Rebuilding the Gemmer Steering Box

by Bob Carabbio, Highland Village TX

Editor's Note:
This is not intended to be a step-by-step rebuilding guide. It supplements the assembly and adjustment procedures found in the February 1929 Ford Service bulletins (readily available). This also isn't intended for those anxious to slap together their steering and "wander" on down the road. It is however intended for those stubborn few that are determined to experience the Model "A" as it once was. Bob has included a couple of modifications that may slightly enhance the quality of the steering, but will be detrimental if not done properly as Bob describes.

I've now done two boxes recently, each of which needed considerable tooth dressing on the sector to achieve good mesh - i.e. a significant amount of tooth contact with the worm. In my box, the sector shaft was junk so I replaced it with a swap-meet unit, and had to do quite a bit of tailoring to get it to mate correctly.

Steering Shaft Inspection
Make sure you check for a bent steering shaft by rotating the shaft without the column in place. If the center of the shaft moves in a circle, then there's a bend which should be corrected. If the shaft is bent, it will destroy the bearing race on the worm, and play havoc with the gear mesh.

Reading between the lines, the last one I saw that wobbled that way was from a car that had body damage commensurate with a fairly hard accident on the passenger's side front. My guess is that the steering column and the steering shaft were both bent in the accident. The effect of the bend was to wear the top bearing race eccentric on the worm.

SO- first thing to check is that the top bearing inner race on the worm is concentric with the worm itself. if it's not there should be pretty obvious wear patterns visible on the race. If it's not concentric, or has worn strangely, then it can (and MUST) be re-cut or ground to true the bearing surfaces. Obviously if the worm is wobbling internally, you're not going to set your adjustments too successfully.

When the race has been confirmed as good, or has been restored, THEN re-assemble and check for straightness at the shaft end.

If it wobbles, then the shaft is pretty definitely bent. Mark the high spot on the shaft, disassemble, clamp the worm in a large vice with hardwood (or copper / brass) liners to protect the worm, and pull against the bend being careful not to overdo it. Do the repair bending COLD don't use heat. Re-assemble and check for improvement. Then disassemble and do it again if need be. Ours took about 4 tries to get it right. The shaft end should spin within 1/16" total wobble before I'd call it done.

Check to be sure whether you have the early or more common late shaft and worm assembly. No worm bearings are available for the early unit so you'll need to determine if it is worth moving forward with your existing parts.

With the selected bearings there are three diameter options for the sector shaft, 1.1235" O.D. (standard), 1.1019" / 1.1024" O.D., or If 1.101" won't clean it up, the last possibility is 1.0625" / 1.0635" O.D. If the shaft won't clean up at 1.062" O.D. then it's too far gone. I'd get a bit nervous about going smaller or building it with weld because of the heat involved. The object here is to go with the largest option that will provide a proper bearing surface.

The sector shaft is tough, but not hardened so it turns well with carbide tooling. Polish the shaft after turning as well as possible, or finish grind it to size if you're equipped. Tolerances should be kept to the large side on the O.D., and the small side on the housing bores. The shaft should "Screw" into the bearings if things are right. If it's loose and just slides in, then the slop in the steering wheel will be VERY noticeable. The kits sold by the Model"A" Parts venders have been reported to go together loosely. The components and machining above result in tight assemblies when done properly.

I also use a Torrington NTA-1828 needle thrust with a Torrington TRC-1828 Thrust washer. Instead of the brass washer between the sector and the housing inside. Since the Needle thrust assy. is thicker (0.173") than the Brass shim, (0.035") the end of the housing must be cut back 0.140" to allow the sector to be in its normal position. Use the thrust washer on the housing side of the needle thrust.

As far as the worm goes, if they're pitted on the thrust bearing surfaces they can be machined or ground. Grinding, of course is preferred, but turning followed by some manual polishing works too, particularly for the limited use car. Duplicate the angle of the race. You can go pretty deep on the upper end (steering wheel end) but any cuts made on the bottom end will have to be compensated for by shimming the lower bearing race to compensate for the lost length. Fortunately, the lower bearing race appears to stay in good shape. Please note: Most worm gears aren't hardened on the bearing surfaces. To be sure you must run a file over the surface lightly to check. If the file bites into the surface easily, it's not hardened. If it skips or glides over the thrust surface, it's hardened and should be ground.

Sector Seal
The seal at the outside end is Chicago Rawhide #11124 for a standard shaft, OR #10598 for a turned down one. Both seals fit in a 1.624" dia x 0.250" deep bore. MAKE SURE that you indicate on the short side of the housing on the frame flange side, or you'll not set the bearings / seal in deeply enough.

