MTFCA Forum

I have been looking for the longer slot (26/27) 5-1 gear box to fix a guys column. I have two of the shorter slot 4-1 boxes. How much turning radius would I loose if I used one of them using 21 inch wheels?

Mark, Just a hunch, but could you simply have the slot in one of the gear boxes machined longer?

Just a thought.....

Keith

Keith;
I thought about that but can see several issues, nothing to compare to to get proper length and farm out cost. If the slot gets too long you will still end up with pitman arm going over center. I think this might be part of the problem on the box that needs to be replaced, got one side a bit too long when I cleaned the slot up. I don't have the car here and customer is aware of the the issue in case he drives it. I need to have the box on hand to do the swap over as fast as I can after the column gets pulled.

Mark, I've switched out two 4to1 sets for 5to1 sets, one on the '23TT that Dallas now has, and the other on our '25 coupe, keeping the original 4to1 gearcases. The only difference that I noticed was that they both steered noticeably easier. That being said, I didn't take any before and after measurements either. Dave

I also made new pins for the gears out of drill rod .001 or .002 over size also. That made them fit nice and snug in the shaft holes and took up just a bit of play in the gear holes. It really tightened things up. Dave

David did you get the two emails I sent the other day? The second one because I forgot the link in the first.
Mark

Ask the forum for dimensions on the slot. Someone will have them. Then get the shaft slot milled as was suggested.

I have a simple question. Something I have wondered about for many years. The 4 to 1 or 5 to 1 is the ratio between the steering shaft and the steering wheel. That ratio changes the amount of force required, and amount of turn of the steering wheel needed to make a turn of any given degrees. Since the amount the steering shaft turns relative to the degrees of turning radius does not change, why did they make the slot longer for the 5 to 1 gear cases?
One could think the lowering of the steering column for some of the '26/'27 models would make a difference. But the fact is that difference is negligible, if there is any at all.
Did they find the earlier slot was overly restricting the turning radius? Did they make this difference to identify the 5 to 1 gear cases? That doesn't really make sense. Allowing it to go farther could allow locking on center extreme and basically negate the whole purpose of the slot.

I have never heard of the shorter 4 to 1 slot restricting turning radius enough to cause problems. I can't see why using a 4 to 1 shorter slot case would make much difference.

Wayne, both the 4:1 and 5:1 have 36 teeth so the only real difference is the slot length. Slot width did change, however, probably to accommodate manufacturing tolerances. This is from the encyclopedia.

02-23-22 Changed angle between centerline of case and the center of 13/64” radius at ends of slot for stop pin from 45 degrees to 51 degrees.
05-27-24 Changed angle between centerline and ends of stop slot from 51 degrees to 60 degrees.
09-27-24 Changed angle between centerline and right hand end of slot from 60 degrees to 65 degrees. Specified for 1925.
10-07-25 Changed angle between centerline and ends of stop slot from 60 to 62 degrees on left side and 55 to 67 degrees on right side.

I took a 4:1 gear case that I got from Dave Stroud and milled it to match the last angle change before putting it in my car. I did not do the research but the slot angle changes may have coincided with changes in pitman arm length.

Mark thanks for that bit of information. Guess I will give hogging out the slot a try. Now all I have to do is find my center build a jig and hope my Craftsman is up to the task.

Assuming that the 5:1 set is on an "improved car," what will happen is that with the 4:1 gears, the thing will steer hard as Hades. Remember that it has the low-pressure big tires. I'd think long and hard about doing that swap. Ford changed to 5:1 gears for a reason.

John Codman wrote: ↑

Wed Jun 26, 2019 11:52 am

Assuming that the 5:1 set is on an "improved car," what will happen is that with the 4:1 gears, the thing will steer hard as Hades. Remember that it has the low-pressure big tires. I'd think long and hard about doing that swap. Ford changed to 5:1 gears for a reason.

Correct. He needs to swap the 4:1 steering shaft for a 5:1 shaft and use 5:1 gears. Pin spacing on the two steering shafts are different. That may be why slots were made wider to accommodate different pin spacing. After I assembled my converted gear case I had to trim two spots in the slot with a dremel tool to clear the pin.

That is likely the engineering change, the wider pinion posts on the 5:1 ratio steering post shaft.

Here are the two cases, on right is the 4:1, on the left 5:1 for the balloon tires, note the longer groove.

To me, Wayne Sheldon's comments sure made sense. The main shaft only rotates so many degrees no matter what ratio is driving it. I don't know why they made the groove any longer, but do know that it had to be wider as the distance from the center of the shaft to the center of the gear pins increased with the 5:1 setup. I've converted 6 Model T's from 4:1 to 5:1 and never had a problem and did not notice a change in turning radius but did notice the ratio change providing more control in actually steering the car(s) . For my '25 Coupe, I found a short pitman arm ( almost 1" shorter ) which also helped although I had to fabricate a blocking plate to prevent the system from going over center.

Bruce;
You said something about blocking plate. Do you have any photos of what you did, was unsure how to approach it? I was thinking along the lines of a larger spindle arm nut that would stop the spindle from going past a point when turning.

Mark : After installing the 1" shorter pitman arm, my car's steering would go over center only on sharp right turns so I bolted a 1/4" thick small plate (maybe 3" X 5") to the left front frame rail that stopped the pitman arm from going any farther and just before it would go over center. With the 5:1 ratio, a 17" wheel and the short pitman arm the car steers like a modern car with "real " steering instead of the stock, almost direct "go-cart" steering that most model pre '25 T cars have.

This one is going over on hard left, so I would have to mount a stop on the pan rail.

Mark : Whether it goes over center left or right depends on the length of the tie rod. There are several different lengths you could try and if you pick the right one it may not go over center in either direction.