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RWD /4 WD conversion for 5EAT


frank_ster
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So as the title says, i have converted my 5 eat from awd 55% rear 45% front bias to rear wheel drive with transfer clutches to engage the front wheels.

so the car is 100% rear wheel torque with a certain amount able to transfer to the front wheels. the exact amount is yet to be determined and can be modified to suit needs.

 

how .. well the trans mission intermediate shaft is welded and trued to the rear output shaft. The center diff planetary gears are removed, however the vtd ( variable torque distribution) clutches are re installed to provide variable torque to the front wheels that is actuated via hydraulic piston and pressure that is controlled by a electric 12volt solenoid in the trans mission control valve body.

 

the vtd is controlled from the tcu ( transmission control unit) on a active and pasive method. if there is a quick throttle demand the clutches are engaged, as well as high throttle angles. the speeds are monitored and if there is a large difference the tcu will also apply added pressure to make both axles to spin at the same speed. This function also works well with the conversion.

for instance on the lift with wheels in the air the rear wheels spin when put into drive. if the accelerator is pressed slowly the rear accelerates but the front are not driven. If there is a stab to the throttle the front wheels then engage. this would be the case of accelerating from a stop. the large amount of requested torque activates the front wheels to aid in pulling preventing the rear wheels from spinning.

 

modification of adding a 3 position switch to disable the tcm control of the vtd will allow rear wheel drive only for purposes of characteristics of a typical rear wheel drive car. another position to force the vtd to maximum engagement so provide as much torque to the front wheels as possible.

and the last position to allow automatic tcm control of the vtd.

 

what this means ? well rwd on demand if the fun of a rwd car is desired.

auto mode for snowy or slippery roads where subaru awd driving charatics are desired. and full 4wd mode for maximum transfer of torque like how a sti 6mt dccd fucntion witch would in most conditions initiate powerslide and oversteer.

 

The 4 eat ( execpt the 4 eat vtd on vdc cars ) actually functions in the same way but only reversed the front wheels are directly driven and the rear is engaged on a active and passive automatic manor.

 

photos: the two shafts are welded together on the lathe, then i machined the weld, and then i annealed and straitened the shaft ( took me hours to figure out how! ). The shaft is strait with in 0.001" over its length of about 30 inches.

 

test fit into the trans mission,

 

reassembly of the bearings on the output portion of the shaft as well as the vtd clutch hub and speed reluctor ring.

 

reassembly into the center differential carrier with the planets removed.

 

here is a video of the car doing a rear wheel burn out.

 

[ame=http://www.youtube.com/watch?v=r1lw7EHm7Ig]Buckaru rwd / 4wd - YouTube[/ame]

 

i will make some more videos of the car on wet grass or mud showing the front wheels engaging.

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Edited by frank_ster

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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well its been a week and its not making any grinding noises:)

 

need to install the switch to disable the auto 4wd.

 

been getting the ass end out but the front wheels engage and bring it back!

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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^ in normal driving no. if you decide to start tractor pulling on pavement for long distances then yes as the clutches are the only means of power to the front wheels. but if there are clutches added to the stack using thinner steel plates the strength of the front clutches would be as strong as the torque output of the engine.

 

i would eventually like to put it on a awd dyno just so see what kind of torque can be transmitted through the stock clutch pack. to the front wheels.

 

but don't forget this setup makes it exactly like a 4 eat

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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driving home yesturday in the rain with rwd only .. eeh! i remember now why i hated rwd cars ! .. damm at an intersection and it shifts hard into 2nd and teh car wanted to do the helicopter.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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^ intermediate and out put shafts need to be welded together.

the job can be easily done with tranny under the car same as center diff bushings install.

 

then electrical if rwd only mode is desired.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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would be good if i could get the parts from all the persons whom broke their center diffs. i could use those broken parts to make a kit. it would be a easy install same difficulty as replacing the center diff bushings. i could do it with in 2 hours.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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^ lol thats never gonna happen on this site !

 

update .. did some mud bogging with it and front wheels flung pretty good rooster tails !

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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this is a 4 eat from a while back. i would think its modded in the exact same way.

notice it does a burnout. but then you see the slicks on the front wheels.

 

[ame=http://www.youtube.com/watch?v=lxrWLysvC9s&playnext=1&feature=grec_index&list=TLlY1-3LxwF6k]Worlds Fastest Stock Chassis AWD 4CYL Subaru WRX STI - 8.358@163.16 MPH - YouTube[/ame]

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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I have been Playin more and more my front wheels aren't driving nearly anything. Things felt funky with those clutches since my rear axle poped out of the differential. About a year ago

I have another set of clutches from my spare tranny I'm gonna put in.

It's a little strange I wonder if that piston has a limited movement range. So it's trying to apply pressure but its just not reaching. Or something didn't line up during assembly.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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i looked at my spare tailhousing and actuated the piston with a air nozzel and looked at the movement of the transfer piston . it moves about between 5/16 and 3/8" (8-10 mm) its limited to a hard stop

 

i took the spare clutches and they dont looks obviously better than my other ones.

 

so i'll look into it this week

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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Yeah, the piston travel (10mm) versus the transfer clutch pack gap (<2mm) is a huge difference. It's definitely fully activating. You might consider pulling out the thicker steels and adding some frictions and the thin steels to transfer more torque. I haven't played with the numbers there yet, but it's definitely possible. You can probably add two frictions and steels for about a 50% upgrade.
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^ yep I was planning on it .

But I don't think it's activating its difficult to measure the transfer clutch and piston since they are on two separate peices. It's like there is a 10.5 mm clearance right now andthe piston does engage te front wheels spin but there is practically 1 ft lb of torque right now.

I playe with it when it was awd years ago with front wheels on ice and rear on cement I did a burn out so I know the transfer clutches have the ability. There is just something wrong right now.

Not sure if the piston o ring blew out or what.

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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so i pulled it apart and it looks like one the the frictions slipped off the end of the splined drum and made it so the others could not get any pressure.

 

measured the stack and its 20 mm thick. measured the assembly and there is 50 mm on the clutch pack and the piston is 54.4 mm down in the hole. so there was about 4 mm clearence. the other clutch pack i took from my other tranny the assembly is 22.5 mm thick. leaving 2 mm clearance.

 

the inner spline drum is 18 mm thick so where the frictions could be 1 could be added using the stock steels of 1.5 mm thick. that limiting 5 frictions over the stock 4. if thinner 1 mm frictions and or steels could be found there could be 6 possibly 7 in the stack.

 

there are two thick steels about 3-4 mm thickness that are spacers after the frictions. so there would have to be at least one of those left there. to keep frictions from falling off the end.

Edited by frank_ster

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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so its back together its better but still not where i would like it to be.

the free ssm data view shows 600 kpa. and the manual says it should be about 900 at wot.

this is requested pressure as far as i can tell,

i think the next step would be put a gauge to see the actual pressure.

 

the manual also says the voltage to the transfer solonoid is only 2-3 volts so would indicate a fairly low duty cycle.

Edited by frank_ster

Now that's thinking out of the boxer!:lol:

fyi all 05 + legacy's have built in code reader

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