How bad is it driving with O/D off?

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guinnessman

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Sometimes i'll drive on the highway (60-70mph) with overdrive off, i just love the way my Mark sounds like this with no mufflers. I'm in the area of 2500-2700rpms i believe (3.27 lsc).

We're talking short highway drives to work around 15 minutes etc. Will the fluid heat up much faster in the transmission? Wear faster? Torque Converter getting killed? Do i have to worry about anything basically besides BAD gas mileage?
 
Absolutely not! 4.10's would put you in that same range with o/d on and many members here drive like that with zero adverse reactions.
 
ripped camel said:
Absolutely not! 4.10's would put you in that same range with o/d on and many members here drive like that with zero adverse reactions.
Click to expand...


actually this is incorrect..

just because its the same rpm range as cars with gears it doesnt mean "its the same", because its not.
try to stick with WHAT YOU KNOW Derek.

in 3rd the stock programming has some issues that mean you dont want to run around in a prolonged state of OD cancel.

it can cause increased torque convertor slip, thus increasing trans temps, which happens when you cancel OD.

this coupled with the factory "steady state slip" can do bad things to your trans.
short times in OD cancel shouldnt be a huge issue, extended periods..could be bad if you dont have a trans temp gauge.
 
Unless I'm on streets that are 45 mph or above, I leave mine off. I can do without all the half ass "wanna shifts into O/D" on the short streets but I always keep it on when I'm on the HWY.
 
Posted in 2001 by JW/Jerry:


JW Fri May-25-01 10:57 PM
Charter member
206 posts
#2. "RE: Overdrive Off"
In response to Reply # 1



I don't know if I posted this on this board or not, but hear goes.

Unless you have the right hardware/chip, I would not drivearound in OD Cancel mode. Here is why.

First off, and most important, is the "dreaded shudder". In short, the shudder is caused by a breakdown between the oil/friction interface in the converter clutch. No matter what they claim, no shift kit can fix this, just give you harsh lockups. The converter clutch friction builds up alot of heat in 3rd gear for this reason. The converter clutch in the AODE/4R70W can be calibrated to slip at steady state in different gears. On the Marks it slips in 2nd and 3rd gear. Now think about this, you have enough apply force to hold 200 ft-lbs of torque pushing on the lockup plate, but it is slipping 20-50 rpm. Think of the heat that generates. This is the heat that causes shudder. Now you guys with 97/98 Marks have a much better calibration for this than the 96 and older guys, but the newer ones still slip, just a smaller window. When you drive around in OD Cancel mode, you are constantly slipping the torque converter clutch making heat. Heat is bad. A chip can remove the slip from the slip tables and eliminate this amount of heat build up.

The other reason is for you guys with roller ONE WAY CLUTCHES. The intermediate one way overruns, spins, in 3rd gear. The easiest way to hurt a one way clutch is to go from overrunning to locked, or a 3-2 shift. A high speed 3-2 downshift can hurt, of fail, a fragile one way clutch. You are less likely to do 3-2's if you are in 4th gear.

jerry
 
Thanks XLRVIII, That's useful info. Not that I do this often, but sometimes when I'm getting off the highway, I will down shift just to hear the car. I DO NOT do this very often and never when I'm in high RPM's, but it will jump up to 3500 or so. This is always done with the O/D on, so I'm assuming I'm going from 4th to 3rd. In the back of my mind I knew it wasn't helping the tranny, but I love hearing it once in a while, on a nice spring day, with the windows down. I will stop doing this all together, no sense in hurting the girl. I'm running a 3400 stall with the 3.27's, any other advice or insight you would like to share?
 
^even the owners manual states you can turn off OD to improve/increase engine braking

that doesnt mean subsequent downshifts from 3-2, and from 2-1 should be done manually
 
XLRVIII said:
actually this is incorrect..

just because its the same rpm range as cars with gears it doesnt mean "its the same", because its not.
try to stick with WHAT YOU KNOW Derek.

in 3rd the stock programming has some issues that mean you dont want to run around in a prolonged state of OD cancel.

it can cause increased torque convertor slip, thus increasing trans temps, which happens when you cancel OD.

this coupled with the factory "steady state slip" can do bad things to your trans.
short times in OD cancel shouldnt be a huge issue, extended periods..could be bad if you dont have a trans temp gauge.
Click to expand...
+1 We are kindered spirits my fiend. :p

I was looking at the programming before and noticed all the little pressure differences for 3rd gear running and can see where prolonged driving in 3rd could cause pump and TC issues.