Parts List
See the following table:

Bearing and Seal Options
Sector shaft size Housing Bore size Bearing Selection
Seal Selection2
1.1235 (standard) 1.374" - 1.375" dia.
by 1.062" deep
(2)Torrington BH-1816 Chicago Rawhide
1.1019" / 1.1024" 1.376" / 1.377" bore
x 1.062" deep
(2)Torrington FJV-2820 Chicago Rawhide
1.376" / 1.377" bore
x 1.3" deep
(4)Torrington FJV-28161 Chicago Rawhide
1.0625" / 1.0635" 1.3115" / 1.3125" bore
x 1.3" deep
(4)Torrington B-1710 Chicago Rawhide
Sector Thrust Bearing and Washer
Bearing Washer Machining
Torrington NTA-1828 Torrington TRC-1828 Cut 0.140" from inside end of sector housing
  2Bore for seals - 1.624" dia x 0.250" deep

Fitting Needle Bearings
I installed needles (Torrington units that I bought locally) and they exhibited considerable pre-load on the sector shaft when installed, but I also installed them in slightly undersized bores to ensure a tight fit. If yours show looseness, I'd take care of that immediately - check for undersizing on the shaft. While needles are "Zero-clearance" they are more compliant than bushings, and should be set up tightly. The first steering box has been in use for well over two years now and still only has - " of rim play with the final adjustment we gave it back when. We also installed a " N.P.T. drain plug in the steering box so that we could easily change the lube since we expected wear when the "high spots" of our grinding job wore off. So far, though, there hasn't been any evidence of wear so the plug is probably a waste of time. A small contact area can result in binding since the teeth "dig in".

Sector Gear Inspection
If you look at the teeth on the sector, you'll probably find a "step" in the tooth down by the root - maybe 1/8" inch up from the bottom of the teeth. This is where the worm has been riding, and the "step" will be the only area of the tooth that contacts if the gearset is tightened. This small contact area will wear away quickly and let the gear loosen again. What you really want at center position is full(er) contact between the worm and the sector which can only be achieved through fitting the gears. SO - bluing and a Dremel or die grinder to knock off the high spots so that you have at least 30% tooth contact after adjustment. Typically smoothing at the roots of the teeth to take out the step, and some chamfering of the tooth tips will be needed to correct jams of the gearing as it's adjusted together. I wouldn't try grinding on the worm -only the sector.

If you've mixed used parts fitting will definitely be necessary to achieve good tooth contact and jam-free operation lock to lock.

Adjustment and Fitting the Gears
Check the Sector thrust adjusting screw. The thrust face often has an eccentric high spot from wear. The surface must be filed or ground flat to obtain proper adjustment.

When tightening the upper race, don't do it as tightly as the books indicates since this appears to distort the top race. I just take the adjustment down so the end play is gone, and maybe turn farther for a LITTLE pre-load. If you can feel drag in the steering wheel because of the steering shaft bearings they're WAY too tight.

Basically, get the lubricant out of the box so that the gears are dry, lightly grease the bearings, and spray the sector with machinist's blue. then re-assemble and adjust as well as possible. Finally heavily load the sector in one direction and crank the steering lock to lock, then load it in the other direction and crank it back the other way, then disassemble and see what got rubbed off.

You'd like a significant amount of the blue to be gone particularly on the face areas of the tooth. It's likely, though that there will be very little rubbed off, and probably concentrated either at the tips, or in the root area where the wear pattern goes away. Then get out your Dremel and commence to grind the areas where the blue is rubbed off so you can mate the gears more deeply and achieve a better fit. Keep at it until you have at least 25 - 30% tooth contact - more if you have the patience. It took about 12 iterations on my box to get there and occupied the better part of two evenings. Bill's box ('30 tudor) was still using the original gear set and came in pretty good in only 8 tries. his main problem had been that his steering shaft was bent, and we had to re-cut the upper race (which is not hardened - go figure) and straighten the shaft - see above.

As a final touch, it is a good idea to blue the teeth one last time and ONLY move back and forth in the middle revolution to check the engagement specifically in that small area that's supposed to be tight. If you're getting about 30% contact there, everything's good.

Parenthetically, you should also make sure that the zero-play area of the steering gear results in the wheels being straight ahead. Before attaching the drag link, find dead center of the steering box by turning the wheel lock to lock deviding the motion. Mark the steering wheel at the top (at center) with a piece of masking tape. Complete the assembly and set or confirm proper toe-in. The car should travel straight ahead with the tape still at the top. If not, a bent pittman arm or replacement ball seat sets in the drag link could be at fault. This must be corrected for smooth, tight steering

Front End Checks
Check the thrust bearings at the spindles. If you can turn it with the weight on the wheels, it's WAY too loose. The cup washer under the axle where the felt is should turn easily, however, and if it doesn't the car may be sitting on it. With the car jacked, though and the drag link disconnected, the wheels should turn lock to lock easily. King pins that are set up too tightly sometimes seize - it's not uncommon to see this, particularly nowadays when most shops aren't as familiar with the old ways.


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©1999 Marco Tahtaras