Do "shift points" really exist?

[PiLOTLiTE]

Everyone talks about these so-called "points" that your computer must know to shift the tranny properly or else you start to have problems. Do these things really exist? It makes sense to me that rpm, throttle position, and the VSS (vehicle speed sensor) are all that the computer can even use to tell the tranny when to shift. What else could possibly be important? When doing a gear swap, the sensors that tell the computer engine RPM and throttle position are unaffected. That would leave the VSS to be fixed. As an example, SLP's speedo recalibrator does just that. It modifies the incoming VSS signal before it reaches the ECM to give the computer the correct vehicle speed reading for whatever gears you swap to. RPM, VSS, and the TPS are all reading correct now, what would be left to cause problems?

I have personal experience with the subject. I swapped to 3.73s almost 5,000 miles ago and still have an uncorrected speedometer on a 75,000 mile vehicle. My transmission shifts just like it did before the swap. The tach still winds to practically 6 grand at WOT in 1st and 2nd, and probably would in 3rd if I didn't have that stupid speed limiter kicking in around 100 now. The gear swap caused NO driveability issues whatsoever. I have even spoken with 2 GM technicians who said it was not necessary to program the computer for new gears, just to modify the incoming VSS signal. And since I've seen no problems for so long, it doesn't even seem like you need even to correct the VSS unless you want your speedo and odometer to be correct.

So for those of you who believe the "shift points" have to be corrected, who can give me an explanation as to why a correctly reading (to the computer anyway since you're modifying the VSS signal) TPS, VSS, and tach signal aren't enough?

[ December 29, 2002: Message edited by: PiLOTLiTE ]</p>

[sped214]

I sense a post coming from "ONLY4U"...

[img]smile.gif[/img]

[Nachius]

I have "shift-point" problems after a gear change. I'm not sure what causes them all I know is that if your Speedometer is not working it doesn't matter what RPM you are at it WILL NOT shift.

The speedo controlled by the VSS with the speedo sitting at 0 you never get out of first gear.... Believe me I know I bounced off the rev limiter all the way down the track in 1st Gear! :D

[PiLOTLiTE]

<blockquote>quote:</font><hr>Originally posted by Nachius:
I have "shift-point" problems after a gear change. I'm not sure what causes them all I know is that if your Speedometer is not working it doesn't matter what RPM you are at it WILL NOT shift.

The speedo controlled by the VSS with the speedo sitting at 0 you never get out of first gear.... Believe me I know I bounced off the rev limiter all the way down the track in 1st Gear! :D <hr></blockquote>

That only happens when the computer doesn't receive a reading from the VSS, like when you switch it off. :D

[morbid]

yeah, what you say makes sense to me, i don't see why there would be preset "shift points." that's a pretty stupid idea (i mean if it is indeed true). i mean, so static and unrobust.

[PiLOTLiTE]

I've seen a lot of responses in other posts about people saying shift points needing to be changed, where are all those members?

[dstrbd1]

in the long run, it is necessary to get thespeedo corrected after a gear change. 5000 miles isn't really long enough to find that out. i went from 3.08 to 3.73's back around april or may of 02, and have just recently run into problems shifting. the shift points in an electronic tranny are determined by throttle position, rpm, and mph. when you change the gears, your rpm/mph ratio changes, and that throws the shift points off. you may still shift at 6g, but where 6g might have been 80mph for me before, now it's 60. months of my tranny shifting that way finally wore it down and i had to pay $1100 to rebuild it. now it's all new inside, but it still doesn't shift in the right places to run as fast as i know it can, because the mph is still off, until i get it recal'd in a couple weeks.

