Mil-spec steering u-joints

[nms553]

Over the past few years we (and most other teams) have been using the standard mil-spec u-joints (the ones with the orange boots). However we had a lot of play in our steering linkage partly due to our steering rack and quick connect, but it was also coming from our mil-spec u-joints. Has anyone else had this problem? Any suggestions for another u-joint supplier?

[nms553]

Over the past few years we (and most other teams) have been using the standard mil-spec u-joints (the ones with the orange boots). However we had a lot of play in our steering linkage partly due to our steering rack and quick connect, but it was also coming from our mil-spec u-joints. Has anyone else had this problem? Any suggestions for another u-joint supplier?

[Kirk Feldkamp]

Did you figure out what the root cause of the play was for the u-joint? I'm going to go out on a limb and guess that it wasn't actually inside the joint. Most wobble I've seen in these is from the attachment to the shaft, not the joint itself. If it truly was, you should cut off the boot and figure out what went wrong, and figure out if it's actually anything you can fix. By saying "the ones with the orange boots," you're talking about Apex joints, right?

-Kirk

[Adambomb]

+1, most of the problems I've seen in this area are either in how the shaft is attached to the joint or even slight amounts of slop in steering column support bushings.

Although I know there are knockoff joints out there, orange bushings and all. I remember seeing what I remember to be knockoff joints at Summit and Jegs (not sure), thinking I saw genuine ones at Pegasus.

Also have personally experienced cases where we found the joint in a drawer and it ended up being pretty haggard and of questionable origin. FWIW our baja team has actually broken these joints before (they still can't tell me what the scrub radius was on that car though).

[oz_olly]

I agree that the play is likely to be coming from the mechanical connection between the steering shaft and the universal joint. We take extra care here by reaming the hole and using a close tolerance bolt. You could also use a tapered bolt as recommended in one of Carroll Smith's books. I have also seen the shaft welded or braised to the uni joint when used in shift linkage on a formula ford. That's probably a pretty good way to go but I imagine you would have to find some way of cooling the boot during welding or how to take it off and reinstall it without tearing the boot.

The joints most commonly used are MS-20271 with -B12 being pretty common size for FSAE. If you google 'Cooper Tools Universal Joints', you will find a pdf file that has a bunch of data on the uni joints. Cooper tools claim that there joints actually exceed the milspec, where as it is highly likely immitation 'bogus' parts wouldn't even meet the milspec. The aviation and race car industry is full of people making dodgy poor quality parts and selling them as something else so be very wary. When ever there are expensive parts that can be relatively easily copied be wary on where you buy them from.

[moose]

If you bolt it on with a regular bolt, it will work loose either at the joint or in the hole in the steel shaft. A tapered pin would probably do a good job. If you go the welding route, they actually sell some grease to apply to act as a heat sink. You just need to be careful, as it makes it much harder to get good weld penetration when using it. Otherwise, just be very careful with a wet rag, etc to keep the thing cool, and don't weld on it 5 times.

[Pico]

Firstly, these u joints aren't made for steering use but for linkages. If you open up the boot you'll see that the amount of material around the T is quite ridiculous. I've personally used these for 3 years first with a bolt through then a dowel pin. The proper way to do this is using saddle washers (Pegasus Racing Supplies), a shoulder screw and a small interference press fit in the u joint hole. You should use a proper steering u joint. The one at Dan's Performance I used this year was excellent.

[oz_olly]

What is a 'proper steering u joint'? It doesn't really matter at all what a mechanical component is designed for so long as it meets your design requirements: cost, mass, strength, availability, durability etc. Saying you must use a 'proper steering u joint' is like saying you shouldn't use duplex chain for your final drive because motorbikes commonly use single link chains. One of the great things about using this type of joint is that it is specifically design to take axial load as well as torque. This means it can assist in axially constraining the steering column, preventing the driver from accidentally pulling the column apart.

Cheers

[Richard Pare]

The joints you want to use are Apex, nothing else.

A 1/2" joint is possibly just a bit too small even for the loads seen on these small cars if you are looking for longevity, but that will depend a lot on the soundness of the assembly method. The standard joint size for Formula Fords and Formula Continentals ( and even many Formula Atlantics)is 3/4", and they will last for many years of much harder use than you will ever see.

Assembly:

Bolting is OK, as long as you do it correctly. At issue is the clamping load and the friction it imparts between the ID of the joint and the OD of the shaft.

First, the shaft at that point has to be solid. You can accomplish that simply by pressing in a steel slug (it can also be an aluminium slug) to keep the shaft from collapsing under the bolting load.

Second, the shaft needs to fit tightly into the joint to keep misalignment to an absolute minimum - any misalignment there will add to the torque moments that the clamping friction is trying to resist.

Third, you need spherical-shaped-undersides washers under the head of the bolt and the nut to correctly spread the clamping load over an adequate area, otherwise all of the loading will be in essentially two short lines in line with the assembly directly under the bolt head and nut.

While the standard for those larger cars may be the 3/4 joint, it is quite possible that once you get the assembly correct , the 1/2" joint will last long enough to suit your needs.