torque split?

[JackV]

does anyone know the torque split on an 87 RX?

[GeneralDisorder]

50/50 front/rear when the diff is locked. Otherwise there is no torque split. The power goes to whichever wheel has the least traction. The RX transmission has a fully open center differential with no traction aids whatsoever. It should have a rear limited slip diff but that won't help you if a front wheel is off the ground (unless you lock-in).

 

Unless it's a 4 speed automatic RX? In which case it's variable depending on the duty-c solenoid.

 

GD

Edited November 7, 2009 by GeneralDisorder

[idosubaru]

Unless it's a 4 speed automatic RX? In which case it's variable depending on the duty-c solenoid.

 

GD

variable up to 60/40

[Numbchux]

variable up to 60/40

 

not really....no.

 

 

autos are 100% to the front wheels. all the time. period.

 

then they direct power to the back as-needed.

[eulogious]

not really....no.

 

 

autos are 100% to the front wheels. all the time. period.

 

then they direct power to the back as-needed.

 

Not with the 4EAT, 90/10 to start. That's why they call it Full Time 4WD, not AWD At least that's what I have read recently when I looked into what the duty c solenoid did in the 4EAT. The 3AT I know nothing about. I also don't know about the RX...

Edited November 8, 2009 by eulogious

[Numbchux]

Not with the 4EAT, 90/10 to start. That's why they call it Full Time 4WD, not AWD At least that's what I have read recently when I looked into what the duty c solenoid did in the 4EAT. The 3AT I know nothing about. I also don't know about the RX though...

 

where did you read that? it's a common misconception. but the front gets full power, all the time, regardless of what the rear is doing. it's really like 100/10, and then as the TCU puts more pressure on the transfer clutch, it varies up to about 100/80 (only reason it isn't 100/100, is the solenoid/clutch will still slip unless mechanically modified, they will not hold all the power). if your transfer clutch burns out entirely, you loose the rear drive, but you can still drive around fine. it's FWD, and you might not even notice it until it snows and you're stuck

 

and I am talking about the 4EAT. 3ATs are not full-time. so they're 100/0, push the button and they're 100/80.

 

 

torque splits really can't be boiled down to just a number ratio. as so many AWD systems have so many variables to how they react. with a mechanical center diff, like in a subaru 5MT AWD or FT4WD system, it really needs to be out of 200, as if one end is stopped, the other spins twice as fast. so a FT4WD system, unlocked, is 100/100, unless one end sees more resistance, and then it changes, all the way to 200/0, with almost no restriction.

 

a VLSD center (EJ AWD 5MT) changes the amount of resistance depending on how much slip has already occurred. so 100/100, one end loose traction, and it goes to 150/50, then the VLSD heats up, and transfers power to the side with more traction, and it goes back towards 100/100.

[idosubaru]

not really....no.

 

 

autos are 100% to the front wheels. all the time. period.

 

then they direct power to the back as-needed.

no? i'm not sure this peeing contest is really worth anything or valuable.

Subaru FSM suggests that the duty cycle is varied in normal driving mode. not sure why it would suggest that if it's FWD? then line pressure is varied when turning, in 1st gear, and when slippage occurs...etc. sounds variable.

[eulogious]

where did you read that? it's a common misconception. but the front gets full power, all the time, regardless of what the rear is doing. it's really like 100/10, and then as the TCU puts more pressure on the transfer clutch, it varies up to about 100/80 (only reason it isn't 100/100, is the solenoid/clutch will still slip unless mechanically modified, they will not hold all the power). if your transfer clutch burns out entirely, you loose the rear drive, but you can still drive around fine. it's FWD, and you might not even notice it until it snows and you're stuck

 

and I am talking about the 4EAT. 3ATs are not full-time. so they're 100/0, push the button and they're 100/80.

 

 

torque splits really can't be boiled down to just a number ratio. as so many AWD systems have so many variables to how they react. with a mechanical center diff, like in a subaru 5MT AWD or FT4WD system, it really needs to be out of 200, as if one end is stopped, the other spins twice as fast. so a FT4WD system, unlocked, is 100/100, unless one end sees more resistance, and then it changes, all the way to 200/0, with almost no restriction.

 

a VLSD center (EJ AWD 5MT) changes the amount of resistance depending on how much slip has already occurred. so 100/100, one end loose traction, and it goes to 150/50, then the VLSD heats up, and transfers power to the side with more traction, and it goes back towards 100/100.

 

I really don't want to add any more fuel to the fire, and you could be right I don't have any experience in working with these trannys at all. The information that I am going off of was what I researched when trying to add in a switch to enable full 50/50 lockup by disabling the duty C solenoid which causes the MPT clutch to fully lockup giving you virtually 50/50 torque split (I was successfull BTW with the mod, and it works). Here's a link to the thread I started regarding this http://www.ultimatesubaru.org/forum/showthread.php?t=105077. All the info is in there that I found out, and I discussed it in these threads. Like I said, I could be wrong since I am no expert, that's just the information that I have been given by members on here.

