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The Volvo rear axle has always been known as a weak link in 544/122/1800 race and rally cars. Several years ago, Rick Hayden wrote an extensive article on how he and others had managed (out of necessity) to survive racing on the original design in the '60s, but the process was expensive and required considerable time, technical know-how, and discipline beyond what the average vintage racer or performance enthusiast can devote. Volvo solved the problem when they changed to a disc brake rear end on the 140, 1800E and ES with redesigned internal axles, wheel bearings, etc., and there have been no problems with this setup. However, for some applications such as the 544, there are reasons to stick with the original axle housing. The following is an alternative to the disc brake conversion applicable to both racing and street cars.
In the late '80s, three different vintage racers on the East Coast had four separate serious accidents using the Volvo drum brake rear axle. Three of these involved multiple flips. These incidents happened to drivers not using racing slicks, but running on 185/15-70 series tires, using some, although I doubt all, of the precautions so extensively detailed in Rick's article.
Both the racers and the vintage organizations felt something had to be done in the interests of safety. With the clubs not wanting to allow the use of the later disc brake rear end -- considered a performance advantage that might open the door to the use of other updated equipment on other makes -- we looked for alternatives and came up with the Ford drum rear end (based on information that this modification had been used on some cars to solve the problem back in the sixties). The standard Dana Spicer rear end is retained and only the bearings, backing plate flange, and axle shaft are removed and replaced by Ford parts. These are the only parts in the rear end (other than the suspension mounts) which are unique to Volvos (although I have been told it was a Studebaker design) and originally were added on to adapt the axle to the Volvo. The same rear end was used on numerous other makes including some Fords, but without the tapered axle/drum design. After the modification, standard Ford backing plates, brake cylinders, drums and shoes are added, and most people don't even notice the difference. Small changes in rear track width to allow for wide tire clearance can be made at the time of modification.
Other than safety, the chief advantage of the change is that brand new brake parts are available at your neighborhood parts store at a fraction of the cost of Volvo parts. In addition, there is a choice of drum brake sizes. The entire conversion, including all new brake parts, can cost less than the cost of a rebuild with new components for either the drum or disc brake Volvo axles. This modification retains the original suspension mounts and bolt circle, both of which are problems with adapting the disc brake rear end to early cars. It has been done on 1800s, 122s and 544s with perfect results, and has been accepted by major vintage racing organizations in the U.S. and Canada as a safety modification, using period parts, which has no significant performance advantage (not technically true, since the brakes run much cooler, the pads last longer and high performance brake linings are readily available). One car has run the Carrera Pan America Race using the conversion, and I have raced on it for ten years and see no disadvantage compared to the disc brake cars.