Offroad gearbox build

[Rally]

Even with a locked diff, the raised wheel will still be spinning, will still have power going through it when it lands. The shock load may be less however.

 

[NachaLuva]

Even with a locked diff, the raised wheel will still be spinning, will still have power going through it when it lands. The shock load may be less however.

Yes true. My thinking is instead of all the power going to the lifted wheel making it spin wildly & the engine to rev up, it will be locked to the wheel with grip so will spin at that speed. So when it comes down there wont be much inertia

 

[Dedman]

The way I see it is that with a locked diff there will be very little slip of the wheel on the ground as it has most of the weight of the car on it. This means that the car should move over the ground at close to the same rate at which the wheel in the air is turning meaning there will be little shock load when it lands. In the event that the wheel on the ground is spinning wildy then there is most likely very low traction so when the wheel in the air comes down it will probably keep spinning due to how slippery the terrain is meaning there will be low shock load again. Im sure there are exceptions to this but for the most part I think it would be far kinder on the drive train than open or lsd diffs when attempting the same terrain.

 

[jf1sf5]

My thoughts Dedman.

I think that the best combination is a torsen type differential front, DCCD in the middle and a clutch type differential in the rear.

 

[Rally]

That is true Dedman I would imagine in most situations. But I know with my plated rear, when I do up hill hairpin turns, the inside rear lifts and when it comes down the tyre chirps.

 

[Dedman]

I am starting to lean towards just sticking with commercial available parts for the gearbox as I dont have faith in my ability to produce durable locking diffs and unlike a rear diff its a lot harder to test prototypes and potentially far more painful and expensive if they fail.

The next decision is what front diff to go for. Helical or plated. I am currently thinking helical as it is less noticeable in a DD but I am not sure how well they actually perform. Does any one know what the max torque bias capable from the different subaru 'torsen' style LSDs?

 

[taza]

I have a spare 6 seed sti diff if your keen? From a pignose sti, aus spec, low km. Its helical.

Rally, Venom and Elfreddo swear by their. Combine with something tight in the rear and something in the centre it'll help.
So with a clutch type in the front you hwve to keep splitting and pulling apart the gesrbox to adjust it every so often. Helical/torsion is maintenence free!

 

[El_Freddo]

The 0.78 5th from the L series box would be a good option but I am not sure if it is compatible. The ratios from 3rd to 5th from the L series box would actually be a good conversion to compensate for the taller final drive.

AFAIK the L series 5th gear is not interchangeable with the EJ layshaft. And the 3rd to 5th of the L box I don't think will interchange unless you've got one of the harder to find L AWD boxes where you can use the whole gearset from that box.

I disagree, a locker allows you to slow down and drive more carefully on the same terrain, crawl instead of bash your way through.

Too right - or as we witnessed last weekend to allow you to go foot to the floor and know all four wheels are going to do the same thing regardless of the surface traction

I had a fault recently with my DCCD controller in my WRX, whereby the auto function failed and I had to use full manual control. Just by locking the centre diff, I could hardly turn the car and I had to manhandle the thing just to swerve through witches hats. The car had fantastic grip, but the car would just not turn. So think what a locked front diff would do to your steering.

On bitumen I can see how that would happen. On a loose surface it'll be different. Also with a manual locker up front you can turn it on and off as needed, which is exactly why I'd want one in my gearbox (and in the rear too!).

We're starting to blur the lines between why we want lockers as Dedman is talking about offroading with lockers - you just can't go past them for ultimate traction! No two ways about it.

The next decision is what front diff to go for. Helical or plated. I am currently thinking helical as it is less noticeable in a DD but I am not sure how well they actually perform. Does any one know what the max torque bias capable from the different subaru 'torsen' style LSDs?

No idea on the torque bias but my cheap OBX unit does the job well, even more so when pushed. Can't go past a traction device up front!

Rally, Venom and Elfreddo swear by their. Combine with something tight in the rear and something in the centre it'll help.
So with a clutch type in the front you hwve to keep splitting and pulling apart the gesrbox to adjust it every so often. Helical/torsion is maintenence free!

Yeah as Taza says, I'm very happy with mine. I do wish I got the factory subaru unit as they started popping up on fleabay for a hundred more than what I paid for the OBX unit. But the OBX is doing a good job and it doesn't make any noise. It does need to have the wheel without traction *just* touching the ground to be of use though.

Venom no longer runs a helical front diff - hasn't for some time now.

