Results 1 to 10 of 10

Thread: Trans Shifts and TC Lockup.....

  1. #1
    Join Date
    Oct 2003
    Location
    Beaufort, SC
    Posts
    7,719

    Trans Shifts and TC Lockup.....

    Well......

    I'm very happy with Dennis' "Custom Tuner" program but wonder about a few things??

    I'll try to explain shifting and lockup:

    Scenario #1: Light throttle
    1-2 shift.....FIRM
    2-3 shift.....FIRM
    Lockup.......MUSHY but OK
    3-4 shift.....FIRM

    Scenario #2: Moderate to strong acceleration
    1-2 shift.....FIRM
    2-3 shift.....MUSHY...TC lockup almost simultaneous
    3-4 shift.....FIRM

    Now: If the TC lockup is programmed in 4th only it would help with the "Mushy 3rd shift" but then when you turn OD off you would have 3rd and no lockup.....I think?? What about making the TC lock above a certain speed say 50 MPH.....would it still work in 3rd above 50 with OD off as in trailer towing?? Also, can the TC lockup be set up on a switch so you can run with or without TC locking??

    I'm mainly concerned with the wear from slipping into "lockup" in third when accelerating moderately to strong?? BTW...RPM drop with 2-3 and lockup is about 900 RPM's!!

    Ideas??

    Marauderjack
    No Marauder

  2. #2
    Join Date
    Sep 2002
    Location
    Florida
    Posts
    4,207
    Quote Originally Posted by Marauderjack
    I'm mainly concerned with the wear from slipping into "lockup" in third when accelerating moderately to strong?? BTW...RPM drop with 2-3 and lockup is about 900 RPM's!!

    Ideas??

    Marauderjack
    I don't know enough about it, I would like to add a question to yours: when you go from 2nd to 3rd and the rpms drop isn't that a normal function of shifting to a higher gear ?

    How do you know when your converter is locked or not ? Do you feel it, lock and unlock the way you feel the car shifting gears ? Sorry, I'm just trying to learn, maybe is a dumb question.
    Smokie
    12.79 @ 107 mph.
    60' 1.851 Street tires & Stock wheels.
    TIMESLIPS
    Performance Mods: Base Trilogy Kit, Exhaust, PHP Airbox.
    Visit my Garage
    Florida "The Supercharged State"


  3. #3
    TripleTransAm Guest
    I'm not aware of Dennis' shift parameters but one thing to keep in mind is that upshifts under the torque converter's stall speed under moderate acceleration might not result in that great an RPM change.

    Think of it this way... the torque converter is "stalling" up until the point where the output speed will match the engine RPM. So, from a dead stop, the engine RPM will remain at close to (picking a number) say 2600 RPM while the car accelerates in 1st. If the tranny upshifts before the output side of the TC manages to get to 2600 RPM, the upshift won't be that noticeable. Let me work on a couple of drawings to illustrate what I'm trying to explain...

  4. #4
    Join Date
    Oct 2003
    Location
    Beaufort, SC
    Posts
    7,719
    Smokie...

    Before Dennis' program I didn't have a clue what it was doing....shifting up, down, back and forth?? Now I see a small RPM drop from 1st to 2nd and again going to 3rd.....TC is still unlocked and "slipping".....Then BOOM....LOCKUP and RPM's drop drastically!! If I accelerate harder above 45 MPH or so 3rd gear and lockup happen at the same time!!

    With the O/D off further acceleration allows the TC to unlock and re-lock at a greater speed.....This even happens in O/D and I wonder if there is a way to skip lockup until you want it or at a greater speed??

    Marauderjack
    No Marauder

  5. #5
    TripleTransAm Guest
    In this drawing, the car is accelerating moderately... the torque converter has a high enough stall speed (a la Marauder) such that it spends a lot of time in a stall condition.

    The red line is the engine RPM. The blue line is the speed of the output shaft from the torque converter to the tranny... this is the speed your engine would have been rotating had the torque converter been replaced by a solid coupling, like a manual tranny clutch for instance, or simply a solid shaft.

    We see the engine flash to a certain speed (red line on the graph) immediately on take off... this flash speed is relative to the amount of torque being transmitted into the torque converter... a harder launch will result in a higher flash speed, until the torque converter's max stall speed (which comes at full engine power while the output side is at a complete stop).

    The output side of the torque converter (blue line) begins to rotate as the tranny output shaft begins to rotate, as the car begins to move. Recall that the tranny provides a SOLID link between the torque converter output and the drive wheels, so no slippage there.

    The blue line drops during the 1-2 upshift. Same as a manual tranny would drop the engine RPM after an upshift. The output side is still far below the speed that the engine side is "stalling" at, so there is little drop in engine speed. There is a small drop in engine speed... one has to account for a certain reactionary force back through the torque converter from the tranny, the tranny is now multiplying torque at a smaller factor because of the slightly higher gear ratio in 2nd gear, so the engine sees a little more resistance to "flashing" up to full stall, at that same throttle opening.

