Syncro Differential Locks, Wheel Size, Final Drive and Transmission Gear Ratios

The neck bone is connected to the head bone…

We get inquiries all the time for estimates on ONLY adding a rear or front locking differential, or ONLY larger tires, or ONLY transmission 3rd and 4rth gear changes. The problem with just doing one thing at a time is that all of these changes are interrelated, and one should first step back and consider the ultimate goal before spending a dime or minute on modifications.

The thing is this: What is required to modify a Syncro Vanagon to be a serious off-road worthy vehicle—while not ruining its on-road practicality—requires a combination of the above modifications. Sure, just adding a set of lifting springs and bolting on a set of taller tires will provide all the ground clearance and traction that will likely ever be needed. The problem is that a 15% taller tire raises ALL the gear ratios, too. That means granny gear is no longer quite so granny for any serious off-roading, and 4th gear may end up too tall to be useful on the highway. To make a significant tire size change properly requires changing the FINAL DRIVE ratios (ring and pinion gear sets) at front and rear. THAT requires complete removal and disassembly of both the front differential assembly and the transaxle assembly in the rear.

The original final drive ratio front and rear on all Syncros sold in the USA is 4.86:1. There are three lower final drive gear ratios available: 5.43 (11.7%), 5.83 (20%), and 6.17 (27%). The original tire diameter fitted to the Vanagon was about 24 inches. So, doing some simple math, you can increase the size of the tire to about 27", 29", and 30.5", respectively, in conjunction with each of the final drive changes above and not change the overall gearing at all, as compared to original. This is because the larger tire size and gear ratio cancel each other out, and everything is back to square one, in terms of overall gearing. This is the place to be with the stock 90HP engine. Now adding the front locker makes sense, even with 90HP, because you can have a ton of fun off-road. 

With a higher output engine, a couple more changes are in order. Namely, changing the ratios of 2nd, 3rd, and 4th gears is all possible, as well. The effect of those changes is a much WIDER RANGE of gear ratios from which to select. Granny gear is still granny, and top gear is TALLER than original, and you end up with a wider selection of gear ratios to take advantage of a more powerful engine. Now we are talking… Dropping the engine speed on the highway can make significant improvements in drivability and mileage, as Tim Schneider writes after we re-geared his rig:

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From: Tim Schneider 
Sent: Monday, December 11, 2006 7:35 AM
To: S. Lucas Valdes; Taylor Subject: A quick report

Hey Lucas, Got the 'improved' ride back home today...

Re: 16" Rims/Tires: --------------------
These rims are a better match for the BFGs than the ones I had on there. The extra inch of ground clearance will definitely be helpful down here in Arizona! Very pleased with these over the 15s that I had on the van.

Re: Transaxle re-gearing -------------------------
With the new gearing, I can cruise at 70mph now, right at the sweet spot for the GoWesty 2.4L engine. Gas mileage was consistently higher all the way back home by 2-3mpg, and the top end is easily 10-15mph faster than it was with the stock gearing. I now realize why I had a hard time keeping up with you guys two years ago (on the way back from Syncro de Mayo in Hollister).

Time will tell on this upgrade, but at the moment it's definitely looking like a winner!

Regards, Tim

90 Syncro Westy

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The problem with all of this is: COST. Adding a front locking differential, lower gears front and rear, and larger tires all in one shot—WITHOUT rebuilding either the front differential OR the transmission—is about 2/3rd the cost (parts and labor) of doing it WITH rebuilding both. So, this really makes the most sense when either is ready for overhaul. Plus, you can’t re-gear JUST the front OR the rear alone. Both have to be done at the same time.

The bottom line is that this should all be done at once. Do it right, and cry one time. Like the saying goes, “There is always time and money to do it right… the second time!”

The neck bone is connected to the head bone!

It is simple anatomy...

Cheers,
Lucas

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