 

You are correct that the torque ratio can't really be made using a ratio/number, since the duty C solenoid use a PWM curcuit, the ratio is actually a percentage of the duty cycle that is being applied, so it's very hard to determine was 57% duty cycle is And with that, I have said my piece

[Gloyale]

where did you read that? it's a common misconception. but the front gets full power, all the time, regardless of what the rear is doing. it's really like 100/10, and then as the TCU puts more pressure on the transfer clutch, it varies up to about 100/80 (only reason it isn't 100/100, is the solenoid/clutch will still slip unless mechanically modified, they will not hold all the power). if your transfer clutch burns out entirely, you loose the rear drive, but you can still drive around fine. it's FWD, and you might not even notice it until it snows and you're stuck

 

and I am talking about the 4EAT. 3ATs are not full-time. so they're 100/0, push the button and they're 100/80.

 

 

torque splits really can't be boiled down to just a number ratio. as so many AWD systems have so many variables to how they react. with a mechanical center diff, like in a subaru 5MT AWD or FT4WD system, it really needs to be out of 200, as if one end is stopped, the other spins twice as fast. so a FT4WD system, unlocked, is 100/100, unless one end sees more resistance, and then it changes, all the way to 200/0, with almost no restriction.

 

a VLSD center (EJ AWD 5MT) changes the amount of resistance depending on how much slip has already occurred. so 100/100, one end loose traction, and it goes to 150/50, then the VLSD heats up, and transfers power to the side with more traction, and it goes back towards 100/100.

 

 

This is probably the best description ever on the operation of both the 4EAT and the true differential action of the the 5mt.

[Gloyale]

The information that I am going off of was what I researched when trying to add in a switch to enable full 50/50 lockup by disabling the duty C solenoid which causes the MPT clutch to fully lockup giving you virtually 50/50 torque split (I was successfull BTW with the mod, and it works).

 

The split hair is whether or not the rear engagement is 80% or 90% or 99.44% or 100%

 

The truth is the every 4eat at this point only transfers as much as it's particular clutch will hold. They are all worn and some work great, nearly full locked for all intents and purposes. However, once worn, the engagement can get a bit, well soft or "soggy" would be my best desciption.

 

I've also encountered a few that have sheared the outer hub of the transfer clutch from the end of the main shaft. (It's basically spotwelded onto the end of the shaft in 3 places. I want to build a beefier one for my 4.44)

[eulogious]

This is probably the best description ever on the operation of both the 4EAT and the true differential action of the the 5mt.

 

Well that's good to know, and then I stand corrected Thanks for all the info. Gloyale was very helpful to me in the mod that I mentioned, and seem very knowledgeable about the transmissions. I guess I learned something new today!

 

Edit: Just realized Gloyale posted more info... Thanks for the clarification on everything. I have now learnt all I can for today, at least with subarus ... Time to take some test for my IBM classes :|

Edited November 8, 2009 by eulogious

[JackV]

wow that was alot of good info, thanks you guys.

[Numbchux]

no? i'm not sure this peeing contest is really worth anything or valuable.

Subaru FSM suggests that the duty cycle is varied in normal driving mode. not sure why it would suggest that if it's FWD? then line pressure is varied when turning, in 1st gear, and when slippage occurs...etc. sounds variable.

 

the duty cycle only varies the power to the rear. the front still gets 100% power, regardless of what the rear is doing. You're not wrong, just not exactly right . I was just clarifying.

 

 

saying that it's variable up to 60/40 isn't really true, as it implies that the front gets less power as the rear gets more. which isn't the case.

 

 

This is probably the best description ever on the operation of both the 4EAT and the true differential action of the the 5mt.

 

Glad to hear it. I've heard so many descriptions, and "torque splits" and stuff on the internet that is just wrong. I'm glad to hear someone else who I know has torn apart at least as many transmissions as I have agrees

[idosubaru]

saying that it's variable up to 60/40 isn't really true, as it implies that the front gets less power as the rear gets more. which isn't the case.

excellent, that is what i wanted to hear. it's the hair splitting i don't typically like or find valuable at all...but, if the rear "gets power" does that have to come from somewhere and would have to incur some losses to the front? though that would be a tiny percentage as opposed to the incorrect implication of "transfering" power from one to another? Edited November 9, 2009 by grossgary

[Numbchux]

excellent, that is what i wanted to hear. it's the hair splitting i don't typically like or find valuable at all...but, if the rear "gets power" does that have to come from somewhere and would have to incur some losses to the front? though that would be a tiny percentage as opposed to the incorrect implication of "transfering" power from one to another?

