Quick Torque Converter Question + general transmission data

[rg2098]

Occasionally I need to pull out really fast where I live. Usually I put my foot on the brake and accelerator at the same time to get the RPMs as close to the turbo as I can. My only question is it safe for the torque converter? I just installed a rebuilt trans and it still had a harsh 1-2 shift but today after doing my pull out fast trick I smelled ATF but no leaks anywhere and it shifts nice now. Did I blow something out good or bad?

[boneheaddoctor]

Originally Posted by rg2098

Occasionally I need to pull out really fast where I live. Usually I put my foot on the brake and accelerator at the same time to get the RPMs as close to the turbo as I can. My only question is it safe for the torque converter? I just installed a rebuilt trans and it still had a harsh 1-2 shift but today after doing my pull out fast trick I smelled ATF but no leaks anywhere and it shifts nice now. Did I blow something out good or bad?

Its more dangerous for the tranny than the touque converter....but its NOT the best way to get a long life out of either for sure.

[pawoSD]

I sometimes have to turn fast by my school to make a turn on a street where cars are allllways coming in the morning, but punching the pedal on my SD results in a VERY brisk takeoff....followed by one of the rear tires going "reeet!" during the 1-2 shift during the turn....it moves very fast. I can't imagine trying to pull off a turn faster than the car can do, thats way risky. Wait for a bigger gap! Factory spec says 4.2 secs for an SD to hit 35mph, I know mine does it in less than that....I'd say 3.5 seconds...tops. My maxed out ALDA helps a lot too, I can take off like lightning.

[rg2098]

Originally Posted by pawoSD

I sometimes have to turn fast by my school to make a turn on a street where cars are allllways coming in the morning, but punching the pedal on my SD results in a VERY brisk takeoff....followed by one of the rear tires going "reeet!" during the 1-2 shift during the turn....it moves very fast. I can't imagine trying to pull off a turn faster than the car can do, thats way risky. Wait for a bigger gap! Factory spec says 4.2 secs for an SD to hit 35mph, I know mine does it in less than that....I'd say 3.5 seconds...tops. My maxed out ALDA helps a lot too, I can take off like lightning.

My ALDA is stock, we are probably at the same speed at fast takeoff. I don't do it all the time and usually can get it up to 1500. Also I don't hold it there, rev up when I see the gap and GO. I only do it when I need to in rush hour traffic where a big gap is usually quite small.

[whunter]

is a great way to fry the clutch plates and fluid.

We need to talk, before you fry the transmission...

[rg2098]

Fluid level is perfect, not burned at all, everythings normal now. I could do worse, like the idiots at school that rev up to redline then slam into D in their new toyotas and pontiacs. Or Starting by placing foot against floor with pedal inbetween foot and floor, turn key, release foot when RPMs hit redline.

Ok word is to stop doing it so I shall, now I need to figure out how to shim the ALDA instead (I like the black plastic cap)

[MB-Owner-in-ind]

Doing this won't hurt the transmission or the torque converter as long as you don't hold it for a long time and heat up the tranny fluid. While you are holding the brake the only thing moving is the TC and the front pump and they will only heat up the fluid with no wear what so ever to the clutches that aren't turning.

[Brian Carlton]

Originally Posted by boneheaddoctor

Its more dangerous for the tranny than the touque converter....but its NOT the best way to get a long life out of either for sure.

I'm inclined to believe that brake torque won't have any affect on a properly designed trans. Unless the clutches slip, there is no wear on the trans due to this practice.

Of course, as said above, the fluid will heat up in the torque converter as a function of time. If the brake torque is simply for three seconds or so, I don't see how any damage can occur, even if this practice is repeated on a frequent (several times per day) basis.

[boneheaddoctor]

Originally Posted by Brian Carlton

I'm inclined to believe that brake torque won't have any affect on a properly designed trans. Unless the clutches slip, there is no wear on the trans due to this practice.

Of course, as said above, the fluid will heat up in the torque converter as a function of time. If the brake torque is simply for three seconds or so, I don't see how any damage can occur, even if this practice is repeated on a frequent (several times per day) basis.

Strain...its just like trying to tow a trailer at way over the rated GVW of the vehicle. Lot of teens fry mommy and daddies transmissions doing this trying to get tire...the damage is cumulative till one day...poof...you end up calling a tow truck.

Talk to a tranny guy sometime....He will back up what I just said.

[Brian Carlton]

Originally Posted by boneheaddoctor

Strain...its just like trying to tow a trailer at way over the rated GVW of the vehicle. Lot of teens fry mommy and daddies transmissions doing this trying to get tire...the damage is cumulative till one day...poof...you end up calling a tow truck.

