DRIVESHAFTS & JOINTS

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DRIVESHAFTS & JOINTS

What is a driveshaft?
The front driveshafts transfer drive directly from the gearbox to the front wheels.
The rear driveshafts transfer drive from the rear differential (dif.) to the rear wheels via the propeller (prop.) shaft from the gearbox rear output.

What is a driveshaft joint?
The constant velocity joint [with six single ball bearings] was patented in 1928 by Alfred Rzeppa. In 1959 Alex Issigonis developed the constant velocity joint to drive the front wheels of the Morris Mini Minor, he also made the fatal mistake of using the shaft to retain the wheel [so they often fell off!].
Update March 2016: - These days there are a lot of variations in the internal mechanical arrangements of joints. "Tripod" is one where 3 sets of ball races (many small bearings within) replace the 6 single ball. These have further variations..
Updated March 2016: - Another variation is how the driveshafts connect to the gearbox and rear differential. They used to be connected by an internal female splined hole in the (inner) DOJ which slid onto an external protruding male splined shaft on the gearbox and rear diff. Now some models have this method completely reversed! This means when a driveshaft is removed, oil will run out of the gearbox or diff! This is a nightmare for you and suppliers!
Earlier Australian Subarus (except Liberty) from 1974 to 1994 (manual and auto models) were driven through the front wheels all the time, and the rear wheels when you selected 4WD via a lever or a button – selectable 4WD. From the Liberty (1989) onwards in Australia, Subarus were all wheel drive (AWD) in manual and autos except the purely 2WD (front wheels) models.

There are two types of driveshaft joints:
1: Constant velocity joint (CVJ). They are the outer joints and attach through the wheel hub bearing on the front and the rear - hence the large visible axle nut. They are similar to the inner joints, but although they do a lot of gyrating whilst steering and driving, they do not slide in and out to accommodate suspension articulation.

2: Double offset joint (DOJ). These are the inner joints attached to the gearbox and rear dif. and are able to rotate, drive, and slide in and out as the suspension goes up and down.
Later model Subarus use a different inner CV joint called a “tripod" style DOJ. Tripod joints do not have six balls but instead use needle-bearing rollers mounted on a three-legged spider.
They are similar on the rear (but non-tripod types) which are attached to the rear dif, but on later models, only the inner slides in and out as the suspension articulates.

Where are the driveshafts?
There are 4 - one for each wheel. Each has a DOJ and a CV joint. That’s a total of eight joints and boots. These are all somewhat vulnerable to rocks and sticks.

What are the boots for?
The eight boots may be of rubber, urethane, neoprene or polyethylene thermoplastic material which are designed to keep out water, sand, dust and other contaminants, and at the same time retain the special lubricating grease. There may be 3 or 4 size boots for your car. They are attached at each end by a stainless steel band clip.
Their age is limited, so you must make regular checks on their welfare. Cary a set for longer trips.

Maintenance:
The first priority is regular visual and ‘physical squeezing’ checks on the condition of the boots.
The second is age ~ 5 years, but perhaps more? Regular inspection is vital. Change them sooner rather than later to avoid a costly error.
Servicing involves removing the complete shaft, stripping, cleaning and inspecting – a very messy operation which I no longer do. Removal is not easy and special tools are required, especially if a lift kit has been fitted. Assembly is done with new grease, boot and clips. I suggest you have this done at a driveshaft specialist (not your corner garage). Full exchange may also be an economical option.

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Ian Johnson @ 10/2014 Updated March 2016