Curing Syncro Driveline
Vibrations
(Rebuild or replace?)
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Curing Syncro Driveline
Vibrations |
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by Brent Christensen
July 7, 2001
Good Vibrations, bop bop...
The vibrations start out so subtly that many Syncro owners don't notice them until it gets really bad - so bad that cassette tapes come rattling out of the deck, change jingles in the ashtray, and the dashboard buzzes. It starts at around 30 mph and then builds to a crescendo at about 40 mph, disappearing again by about 50 mph. It is described by some Syncro owners as mildly irritating, but left alone it will gradually get so bad that it can cause real damage to your entire drive train.What the heck causes this vibration? Typically, it is wear in the drive shaft that connects your transaxle in
the rear to the front differential and transfers power to the front wheels when needed. The Syncro drive shaft assembly consists of a tube with a pair of u-joints at each end, and a rubber "flex disk" that acts as a vibration dampener. This drive shaft unit is not designed to be disassembled, nor was it intended to be rebuilt (unlike most drive shaft assemblies). When it wears out, VW expects the Syncro owner to replace it with a new unit (about $1,000 USD!)
How does this wear happen?
The Syncro transaxle and front differential each point down toward each other at a 4 degree tilt; this gives the drivetrain the ability to absorb movement while underway. Vehicles with "floating" axle assemblies like a typical Jeep or Chevy use a greater angle, and require more movement in the driveline. In either case, this tilt eventually wears out the needle bearings in the u-joints (which can be seen inside the cup in the photo to the right). It is this wear, and the subsequent "play" which causes the drive shaft assembly to rotate unevenly - this uneven rotation causes the shaft to turn in an elliptical orbit instead of a perfect circle, causing noticeable vibrations to occur at certain rpm ranges. In most vehicles, the solution to this problem is simple and inexpensive: replace the u-joints. In most cars, this can be done by even the most casual shade tree mechanic with basic hand tools. Unfortunately not so with the Syncro driveshaft.
So what are my options?
Basically, you have three or four options when you start to experience the Syncro "Magic Fingers" syndrome:
- Buy a new shaft assembly from VW for about $1,000,
- Buy a rebuilt shaft assembly for about $800, or
- Roll your own using OEM VW parts
- Roll your own using aftermarket parts that seem to fit.
For most people, the idea of saving upwards of $500 is worth some element of risk, and is the way I chose to go first. The least expensive way to go is to roll your own using aftermarket U-joints that seem to fit. To me, this represented an element of risk I was unwiling to accept, when I could use OEM U-joints for a few bucks more (see summary below). One of the things that convinced me to use the OEM U-joints was a call to Danny at Driveline Service of San Jose. Danny has experience with Syncro drive shafts and was recommended to me by another member of the Syncro List.
Unfortunately, when I called he told me that he no longer does Syncro driveshafts due to problems with the vibrations recurring after a relatively short period of time. After probing for more information, he mentioned that the problem was really with the U-joints, and not the shaft itself. Evidently, the aftermarket U-joints that had been discovered to work in Syncros didn't seem to give perfect results (i.e. the NEAPCO units). He mentioned that there were OEM U-joints available, and that if I could find them, he would be happy to balance the shaft assembly. So I searched around and found a couple of sources for these elusive OEM U-joints (evidently made by Lobro). See below for vendors that carry them.
After securing the U-Joints and flex plate, I will be sending the entire assembly to Driveline Service of San Jose to have them assemble everything and give it a good spin balance. Since I am basically replicating the process that I assume VW is using when rebuilding these units (and selling for $700), I expect to be pretty happy with the results. I will post a follow up when the project is completed (with more pictures) and let everyone know how it goes.
For now, here is a chart that outlines the options as I see them for dealing with a Syncro driveline vibration problem:
Shaft Incl. Incl. Re-use Re-use Flex Disk Incl. Incl. 251 521 001 Re-use U-Joints
(price for 2)Incl. Incl. 251 521 000 NEAPCO 1-0321 Baum Hydraulics Balancing Incl. Incl. List of shops Total (approx)
There is a very good post to the Syncro Mailing List (November 2000) by Jerry McCavitt here that discusses the least expensive way of treating this problem. You will notice that he mentions some continued vibration at 35 mph after installing the aftermarket U-joints; this combined with the comments from Danny at Driveline Service are what convinced me to pony up the $280 to try and get it done "right" the first time.
One side note - I noticed that when I removed my drive shaft, it was obvious that the U-joints had been replaced once before. I have an invoice from a VW dealer showing a drive line for $800 (VW part number); I have to assume that this is a "rebuilt" VW drive line. The interesting thing is that it was installed almost 100,000 miles ago. I am hoping that this approach will be equally long-lived.Brent Christensen
'89 GL Syncro Westy (215,000 miles)New information
Since this article was written, rebuilt drive shafts from the dealer have become unavailable.
Vanagain now sells aftermarket, redesigned syncro driveshafts. These are brand new shafts that delete the rubber flex disc and use u-joints that are much less expensive and domestically available (you could buy them from NAPA if you needed to in the future). The problem with rebuilding the stock shaft is that there is a bronze bushing that lives in the center of the rubber flex disc. This bushing wears over time and then, no matter how many times you balance your shaft or replace your u-joints you will still have a vibration. Their new shafts eliminate this problem.
Driveline shops that will balance Syncro shafts:
(Please e-mail me if you have had success with other shops)Driveline Service of San Jose
1567 Almaden Road
San Jose, CA 95125
fax 408.286.0174
408-286-0162Driveline Service of Sacramento
702 Houston Street
West Sacramento, CA. 95691
fax-916-371-6477
800-332-2800Sources for parts mentioned in this article:
Vanagain.com
U-joints and flex disks. Go to the search section and change the category to "Transmission and Drivetrain".
Vanagain also sells aftermarket, redesigned syncro driveshafts. (See the section above.)
Ken Wilford
2001 Lakeshore Dr.
Millville, NJ 08332
(856) 327-4936
(888) 315-1858 (toll free order line)
