MTFCA Forum

The MTFCA book calls for .002-.003” clearance on drive shaft. What is the best size to ream it?

John

Why not try a combination reaming and facing tool. They are available.

You have to consider the lubricant used - grease, so at least that.

John Illinois wrote: ↑

Mon Jan 06, 2020 4:35 pm

What is the best size to ream it?

John

That would depend on the diameter of the machined bearing surface on your drive shaft. A new drive shaft should be 1.000" in diameter and for a used drive shaft the upper wear limit would be 0.005" (0.995" minimum diameter). So if you are going by the MTFCA booklet, 0.002" over whatever your major diameter is. The last axle/drive shaft that I had done needed a new drive shaft and the bushing was reamed at 1.000" and had a slip fit. Hopefully this is helpful.

It depends on any wear on the driveshaft journal to a large degree. If the shaft is worn .010" then the bush needs to be undersized, and a fixed reamer will not be of much use. To use a driveshaft with such wear will also mean the square end needs to be machined back to allow an undersized bush to slide over it to run on the worn journal.
If the shaft is new, none of this applies.

Allan from down under.

Allen - you brought out the important point. No matter what your measure you can start reducing the size of the square end to fit through the bushing. If you do that then it will be loose in the u-joint, unless you have a u-joint with an undersized square end.

The flats would remain the same, only the corners would require machining.

The drive shaft square end only gets reduced a small amount on the corners when you have them cleaned up. The corners in hole in the U-joint are not right angles, they are curved and I would have to go look for sure but I think the radius of the corners are already larger then the corners on the drive shaft from the broching process. The flats turn the shaft not the corners.

Thanks for all the ideas. I am using a new drive shaft but I do not have it yet. If I have to enlarge the bushing, I plan on boring it close to size with a lathe. I will then install it and finish it with a hone.

John

John Illinois wrote: ↑

Tue Jan 07, 2020 9:59 am

I am using a new drive shaft but I do not have it yet.

John

There are 2 issues that I found with the newly made drive shafts, both on the machined square end for the universal joint. The first is the chamfer on the end, they only chamfer the edge of the machined flat surfaces and ignore the "corners" that are left (I apologize for the photo quality, it is the only one that I have):

Be sure to chamfer those four corners. If you look at an original Ford Drive shaft versus a modern made drive shaft you will see that Ford chamfered the entire leading edge and the newly made ones only chamfer what they machined. Those sharp edges can/will dig into your nicely reamed bushing and raise some material and create a bind.

Second, you may need to dress/break/reduce the aforementioned corners down their length to get the u-joint to fit. If you look at an original Ford drive shaft, they not only machined the flats for the u-joint, but also the corners that were left. The new drive shafts leave the corners at a 1.000" diameter and that can create an interference problem when trying to install the u-joint to the drive shaft. Check your u-joint fit to the drive shaft end and if it is tight or does not want to go on, that is your problem. On the original drive shafts, these "corners" were machined flat. Aside from those 2 issues, the drive shaft is excellent, they just missed a couple of steps.

Pep,thanks for the tip. My old driveshaft is in bad shape but I get the idea. I will make a 1" hole in a piece of aluminum and make sure everything clears and is not sharp.

John

Has anyone welded a driveshaft end and machined it to 1.000". Thanks Ray

Ray, I have had a few hard chromed and ground back to 1.000" That way there's not so much heat involved, and the ground journal is smooth and hard.

Allan from down under.

I recently did the rear axle on my roadster and with a new bushing and new drive shaft. All I had to do was run a ball hone in the bushing to clean up the bur from drilling the grease hole and polish the bore a bit and it fit fine. I just installed another one for my coupe and it was the same. The new bushings fit on the new drive shafts before pressing them in. So they compressed very little when installed. I think the press fit is around .002"?

That is good to hear.

Thanks Allan. I like that idea! Ray