Shifter linkage tubing

[Earley Motorsports]

Hi all. I have made my shifter linkage out of 1/2" mild steel tubing but there is too much torsional strength in the reverse lock out to depress the pin. I don't have room for 3/4. What is best to use, 4130 or stainless. Would these have enough strength to depress the lock out. Thanks for the help.

[john f]

Do not mix up an increase in tensile or yield strength as an increase in stiffness. Stiffness is a function of modulus of elasticity (rigidity) or dimensions. The modulus for steel is the same whether it is 4140, 1018 and very close to the same for stainless. The only way you can increase the stiffness of your shift rod is to increase the dimensions of it. Seeing that the OD can not be increased, you can increase the wall thickness. This will increase the stiffness, although not as much as increasing the OD. Torsional stiffness is a function of D^^4. Just my $0.02

john f

[Earley Motorsports]

OK. Thanks John. What I used was 16 gauge. I see half inch used on other cars with a MK9 Hewland and was wondering what they use. All my apex joints are good, there is no slop in the joins along the linkage. It selects all the forward gears no problem, it is just when I go for reverse it twists the tube by the look of it, The tubing doesn't bow or anything and it's pretty much straight right back to the rear bulk head. Would I be better to go solid?

[Randy Cook]

Have you considered the easiest and cheapest alternative? Change the lockout reverse spring, either the detent spring or the plunger spring or both. It shouldn't take a gorilla to operate reverse gear.

I'm curious, what happens to the current shift linkage when you attempt to engage reverse gear? Too much twist in the shafts in total and the shift lever bottoms against a chassis component? What?

Let us know what change eventually solves this for you, please.

[Earley Motorsports]

I was thinking about the spring tension. I know it is there to stop accidentally stuffing it into reverse instead of first. If I take the rear cover off it goes in as easy as the forward gears. Is there different tension springs for these? The shift lever does hit the frame tube. Thanks for the responses so far.

[Jerry B.]

Graham:

You might re-look your shift linkage using two pairs of eyes, operator and looker....might be if you oversized the bolt holes, tubing to Apex joints or if the linkage is two pieces, 2 joints, see if the pillow block/bearing mid way tween the two rods is moving around.

Moving to reverse using the shifter is only about 10-15 pounds. Even if the tubing is garden variety metal it should not twist in using not so long pieces.

[stephen wilson]

The solution is to change the lockout spring, there is no way you should be over-stressing 1/2" steel tubing. My RF'78 had 1/2" x .095" mild steel tubing with no issues (now 5/8" x .058 4130 to save weight). As mentioned, look for excess play in the joints, and the mountings.

[Brian]

Lots of people over-shim the reverse spring to prevent engaging reverse by accident. Lots of shifter mechanisms have a restricted range of movement of the shift lever, and it's easy to adjust them wrong and have the lever itself not have sufficient range of motion to overcome the spring. I built a shifter linkage out of 1/2" .065" wall stainless and while I happen to think it is too small a diameter tube with insufficient strenth, it does work in a sucky kind of way. I use 3/4" tube now, usually .065" stainless so I don't have to worry about it, paint it or plate it and it looks great forever. I weld the apex joints to the tube unless you can't physically install it without a bolted joint.

[stephen wilson]

Now that you mention it, I did weld a piece onto the end of the detent to take up some play, requiring less linkage travel. Just remember to re-drill the vent hole.

[Earley Motorsports]

Hi. I just wanted to thank you all for your comments. I have welded all the apex joints and things and all is good now. I also changed the spring in the lockout for one with less tension. Still takes some force to get into reverse which is good. Thanks again.