Talk to a tranny guy sometime....He will back up what I just said.

Not on the topic.

The discussion is brake torque. The vehicle is not moving and the clutches are not engaging or disengaging. So, there is no wear on the clutches.

You are speaking of high powered shifts where there is significant clutch wear and high heat conditions for an extended period.

Why would I want to talk to a "tranny guy"? I'm a mechanical engineer, as you know.

[boneheaddoctor]

Originally Posted by Brian Carlton

Not on the topic.

The discussion is brake torque. The vehicle is not moving and the clutches are not engaging or disengaging. So, there is no wear on the clutches.

You are speaking of high powered shifts where there is significant clutch wear and high heat conditions for an extended period.

Why would I want to talk to a "tranny guy"? I'm a mechanical engineer, as you know.

It is pertanent..and on topic...exactly what is holding the engine output and disipating it? The transmission.

I know you are talking drop shifting...thats not what I was talking about....
and that is a whole different issue I agree, and is far worse.

Yes I know you are a mechanical engineer...but you are not an experienced Transmission mechanic....I got that from several long time and very good mechanics who do that for a living. The strain you are exerting on the trans is exactly the same as towing a trailer that is way too heavy for the vehicle..or drag racing....as far as the type of load the trans sees which is a heavy load.

And it will shorten the life of the transmission.

[Brian Carlton]

Originally Posted by boneheaddoctor

It is pertanent..and on topic...exactly what is holding the engine output and disipating it? The transmission.

Wrong again.

The transmission is not dissipating anything. It's just sitting there with torque on its input shaft and through its gears and out through the drive shaft to the rear wheels. There is no wear on the transmission.

The dissipation of the engine output torque is performed by the torque converter in the form of heat. The torque converter is more than capable of handling three seconds of full engine output torque without overheating the fluid.

The strain of a short period of brake torque has no relevance to pulling a heavy trailer for an extended period of time. Totally different and irrelevant situation. Maybe you ought to stop speaking to these so called "mechanics" and listen to someone who knows how a transmission operates.

[boneheaddoctor]

Originally Posted by Brian Carlton

Wrong again.

The transmission is not dissipating anything. It's just sitting there with torque on its input shaft and through its gears and out through the drive shaft to the rear wheels. There is no wear on the transmission.

The dissipation of the engine output torque is performed by the torque converter in the form of heat. The torque converter is more than capable of handling three seconds of full engine output torque without overheating the fluid.

The strain of a short period of brake torque has no relevance to pulling a heavy trailer for an extended period of time. Totally different and irrelevant situation. Maybe you ought to stop speaking to these so called "mechanics" and listen to someone who knows how a transmission operates.

no..then exactly where is the rotational energy of the crankshaft going if its not in neutral? That torque converter IS dispating that energy right up until it hits its stall speed......and trans hydraulic pressures do climb quite high during that time.

Talk to drag racers because that is exactly how they stage a car until launch...and thats damned hard on a transmission...lotta transmissions die right at that time.

Heck talk to Roy...........WHunter.. He will tell you the same.

[deerefanatic]

Ok guys, cool off a little.

You're both right in a sense of the way, and both or your arguments make sense. I agree with bhd on the fact that this is not a practice you should do often, but with brian on the fact that doing it once in a while for a true emergency (think, wreck avoidance) is OK.

[Brian Carlton]

Originally Posted by boneheaddoctor

no..then exactly where is the rotational energy of the crankshaft going if its not in neutral? That torque converter IS dispating that energy right up until it hits its stall speed......and trans hydraulic pressures do climb quite high during that time.

Talk to drag racers because that is exactly how they stage a car until launch...and thats damned hard on a transmission...lotta transmissions die right at that time.

Heck talk to Roy...........WHunter.. He will tell you the same.

I already told you where the rotational energy of the crankshaft is going...........into heat generated by the torque converter. The torque converter dissipates the energy at all times, even at stall speed. The energy is converted to heat within the torque converter. The transmission is not affected by this process. Trans hydraulic pressures are well within operating limits and won't cause excess wear on the transmission for the three seconds that we are speaking about on this topic.

Drag racing has nothing to do with this topic. Again, stay with me here.......we are talking about brake torque for three seconds.........nothing more and nothing less.

If a transmission dies on brake torque then it wasn't designed to handle full engine output torque anyway. Brake torque didn't kill it. Too much torque killed it. It would have died anyway.

Roy is too busy ressurecting old threads for new members.