The engine itself dont care but the trans does. My car spends 2 hours every single day at 2700-2800 RPM and the engine seems very happy there.... other then the crappy mileage. I cant get it above 18.4mpg :(
 
XLRVIII said:
^even the owners manual states you can turn off OD to improve/increase engine braking

that doesnt mean subsequent downshifts from 3-2, and from 2-1 should be done manually
Click to expand...
I use manual 4-3 downshifts quite often on these back roads. When I enter a corner at 70 I want to keep the rear loaded and in 4th its just not loaded enough and I can hear the rear tires start to slip. In third they stay nice and hooked as I can easily keep some more weight back there.
 
XLRVIII said:
actually this is incorrect..

just because its the same rpm range as cars with gears it doesnt mean "its the same", because its not.
try to stick with WHAT YOU KNOW Derek.

in 3rd the stock programming has some issues that mean you dont want to run around in a prolonged state of OD cancel.

it can cause increased torque convertor slip, thus increasing trans temps, which happens when you cancel OD.

this coupled with the factory "steady state slip" can do bad things to your trans.
short times in OD cancel shouldnt be a huge issue, extended periods..could be bad if you dont have a trans temp gauge.
Click to expand...

Learn something new everyday. I thought engine wear and heat was directly related to RPM's and length of time a specific RPM was held.

Maybe I didn't retain what you said right on the gear aspect but why is it acceptable for the car to run in that RPM range with gears as opposed to not with gears...A dumbed down answer would be nice for us that need bigger spoons :D
 
Ripped, your answer was incorrect even in the original context of the thread.
he was never concerned with ENGINE SPEED/ rpms.

he asked about increased trans fluid temp and related issues "Will the fluid heat up much faster in the transmission? Wear faster? Torque Converter getting killed? Do i have to worry about anything basically besides BAD gas mileage?"

To wit: all his concerns are real and valid

Now, Roll up the blank piece of paper that someday will be your "Lawyerin' Dugree",
Roll it up into a funnel shaped hat, place it on your head and go sit in the corner.
(this IS still "kick derek in the nutz month...isn't it?)
 
:d
xlrviii said:
the converter clutch in the aode/4r70w can be calibrated to slip at steady state in different gears. on the marks it slips in 2nd and 3rd gear. now think about this, you have enough apply force to hold 200 ft-lbs of torque pushing on the lockup plate, but it is slipping 20-50 rpm. Think of the heat that generates
Click to expand...
 
XLRVIII said:
The easiest way to hurt a one way clutch is to go from overrunning to locked, or a 3-2 shift. A high speed 3-2 downshift can hurt, of fail, a fragile one way clutch. You are less likely to do 3-2's if you are in 4th gear.
Click to expand...

So now 3-2 downshifts are bad for your car? I always heard 4-2 was a bad idea, so obviously I would turn off O/D when I wanted to give it the beans. :confused:
 
on a pre 98 4r70w any forced downshifts are pretty much bad news.
turning off your OD helps, dont doubt that for a second
it does not engage bulletproof mode

turn off od when your thrashing it, leave the shifter in drive otherwise.
anything else is "rolling the dice"..IMHO
 
XLRVIII said:
Ripped, your answer was incorrect even in the original context of the thread.
he was never concerned with ENGINE SPEED/ rpms.

he asked about increased trans fluid temp and related issues "Will the fluid heat up much faster in the transmission? Wear faster? Torque Converter getting killed? Do i have to worry about anything basically besides BAD gas mileage?"

To wit: all his concerns are real and valid

Now, Roll up the blank piece of paper that someday will be your "Lawyerin' Dugree",
Roll it up into a funnel shaped hat, place it on your head and go sit in the corner.
(this IS still "kick derek in the nutz month...isn't it?)
Click to expand...

In the original context of the thread I understood what he was asking and my answer absolutely was related. I mentioned RPM's because I was making the point that people with 4.10's that are at a similar RPM on the highway don't have any issues which was insinuating there were no adverse reactions reported by people running at that RPM. Are you saying that 2000RPM's are no harder on a driveline than 7000RPM's?

He in fact did mention an RPM range which is why I brought it up in the first place, and explained the reasoning behind my logical conclusion. However you showed that even though my conclusion at first sight may have looked logical it was incorrect when looked at in a more in depth analysis between tranny in o/d with 4.10's and tranny with o/d off with stock gears.

I guess I'll sit in the corner with my future degree now.....So I guess that means if we get into a philosophical conversation or a legal one you'll be wearing your dunce cap because that's my area of expertise (legal will be later, philosophy is now)...?
 
I too leave my OD off in 'around town' driving-the OD will engage as low as 38mph, much too low IMO. If on a highway/xway, I will leave it on. I think what is more important for these trans is having a cooler after the radiator cooler, heat is bad for any trans but these seem especially vulnerable.
 
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