Tranny shift points

Chris · #1 04-09-2001, 05:19 PM

Ok.. at wide open throttle my car shifts from 1st to 2nd at 50mph and 2nd to 3rd at 80mph. It seems that the maximum speed that my car will downshift into 1st gear is about 32mph. Now my math shows that the maximum speed it will drop into first gear is 18mph below its top speed in this gear. BUT... the car will lurch into 2nd gear at 75mph or just 5mph less than its maximum speed in that gear. My question is this: Why will it drop into second at just 5mph under its shift point when it seems to be very doggy in a first shift downpoint at 18mph under its maximum speed in that gear? Can the TCU be told to dump down into 1st gear at up to 40mph or a mere 10mph under its maximum gear speed? I hope this wasnt too confusing

(Eddycat... any ideas?) Anyone?

Chris

eddycat2000 · #2 04-09-2001, 07:03 PM

Quote:

Originally posted by Chris

(Eddycat... any ideas?) Anyone?

Chris

Chris, that was *very* confusing to me. It might help to know what year SVX you have, and if it has the original tranny and such. My shifts in the SVX are silky smooth and I can't predict where they will happen because I don't think I drive that predictably. Some days I'm in a hurry and some days I'm just cruising. But if you have a problem, (or think you do), my best suggestion is to flush the tranny and cooler lines and take a look at what comes out, you don't want excessive clutch matter to be evident. Shift points are determined by the tcu and the ecu talking and getting various sensor inputs, so I doubt anyone could get consistantly regular shift points.

svxistentialist · #3 04-10-2001, 02:53 PM

<It seems that the maximum speed that my car will downshift into 1st gear is about 32mph.>

Your maths seem to be spot on here Chris. I see what you are getting at, but can't compare, my car doesn't shift.
According to the FAQ, the Power mode for holding the gears longer comes in in relation to a few things like Eddy says. One is road speed, it's easier to get into Power mode at high speed. Another is the rate at which you depress the pedal. Am I right in assuming your 32 mph above is the best you can achieve kick-down by really quickly burying the pedal?

If so, then it must be the way the factory have set the map in the TCU. The main reason I can think of is they would wish to avoid the sort of shock to the transmission you would inflict for such a spirited move. Or maybe just to keep it smooth. Remember, if you floor the pedal in second to get kickdown, you are revving way up the powerband. You will be thumping first gear with all the 200+ horses, and with 4 wheel traction, the tyres won't break to let off the pressure. They may just want to stop you doing that to keep it from breaking up.

Joe

Chris · #4 04-11-2001, 09:55 PM

Seems quite possible. Its just very depressing. I can eat most cars with a 32mph down shift into 1st gear. Yea, the car lurches like a bunny with a tazer up its wazzu. But its very depresing to be doing 35mph and floor it only to get a mild acceleration from the bottom end of second gear that lasts FOREVER.. or at least till 80mph. By then I am toast and or the light to light competition is over. Its rather depressing.

Chris

svxistentialist · #5 04-12-2001, 01:37 AM

Don't despair, Chris, and don't forget;
you've still got your left hand!

Joe

svxistentialist · #6 04-13-2001, 05:36 AM

That last post should be read in the light that I am sitting on the right side of my car while driving, forgot about you US lefties.

Joe

#7 05-01-2001, 09:04 PM

This is indeed an interesting thread. I have been spending most of my time in the MOD MANIA section, because I have no qualifications to give technical info.

Anyway, I believe I have encountered this in my '92. Have you tried to shift it manually to first (like Joe suggested)? I almost always use the shift selector to change gears now, and the car seems to drive a lot better. No matter how well the TCU programmers were, they can't predict and account for every driving situation.

Now that I manually shift, I've been able to take corners at speed, much more smoothely. Before, I'd have to shift with the throttle, and the car would lurch around, during the automatic shifts, upsetting the balance. Now that I shift manually with the gear selector, I can match revs with the throttle, and setup before entering the curve.

One thing I don't like about the upshift point is the 2-3 shift. Like you said, it upshifts at around 80mph. Well when we dragrace on the 1/4 mile, SVXes usually complete it @ 85 or so mph. That means that we upshift just before the end, which robs us of potential speed and power. If only 2nd gear was a little more taller or redline was higher, we'd be alright.

Oh well, just have to make the car more powerful at those lower revs! Then maybe it would shift earlier at maybe the 3/16 or 5/32 mark! But that's subject material for the other section!

I hope my intrusion into this technical arena hasn't caused too many waves! I'll return to lurking now.

FlagstaffSVX · #8 05-08-2001, 02:58 AM

Quote:

Originally posted by svxistentialist
Don't despair, Chris, and don't forget;
you've still got your left hand!

Joe

A normal 17 year old teenager would take this the wrong way but as I own an SVX, I am not normal. :-)

Aredubjay · #9 05-08-2001, 09:12 AM

Quote:

Originally posted by FlagstaffSVX

A normal 17 year old teenager would take this the wrong way but as I own an SVX, I am not normal. :-)

I used to sign all my communications at the Advertising Agency I worked for as the fictitious person, "Y.B. Normal" I don't think you have to be abnormal to own an SVX, but it sure as heck helps.

"Growing old is mandetory . . . growing up is an option."