juvius

hello.
i've had this car for a few weeks now. it's an 81 auto. the previous owner put another tranny and torque tube in it before i got it.
the problem is as follows: when i give it gas it doesn't have any zip to it, in fact it takes of rather slowly in both reverse and drive. Also, when going down the road, it will get up to speed, but will not shift until i let off the gas. it seems to be full with fluid.
if anyone know what my problem is or what it could be, please let me know. I have the workshop manual cd's but can't figure it out on my own. if your answere is a little complex and would be easier explained by phone please call me at (567)224-7538 or send me your number by message and i'll call you.

thanks in advance,
steve

soontobered84

Does it seem to be engine related or transmission related?

juvius

engine seems to run strong, so i'm thinking probably tranny.

ZEUS+

Not shifting until you let off the gas sounds like a control pressure problem. A good start would be to check the bowden cable adjustment.

juvius

would the bowden cable adjustment cause the problem with no take off power also?

danglerb

The reason I have an 83 5spd is that I owned a 81 automatic. Yours sounds like it has a problem, but its just not a fast car off the line in early year US AT models. The 0-62 mph time for a US model 81 AT is 8.5 seconds with a 16 second 1/4 mile time.

Once you get to 30 to 40 mph the performance is fine, but off the line it failed to meet my expectations. Later model years the gap between AT and manual is much smaller, but its hard to make a "nice" AT that has the sort of jump off the start that a clutch can give.

juvius

i understand what you're saying, but the way my car is now, you could take off faster on a bicycle

danglerb

Has anybody that knows 928's looked over the car?

No point in spinning your wheels, post your location and find out who can look it over, and skip all the guessing stages. Even if we guess right, somebody local is going to have to see the car to fix it, and they won't need to guess.

juvius

thanks for your responses
i'm in plymouth, oh.... it's located in north central ohio. i won't be taking it to anyone else to fix, cause i want the satisfaction of knowing "i did this"... but i do like the idea of knowing someone a bit more local that could help me out. if i get too hung up, my dad is a gm mechanic, so i figured even if he don't know porsches, he has experience. that's if i can get him to take time for me.... that's a hard one...

WallyP

First: Go to Page 37-115 in the manual.

Look under the intake tubes near the front of the engine, and find the cable quadrant (the bellcrank that all of the cables snap onto).

Figure out which cable runs from there to the firewall (this is the cable from the pedal to the quadrant);
which one runs from there (the quadrant) under the intake manifold to the throttle body;
which one runs from there to the left front fender (this is the cruise control); and
which one runs under the firewall toward the rear of the car (this is the Bowden cable that tells the transmission how much throttle you are giving the engine).

Make sure that the cable from the quadrant to the throttle body has from zero free play to just a tiny bit of play.

Adjust the Bowden cable to the transmission until it has zero free play.

Next: Jack and support the car so that you can work SAFELY underneath with the engine running.

Find the transmission fluid tank on the right side of the transmission, and clean it so that you can see the indicator lines clearly.

The following conditions MUST ALL be met:
- The car MUST be level fore-and-aft and side-to-side.
- The engine MUST be running.
- The transmission MUST be in neutral.
- The fluid level MUST be between the top two lines on the tank.

If you have to add fluid, clean the area around the cap carefully, and add Dexron until the fluid level is between the lines with ALL of the above conditions met. It takes very little fluid to go from the middle line to the top! You can use a small hand pump, or a funnel located outside the fender with a plastic tube reaching to the tank to add the fluid.

Next: Look on the left side of the transmission and find the vacuum modulator. This is a round metal pie-pan-shaped device, with a vacuum line attached. With the engine running, make sure that you have full manifold vacuum on the line, and that the line is propely attached.

Next: Go to Page 38-103 in the manual and read the entire Section C, telling how to check the stall speed. If the stall speed is too low, you will have very poor take-off performance.

danglerb

I admire your self reliance and few things match knowing you fixed something yourself. You still might want to have a professional or at least knowledgeable person do the diagnosis.

Listen to Wally and Zeus, not me (speculation edited).

Good luck,

juvius

thanks WallyP

i'll try that out in the morning. looks like i need to find out what transmission type i have before i check the stall speed. i read that, i'll have to go borrow a tach from my dad. is there a way to adjust the stall speed? also, stall speed is new to me. does it actually stall or is that the point where the rpm's level off? sorry, I have the ability just not the knowledge.

juvius

thanks danglerb

WallyP

Stall speed is set by the design, and is not adjustable (unless you get a custom torque converter).

As you can see in the manual, this is a diagnostic procedure.

Go to our web site, then tips/links, then tech specs, then transaxle.

danglerb

A rough answer to stall speed, its how fast the engine can spin without the wheels turning.

The torque converter "slips" out is a lower rpm than in, that wastes power (force times distance, and the lower out rpm is lower distance), but the force or torque goes through. So with a 1600 rpm stall speed you get the torque the engine produces at 1600 rpm when the out is barely turning. Torque varies with rpm from very low at low rpm to a peak about 3500 rpm on a 928 and then dropping as rpm increases. 1200 rpm stall allows less torque then something closer to 3500. Lower stall speed makes better mpg and better driveablity, really high stall is only practical on a drag car.