Automatic Trans Adjustment Write Up
08-08-2008, 11:26 PM
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Automatic Trans Adjustment Write Up
Figured rather than continuing to hijack the Why Don't People Like the 928 thread, we'd take this discussion to a new thread for those who might be interested. We were discussing how to adjust an auto trans to get it to chirp tires when shifting into 2 and 3....
First, it is of course recommended to follow the workshop manual's directions for adjusting the vacuum modulator (or vacuum servo) on the transmission. But, if you don't want to spend the money on the gauges and don't have them, this works. We did these adjustments to my car two years ago, and it has been running great, even when it was supercharged last year for a while, and we beat the crap out of it, manually shifting even though it's an automatic, and often shifting at rev limiter. Well he does....I shift a little earlier than that, but it still chirps the tires at close to 4500 rpm and up.
So, if you want to do it at home without the official tools, here's a step by step of the process.
First service the trans (new pan gasket and fluid and filter), then adjust the bowden cable properly to 1 millimeter of play at idle stop. Now drive the car around the block and come back and check the fluid again, car in neutral, emergency brake on, and running. After checking the fluid is right, now drive the car and see if you're happy with it before moving to the next step.
Remove the wire from the kickdown switch by the accelerator and install a toggle switch or momentary button, whichever you prefer, but we use a toggle switch so we can just leave it on. It's already relayed and fused from the factory, as long as you use the wire right off the switch. Don't install your own power source. No need.
Drive the car again, if you're still not happy with it, now go to the next step, which is to remove the rear exhaust hangers so the exhaust hangs down. Remove the exhaust shield next to the transmission. Find the vacuum servo on the driver's side of the transmission (it has about a 1/8 inch vacuum line going to it).
It is recommended that that line be replaced all the way to the front of the car while you are there, because they usually leak on the two rubber sections between the solid hard lines. You have to drop the torque tube to do it right, so run a new line along with your gas line up to the front of the car. Use brake line to run it from the front to the back of the car, and then use rubber line to reconnect the trans servo and vacuum source. If there is any transmission fluid inside that vacuum line, also replace the servo because it's bad.
Now that you have found the vacuum modulator, it has a small rubber cap on it about the size of a dime. There will be something like a T allen wrench under the cap, with notches that it locks into. Turn it two notches to the right. Put the cap back on. Rehang the exhaust, but don't put the shield on until you know you're done. Test drive the car, see how it shifts now. When you're happy with how it shifts, make sure it will shift into 4th at wide open throttle. If it doesn't, now you need to start backing down on the bowden cable, increasing that 1 millimeter gap until it shifts into 4th gear at wide open throttle.
Now at this point, if it's slipping or mushy in between shifts, you need to go back to the modulator (servo) and go another two notches.
Repeat the above process until you've got the car shifting nice and firmly, but don't go further than that because you are increasing the fluid pressure. Eventually you will find that when hand shifting, it will chirp the tires on the shift into 2nd and 3rd, leaving the kickdown switch on. It hasn't failed us yet, on our third car now.
Make sure your trans cooler lines are good too. They are easy to replace at the local auto parts store, just get trans cooler line and good hose clamps, remove the pressed fittings from the hoses, and there's a barbed fitting underneath. Now you can put the cooler line on with double clamps on each side -- never blows off. And it's a lot cheaper than the spendy stock ones.
There are many threads on the kickdown switch bypass if you need a little more info on that. And we believe we have seen threads on the modulator adjustment and bowden cable adjustment as well.
Hope this helps someone!
First, it is of course recommended to follow the workshop manual's directions for adjusting the vacuum modulator (or vacuum servo) on the transmission. But, if you don't want to spend the money on the gauges and don't have them, this works. We did these adjustments to my car two years ago, and it has been running great, even when it was supercharged last year for a while, and we beat the crap out of it, manually shifting even though it's an automatic, and often shifting at rev limiter. Well he does....I shift a little earlier than that, but it still chirps the tires at close to 4500 rpm and up.
