Last Modified
2006.02.25
© Felix Miata
Felix's Home
Most 1st gen owners eventually have to deal with less than ideal steering. The systems wear over time until the driver starts becoming aware of "play" in the steering wheel. Information on how to tighten the system to minimize play is often contradictory, and results can be short lived and disappointing. The steering system on 1st gen RX-7s is called "recirculating ball." All other RX- 7s use "rack and pinion" steering. Both manual and power steering were available for 1st gens, and while both work on the same principle, they differ significantly in internal details. The shop manual actually has two different sections (10A, and 10B) to deal with the two steering boxes. This essay will describe how the systems work, how to adjust them, and what the alternatives are as they wear.
There are two major moving parts to both the manual and power steering boxes. The first is the sector shaft which runs vertically through the assembly. The bottom inch or so is splined, and a 6" long arm (the pitman arm) is attached at a 90 degree angle. The second major moving part is a "car" that moves back and forth on a large threaded screw which is turned by the steering wheel. (The term "car" is in quotes because it is simply a descriptive word I am using.) As the "car" moves back and forth on the screw threads it causes the sector shaft to twist, which swings the pitman arm. The pitman arm is connected to the steering linkage, which translates its movement into steering changes at the front wheels.
The internals of the steering box are interesting, especially the connection between the "car" and the sector shaft. The meeting point is located near the top of the sector shaft. There you will find three or more protruding vertical ridges--cut like straight gear teeth. For you visual types, imagine your hand on top of your shifter with your palm on top of the shift knob (as opposed to the side). Imagine that your three middle fingers are slightly spread, and that the shifter is the sector shaft. Your fingers illustrate the orientation of the "gear teeth." To twist the sector shaft (which swings the pitman arm) these teeth must be pushed side to side.
The "car" has teeth to match the teeth on the sector shaft. The pressure between these two sets of teeth (the "car" and the sector shaft) must be enormous due to the considerable leverage coming from the steering wheel at one end of the system, and the considerable friction where the tires meet the road--especially when the tires are not rolling. The power to turn the wheels is transmitted through just the few teeth on the sector shaft at a radius of only about an inch.
Needless to say, the quality of the contact between the teeth on the sector shaft and the teeth on the "car" is critical. If the fit is too loose, you will have play in the system. If it is too tight the teeth will wear prematurely. As most of us have experienced, the contact gets sloppy over time, so we reach for the adjustment screw on top of the steering box. This screw is threaded into the top of the sector shaft. Turning the screw actually raises and lowers the sector shaft relative to the "car." This would make no difference if the teeth on the sector shaft were straight cut, but they are not. The teeth actually get thicker toward one end. So, as you use the adjusting screw to raise or lower the position of the sector shaft relative to the "car," the teeth mesh more or less tightly, and any slop in the system is minimized. To illustrate, spread the fingers on your right hand and look at the spaces between the middle three fingers. The clearance between your fingers narrows as you move from tips of your fingers toward the palm of your hand. Anything of fixed dimensions will fit between your fingers more tightly if moved toward the palm of your hand. This is roughly how the adjustment is accomplished in the steering box.
The system for moving the "car" back and forth is equally interesting. As I mentioned, the shaft coming from the steering wheel continues into the steering box and is formed into what amounts to a large threaded shaft like a screw. Turning the wheel turns the screw, which moves the "car" forward and backward. On the manual steering box the threads on the steering shaft are cut with very course ridges like a giant screw of the type designed to go into plaster board. The screw shaft is supported at each end by ball bearings.
The situation is more complex with the power steering system because the "car" is the part which has its movement assisted by the hydraulic pump. To accomplish this, the ends of the "car" are rounded into a piston shape, fitted into a cylinder, and sealed via o- rings. In fact, the "car" in the power steering section of the shop manual is referred to as the "piston assembly." The fluid pressure from the PS pump acting on the piston is what provides the power assist.
Unlike the manual set-up there are no self-contained ball bearings to support the threaded shaft in the power steering system. Instead of being threaded like a machine screw, the power steering version of the threaded shaft is more like a solid shaft with a spiral trough running from end to end.
The "car" or piston has a similar spiral trough on its inner surface where the shaft comes through. Running in both troughs (thus keeping the shaft and the car separate) are 30 (count-em) ball bearings made of two different materials. If you pull one of these things apart, whatever you do, don't unscrew the threaded shaft from the "car." If you do, you better have a shop manual handy. I won't make any jokes about losing your balls here.
