U Joint Too Tight?

[ArthurB]

I am assembling a brand new U-joint with a brand new drive shaft. The u-joint slides halfway into place on the greased up drive shaft and binds up (test fit outside torque tube). I suspect I could get it on with a mallet or heat but then I don't know how I would get it off. I know tight is good, but this seems too tight.

I measured the drive shaft: Perfect 1.000 all the way from end to end, with 0.810 squared off for the u-joint, with 1.000 at the chamfers. The inside of the u-joint measures 0.812 for the first inch, but I can't measure beyond that. Chamfers seem to be 1.010 but its hard to see if their profile matches the shaft.

No obvious dirt or high spots.

How would you address this? I know I don't want slop at this joint. I figured it was smart to stop and think before I get out the sandpaper and files.

I don't see this problem mentioned in the Chaffin booklet, and I don't see dimensions for these parts in the "rebuilding the rear end" checklist.

[Stephen_heatherly]

It's probably getting stuck on the chamfers. A few light passes with a file will probably get it to slip on. Before you assemble the u joint to the drive shaft, make sure the square end slides freely in and out of the transmission output shaft. I've seen a couple new u joints that were too big on the square end. This is very important otherwise if the u joint is forced into the transmission all the drums and gears will be forced towards the flywheel which car result in a destroyed transmission. Personally I don't like the new u joints and only use good original ones.

Stephen

[Stephen_heatherly]

Btw, filing the chamfers won't make the u joint fit too loose. The u joint drives the shaft through the flats not the chamfers.

Stephen

[Original Smith]

If you still have problems, try a Ford script U-Joint. I've never had that problem.

[Scott C.]

I would contact your vendor. I rebuilt 2 rear ends this winter. Both with new drive shafts and ujoints. Both fit the shaft fine. However, the male ends of the ujoints were a little bit big and needed a little bit of fitting to the transmission shafts.

[Kerry]

Sounds like the builder of the uni's has slipped back into a mistake that was made several years ago, or it's old stock from that time,
instead of .002" undersize clearance, they had .002" oversize, jamming the works up

[Pep C Strebeck]

Here is a quote from an earlier post on the same issue. The original post was about reaming the drive shaft bushing but this is also a problem that I ran into with a new made drive shaft, and using a N.O.S. Ford universal joint

viewtopic.php?f=2&t=9553&p=71150#p71150

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.

[CudaMan]

I found the same thing on a new reproduction drive shaft that I bought, I had to file on the chamfers a bunch to get the driveshaft to fit smoothly into the back of the transmission. Just another case of a low cost supplier cutting (or not cutting enough!) corners.

[ArthurB]

Thanks for the responses. I cleaned up the "corners" and chamfer on the drive shaft (from Fun Projects) but that doesn't seem to be where it is binding. I have two old u-joint and drive shafts-- the new u-joint binds on the old drive shafts too, and the old u-joints fit on the new drive shaft fine.

I also checked the fit at the transmission end of the new u-joint (thanks for the warning!), and sure enough that was way tight. The old u-joints slid in nicely.

Unfortunately my old u-joints have popped rivets and badly worn bearings, well beyond repair. I bought the new u-joint from Langs so I will contact them.

[ArthurB]

Have any of you seen Ford drawings for the mating surfaces of the drive shaft and u-joint? I can't seem to find dimensions except the bearing surfaces, which are not the issue.

[Mark Nunn]

FYI, the u-joints that are sold by Lang's, and probably others, come from Snyder's. They have them made by someone else. My point is that new u-joints are probably all from the same manufacturer.

[Scott C.]

Mark is probably right on that. I bought one from Lang's and the other from Snyder's. The packaging was identical. Form memory, I think the packages said made in Taiwan.

[John Illinois]

I tried 2 new joints and ended up returning both. Model T Haven sent me a nice used one that fit perfect.

John

[DanTreace]

New driveshaft sticks on the way into the new reproduction U-joint.

IMG_7944 (550x413).jpg (87.88 KiB) Viewed 5462 times

Arthur

Have the same fitting issues with reproduction parts, it happens. We can't go get NOS factory parts anymore, but sure glad reproductions are available.

Of course in a perfect world, new parts would fit, but many times a bit of 'custom' fit is necessary,

On the new driveshafts as noted, the chamfer isn't there, so you have to file it to shape, easy to do as the driveshaft isn't hardened steel, its soft.

Same with the square end, the flats aren't in dimension either to fit to the new U-joint or maybe the new U-joint dimensions are off, either way custom fit it. There's no filing on the new U-joint, its hardened steel!

So get out the mill bastard file and drawfile the 4 flats down some so that the female U-joint slips easily, all the way to the bottom, remember to add a bit of grease on assembly to the flats.

IMG_7978 (500x375).jpg (71.6 KiB) Viewed 5462 times

[CudaMan]

Dan's photo shows another feature of the currently available driveshafts that cause me to worry - note that the blend radius at the base of the square section is much tighter on the reproduction than the original. That could increase the stress at the fillet, increasing the chance for a crack.

[Pep C Strebeck]

Dan's photo shows another feature of the currently available driveshafts that cause me to worry - note that the blend radius at the base of the square section is much tighter on the reproduction than the original.

Radius? What radius? The most recent drive shaft that I had purchased (September of 2019) looked just like the one on the left in the photo that Dan had posted. There is no radius to speak of, almost a square corner. The vendors website descriptions state that these are made to Ford specification and all dimensions are correct, but they do not say "made to the blueprint".

There are obviously a couple of fitment and dimension issues due to them not being made to the print, and these could be easily corrected, the vendors just need know about it. As I had said in my earlier post, the new drive shafts are excellent, with the exception of a couple of small and correctable issues. These issues could be sorted-out/corrected on new production.

As for Mark's concern about the radius, I agree, there should be a radius there. A radius reduces a stress point where a crack or break will/can form. As made now there is no radius to speak of.

[ArthurB]

I got my drive shaft from Fun Projects. It has a nice blend radius at the end of the mating surface, and the chamfers were fine. The only obvious difference from the original Ford script driveshaft was that it is smooth and shiny the entire length instead of just at the bearing surfaces. I don't know who makes the shafts for Fun Projects, but it definitely looks nicer than the one Dan shared.

I'm confident my problem is the reproduction u-joint. I'll decide this weekend if it's time to touch up with a file or look for a good old part. Thanks for all the advice. I'm much more confident I understand what's going on.

[Scott C.]

My drive shafts did not look like Dan's. They both had a radius.