So, if you want to do it at home without the official tools, here's a step by step of the process.
First service the trans (new pan gasket and fluid and filter), then adjust the bowden cable properly to 1 millimeter of play at idle stop. Now drive the car around the block and come back and check the fluid again, car in neutral, emergency brake on, and running. After checking the fluid is right, now drive the car and see if you're happy with it before moving to the next step.
Remove the wire from the kickdown switch by the accelerator and install a toggle switch or momentary button, whichever you prefer, but we use a toggle switch so we can just leave it on. It's already relayed and fused from the factory, as long as you use the wire right off the switch. Don't install your own power source. No need.
Drive the car again, if you're still not happy with it, now go to the next step, which is to remove the rear exhaust hangers so the exhaust hangs down. Remove the exhaust shield next to the transmission. Find the vacuum servo on the driver's side of the transmission (it has about a 1/8 inch vacuum line going to it).
It is recommended that that line be replaced all the way to the front of the car while you are there, because they usually leak on the two rubber sections between the solid hard lines. You have to drop the torque tube to do it right, so run a new line along with your gas line up to the front of the car. Use brake line to run it from the front to the back of the car, and then use rubber line to reconnect the trans servo and vacuum source. If there is any transmission fluid inside that vacuum line, also replace the servo because it's bad.
Now that you have found the vacuum modulator, it has a small rubber cap on it about the size of a dime. There will be something like a T allen wrench under the cap, with notches that it locks into. Turn it two notches to the right. Put the cap back on. Rehang the exhaust, but don't put the shield on until you know you're done. Test drive the car, see how it shifts now. When you're happy with how it shifts, make sure it will shift into 4th at wide open throttle. If it doesn't, now you need to start backing down on the bowden cable, increasing that 1 millimeter gap until it shifts into 4th gear at wide open throttle.
Now at this point, if it's slipping or mushy in between shifts, you need to go back to the modulator (servo) and go another two notches.
Repeat the above process until you've got the car shifting nice and firmly, but don't go further than that because you are increasing the fluid pressure. Eventually you will find that when hand shifting, it will chirp the tires on the shift into 2nd and 3rd, leaving the kickdown switch on. It hasn't failed us yet, on our third car now.
Make sure your trans cooler lines are good too. They are easy to replace at the local auto parts store, just get trans cooler line and good hose clamps, remove the pressed fittings from the hoses, and there's a barbed fitting underneath. Now you can put the cooler line on with double clamps on each side -- never blows off. And it's a lot cheaper than the spendy stock ones.
There are many threads on the kickdown switch bypass if you need a little more info on that. And we believe we have seen threads on the modulator adjustment and bowden cable adjustment as well.
Hope this helps someone!
Last edited by Leslie 928 S2; 08-09-2008 at 01:43 AM.
08-08-2008, 11:44 PM
#2
Leslie,
Did Kevin ever rebuild that transmission we sent you? I never heard one way or the other as to if it worked out afterwards. I just heard that it didn't work when you received it and went from there.
Did Kevin ever rebuild that transmission we sent you? I never heard one way or the other as to if it worked out afterwards. I just heard that it didn't work when you received it and went from there.
08-09-2008, 01:00 AM
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Hey Sean, actually, it's currently sitting on the side of the garage. He hasn't yet had time to really address it.
He was able to fix the 85's original Euro trans with parts from our old white 84 US. It turned out in the end to only be the torque converter, which we had. The reason we bothered bothering Roger in the first place, was because we were told by the PO that it was a bad torque tube originally. So that was what we were looking at. But soon Kevin found that the modulator was bad and the modulator plunger behind it was broken. Also the gear oil was none too good in there when we got the car. There was half an inch of sludge in the bottom of the rear.
But it made no noise though, then or now, and runs smooth, so he figured he'd run it for now while he finished the complete rebuild of the car (check our my Welcome our Newest Addition thread of about the purchase date for some info about the rebuild, and there's also a dyno chart in the NJ dyno day thread that was floating around here recently, although the car was really running half-assed at the time).