Since the troughs in the power steering threaded shaft are of courser pitch than the ridges in the the manual steering shaft, the power steering system allows you to move the "car" further for each turn of the wheel. The steering ratio for manual steering is "17~20:1" according to the manual, while the power steering is 15 to 1. So, while I understand why some people prefer the manual steering for the feel of it, the power steering boxes are quicker, and the variable assist was considered pretty sophisticated for its day. People who talk about removing the hydraulic pump from the power steering system to save a little drag on the engine will end up with heavier than manual steering due to the higher ratio in the system and the added friction of pushing the piston back and forth. Better to have the steering converted to manual by replacing the box and associated mechanical parts.
If your steering box is leaking, you can buy seal kits. Be sure to specify if you have power steering. The sealing technology is quite different between the two boxes. Besides the obvious need to deal with the hydraulics on the PS box it is designed to run on automatic transmission fluid (Type F) whereas the manual box is not pressurized, and runs on GL-4, 90-weight gear lube.
A final note on the power steering systems is that the power steering pumps are known to fail by leaking or by mechanical failure associated with the pulley. If you have a power steering fluid leak, look first to the hoses for cracks or breaks, then check the pump, then the power steering box. I have known cars with close to 200,000 miles on them and no power steering problems, so there may be some merit to the notion that cars which are not driven much are more prone to seal failure. If you have to replace the power steering pump, you might look into modifying a 2nd gen pump to fit. These pumps seem have proved to be less prone to failure. The people at Sun Auto may be able to advise you on how to do it.
There are differences between the power and manual steering systems that trip us up when we attempt a discussion on how to adjust steering. Both systems have an adjusting screw secured by a lock nut. Turning the screw moves the sector shaft up and down. The hardware depends on whether it is a manual or power steering box. Also, the power steering system "tightens" by turning the adjusting screw clockwise. The manual steering system "tightens" by turning the adjusting screw counterclockwise.
To create further confusion, Mazda changed the manual steering boxes sometime between the 1982 and 1983 model years. The update may have occurred as a running change (we don't know for sure). On later manual steering boxes, the central portion of the cap has several indentations in it. This part is threaded and secured with a very large nut. The "adjusting screw" I mentioned is in the center of the larger threaded part--under a trim cap (if someone has not removed it and left it off when trying to adjust the steering).
This is where things get complicated. As I said earlier, moving the sector shaft up and down varies the closeness of the contact of the vertical gear teeth. There is a bearing between the top of the sector shaft and the top of the steering box. The sector shaft is supposed to be snug against this bearing. The adjustment for that is called "preload," and is supposed to be made with reference to a fancy spring tool like a fish weighing scale while the steering box is off the car. The adjustment is made by undoing the big lock nut and using a punch in the holes of the large threaded part on top of the steering box. Clockwise tightens the preload.
The second adjustment is called "backlash," and is supposed to minimize play in the system. This is the same adjustment described for the earlier boxes--a slotted screw in the center, secured by a 14mm locking nut.
The two RX-7 specialty shops I interviewed for this article ignore the "preload" adjustment, and only work with the "backlash" adjustment. Felix Miata's experience is that on boxes that haven't been adjusted in a considerable period of use, the "backlash" adjustment won't last very long unless the "preload" is adjusted first.
The shop manual offers specifications for adjusting the system, but most of us are just trying to get the play out of the steering wheel. With that in mind I offer the following information:
Mazda used to sell sector shafts for the manual steering systems for about $200, but they are no longer available. This may seem mean-spirited on Mazda's part, but I can guess at the reason. Most of the wear to the vertical gear teeth in the steering box will be to the teeth that mesh when you are driving in a straight line. This is the position the system is in for the vast majority of the miles driven. If you adjust the sector shaft to take up for the slack when the car is going straight, the vertical gears will mesh too tightly in a turn, and the steering will not self-center. Loosen the steering so it self-centers, and you again have slop at the steering wheel.
The only solutions are either to live with the steering wheel play, or to buy a new steering box. Mazdatrix sells manual steering boxes for $525. If you have a worn out power steering box, a new one will set you back $1,248. The good news is that if the only problem you are dealing with is a fluid leak from the box, the "seal kit" is only a few dollars (probably under $25 if I remember). There are other options including buying a used box--with or without new seals in it. I would be cautious about installing a power steering box that had been sitting around for awhile without replacing the seals. And any steering box you find from a car with high mileage on it is likely to be in no better shape than the one already on your car.