It is a gear. 0.7 ratio. And the TC will lock up if the TPS voltage is low enough, and you're above 48mph, for further economy.

Sounds good, but I'll add that third will get lockup lower than 48, high 30'* I think. And maybe it'* just mine, but I get lockup in fourth as low as 46.

you know, i think i hate finding out all this neat stuff out about bonnie <gx3 tranny, tcc lockup, heated mirrors, etc> only after she has been wrecked. that would explain why the rpms go from 2700ish climbing up a hill, jump to about 3200rpm <i just thought it was giving the car the most throttle without downshifting> then go down and catch 3rd for about 4grand and some change. life sux when you find out how nice the crippled mass of twisted metal in your back yard really was.

TCC is a whole different subject. For instance it is the only thing in a 440T4/4T60 (just a naming change) that is controlled by the ECM (computer).

Lockup is a function of speed and TPS but also unlocks if the TPS goes under 2% for freewheeling. You really do not want 4th/lockup under 45 mph as the engine speed is only 1200-1300 rpm (3.33 slightly higher). If everything is right (particularly the ignition) the 3800 can pull a moderate grade at that speed without unlocking but any problems will really show up then.

Like other computer controlled functions, the parameters relating to lockup can be adjusted with a new program in the PROM. Here in the Flatlands, we have a lot of 45 mph roads so being able to get into lockup helps economy.

you all sure my '87 has a 4th gear in ADDITION to the TCC?
I've tried often to feel every shift in my transmission while i'm driving and all i ever can feel is
1 -> 2, 2->3, 3->TCC engage.

I have never EVER felt a 4th and a 4th TCC engage.

My tCC kicks in at mid to upper 30s (mph) depending on how light / heavy my foot is on the throttle.

I'm checking my factory service manual now to see if it mentions anymore info.

Welll here'* some of the juicier tidbits i found in my 87 bonnie FSM.
"... the transmission does not have to be in fourth gear in order for the ECM to turn the clutch on."
"124 and 440 transmissions use a third gear switch (normallly open) is placed in series on the batery side of the TCC solenoid. This switch prevents TCC application until the transmission is in third gear,. Then the switch closes, completing the circuit to the ECM."

Under the first quote, I would think that there is 4 gears with the TC lockup possible in 3rd and 4th.

later in the manual it discusses the components of the 440-T4 trans:
"Torque converter with converter clutch....Input, 3rd, 2nd, and 4th clutches"
Then it also says in the diagnosis info section:
"Note shift speed point gear engagements for:
-2nd gear
-3rd gear
-Overdrive...
Note the speed shift point for TCC apply. This should occur while in 3rd gear or Overdrive."

This basically seems to further the theory that there are in fact 4 real gears, and a TCC lockup available on the 3rd and 4th gear. (although throughout the FSM, "4th gear" is referred to only as Overdrive, but that'* not really important)


This is evidence enough for me to say that there are truly 4 gears in the Turbo Hydramatic 440-T4 ("THM 440-T4") and that I have done a bad job paying attention to the gear shifts in my car.

As for the later transmissions, I guess that'* up to you all to debate but I also believe it is safe to assume that if the '87'* 440-T4 has 4 gears (plus TCC in 3rd and 4th) then so should the future models.

Fin.

Mike Diaz

a word on terminology,
let OD or Overdrive be equivelant to "4th Gear" as that is how the factory manual referrs to it.
I think its funny that since forever people say things like "shift into overdrive" when they are attempting to connotate stepping up the pace and such when in reality overdrive is actually a lower drive ratio and so you get much less torque out of it. but that'* just an asside.

and in response to the title of this thread:
All bonnevilles since 87 have 4 gears.
Which is 3 + overdrive
But it is important to note that all of them also had torque converter clutch lockup.
However whether you personally feel that the TCC means 'another gear' to you or not is a matter of self-pondering of what your definition of "gear" is in your auto trans.
If you think a gear in this case has to mean a clutch and a band then no the TCC doesn't cout (this is how the rest ofthe world usually takes a gear to be)

But if you take "gear" to mean a different drive ratio then the TCC is another "gear" in that definition.

At that point (if you come to your own mental conclusion that the TCC is a gear) then you still have one final hurdle to jump: This one being "Is the fact that the TCC is available in both 3rd and 4th gears mean that my bonneville has 5 gears (1+2+3+4+4/TCC) or 6 (1+2+3+3/TCC+4+4/TCC) Although I would have to argue in that case that No, even by your definition of 'gear' you still only have 5 gears Because when TCC engages (regardless of whether the car was in 3rd or 4th) you still have the same TCC drive ratio.

I hope that didn't confuse anyone.

mike diaz

p.*. as far as my personal opinion goes, i'd tell someone that "my transmission has 4 speeds but actually has 5 when you count the TCC"

... any questions?

Of course what is a "gear" to a planetary gear set ? The number of available ratios has nothing to do with the number of actuall gears but rather how many clutches it has and in what combination they are applied (and to be really AR, some ratios result from holding the "gear" stationary and letting the others move inside or around it (what is meant by "holding" in the "Clutch Application Chart" on page 4T60-7 (which naturally follows chapter 6) of the 1990 Bonneville Service Manual.

A description of planetary gearsetsmay be found on http://science.howstuffworks.com/gear-ratio4.htm toward the bottom of the page.

However when the TCC engages, there is about a 500 rpm drop at cruising speed so there is the same effect as another gear.

Now to really confuse matters, is third a "gear" ? Like "top" gear in a Muncie or Saganaw gearbox, it is not a geared ratio at all, rather the input shaft is locked to the output shaft which is how you get a 1:1 ratio.

This is often recommended for towing since there is minimal stress on the transmission and lockup eliminates the slip in the torque converter hence third-lockup would have the minimum drag (heat buildup) in the drivetrain.

All valid points. however, for the intensive purposes of this forum, shall we settle on the fact that according to the manufacturer and the general auto industry and reporters thereof, the 1987 and up Pontiac Bonnevilles contain "4speed automatic transmissions."
?