NEVER gas & brake as same time

[rob-the-oil-nut]

One of my favorite mechanics was telling me about transmissions and how ATF should be changed a lot more often than most people do. Towing, weight of passengers, etc all played a factor. This is mainly covered in another post
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=8;t=001675
but I wanted to deal with this specific issue in a seperate one...
Among other things, he said to NEVER have the gas and brake on at the same time to get a faster launch from a stop. Not even once. Not even with synthetic ATF, not even with RedLine, not even revving to only 2000 rpm. This was in the context of my entirely stock auto trans with stock TC (Torque Converter) and I'm not saying this has anything to do with racing cars or the like.
He explained it only takes a second for one portion of the fluid to over-heat and thus cause a chemical reaction. A trans cooler (not applicable in my case) would NOT prevent this.
BTW what about revving to a fast idle with the gas & brake both on, at colder than -20??
Counter-point? Agreement? Clarification? I'd like to hear from you.
Please & thankyou
Rob-the-oil-nut

[ April 15, 2004, 07:11 AM: Message edited by: rob-the-oil-nut ]

 

[Schmoe]

I don't know about that.....I know I've done that umpteen times in my truck to smoke the tires and have never noticed contaminated trans fluid when I changed it out. The only harm I could think of is that if you were "power braking," as we call it here, the clutches might slip and then they would prematurely die. But if the tire spin is fast enough, the clutches would lock and then there wouldn't be a problem. If you sat there and power braked for a long time, maybe the trans might over heat.....I would have to respectfully disagree with your mechanic.

 

[novadude]

The torque converter generates a LOT of heat when you "stall" it. All that engine power has to go somewhere. If the wheels aren't moving, the power gets converted to heat. Simple (work in) = (work out) relationship.

I wouldn't say "never", but I certainly think it is a bad idea to do this for any length of time. If you limit it to a few seconds, I do not see the harm. Remember, fluid is constantly being pumped through the converter, it is not like a sealed fluid coupling. With oil flowing through the converter, I can't see it getting super hot in 1-2 seconds. If this was true, you be burning up fluid everytime you pull a hill in a higher gear with the TCC unlocked.

[ April 15, 2004, 11:26 AM: Message edited by: novadude ]

 

[Gary Allan]

I think that what is being evidenced is the fact that ATF is more of a coolant than a lubricant. If it's overheated it allows metal to metal contact very easily. Many FWD transaxles are lunched because the housing gets worn after the owner spins tires in a snow bank. The fluid only has so much tolerance for excessive heat.

Keep in mind that usually the entire transaxle is lubricated with ATF. I would think that if you compared the heavy gear lubes with their phosphorus high pressure tolerance formulas to ATF you would see that it would be far easier to destroy a trans(axle) lubed with ATF.

The trans doesn't know that the brake's being applied ..it only sees load. Typically most of your heavy towing (or other loads) is done in a RWD vehicle. Hence, IMHO, you don't see the "spontanious" failures that this guy was referring to.

Would your rear last with ATF in it??

 

[Patman]

I do that everytime I pull into the burnout box before I make a run down the quarter mile in my car. I don't have an exact number on how many runs I've made with this car, but it's over 100 for sure. I've done the same in other auto equipped cars I've drag raced with too. Not once has an auto trans grenaded on me.

 

[XS650]

When you rev the engine in gear with the brakes on, the only slippage in the transmission is in the torque coverter where most of the oil is in the transmission. There is not "slippage" of parts in contact with each other, it's all hydraulic. The torque converter has a few quarts of fluid (most of the oil in the trans) being circulated and mixed very rapidly. When your mechanic says that it will "one portion of the fluid to over-heat ", it just shows that he doesnt have a clue how an automatic tranmission works. Not a good thing for a mechanic. How deep is his cluelssness? Time to find another mechanic?

 

[tom slick]

i'd hate to see what he has to say about the effects of a "trans-brake" for drag racing