New Build Thread: Subaru 5MT AWD into Syncro Vanagon

[D Clymer]

Entry #1: Something Good. Something Even Better.

It's been two years since I finished the build of my original Subaru 5MT Vanagon. The way this van drives is nothing short of a revelation. The Subaru EJ25 engine comes alive when mated to a transmission with gear ratios that were designed to work hand in hand with the EJ25. The van accelerates smoothly and effortlessly around town and makes easy progress over highway grades due to the perfect gearing.

Since Day 1, the question has been asked many times, "Can we use the Subaru all wheel drive system to make an all wheel drive Vanagon?" Indeed, this has been something Todd at Subarugears and I have discussed many times over the last few years. In fact, we've both had the blueprint in our minds of how to do a Subaru AWD Vanagon for some time, but there were three missing ingredients that had to be custom made to make this drive format a reality.

I'm happy to report that two of the three needed parts arrived on my doorstep last Friday afternoon and I am now ready to get started building the first Vanagon running the Subaru Continuous AWD system.

The first of these necessary parts is a reversed ring and pinion for the Subaru 5MT transmission in the standard Vanagon 4.86:1 final drive ratio. It would have been possible to run one of the Subaru ratios (taller) and use the Subaru R160 rear differential up front. But I wanted to retain the Syncro front differential for several reasons. First of all, It already fits and needs no custom components to mount it. Secondly, I wanted the 4.86 gearing because an AWD Vanagon should be geared fairly low for terrain reasons and so bigger tires can be fitted. Lastly, I wanted to keep the installation practical and straightforward, and that meant being able to drive the stock speedometer off the stock front differential.

Here is the Subarugears 4.86:1 reversed ring and pinion set.

The quality of these looks very good. Todd tells me these are notably quiet and smooth. He has received a full production run of these and it's great to finally have this lower ratio available.

Now some background on Subaru Continuous AWD. This system debuted in 1987 on the Subaru XT6. Subaru has continued to evolve it over the last two decades in much the same way Audi has done with the Quattro system. In fact, the similarities don't stop there. Subaru Continuous AWD is a true full time AWD system with a center differential directing 50% of transmission output to the front and 50% to the back. The front of the transmission (as mounted in a Vanagon) houses a center differential that looks like this:

It's a common misconception that this system uses a center viscous coupling. It sure looks like one. But closer study shows that it is in fact a conventional side gear differential with a small viscous coupling integrated into one end of it that acts as a diff lock if the speed at either axle starts to exceed the other.

Here's how the differential fits into the transmission end housing.

It looks kind of lonely in there because the transfer shaft isn't in place. I'm not sure why Subaru chose to do their prop shaft output this way, but they send drive to the rear axle through a 1:1 set of transfer gears and then through a secondary shaft before connecting to the center prop shaft. Here's what the setup looks like:

I'll stop here for tonight, but I'm hoping to get into a groove of weekly updates to this build thread. In the next entry I'll show how we are going to modify the output configuration to best match the layout needs of the Vanagon chassis.

[ftp2leta]

Here come the future. The vanagon may stay on the road for ever.
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Working with rust, grease, dirt and dust is a sad truth.
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FI part for sale: http://www.benplace.com/parts_sale1.htm
My site: http://www.benplace.com/vw2.htm
Subi conversion: http://www.benplace.com/vanaru_eng.htm
Youtube http://www.youtube.com/user/ftp2leta

[insyncro]

...looking forward....

[MarkWard]

David, awsome. Looking forward to watching your progress. This is much further along than I thought. Book Marked and watched. mark
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[furrylittleotter]

[DAV!D]

Awesome, it will be nice to see how it all comes out. I don't know much about Subarus, do they have a low gear, or anyway way to re-gear them to get the low gear like the Syncro has?
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86 Syncro Build - Ecotec Motor Swap - Pop Top Conversion - Camper Build & Syncro Conversion

[MarkWard]

I believe the initial goal is to have an all wheel drive, highway cruiser vanagon, powered and geared for the Subaru engine. Not an off road vehicle persay.
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[D Clymer]

[D Clymer]

[syncrodoka]

I assume that since you are using stock gearing that stock size tires must also be used? Will the popular 27" tires be too big?

Thank you for sharing. Looking forward to updates.

[flomulgator]

Super excited about this build too!

D Clymer - I know it is a huge step backwards but are the on-demand, full low-range transmissions from certain 80's GL wagons (mated to the early EA engines) an option?

To expand on an Mr. Clymer's early explanation of "why", I'll share my experience:

In the PNW we have no (okay very little) offroading. Sure there are some government-sponsored ORV parks but for the most part a road is structurally sound and drains well or closed and impassable. When I got a van, I did not want to pay for a syncro. But as an avid skier the AWD was very desirable for the snowy hills I constantly drive, and means legally I am not required to put on chains at many places on many occasions. And there are many like me. Thus, the reason I own one and the reason there is a strong local need for AWD, but not low-range off-road.
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She's built like a steakhouse, but she handles like a bistro!

[NC Dude]

Subscribed!
I'll be watching this one with keen interest.
Now, we just need someone to manufacture the front sub cradle-the most crucial component of an AWD syncro style conversion imo

[phlogiston]

bookmarked.

these are the kind of threads that make forums like this worthwhile.

[D Clymer]

[D Clymer]

[D Clymer]

[flomulgator]

[t'sunamibus]

[D Clymer]

[t'sunamibus]