Changing a 1921 Steering from a 4:1 to a 5:1 Ratio

[J1MGOLDEN]

The 3507 Steering Gear Case is the same from 1909 to 1927.

The 3512C Steering Tubing assembly is the same from 1912 to 1927.

The 3516D 4:1 Steering Post is used for 1921 to 1925.

The 3516E 5:1 Steering Post is used for 1926 to 1927.

Can the 1926 Steering Post be used in the earlier year cars with a different set of Steering Gear Pinion Gears to change the steering ratio?

What else would have to be changed?

[DanTreace]

The steering case is different over the years.

For the later 5:1 you really want the case with the wider groove for the 'long' pinion post to ride in until the stops at each end.
The case with the groove and 4:1 has a more shorter groove.

The cases before '21 don't have the groove feature for a longer stop pinion post.

gear case copy.jpg (44.82 KiB) Viewed 1667 times

And that slot has to be at the top of the case on install of the case on the steering tube.

5 to 1 steering gears.jpg (38.85 KiB) Viewed 1667 times

Use these measures to confirm the right parts, the center distances from the pinion posts on the steering post lets you know the difference of a 4:1 and 5:1 steering post.

[speedytinc]

Steering shaft, 3 gears & steering wheel stub shaft must all be 5:1.
The gear case differences arent critical. I did the conversion on a 14. No slot, no issues.

[Dan Hatch]

Seems to me that there is a Service Bulletin about this? Dan

[TXGOAT2]

Has anyone ever fabricated a pitman arm stop to be attached at the lower steering shaft bearing mounting to positively limit the pitman arm movement?

[John kuehn]

Doesn’t it make a difference if the centerline on the 5 to 1 case is moved over half a tooth compared to the 4 to 1 case?
Seems like this has been brought up before when trying to fit the later gear set up in the older cases.

[J1MGOLDEN]

Thanks Dan! Your memory is better than mine! when I looked it up, I had bookmarked the page!

May 1925 Page 22 had all the answers.

Steering Change Details.jpg (102.95 KiB) Viewed 1619 times

[Bruce Compton]

Pat : I actually fabricated a mechanical stop for the pitman arm on my old '25 coupe. It would go over center on left turns with the 5:1 gearing. I later discovered that the drag link was too short so fixing that issue made the mechanical stop redundant. No matter what ratio, the pitman arm must extend perfectly straight down when the front wheels are in the straight ahead position, providing an equal arc of travel in both directions.

[speedytinc]

Pat : I actually fabricated a mechanical stop for the pitman arm on my old '25 coupe. It would go over center on left turns with the 5:1 gearing. I later discovered that the drag link was too short so fixing that issue made the mechanical stop redundant. No matter what ratio, the pitman arm must extend perfectly straight down when the front wheels are in the straight ahead position, providing an equal arc of travel in both directions.

??? Your 25 should have had the steering gear body with a stop slot milled in. With the correct long pin in this slot, over steer is not possible?
This was the point of these improvements. What happened in your situation? Where was the fail?

[Mark Nunn]

The change from 4:1 to 5:1 required a change in the width of the stop slot from 13/32" to 15/32" to accommodate the different pin location in the 5:1 assembly. That change was noted on 9/27/24. A later change made the angles between the centerline and ends of the stop slot 62 degrees on the left and 67 on the right. When I replaced my gear case, I milled the slot to match the later specification.

[Bruce Compton]

John: It was more than 10 years ago, but I think that all three pins were the short ones (replaced previously). My recently purchased 1914 had an over-center issue as well and I replaced the drag link with the proper one to fix it. I recall that on one of my T's to improve the steering ratio, I came across a 3/4" shorter pitman arm (not one that had been cut and welded). It actually helped but came very close to going over center in both directions.