Anyway, as it turns out, he's going to be using the rear from Roger's trans very soon, because the car's original posi is now acting like an open after a block long burnout recently.
So it turned out to be useful after all...and the car's kickin' *** now!
Don't know what we'll do with the rest of it yet. We have a US trans with a bad case, with any exposed bolt broken off in it, and it needs internal seals (it hestitated going into reverse), so Kevin's thinking about blending the two into one just to have a spare around. That's probably not a bad thing when he keeps tryin' to pump more and more BOOST in his car.
Too bad the Powerdyne doesn't have anymore.
Knowing him, he'll end up fitting something else in there somehow, and I'll end up with his castoffs, as usual. In this case, not a bad castoff for a grocery runner, huh? LOL. I already need new back tires, and my posi works.
Hey Ernest, think I'll get in trouble now?
He was able to fix the 85's original Euro trans with parts from our old white 84 US. It turned out in the end to only be the torque converter, which we had. The reason we bothered bothering Roger in the first place, was because we were told by the PO that it was a bad torque tube originally. So that was what we were looking at. But soon Kevin found that the modulator was bad and the modulator plunger behind it was broken. Also the gear oil was none too good in there when we got the car. There was half an inch of sludge in the bottom of the rear.
But it made no noise though, then or now, and runs smooth, so he figured he'd run it for now while he finished the complete rebuild of the car (check our my Welcome our Newest Addition thread of about the purchase date for some info about the rebuild, and there's also a dyno chart in the NJ dyno day thread that was floating around here recently, although the car was really running half-assed at the time).
Anyway, as it turns out, he's going to be using the rear from Roger's trans very soon, because the car's original posi is now acting like an open after a block long burnout recently.
So it turned out to be useful after all...and the car's kickin' *** now!
Don't know what we'll do with the rest of it yet. We have a US trans with a bad case, with any exposed bolt broken off in it, and it needs internal seals (it hestitated going into reverse), so Kevin's thinking about blending the two into one just to have a spare around. That's probably not a bad thing when he keeps tryin' to pump more and more BOOST in his car.
Too bad the Powerdyne doesn't have anymore.
Knowing him, he'll end up fitting something else in there somehow, and I'll end up with his castoffs, as usual. In this case, not a bad castoff for a grocery runner, huh? LOL. I already need new back tires, and my posi works.
Hey Ernest, think I'll get in trouble now?
08-09-2008, 01:15 AM
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Nice, all of this is in the manual of course as far as the adjustments. It doesn't actually tell you how to get your tranny to shift harder, but it does show the procedure to tighten up the shifting. Make note though, the more you increase fluid pressure, the more chance of failure...be it internal or trans lines. the autos are pretty robust, but use caution, this will speed up the "aging" process of the transmission...not to mention the final drive and CV joints. Still fun though
KDBP is essential for the fun factor regardless of 3 or 4 spd. I always recommend a momentary foot switch on the dead petal up high so your foot doesn't rest on it or when you are actually using to steady yourself in corning. I say the momentary switch because its only natural. The gas petal switch is a momentary switch. Leaving a toggle switch activated is another straight line to early tranny failure. The momentary gives you the KD anytime you want it and without taking your hands off the wheel. JMHO.
I set my autos to shift just under readline, but I think the best thing to do is get the car dyno'd and find out where the sweet spot/greatest tq is at what rpm. You can do this by making runs in every gear and just read your curve. Adjust your shifting to match this and the car will pull through all gears without the wind-out/lag these cars usually have.
KDBP is essential for the fun factor regardless of 3 or 4 spd. I always recommend a momentary foot switch on the dead petal up high so your foot doesn't rest on it or when you are actually using to steady yourself in corning. I say the momentary switch because its only natural. The gas petal switch is a momentary switch. Leaving a toggle switch activated is another straight line to early tranny failure. The momentary gives you the KD anytime you want it and without taking your hands off the wheel. JMHO.
