drive ranges. I hate to be so vague but there are so many variables. What you want to se though is that line at least doubles and that pressures are steady at all ranges.
 
As far as the low RPM shifts are concerned, you may want to check if the governor spring is still in place. This would affect the low RPM shifts. It happened to me one night after a 1/4 mile pass with excessive wheelspin on street tires. No low RPM shifts! If you pull the pan, the governor is located under a plate with 4 bolts on it, toward the rear. HTH.

Geoff
 
Does anyone have a pic of what the govenor spring should look like installed correctly. I am going to pull mine out Saturday morning and would like something to go by.

My car started wining yesterday and I think it might be the trans but I don't really know. If anyone has any suggestions please let me know.
 
Governor

You can't see it in this photo, but the spring goes between the governor shaft and the smaller of the two weights. It is only held in by a small dimple, and sits perpendicular to the governor shaft. Hopefully this is the problem, as it was in my case! :D

Geoff
 
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