Randy V

There's been much discussion lately on the proper method for adjusting the shift points on auto trans cars.

Clearly, properly adjusting the throttle and kickdown cables is very important in achieving crisp kickdowns and full WOT.

I had previously made the bold claim that adjusting the vacuum modulator not only changes the 'firmness' of the upshift but also adjusts the speed at which the trans upshifts.

Here's the exact language from the Porsche workshop manual, Volume II, secion 38, page 8, on adjusting the vacuum modulator on the 3-speed auto trans (also applies to the 4- speed):

1. Compress circlip and remove vacuum modulator cover.
2. Slightly pull adjusting key out and turn screw.
3. After adjusting, push key into nearest slot. One turn of setting screw results in 0.2 bar (2.8 psi) pressure change.

Note

Changing modulator pressure also changes shift points.


If you still question if adjusting modulator pressure changes the shift points - You are the weakest link - Goodbye!

2V4V

Randy,

Just to be completely factual (and we are all striving for factuality here, right?), the directions for adjusting the vacuum modulator on the 3 speed are DIFFERENT than the 4 speed.

Please see VOL III, sec 38, p 108.

Also, FWIW, the 4 speed adjustment procedure contains no wording that adjusting modulating pressure changes shift points.

Jay Wellwood

Randy-

'If you still question if adjusting modulator pressure changes the shift points - You are the weakest link - Goodbye!'

Surely this is meant with tongue in cheek coming from someone designated as a moderator???

Randy V

C'mon now Jay - you saw the smiley face after that statement. Play nice.

I prefer aquarium gravel over sawdust Snowy - a nice crunchy shift!

John Struthers

Randy, Oh wise and sweaty one,
I am the only 928 in town and I'm up to my *** in Mustang''s and wannabe Pro Street pickup truck operators. When I cruise
I usually find myself in second between 2800 and 4700rpm - Pattycakes feels and sounds like she's about to pass a watermelon at 3200rpm and above in 1st -.
Since I began my inadvertant street racing career I've noticed a few things.
1.) When I romp on the velocity control pedal
,while in auto., My sHARk shifts pretty hard without adjusting the modulator.
2.)There is a completely predictable and observable difference in shift points as displayed on the speedometer from 'normal'
acceleration and 'putting your foot into it' acceleration. WHY? Though I have yet to try it I have a strong suspicion that if I go one step beyond and hit the BahWaaah switch in auto. I will be looking at another set of shift points.
3.)While trolling around town for victims with my near drooling, slack-jawed, spaced-out, geezer face on and Pattycakes humming along in second at, Oh, say 3600rpm the victim approaches from the rear I back off to 3400 just as they pull out to pass. This makes them back off in the middle of a lane change by which time I'm heading to 4800+ at which point I'm gone and its time to shift.
At 4800+ I have now developed the dreaded TT CLUNK. No noticeable clunk at cold start-up reverse, or 'normal' acceleration. YET.....
So! What I want to know is : Why the observable difference in shift points? Is this simply caused by the difference in the RATE of speed increase between normal and hard acceleration or what?
And if the shift points can be adjusted for speed and 'hardness' and hardness tears up the TT bushings/bearings faster what is the STREET value if any?

gByron, What are your shift points now?
Both RPM and indicated Speedometer if you got em',
Carlos,was that hardwood or softwood sawdust?
Thanx all,
Keep em' rolling
John 82' Weissach, Auto. 'Pattycakes'

2V4V

John,

One thing I failed to mention is that on the 4 speeds, WOT control pressure CAN be adjusted via a bolt on the shift valve casing , which will change the full load upshifts. (I kinda left this out, as you have to drop the AT pan to get at it, and it's probably not something to casually mess with, IMHO)

Currently my shift points are somewhere in my mind...

I have finished installing a GTS a/t (with PSD) and a new TT in my 84. I however, have not finished my list of "while it's up I might as well..." stuff. I'm hope to finish the exhaust update Friday, but if I get a good deal on the GTS brakes and senders and stuff, it could be another week before I'm rolling - I'd like to hook up all the wiring for the PSD, so that I have 2 black lines behind me!

I will let you know as soon as I get it on the road and sorted...

84S, swallowing a GTS piece by piece...

Randy V

Some good questions there John, but without enough comprehensive knowledge on the topic I would only be guessing. If you have the worshop manuals, they give detailed information as well as troubleshooting guidance. If you like, send me an email (click on the envelope icon next to my screen name) with your fax number and I could fax you the pages that address your questions.

The benefits of a firmer shift are improved (faster) power transfer through the transmission during the upshift sequence.

Are you sure the 'clunk' you hear is the torque tube? This noise is most often associated with worn CV joints and/or wheel bearings. I suppose it could also be the torque converter bearing.

John Struthers

Randy V.
Stop it. You are breaking my heart!
I guess I should check the CV joints as the clunk does not appear when cold and shifting to reverse or the forward gears.
I know its not the wheel bearings. I checked them right after Carlos posted his recent mechanical invasion of Snowball.
I should have thought about the CV joints but at the time I was thinking "the engine is spun-up and the only thing under load is the trans." Duh... Converter bearing? OUCH !
I wanted to put off buying the pubs until I installed the new stereo. Now I feel guilty and will probably spring for the pubs.
Thanks for your thoughts.
John

Jay Wellwood

In as far as the clunk is concerned - could it be the rivets used in the Torque Converter drive flange?

I know that I've heard of a marble sound in most cases - but wonder if this could be a precursor to this failure?

Just wondering aloud...

John Struthers

Jay,
Don't know about the rivets, It is a thought though.
I'm going to slap a set of ramps together later today and will do a cursory visual inspection. I'll be looking for missing, and loose rivets among other things.
Thanx,
John S. Weissach, Auto. 'Pattycakes'

Big Dave

Any luck with your trannies, Randy?