'80 3sp AT - stock - WOT:
1st to 2nd = 6200
2nd to 3rd = 5800

Would like 1st to 2nd to shift at 5800 as well, since hp drops off and the overrev to 6200 is wasted time. Can this adjustment be made or is it computer controlled. Clueless why both aren't 6200. Normal driving bowden kickdown seems appropriate.

'86 4sp AT - eBay chip only:
1st to 2nd = 4400
2nd to 3rd = 6300
3rd to 4th = 6300

Would like 1st to hold to 6300, since it's just beginning to pull onto cam when it shifts to an undesirable bog rpm in 2nd...and then has to catch up to itself. The chips added ~1500 to get to 6300, but 1st to 2nd remained 4400 with stock and chips. Normal driving bowden kickdown seems appropriate. Is 1st always limited and I need to burn a custom chip?

Ideas for either MY's is greatly appreciated??

 

funny haw this is. 1-2 shift is short shifted UGH what a pain in the ****

 

There is no computer involved in the shift points.

 

None of the 928 transmissions are computer controlled it is all vacume,pressure cable,kick down switch ,internal mechanical bits and pieces but no computer, no chips.

 

I suspect that the trans is configured to short-shift 1 -> 2 so that it lasts a while. Torque multiplication in those lower gears could exceed the capabilities of something else like the CV joints or the half-shafts. Or tire traction with the original tires. I'm sticking with the "Only one way this trans will make it through the warranty period" theory on weak parts.

IIRC, you can force the 1 -> 2 shift to redline by holding the level in position 2. If the trans is adjusted correctly, it should shift just before the time the fuel cut-off kicks in. In my '89 with the quicker rear end, first gear goes away in a hurry too. If there was much flare in that 1 -> 2 shift the engine would be way into the rev limiter. After a few full-throttle tries, there definitely would be some shift flare...

 

Interesting. Good to hear that it isn't computer controlled.

dr bob, it is in "2" when this occurs, and it forces it to hold 1st until 4400, but not to redline.

Jim, my thinking is that if it were "vacume,pressure cable,kick down switch" related, it would occur for all shifts, rather than just for 1st to 2nd; similar for the '80 and 2nd to 3rd only.

Funny thing if considering both cars behavior together, it would seem that each gear must have it's own adjustment (maybe as you suggest Jim, internally).

Anyone ever stumble across gear-specific internal adjustments for your AT?

 

my 85 shifts 1-2 at about 4800 or 5k...I too would like to get the other 1k outta 1st but i am not sure how either...I have come to understand my confusion (I think)on why it does not shift out at the same RPM for all the shifts. This is my theory: The amount of "load" seen by the TC is not as high when in 1st as when it is in 2nd or 3rd because of the gearing in the tranny and rearend. When the tranny is in 2nd or 3rd, the TC see more load and thus the tranny holds the gear to a higher RPM value. Even though this makes sense to me, I still wish that we could figure out a way to get the tranny to hold 1st gear for that next 1k rpm. Any thoughts?

 

I'd go looking for an MB S Class expert. There were a lot more of that car on the road than ours, and the tranny is the same. If there is any internal valving that can be done to change this, I bet they would know.

 

wish it were that easy Rng Trtl, but the TC is merely rpm sensitive to know when to lock up and transmit the rotating power, so load is not respected.

guess we're just stuck with a short-shift to 2nd, although <again> my '80 does it 2nd to 3rd rather than 1st to 2nd, so it would seem there is something unique to each gear (all other factors vacume,cables,etc, in normal operation) to determine when to shift.

I think you're right jayc67, Any MB Transmission experts out there?

 

damn, and i thought I had a good theory...phooey sticks!

 

Kirt
Odd.....mine will hold every gear to redline 6200rpm......I did drive a 90 S4 that shifted out of first at 5500rpm and everything else at redline? Have you tried tightening the bowden cable?

 

the book must be wrong then? I just had a manual toggle installed to bypass my kickdown switch to insure 1st gear rolling starts/low speed kick down to 1st (it doesn't like to do that usually). we (Ole' at precision) traced the kickdown wire in the schematic and the wire goes to the ECU, iirc (maybe I missed something?). I'd guess on the 85S at least theres a tach related kickdown cutoff to keep it from overreving in case the revlimiter/fuel cut off didn't come in quick enough in 1st?

iirc, there are also some different valve bodies available and shift kits around that can make it shift at redline if it doesn't cooperate by just leaving it in 2nd... been some interesting/informative threads here about AT options too

steve cattano seems to be a 928 trans guru and made some interesting AT posts.

 

928SS, haven't heard of tach related cutoff, but I'd still expect it would be near redline... I'll have to check archives for Steve's AT posts to see if there's any insight.

Brian, good to hear someone is getting full rpm out of 1st. You mention the bowden, but I was under the understanding that it only triggers downshift points (too loose=too much throttle pressure to trigger downshift; too tight=barely any throttle pressure to trigger downshift). Did I misunderstand what the Bowden controls?

 

There is a "transmission protect" switch which retards the ignition timing for the shift in two of the four gears....as I recall So the transmission is talking to the computer not the computer to the trans.

 

Thats interesting to hear, will diconnecting thsi wire give us more firm of a shift? Even my SRT has this protection its called shift anticipation. and torque mgmt. We can defeat it with a small switch purchased after market. It also has a mercededs tranny