Need engineering advice re rear radius rods

[Texas Tom]

In assembling my 1930 fordor, today I set about to connect the rear radius rods to the torque tube (which now has a Mitchell O/D on it).

As seen in the attached photo, the bolt hole in the radius rod does not align with the hole in the torque tube. Same on the other side. The torque tube holes are too far forward by nearly 1/4 inch. It seems I need to somehow bring the entire drive shaft/rear end assembly forward a tad.

I've installed Mitchell Overdrives on two other Model A's and not encountered this issue.

Any engineering (or other) advice?

Thanks.

[John Kuhnast]

If your sure all is mounted correctly on the driveshaft I would slot all six holes about 1/8 inch.

[BRENT in 10-uh-C]

Tom, while I cannot speak for a driveline with a Mitchell, I have run a rear axle sans the radius rods and I could not tell a difference. If you look at what the radius rods actually do considering the one bolt, they are only there for catastrophic needs. I think I would cut the radius rods with a Port-a-band and re-weld them to the proper length and call it good.

[MikeK]

I just stood a torque tube on end and measured from the banjo flange face to the radius rod hole centerline. 46 3/4". What does your Mitchell buildup measure?

[160B]

You should measure the torque tube you removed from your car.

Measure as MikeK suggests "from the banjo flange face to the radius rod hole centerline".

Then take the same measurement on your Mitchell installation.

Then call Sue Mitchell and discuss the situation.

I have installed several Mitchell overdrives and never seen this problem??

[SAJ]

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Hi Tom, I had the same issue as you. I used a piece of the shaped timber from the box my Mitchell came in and a long carpenters clamp to squeeze the radius rods against the Mitchell. See pic attached. Where the extra length went to I do not know. maybe the rods bowed slightly. It was too long by about 1/4 inch and I could not get a podger through all the holes to lever them into position. Even if I could line them up this way, it would have been impossible to get the bolt through while the tapered podger bar was in there. Anyway it workedI
SAJ in NZ

[Texas Tom]

My setup measures 46-11/16. It may actually be 1/16 or so shorter than that, however, as I must measure three sections and total them up. If the O/D were not already installed, I could measure more accurately by standing it on end. In any event, it's too short!

[Bob C]

Are the bolts that hold the radius rod to the axle tube loose to
give a little extra movement.

Bob

[john in illinois]

I agree with Brent. Cut and weld to fit or slot the holes. The radius rod's job is to keep each side of the the axle from pulling back, eliminating stress on the torque tube.Either way you could keep tension on the axle housings.

John

[Texas Tom]

I spoke this afternoon with Steve Mitchell at Mitchell Manufacturing in California. He said my problem is not uncommon. He said he's found that the best way to solve the problem is to remove the six bolts that hold the torque tube to the differential housing. Then install the bolt that holds the radius rods to the front of the torque tube. Then re-install the six bolts that were previously removed. He says this will resolve the problem almost every time.

I'll give this a try tomorrow. If it doesn't work, I'll try the "squeeze" method suggested by our Model A friend in New Zealand. If THAT doesn't work, I'll try Brent Terry's suggestion that I cut a very small section out of the radius rods to shorten them ever-so-slightly.

Thanks for the advice!

[kenparker]

I would first try Steve Mitchell's solution. IF that does not work, second option would be Brents way. I build F150 OD Kits and cut and splice Radias Rods, in order to shorten them, for the kits on a regular basis. BUT if your cutting and welding is off by even 1/16" of and inch you will still have the same problem. I cut the Radias Rods at the small end - about 1 inch back from the original weld. A short piece of "black Iron" 1/2" pipe is inserted into the tube. It acts like a slip joint. The Radias Rods are then bolted to the Torque Tube and the Backing Plates. Bolts are tightened up. The "slip joint" finds its correct length. The Rods are then welded while still in place giving a perfect fit.

If this is confusing send me PM and I can send you pictures.

[Texas Tom]

KEN:

The description of your method is quite clear. And doing it your way ensures that the final result is a perfect fit. Thanks for the advice.

I'll report tomorrow evening how it all worked out.

Tom

[chiliman]

ken parker what what is the OD % 26,37, or41 Ihave a37% in my 30 four door seams to work good running 16inch wheels I have another unit that I'm going to install in my 30 rodster picup gona run 16 inch with 650 tires found out it is a 41% wondering should I GO with a 411 gear in the rear or the 378? any information help full thanks

[Pete]

Forcing, wedging, pulling things together is WRONG WRONG.
Brent has the proper method.
To expand on that, after you cut the rods, bolt the two short pieces to the torque tube.
Align the rear part of the radius rods to the front parts and weld together.
With a Mitchell you NEED the radius rods for strength. Otherwise you are driving the car forward ONLY through the aluminum overdrive case. Not good.

[columbiA]

If you have a 41 % OD,I would go with the 4.11 gears.I run a Columbia OD with a 28.5 % OD & 4.11,s & it seems to be perfect gearing for me.A 41% OD with 4.11 gears would be way to high geared for me as to be almost unuseable.3.78 gears would be even worse.The Columbia has a 2.94 ratio in OD.Same RPM at 60 as at 43 in high gear.

[Kurt in NJ]

If you want to compare position of the bolt hole, and length you can place both tubes the same angle ---or if out of the car on sawhorses and use a plumb bob and lay it out on the floor and then it is easy to get an accurate measurement with an ordinary ruler

[Tom Wesenberg]

If you use a longer bolt and put a spacer between each bar and the torque tube, you can also gain the needed 1/4".

[Tom Wesenberg]

You can also go with the next size smaller bolt in grade 8 to gain some distance.
So, if you place some flat washers between the radius rods and torque tube, then go with a longer, next size smaller bolt, you should be in good shape with no cutting or welding needed.

[Texas Tom]

Sometimes the simplest suggestion provides the best solution.

I tried Tom Wesenberg's idea of using a grade-eight 1/2" diameter bolt in lieu of the original 9/16" diameter bolt. Worked like a charm! No slicing/dicing/welding needed. Everything is now tight and tidy.

Thanks for all your input.