[PiLOTLiTE]

<blockquote>quote:</font><hr>Originally posted by dstrbd1:
in the long run, it is necessary to get thespeedo corrected after a gear change. 5000 miles isn't really long enough to find that out. i went from 3.08 to 3.73's back around april or may of 02, and have just recently run into problems shifting. the shift points in an electronic tranny are determined by throttle position, rpm, and mph. when you change the gears, your rpm/mph ratio changes, and that throws the shift points off. you may still shift at 6g, but where 6g might have been 80mph for me before, now it's 60. months of my tranny shifting that way finally wore it down and i had to pay $1100 to rebuild it. now it's all new inside, but it still doesn't shift in the right places to run as fast as i know it can, because the mph is still off, until i get it recal'd in a couple weeks.<hr></blockquote>

That I understand, but people say modifying the VSS signal (like with SLPs calibrator) to give the computer the correct MPH still results in problems. That makes no sense to me. What are you doing to get yours recalibrated? What year car?

[dstrbd1]

98 camaro, and i'm taking it to a dealership service dept. i called a couple places and they all say that the dealership has to do it cuz it's through the computer.

[PiLOTLiTE]

Your dealer will reprogram for a non-factory ratio???? Must be nice.

[Tri-Flo 99]

what would happen if i unplugged the VSS? would my limiter kick in (i wanna have some of my buddies pace me bc im curious)

[PiLOTLiTE]

<blockquote>quote:</font><hr>Originally posted by Tri-Flo 99:
what would happen if i unplugged the VSS? would my limiter kick in (i wanna have some of my buddies pace me bc im curious)<hr></blockquote>

Since your tranny is electronically controlled, you'd never get out of first gear unfortunately. =)

I just got SLPs speedo recalibrator, I'm gonna see if this thing works. [img]graemlins/thumbsup.gif[/img]

[Only4U]

<blockquote>quote:</font><hr>Originally posted by sped214:
I sense a post coming from "ONLY4U"...

[img]smile.gif[/img] <hr></blockquote>

right on, and yet, it's not even going to be complicated:

when i had my 3.42s and my computer un-programmed, my friend's manual bird flew from a car length behind me to a good full length in front of me on my 2-3 shift.

the DAY after i got the thing programmed, my 1-2 shift put me 2 cars in front of him, and on the 2-3, he gained NONE on me.

"recalibrating" the shift points is the only reason our racing made any difference...and we raced quite a few times.

my car was shifting into third at 5200 rpms or so. the slp recally won't work because of this connection:

PCM to VSS to SLP-RECALLY to GAUGE CLUSTER

MAYBE if it went:

SLP-RECALLY to PCM so on... it MIGHT work, otherwise, the pcm is just sending the same signal out and the slp recally is just chaanging the gauge cluster, but the actual shift is still determined by the computer.

and another thing: buy a-tap and then you'll really be able to tell when your car is shifting. that, or you could race someone with a similarly modded f-body, and see if they gain any on you on the shifts.

reprogramming the pcm obviously does something, because my races with my friend prove that, if it isn't the shift points getting fixed, then i don't know what the hell it could be, but it probably made a half a second difference in my quarter mile time easily.

[ January 08, 2003: Message edited by: Only4U ]</p>

[Nachius]

ONLY4U thats the exact same problem I'm having.

My car is falling on its face every time it shifts after my gear change. I'm going to get it reprogrammed for 3.42s very soon I'll come back here and post the results and see if they are the same as your results.

navyblue2000 can verify this my car pulls hard in 1st then he just pulls past me on the 1-2 shift :D

[PiLOTLiTE]

<blockquote>quote:</font><hr>Originally posted by Only4U:



my car was shifting into third at 5200 rpms or so. the slp recally won't work because of this connection:

PCM to VSS to SLP-RECALLY to GAUGE CLUSTER

MAYBE if it went:

SLP-RECALLY to PCM so on... it MIGHT work, otherwise, the pcm is just sending the same signal out and the slp recally is just chaanging the gauge cluster, but the actual shift is still determined by the computer.


[ January 08, 2003: Message edited by: Only4U ]<hr></blockquote>


Oh I think it does change the signal before it reaches the computer. I noticed (thru my manual fan switch with LEDs) that my low side fan for the defroster came on at 40mph with the 3.08s. When I ran the 3.73s with no calibration, it still turned on at a speedo read 40mph, which was actually slightly less. Now with SLPs thing, it still turns on at a speedo read 40mph which means the computer does know its going 40mph, not just the guage cluster.