    As the road speed continues to climb in 2nd, we notice that the blue line starts going back up (in direct connection with the input side of the tranny). The red line stays the same... the blue line hasn't really reached the converter stall speed (ie. close to 1:1 with the red line). In this "program", the torque converter is not allowed to lock up in 2nd, so slippage continues until the next upshift point.

    2nd to 3rd upshift: same thing, the new tranny gear lowers the tranny input shaft speed (blue line) and the greater load on the whole shebang causes another slight dip in engine speed, considering we're keeping the throttle pedal constant. As the car continues to accelerate, the blue line resumes climbing (it really should be climbing at a slower rate after each shift because of the subsequently higher gear ratios, but cut me some slack here...).

    The car keeps accelerating, and then the torque converter is commanded to lock up. It applies an internal clutch between the engine and the tranny input side (its own output side) and the engine speed (red line) is forced to match the tranny input side speed (the blue line). Now that there is a physical connection, the engine RPM drop is more noticeable and is felt more than during any other unlocked shift.
    Attached Images Attached Images

  6. #6
    TripleTransAm Guest
    In this next scenario, the car's programming allows for an early TCC lockup, in 2nd in fact.

    So the car accelerates in first, you see the same hovering of the engine speed, and then there's an upshift (1-2), dropping the tranny input shaft speed but the engine only feels a slight increase on workload.

    Here's where it's different:
    The small black arrow (middle) shows the 2nd gear TCC lockup. VERY noticeable drop in engine RPM (the engine and tranny are now solidly coupled).

    Then the 2-3 shift comes about. From what I understand, the TCC unlocks for a brief second during the upshift, but locks up immediately afterward. The net result is that the driver really FEELS that 2-3 upshift (which is actually a combination of the upshift and a new TCC lockup event).

    From memory: my stock MM's 2-3 upshift is followed by an immediate TCC lockup. This is what results in a noticeable drop in RPM so early. When the engine is cold (ie. the PCM doesn't ask for TCC lockup until it's warmed up), my 1-2 and 2-3 upshifts are equally as smooth. It's only once the TCC is enabled that I really feel my 2-3 upshift (which is actually an upshift followed by an immediate lockup). Same story with 3-4... very noticeable because of the immediate lockup after the upshift.

    I believe you can have a very firm upshifting transmission that will STILL give you what seems like a fluffy upshift, simply because the torque converter is still operating in a stall condition. Misleading, but it's the price to pay for a looser converter like that in our MM's...
    Attached Images Attached Images

  7. #7
    Join Date
    Sep 2002
    Location
    TX
    Age
    61
    Posts
    1,685
    Very nice explanation 3TA.

    Now add a 3500rpm TQ and you'll see what I have to deal with.
    Everything works well until the TC unlocks in OD.Then RPM jumps in 4th gear when the converter unlocks right to 3500 RPM!Back off a little and "snick" the converter locks and the R's drop.

    With the higher stall in 3rd and OD you know when the converter unlocks,the RPM comes up right now.


    Driving at light throttle the 1-2 shift feels good,the 2-3 is noticed and the converter lock is also felt,they all feel like shifts.

    Heavy throttle,RPM to 3500 from a stop,tires spinning,then the 1-2 shift,BAM,RPM drop to about 3800-4000 then the R's climb again,speed climbing through 80mph,back off wait for a trip to the track to find out what the 2-3 WOT shift does! Sorry.....


    BTW I still have the stock rear gear with the PI 3500 stall and I can SMOKE EM from a dead punch!

  8. #8
    TripleTransAm Guest
    Thanks, Cyclone03...
    To address your following quote:

    Quote Originally Posted by cyclone03
    Heavy throttle,RPM to 3500 from a stop,tires spinning,then the 1-2 shift,BAM,RPM drop to about 3800-4000 then the R's climb again,speed climbing through 80mph,back off wait for a trip to the track to find out what the 2-3 WOT shift does! Sorry.....

    What's happening here is that your upshifts happen beyond the stall speed. The Engine RPM and the tranny input are beginning to match up (not perfectly, since things aren't physically locked up yet), and the upshift still puts you beyond the stall speed. There is slippage, but not enough to "soak up" the upshift "jerk", if you get my drift.

    I cobbled up the following drawing of what would happen on a pretty heavy acceleration... not WOT, but close.

    Goosing the throttle flashes the RPM against the converter, keeping it at stall speed as the output side pushes the tranny and the car through 1st gear. This 1st gear is maintained as both sides of the torque converter begin to match up, and the engine RPM begins to climb as well, no longer being bound by a completely stalled converter. Note this happens very quickly, probably much quicker than I drew it. Also, DISREGARD the hump (arrow 1) as the blue line comes to meet the red line, there is no 'hump' in acceleration as the output side of the torque converter approaches the stall speed, so please don't be misled.