 

yea, it is splitting hairs a bit. it is annoying, but I want to make sure the information is correct as possible.

 

that is a good way to think of it. yea, as the transfer clutches grab, it does use up more of the available power, and therefore making less go to the front. but it is still a 100% mechanical connection from the output shaft to the front pinion shaft. so the front drive speed is still directly proportional to engine speed.

 

you literally could remove the rear driveline from a car with a 4EAT and still drive it. without putting the FWD fuse in, or any other modifications. but not the other way around, and not in a 5MT (the EA FT4WD centers do have the full-lock option, so it's not hard to make them FWD....but it's not the same setting you'd use on pavement).

[idosubaru]

right on i've driven a few FWD "converted" transmissions before of the auto and manual variety.

[WoodsWagon]

you literally could remove the rear driveline from a car with a 4EAT and still drive it. without putting the FWD fuse in, or any other modifications. but not the other way around.

 

Actually no, the 4eat's will lock up the transfer clutches hard enough that the car will drive in rwd with only the TCU controlling it. I had a friend come to me with his legacy, said he was worried that he'd trashed the transmisison. He had heard a bang, and after that it would hesitate to move forward from a stop for a moment, then drive fine. It would spin both rear wheels fine on hardpacked dirt, so it was putting the power of the 2.2 turbo through the transfer clutches just fine. We replaced the front CV that had blown and it was back to AWD.

 

With the broken front cv, the power would go to that axle and spin it, TCU would see that as wheel spin and lock up the transfer clutches, car would lurch forward and drive fine after that. I'm sure with continued use it would smoke the clutches as the TCU would constanly be trying to reduce drive to the rear, see more "front wheelspin" and reaplying rear drive.

[zukiru]

the duty cycle only varies the power to the rear. the front still gets 100% power, regardless of what the rear is doing. You're not wrong, just not exactly right . I was just clarifying.

 

saying that it's variable up to 60/40 isn't really true, as it implies that the front gets less power as the rear gets more. which isn't the case.

 

Glad to hear it. I've heard so many descriptions, and "torque splits" and stuff on the internet that is just wrong. I'm glad to hear someone else who I know has torn apart at least as many transmissions as I have agrees

 

 

when you put it that way I see what you mean.

but when you had more than a 100 percent up there it really got me for a moment

 

I always hated that rump roast who said he'd give 110%

that brown-noser knows good and darn well all he has is 100... and that 75 percent is the most he'll likely give.

 

 

one thing I KNOW for sure... I have 100% to the front wheels at all times.

[idosubaru]

I always hated that rump roast who said he'd give 110%

that's awesome!!

 

Actually no, the 4eat's will lock up the transfer clutches hard enough that the car will drive in rwd with only the TCU controlling it.

 

With the broken front cv,

that was not my experience. I had a broken CV as well in a 4EAT and it was not really drivable...but i didn't try to drive it much. it did a lot of lurching and it was obvious the TCU was "confused" by the loss of the front axles. it barely hobbled around the parking lot.

 

wonder what the difference was?

 

funny thing is that CV axle had like a couple miles on it, it was brand new one of the many reasons i'm now an MWE or Subaru only guy.

[Numbchux]

Actually no, the 4eat's will lock up the transfer clutches hard enough that the car will drive in rwd with only the TCU controlling it. I had a friend come to me with his legacy, said he was worried that he'd trashed the transmisison. He had heard a bang, and after that it would hesitate to move forward from a stop for a moment, then drive fine. It would spin both rear wheels fine on hardpacked dirt, so it was putting the power of the 2.2 turbo through the transfer clutches just fine. We replaced the front CV that had blown and it was back to AWD.

 

With the broken front cv, the power would go to that axle and spin it, TCU would see that as wheel spin and lock up the transfer clutches, car would lurch forward and drive fine after that. I'm sure with continued use it would smoke the clutches as the TCU would constanly be trying to reduce drive to the rear, see more "front wheelspin" and reaplying rear drive.

 

wow. must have been fairly low mileage transfer clutches. I moved my XT6 around a bit with a broken axle, but it didn't like it at all.....once you get moving a little bit, and both speed sensors match, then it tries to release the clutches, at which point, you slow down again, then they lock again...etc. etc.

 

 

put it this way. Years ago when the guys did the Rubicon. Mudrat had a 4EAT in his hatch in front of a divorced tcase. he killed power to the dutyC, and IIRC had brand-new transfer clutches. He said, that even with the substantially lower gearing (something like double the stock EA82 D/R crawl ratio), it would not have driven up a curb. he had to pull it apart and mechanically lock it.