Worn out universal joints on shift linkage-93 Van Diemen

[John Green]

I have the worlds sloppiest shift linkage. Pretty sure the universal joints are original to the car. I plan to replace with the Apex covered joints. Has anyone made this change? I assume I will need to cut the old joints off where it tapers down to the smaller OD tube and then drill and bolt the new ones on. Are the Apex joints long enough to extend to where the old joint is cut off?
Just looking for input from someone who has done this so I can avoid screwing it up.
Thanks!

[teamwisconsin]

If its all original Van Diemen linkage, you're better off just fitting all new tubing. They used 1/2" solid rod in most of the linkages I've seen. Take the whole linkage out of the car and assemble it all on the bench. You can get a 6' stick of 4130 in .065" wall from McMaster for about $40. Then you can cut the pieces and fit it all on the bench with the other linkage right next to it with the new apex joints in the same locations as the old borgeson joints. If you don't have a joint that allows left-to-right "clocking", its probably good to pull the hockey stick to make sure the whole thing lines up the way you want it to. Done this way, the only place you'll need to cut the old linkage is where it meets up with the shifter. But doing it all on the bench pretty much guarantees you'll have a piece that lines up and works properly. There are truly few joys in motorsports that are as wonderful as a nice shift linkage!

[Rick Iverson]

……..They used 1/2" solid rod……..You can get a 6' stick of 4130 in .065" wall from McMaster for about $40.

That is why big helicopter masts are tubes: more than double the surface area, way stronger that solid shafts.

Next investment are the two (2) Apex joints.

[Rick Kirchner]

I built a new linkage for my 94 exactly the way its described above. Another benefit of tubing - when you cross-bolt it it will oval ever so slightly and that will help prevent rotational slip in the joint.

On the 94/95, you might want to turn the adjustment device around so that you don't weld a joint to the fabricated piece. That way if a joint ever fails, you won't end up having to shorten it further. I put the joint on the straight rod section which is cheap and easy to replace.

I've also used a stone in a dremel to clearance the uniballs supporting the tubing so it slips through easier. I've always been surprised at the tooling marks on the stock linkages from turning the rods down on a lathe to produce the same results.

[Mike B]

John,
I have a complete shift linkage removed from my old RF93 that you can have. It might be better than the linkage you have now, or it might not but you're welcome to it. I can ship or you can take a road trip to GB to pick it up.

[BeerBudgetRacing]

On my 94/95 I countersunk the screws that assemble the linkage.
So the joints slip on part AND the rod get a matching countersink.
What this did is pin and align one side of the connection and eliminated the slop provided by elongating holes and reduced the friction (and clamping) needed.

If that didn't work (which it did for 5 years without further adjustments), I was going to use a cap head screw and drill out one side of the slip joint so the head just passes through making the clamping on the other side but the head would provide support.

I think both of these methods would work better than the scalloped washers.

[John Green]

Thanks, a lot of good information. I thought I would stay with a solid 1/2" rod rather than tubing. Should I change my mind?

[John Green]

John,
I have a complete shift linkage removed from my old RF93 that you can have. It might be better than the linkage you have now, or it might not but you're welcome to it. I can ship or you can take a road trip to GB to pick it up.

Thanks Mike! I am going to craft a new one. One way to keep busy at the shop for the next 9 months of Winter in Milwaukee!

[BeerBudgetRacing]

Thanks, a lot of good information. I thought I would stay with a solid 1/2" rod rather than tubing. Should I change my mind?

I would look at cost and weight.

You'll never reach the forces needed to benefit from superior rotational strength of tubing.

One benefit of solid is the screw holes "should" wear less.

All these things amount to very little IMO.

[Rick Iverson]

On my 94/95 I countersunk the screws that assemble the linkage.
So the joints slip on part AND the rod get a matching countersink.
What this did is pin and align one side of the connection and eliminated the slop provided by elongating holes and reduced the friction (and clamping) needed.

If that didn't work (which it did for 5 years without further adjustments), I was going to use a cap head screw and drill out one side of the slip joint so the head just passes through making the clamping on the other side but the head would provide support.

I think both of these methods would work better than the scalloped washers.

I used 10-32 saddle washers (Pegasus).

[BeerBudgetRacing]

I used 10-32 saddle washers (Pegasus).

The amount of force needed on those to remove slack is over the top. Need to crush a larger surface area.
That's why the holes all wear.
Tried them. Unsatisfactory results.

[jrh3]

Consider reaming the holes to a precise fit and use AN bolts with no threads in the grip area.

[DaveW]

I would look at cost and weight.

You'll never reach the forces needed to benefit from superior rotational strength of tubing.

One benefit of solid is the screw holes "should" wear less.

All these things amount to very little IMO.

Solid will be stronger/stiffer if its OD is the same as the tubing. Tubing will only be stronger/stiffer if its outside diameter is larger. That may require major revisions to the shaft guides.

[Rick Kirchner]

Shaft strength isn't going to be an issue anyway. Human wrist strength isn't going to bend any of this stuff.

Strictly speaking, make it lighter and your shifts should be faster from a physics/inertia point of view (probably only sigle digit percentages though)

If you want both worlds you could press a slug into the ends of the tubes.

[JHerscher]

For over 30 years I have used a set screw on a second axis to keep holes from wallowing. This photo shows my RF94 with a set screw & lock nut, conveniently circled by one of the O-rings used to keep bodywork in place. If the wall of the joint isn't thick enough to allow sufficient threads, you can weld or braze a nut to it and use a longer set screw. Also shown is a length of bicycle inner tube used to keep the original joint clean and tight.

John

[DaveW]

Shaft strength isn't going to be an issue anyway. Human wrist strength isn't going to bend any of this stuff.

Strictly speaking, make it lighter and your shifts should be faster from a physics/inertia point of view (probably only sigle digit percentages though)

If you want both worlds you could press a slug into the ends of the tubes.

That's likely true, but the increased diameter and torsional stiffness of an equal weight tube would make the shift linkage more precise and easier to use. The solid rods work OK, but I'd bet shifting feel with the stiffer tube would be better. It's the same logic as trying to get rid of all the slop - it just works better.

[Hawke]

That's likely true, but the increased diameter and torsional stiffness of an equal weight tube would make the shift linkage more precise and easier to use. The solid rods work OK, but I'd bet shifting feel with the stiffer tube would be better. It's the same logic as trying to get rid of all the slop - it just works better.

When I studied engineering a million years ago - when we used slide rules - I recall that hollow shafts had greater torsional and bending strength compared to a solid shaft of the same diameter. However, I may have got it wrong, I have forgotten much stuff in the last 50 years. Perhaps someone can confirm?

[DaveW]

When I studied engineering a million years ago - when we used slide rules - I recall that hollow shafts had greater torsional and bending strength compared to a solid shaft of the same diameter. However, I may have got it wrong, I have forgotten much stuff in the last 50 years. Perhaps someone can confirm?

As I said above - for the same weight/cross-section area, hollow is stronger/stiffer in torsion (and bending). For the same outside diameter, solid is stronger/stiffer. All the material in the cross-section area contributes to strength/stiffness. One subtracts the missing strength/stiffness of the hollow area from the solid rod torsional strength/stiffness.

BTW, I still have and occasionally use my 60+ year old slide rule - when my calculator out in the shop craps out.