    The engine (redline) and torque converter output shaft (blueline) both race towards the upshift point... note that there is always a little slippage between the engine and the tranny input. It's still just a fluid coupling in there, no physical lockup, so there is slippage.

    The 2nd black arrow denotes the upshift. Depending on tranny gearing ratios and converter stall speed, the upshift may bring the RPM of the output side of the torque converter down to where it's below stall speed... the engine will decrease in RPM but only to the point where things are loose enough for it to push against... ie. the stall speed. That's why the blue line drops hard (to match the gearing change) but the engine RPM just drops to stall speed.

    Same thing happens in 2nd all the way up to the 2-3 upshift (third black arrow). Again, note that the blue line and red line never meet up perfectly, the engine is always rotating a tad faster than the torque converter output shaft.

    After the 2-3 upshift (3rd black arrow), the same thing as we're assuming the gear ratio change to 3rd causes the tranny input shaft / torque converter output shaft to drop below stall speed. The engine drops to around stall speed and continues tugging against this fluid resistance while the road speed increases.

    At the black arrow labelled TCC, we're either going fast enough or have backed off the throttle just a *tad*... in any case, the PCM decides that this is where it's a good idea to lock things up. It orders the converter to lock up and physically join both engine and tranny. The blue and red lines should now pretty much line up perfectly (although I left a little space to show they are following each other 1:1 now).

    In this scenario, each upshift is felt much more dramatically than the easier scenarios above, since the engine RPM drop is more noticeable. Remember that with each upshift, you are physically braking this raging charging hunk of rotating explosions down to a lower RPM... this should give you an idea of the magnitude of forces which occur during an upshift.

    When this driveline shock is harsh enough (or the engine powerful enough to resist being braked in this fashion), you get wheelspin on the upshift, until the engine gives in and slows down to match the driveline conditions for this roadspeed.
    Attached Images Attached Images

  9. #9
    TripleTransAm Guest
    And for my final presentation, we can look at a WOT kind of acceleration.

    In this case, the upshifts happen high enough that the engine never falls to stall speed after the shift. There is an obvious constant slippage between the engine RPM and the TC output shaft, but the difference is never as great as when the TC output shaft is made to fall below TC stall speed.

    In third gear (after the 2nd arrow) I intentionally left an excessive space between the blue and red lines to illustrate that even at high RPMs in 3rd gear the TC is still slipping. If your engine is at 4000 RPM in 3rd under unlocked WOT, the tranny input only sees maybe 3800? Maybe 3500? I don't know how much the Marauder TC slips once past the stall speed, under WOT load in 3rd gear (ie. 1.00:1 ratio).

    The third arrow is when the PCM decides it's time to lock things up in the TC. The result is what seems like a hesitation or surge, nothing more. This is the hesitation I believe some of us feel at 3000-3500 under moderate acceleration... it's the TCC locking up at a point where the engine RPM may be around 3000-3500, and the actual TC output shaft is only slightly off. Therefore the difference in RPM during the lockup is less. I suspect raising the TC lockup speed would lessen this effect.

    The yellow line, by the way, is the stall speed (RPM) of the converter, in order to visualize that in this scenario, things are kept above the stall speed due to high RPM upshifts.
    Attached Images Attached Images

  10. #10
    Join Date
    Feb 2003
    Location
    Earth
    Posts
    8,598
    Blog Entries
    2
    Thanks Steve!
    1/4 Mile Time 11.542 @ 121.19 MPH
    195,000 Miles & 275+ Runs Down the 1,320’
    541.57 RWHP & 476.64 RWTQ on DynoJet
    Tuned by Aric at Injected Engineering
    Vortech Super Charger V-2 “T” Trim, 19 PSI
    8 Rib Belt, Innovators West 10% Overdrive Dampner
    Air to Air Intercooler, Mini-race Bypass
    Ford Cobra Remanufactured Long Block
    Snow Performance Water-Methanol Injection
    Kooks Headers & X Pipe
    GT MAF, 60lb injectors, Dash 8, Aero Rails, Twin Ford GT Pumps,
    Kinsler Fuel Filter, Kenne Bell Boost-A-Pump
    Monroe Sensatrac, Metco Control Arms, Addco Rear Sway Bar
    31 Ford Spline Axles & Detroit Truetrac, 4:10 Ford Racing Gears
    Dynotech MMC Driveshaft
    A-1 Performance Trans, Forced Tailshaft Lube, Carbon Clutches
    3,500 RPM Stall Precision Industries Torque Converter
    B&M Deep Finned Trans Pan
    AeroForce Scan Gauges , Auto Meter Oil, Fuel & Boost Gauges
    Kenny Brown Dead Pedal, 35% Tint, Silver Star Head Lights
    AutoPage Alarm RS-727LCD, Boston Acoustic NX87

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •