'61 Invicta Steering upgrade

[s_hilmoe]

One of the biggest gripes I have with the car is the steering ratio of the box. Four plus turns lock-to-lock just doesn't cut it. There have been time that I've had to hit the brake pretty hard because I couldn't turn the wheel fast enough to turn into a driveway. I'm so accustomed to the modern feel and quicker turning.

 

 The steering gear on these cars are Saginaw made and have the larger bore. GM Saginaw boxes are pretty much the same internally with two sizes. There are many interchangeable boxes for many cars out there but the '61 is a one year only and has different mounting hole locations. I happened to have an extra large bore box from a 1998 Chevy 3500 4x4 truck. The box is has an 84 cast into it. This box has a 16:1 variable ratio instead of the 20:1 ratio or even 22:1 ratio of the '61.  After making several measurements I determined I could swap the internals from the '98 truck box to my '61 box. I ordered two steering gear rebuild kits, one for the '98 and one for the '61. I used the pitman arm seals from the '61 kit, and internal seals and input shaft seals from the '98 kit. There are several videos out there on rebuilding a Saginaw box so I won't get into too much details. One thing though is to make sure the recirculating balls are sorted out and put back in alternating big and small, or dark and light. Many videos out there talk about the light and dark bearings but when doing the newer ones they are the same color. Many videos show them just putting them in, disregarding the size since they are the same color. You MUST measure them and sort them out. The smaller bearings are .0005" smaller than the bigger ones. The bigger bearing are the actual bearing and the smaller ones act as a bearing cage. They will float, turning the opposite direction as the bigger ones. If two bigger ones are placed next to each other they will grind against each other causing quick wear and binding. 

 

The result is a totally different driving car. It has two and a half turns lock-to-lock and I can actually feel the road more since the '98 box has different valving for a more modern feel.

[NTX5467]

Thanks for the information.  WHERE does the ratio change come from?  Different gears which the bearings move or elsewhere?

 

In the earlier days of power steering, the normal steering gear ratios were used, which could be up to 6 turns lk to lk, but with power assist for easier steering wheel turning.  By the earlier 1960s, most of GM was using that ratio, as was Ford, as Chrysler went to the 3.5 turns set-up.  GM gravirtated toward that radio too, until the first variable-ratio Saginaw boxes caem out in about 1965.  Some of the later boxes were more like 2 turns on some of the Camaro/Firebird cars, as I remember.

 

Allegedly, "road feel" is varied with the internal torsion bar in the box.  Combined with the "high-effort" items, a more "European" feel was supposed to result, but it was more like decreased boost, I suspect.

 

The GM800 gear box has been used in circle track racing for decades.  Some rebuilders which cater to that crowd can rebuild a GM800 box with a desired gear ratio the customer might desire.

 

Enjoy!

NTX5467

 

[s_hilmoe]

The ratio change comes from worm shaft where the balls ride and some from the pitman and rack inside. The box from the truck has a variable ratio, meaning the wheel has a quicker ratio the more it is turned from center.  In the constant ratio box the gear teeth on the pitman and rack are all the same size. In a variable box the center tooth of the pitman is longer and the center groove in the rack is deeper to go along with the pitman. The ratio is determined by the groove pitch of the worm shaft much like thread pitch of a bolt. The stock 61 worm is like a fine thread bolt, the newer box is like a coarse thread bolt. There is also a difference in the valving. The torsion bar determines how much hydraulic pressure is applied to the piston. The harder your effort the more the bar twists, the more the pressure is applied. The early cars had a weaker torsion bar giving the easy one-finger steering known back then. Newer cars have a stronger torsion bar that requires just a little more effort but you can "feel" the road better. 

 

The GM 800/808 box is an inside-the-frame mount common in a lot of GM cars. The 700/708 is an outside-the-frame mount common to GM trucks. The GMT 83/84 is an inside-frame for GMT 400 series trucks. The 700,800,and 83 boxes are small bore and the 708,808, and 84 are large bore/ heavy duty boxes. The 1961 Buick box is an outside-the-frame, large bore box with a unique mounting bolt pattern of one year only, so gear sets from the 708/808/and 84 are candidates for swap. The gears inside the boxes are the same between inside and outside mounted boxes. You do have to check pitman shaft splines to make sure they are compatible. There are 4x4 shafts from squarebody trucks that wont fit the 61 pitman arm. There are also some shafts with 3-way splines that won't work. 61s will need the 4-way splines. There are also internal stops in some boxes. The main bore endcaps will have various thicknesses. The GMT 84 box that I had on hand, fit the requirements. Large bore and 4-way splines. I used the 84 boxes gears and valving and the 61's box and main-bore end cap.

 

When I started, my '61 had about 4.25 turns lock to lock. Now it is about 2.5 turns, better "feel", and I have the same turning radius.

 

 

Edited November 12, 2023 by s_hilmoe (see edit history)

[NTX5467]

"Boost" is also controlled by the size of the orifice/fitting where the pressure line attaches to the rear of the power steering pump.  Too much boost results in "breathe on it" steering with even more minimal finger use, by observation.  Seems like I found about three or four different fitting orifice sizes?  Larger orifice size means more boost and vice versa.

 

Now, you need some of the polyurethane front sway bar end link grommets to make the existing sway bar act like its about 20% stiffer for flatter cornering.  Moog has them as to other front suspension parts suppliers.  The GM OEM ones on the '79 WS-6/7 TransAms were white and inexpensive.  Other aftermarket ones were red.  Moog has light blue ones which are a bit softer, but still polyurethane.

 

Thanks for the information,

NTX5467