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When my stalled A4 Is about to come to a stop I feel a weird little jolt. I was told it's the trans automatically downshifting into low gear. I don't know if that means it's downshifting into first or doing something else. Can I have a tuner lower the MPH downshift at the bottom of first or is this something mechanical in the transmission? It's not horrible but my PCM is going to a tuner for something else. if it can be smoothed out that would be even better. Is there anything else that would control this other than a transmission downshift table? Or, is it just a characteristic of the transmission and I should leave it alone because they all do it? Ty.
Hmmm.. It is very easy to change the downshift speed in the trans shift scheduling table. It would not hurt as a test to lower the 2>1 downshift MPH to see if it makes your jolt disappear. Essentially as you are decelerating and the trans transitions from 2nd to 1st, all that is happening is that the band is releasing... next time you are driving watch your tachometer to see if it bumps up just a little bit as it downshifts from 2 to 1.. If it does, that probably means it is kicking down into 1st gear a little early and lowering the downshift MPH *might* fix it. Nothing to hurt-just try it.
There is also a shift pressure/downshift/pressure modifier/2>1 table that you might look at to see if the tune has been altered and if this table is adding any pressure to that downshift. This table too can easily be manipulated to see if it is causing the jolt that you are feeling. It would be much easier if YOU had hp tuners to try this yourself. I can't see a "paid" tuner getting excited about wanting to spend time driving around with you trying to resolve a "jolt". I enjoy figuring things like that out though. Chasing small problems has really helped me figure the different tables out in HP Tuners over the last few years.
Thank you both, this is exactly what I needed. My car originally had a frost tune, then. dynoed about 10 years ago. The AFR should be on point, but most tuners set part throttle shift points. way too low for me. I think the last tuner adjusted that downshift pressure to where I'm feeling that jolt. I should've broke down and bought HP tuners years ago. I'm not confident enough to tune, but I can change shift points. Now I'm too close to the finish line to buy it. I did have a friend who let me raise the part throttle shift points & lock up a bit A few years ago but I don't have access anymore. I am about to send my pcm out, here is what I sent him. I will add what you said.
1999 Trans AM LS1 4l60 3.42 rear swapped from 2.73 2G2FV32G9X2233895
Only mods are:
Circle D 278 non billet converter
No name cat back
SLP lid
My car was dynoed many years ago, I sent the sheet so AFR should be as good as it gets? If anything on the tune looks out of line please do your magic. It actually runs good now but you will make it even better.
1-2 upshift and downshift from first to second seems perfect. I do feel an additional bump for lack of a better word when coming to a stop around 10-5 mph. I was told the trans is going into low gear? If you can smooth it out a bit that would be great, if not I can live with it.
Please adjust 2-3 upshift starting @ 28mph, 3-4 starting at 45 mph, 4th lock up starting @ 58 mph all increasing with more pedal.Shift pressure feels fine but you know more than I do.
Please raise the downshift 4-3, 3-2 and converter release to what you think is best. The converter unlock feels 6-8 ish mph low.
4-3 & 3-2 need help. The car stays in 4th on decyl until around 25mph. Even when going slow it is re-accelerating in 4th, rarely 3rd or 2nd. Also, when I take my foot off the gas it immediately upshifts to 4th.
How much are you paying for this tune? For not much more I’d imagine, you could buy hp tuners and get it exactly the way you want it. I did the “paying a tuner” to do my tune on my 5th Gen. Camaro I used to have and the transmission tune was horrible. I kept bringing it back. I was never happy with it. Had I bought hp tuners before selling the car, I could have set it how I want it. The car I have now shifts flawlessly because I tuned it the way I want it.
I should have did that years ago but I'm way past that point. I'm paying a hundred plus the ride for a professional to do it. If he does what I ask it should be exactly what I want.
One more thing to mention if the tuning side of it does not cure your bump..... Your car has a torque arm that comes off the rear differential and bolt so the rear end of the transmission. I have been in F-bodies before that had a bad rubber insert, or isolator, in the torque arm bracket at the rear of the trans and it would do a bump sound, and FEEL, every time it downshifted. Same for the trans mount.. Check BOTH and replace BOTH if necessary. To check the trans mount, go under the car and simply lift up on the tail shaft of the trans.. if it starts to move up and away from the cross member-the mount is bad! Sometimes you can just visually look at them and see they are deformed from age, cracked, flattened, disintegrated.. but you still should give them the trans lift test to see if it is actually holding the trans DOWN against the cross member... Sounds crazy but that torque arm WILL lift the trans UP off the cross member under hard acceleration with a bad mount. I've seen them so bad that the trans was rising up and hitting the under side of the trans tunnel under the center console....
Great points, the torque arm is UMI and my trans mount was replaced with Moog or AC Delco rubber. I think it is the downshift modifier I never knew about. It doesn't feel like a suspension jolt. Jus about everything was replaced and the car rides nice.
08-09-2023, 08:37 PM
Trains tuning question please 
