I regularly work on old volvo's Amazon, 164, 144 etc. They all use worm and sector steering with the pitman arms, a very much inferior steering system. A lot of play is always present in the steering system, even with new bushings fitted. And there is a dead point when the wheels are parallel. I can't think of a single positive thing about it. Lots of other classics also use this kind of steering system, while the superior rack and pinion system was also used widely. Many British cars use rack and pinion, like the MGA and my TR7, and it gives them excellent steering behaviour, with no discernible play. But even volvo's sportscar P1800 uses worm and sector. Why was that?
In the red corner...
According to this SuperChevy article, when compared to rack-and-pinion designs, recirculating-ball (or worm-and-sector) steering systems are typically:
- able to accommodate more steering travel
- more "rugged"
Here are the advantages of the recirculating-ball setup in the article:
There are several advantages to recirculating-ball systems.
First, by varying pitman arm length you can easily offer more or less steering travel than a rack-and-pinion system.
Second, it is typically less expensive than converting to a rack-and-pinion system, perfect for someone on a budget. This time-tested steering system is very rugged and it is still preferred in racing organizations like NASCAR.
And here are the drawbacks of the rack-and-pinion according to the same article:
... Due to the limitations on the number of teeth that can be cut into the rack, there is typically less travel available compared to a recirculating-ball system.
... In some cases you will have to notch the frame and relocate the sway bar. You will also have to calculate the geometry so that you don’t end up with poor handling due to bumpsteer and a host of other issues.
... Lastly, a rack-and-pinion system, especially in kit form, will make your wallet quite a bit lighter than tossing in a rebuilt close-ratio box.
In the blue corner...
On the flip side, rack-and-pinion setups are:
- less prone to failure (fewer points of failure)
- easier to package into engine bays
From the same SuperChevy article:
Advantages of the rack-and-pinion systems are many.
First is its simplicity. With only two moving parts there is not only less friction, but the positive engagement of the system gives a very tight and responsive feel to the steering.
Secondly, the complete system has only four wear points in the linkage: the inner ball joints and outer tie-rod ends. This simplicity and lower number of parts is one reason why most new cars use rack-and-pinion.
Third, a rack-and-pinion system is quite a bit lighter than a traditional box system. Less weight off the front of the car is always a good thing to strive for.
Fourth, because of its design you often gain added clearance for headers and the rack-and-pinion is sometimes easier to package into the car.
And the Bosch Automotive Handbook agrees with the superiority of modern-day rack-and-pinion systems:
The increasing performance of rack-and-pinion steering has meant that recirculating-ball steering is practically no longer used in passenger cars.
Here's some insight from the auto manufacturing world on how this happens;
OEM: Lets refresh the model W steering for next year.
Engineer: Ok the new steering rack design will cost about quarter of a million dollars and a few thousand labor hours to implement.
Supplier: We have several hundreds of worm/sector parts on hand, did you still want any of these?
OEM: As it turns out, we just changed our minds on the steering redesign.