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Al Vandervelde
Drive Shaft Basics Glidecote
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Al Vandervelde
By Al Vandervelde
If you’re a four-wheeler it won’t be long before you run into drive shaft mods, breakage or changes. It might start with that 4-inch lift then maybe a slip yoke eliminator and then perhaps an axle change to a larger yoke style. Even if you’re not planning to do the work yourself, it’s good to know why the work is being done and if nothing else, you can pipe in during those trailside debates.
First of all there is no “miracle” drive shaft parts. All the high-end companies you read about use Spicer parts; there are a couple other brands for imports, Toyotas or those in need of severe high angle shafts. But at the end of the day, all the big shops use the same parts with small tricks and mods to make things flex the way many of us need them to do. Pat’s Driveline is one of North America’s largest driveline shops and Canada’s largest with 10 locations from BC to Mississauga and I’ve used them extensively for shaft work over the years.
How do drive shafts work? Drive shafts can be separated into two and three U-joint shafts.
Shafts with two U-joints
Typically you will have a slip yoke that slides into the back of your T-case or a fixed yoke on the T-case with a slip in the shaft. The trick here is to have both U-joints turning at the same angle. If your T-case has a two-degree downward slope you want your pinion to be on a two-degree upwards slope. In many cases with suspensions that have a lot of wrap (when the axle rotates under load), you will want the pinion slightly lower at rest so under load when it picks up it will run at the same angle as the T-case.
When your U-joint is flat on the ground and you spin it, the outside is a circle, the greater the angle the more it turns on an oval path. That oval is what creates an imbalance; two opposing ovals turning at opposing angles cancel each other out. That’s why in a two U-joint shaft the T-case and differential must be on the same basic angle.
Shafts with three U-joints
Many people call them CV shafts or a constant velocity joint, but the correct term is double Cardan joint or Cardan joint (a Toyota Birfield joint is a constant velocity joint as well). CV joints are commonly found in the front axle shafts of front wheel drive cars. CVs are turning up more frequently in downsized SUVs but for the most part won’t be used by off-roaders and are extremely hard to service so we will pass on them here.
Shafts with three U-joints have a similar system to those with two, but now you have an odd number of U-joints. As the Cardan assembly bends, (a Cardan assembly is a coupler that contains two U-joints with a pivot ball in the center to keep them aligned and in phase) it keeps the two U-joints turning on opposite angles within the joint canceling out vibration. Now the third U-joint needs to turn flat, so it turns in a perfect circle and vibration free. This requires the yoke on the axle to be inline with the driveshaft so the pinion will need to be tipped up. The same applies if you have a suspension that wraps here, you’ll also need a slightly lower pinion angle at rest.
Why a Cardan? The Cardan gives you the ability to tip up the rear axle yoke to gain that flat turning circle of the third U-joint. This reduces overall driveshaft angle, lifts the driveshaft higher for better rock protection while still turning in a smooth rotation. The downside is far more moving parts and a much more expensive driveshaft.
U-joint size
There are four basic sizes of drive shaft U-joints. New numbers for greasable and non-greasable units are available these days but they still represent the four sizes used in the common light truck and SUV drive shaft. I’ll break them into two categories.
1310/1330
This is the small cap size. These two joints have the same size caps but the caps on the 1330 are spread wider allowing the potential for greater overall angle. They have the same strength and are typically found in 1/4-ton rigs like Jeeps.
1350/1410
This is the large cap size. These two joints have the same size caps but in this case the caps on the 1410 are spread wider. However you can’t get a 1410 Cardan shaft - they top out at 1350.
How much slip do I need?
Ah, the million dollar question. In many of today’s link suspensions the drive shaft travels on the same plane as the suspension and requires very little slip yoke travel. But in cases like a Toyota leaf set up, where the shackle is under the cab, or a shackle flip kit (on an older Jeep rather than at the front like the old Jeep YJs and CJs), the drive shaft is working against the flow of the leaf springs and this requires a longer slip in the shaft.
How much angle is too much?
I have some experience with this issue as I ran a custom CJ on 46 inch Baja Claws and 650HP under the hood. At rest, my rear drive shaft had 28 degrees of down angle and this included a high pinion rear differential. I had to limit down travel so I didn’t tear rear drive shafts apart. I went with a high angle shaft. They can increase the rear drive shaft angle from 32 degrees in a typical Carden to over 40 degrees – a huge difference – but it does cost a few bucks and due to the extreme angles they are not recommended for rear drive shafts, or vehicles with constantly turning front drive shafts, as they need to be greased constantly.
That “blue stuff” on the splines of the slip yoke is called Glidecote. The blue, nylon, wear-resistant coating on Spicer yoke shafts helps reduce vibration. The coating is machined on the splines for a tight fit. Slip yokes without Glidecote can be purchased, but they are considered an agricultural shaft and may not balance as nicely but they do offer superior strength. For most, Glidecote is a great way to go and will be found on almost every factory drive shaft with a slip yoke in the shaft. If you have an older driveshaft with pealing Glidecote, the only way to repair it is with a new slip yoke.
When ordering a drive shaft you need to provide an accurate and complete set of measurements. These include the measurements for length at rest on the suspension and with the suspension fully extended. Pretty tough with floor jacks but for a true measurement it's required. Length measurements are taken from the face of the yoke or centerline of the U-joint caps. In the case of flange yokes, measure from the centre line of the flange face right beside the nut.
Other measurements that may be requested are:
- Floor to centerline of the transfer case yoke
- Floor to centerline of the diff yoke
- Angle of axle yoke and angle of the T-case yoke
- Floor to centre of T-case
Pat’s Driveline will provide you with a worksheet which takes a lot of the guess work out of your driveshaft builds – make sure you ask for one, or bring your rig into one of their shops and the staff will be happy to help you get the right shaft for the job. Check out www.patsdriveline.com for more info or to find the location nearest you.