I set my autos to shift just under readline, but I think the best thing to do is get the car dyno'd and find out where the sweet spot/greatest tq is at what rpm. You can do this by making runs in every gear and just read your curve. Adjust your shifting to match this and the car will pull through all gears without the wind-out/lag these cars usually have.
08-09-2008, 03:02 AM
#6
Burning Brakes
Is the speed that the transmission considers to be redline set by the bowden cable? (I know it's the governor, I guess I'm asking can it be adjusted by the bowden cable)
08-09-2008, 05:14 PM
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Nice, all of this is in the manual of course as far as the adjustments. It doesn't actually tell you how to get your tranny to shift harder, but it does show the procedure to tighten up the shifting. Make note though, the more you increase fluid pressure, the more chance of failure...be it internal or trans lines. the autos are pretty robust, but use caution, this will speed up the "aging" process of the transmission...not to mention the final drive and CV joints. Still fun though
Also, in our case, with the supercharger installed, the transmission flaired up on shifting, and it needed to be firmed up to prevent undue slipping.
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08-09-2008, 10:35 PM
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When you're happy with how it shifts, make sure it will shift into 4th at wide open throttle.
08-09-2008, 10:53 PM
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Burning Brakes
The firmness setting helps with shifting flare for modified vehicles, eh? So, does that mean this could be the cure for why my car on the 1-2 shift has a stage where at first the rpms are dropping even though the car is still accelerating, and then you feel it catch and it feels like someone gave it a shot of nitrous? I know my car has this same setting (though for me I don't have to take off the exhaust shield to get to it), but I'm about 400 miles from my ramps right now and don't want to waste time trying to wiggle under there without ramps/jack stands if it's just going to turn out this doesn't do what I need.
08-09-2008, 11:05 PM
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LOL....well, yeah, sure.....it's n/a.....but I didn't say it was stock......
Ok, maybe the 78 cams and headers and a little porting to the heads have a little something to do with it, but it did it with the Euro cams too.
Ok, maybe the 78 cams and headers and a little porting to the heads have a little something to do with it, but it did it with the Euro cams too.
Last edited by Leslie 928 S2; 08-09-2008 at 11:21 PM.
08-09-2008, 11:14 PM
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The firmness setting helps with shifting flare for modified vehicles, eh? So, does that mean this could be the cure for why my car on the 1-2 shift has a stage where at first the rpms are dropping even though the car is still accelerating, and then you feel it catch and it feels like someone gave it a shot of nitrous? I know my car has this same setting (though for me I don't have to take off the exhaust shield to get to it), but I'm about 400 miles from my ramps right now and don't want to waste time trying to wiggle under there without ramps/jack stands if it's just going to turn out this doesn't do what I need.
08-09-2008, 11:16 PM
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08-09-2008, 11:22 PM
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Burning Brakes
Hmmm, it could be that the cams are so lumpy that it feels like the transmission is catching when it in fact it is just hitting it's powerband, but if it were an engine issue wouldn't I also feel it in 1st when flooring it from a standstill? It's a weird phenomenon for the car to still be accelerating fairly hard while the rpms are going down. I guess I"ll just have to try it and find out. But at least I now know how I'll be able to raise the redline once I find a higher cut off fuel pump relay.
08-09-2008, 11:44 PM
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Nothing to lose, I guess. Unless your transmission isn't kicking down properly, a slight cable adjustment to the stock 1 millimeter play at idle stop (according to the wsm) could help bring your rpms up. It certainly couldn't hurt.
Check your accelerator cable too, because it might have stretched and not be going all the way to the floor. Two of our Euros were found to be missing a quarter of their throttle due to accelerator cable stretch or misadjustment.
Do the accelerator cable first, btw. Then the trans.
Check your accelerator cable too, because it might have stretched and not be going all the way to the floor. Two of our Euros were found to be missing a quarter of their throttle due to accelerator cable stretch or misadjustment.
Do the accelerator cable first, btw. Then the trans.