I've still only got an open diff in the rear and it's not much of a hinderance in the grand scheme of things. I'll happily wait for a rear locker to appear - then it'll be stepping things up a whole new level in offroad ability!

As for your build Dedman - go the 4.44, you won't regret it even with the extra work required to fit the L series low range in there

Cheers

Bennie

 

[Rally]

Compromise. You can go 4.44 if you want, but I look at the fact that I travel some distances to go off road, plus normal driving. Lots of annoying high revs and increased fuel consumption. For that reason I have elected not to go 4.44 and you may wish to keep those factors of noise and consumption in mind.

I am delighted with my STI front diff and plated rear diff. I also find the 1.447 low range a good improvement as well. Had I the time to try and install 1.59, I would have.

 

[Dedman]

Compromise. You can go 4.44 if you want, but I look at the fact that I travel some distances to go off road, plus normal driving. Lots of annoying high revs and increased fuel consumption.

Yes if I decided to go down the 4.44 route the I would only do so if I could install a taller 5th gear to compensate. 0.78 5th out of a L or SG would see a 3.2% drop in rpm or a .825 out of many of the 4.44 boxes would see a 2.4% incease. Bearable but I would prefer the SG 5th

 

[NachaLuva]

I think that the best combination is a torsen type differential front, DCCD in the middle and a clutch type differential in the rear.

+1, I think thats what I'll be doing

I have a spare 6 seed sti diff if your keen? From a pignose sti, aus spec, low km. Its helical.

I'm interested in your diff Taza, can you PM me how much you want for it?

I am delighted with my STI front diff and plated rear diff.

Is yours a plated or helical front diff?

 

[Rally]

Helical.

 

[Dedman]

AFAIK the L series 5th gear is not interchangeable with the EJ layshaft. And the 3rd to 5th of the L box I don't think will interchange unless you've got one of the harder to find L AWD boxes where you can use the whole gearset from that box.

Bugger. I was hoping it might be a direct swap as the SG 5th is the same ratio as the Ls and I was hoping it was just going to be a case of Subaru lego

But the OBX is doing a good job and it doesn't make any noise. It does need to have the wheel without traction *just* touching the ground to be of use though.

Have you tried driving through the brakes with it? This was the main reason why I was curious of the torque bias of these diffs because unlike vehicles with open diffs driving through the brakes actually makes sense mechanically with a helical diff.

I have a spare 6 seed sti diff if your keen? From a pignose sti, aus spec, low km. Its helical.

I'm interested in your diff Taza, can you PM me how much you want for it?

I'm hoping to get a 5 speed DCCD lsd box and use the lsd, DCCD and 4.44 gearing from that so the diff is all yours NachaLuva. If you are still trying to get rid of it at a later date I might be interested if its not gone by then.

I am also concerned as I have not heard of anyone installing a 6 speed lsd with L low range

 

[Rally]

Once you have done all that Dedman come up to Sydney and show us. Might be able to put it through it's paces at the same time.

 

[El_Freddo]

Have you tried driving through the brakes with it? This was the main reason why I was curious of the torque bias of these diffs because unlike vehicles with open diffs driving through the brakes actually makes sense mechanically with a helical diff.

Nah I don't think so - either haven't had the situation to do it or I've not been quick enough/lost too much momentum and had to try a second approach...

Also forgot to mention that to fit the OBX LSD you need to shave the opposite edge from the crown wheel to clear the L series low range. This shaving takes off part of the bolt head that holds it all together. Definitely not ideal, I only did it as others had done it before me and not had issues.

Like I've said, I'd chase down a factory front helical ex japan on fleabay if I did it again...

Cheers

Bennie

 

[Dedman]

Pulled out my 1.5928:1 L series gearset today and cleaned it up. A few little trick caught me out but I got there in the end.

Cant wait to get my other parts so I can do some assembling instead of just disassembling!

 

[jf1sf5]

Nice, remembers me last year….there's gonna be machining soon ! Are you following Phizinza's thread ?

 

[Dedman]

Yep following a few different threads. Do you know what box your DCCD came from? What gearbox did you put it all into as well?

 

[jf1sf5]

It comes from a TY752VB6EA gearbox out of a '97 V4 STI RA V-LIMITED and put all into a 4 bolt dual range '97 Forester.

If your Foz is a '99+, it will only fit with the housing as the parts inside the housing are not interchangeable (different splines on the diff, different diff…)

I did the housing bolt off/on and its an easy job !

 

[NachaLuva]

I've been told to get the complete DCCD assembly as well, housing, diff & esp the input shaft. Don't forget the input shaft!