Lower Wishbone Dimensions

[RoddyMac]

I've come to the conclusion that my original design of lower front wishbones just don't work well enough.  I have to add spacers to allow clearance around the damper which means spacers at the trunnion and at the inner end.  So, I'm going to make a set of stock looking wishbones but I need some more dimensions before cutting metal.  I've attached a sketch of the wishbone, I'm hoping someone on the board can help with the clouded dimensions:



Basically I'm looking for the thickness of the material used, the width at the bushing end and some overall dimensions.  I have used the information in the workshop manual to get the "important" dimensions.  Ideally I would prefer measurements from the early wishbones, but I'm sure the later S2/TC ones will give enough info to get things started.

Rod

[BDA]

Roddy, you could probably make money selling replacement front A-arms. Not everybody is comfortable with the tubular ones that are available.

As you probably know, the TC and S2 parts have the same geometry. The TC parts have a tube welded in the shock hole and the arms are spaced out to clear the larger diameter spring on the shock. (this is relatively new information to me so if I'm wrong, hopefully somebody will correct me)

Thickness = 0.085
Bushing tube length = 1.25
width of the arm at the inner bush (what you have as 3/4") is difficult to measure. There is a "cap" that wraps around the bushing tube to beef it up. The best I can measure is 0.8 but 0.75 is reasonable.

The flat you have at 3 3/8" is close enough. It's hard to measure because of the bends.

I have the end depth at 0.260 (you have 1/4")

Your 1 1/8" is pretty much on, too.

I have your 5/8" radius dimension at .739 (hole = .428 and from the hole to the edge = .525). Because the piece was stamped, there is a draft so that my measurement is up to interpretation (measure where the edge starts to turn or where it finishes turning).

I think you pretty much have it. With the added strength of the "cap" I mentioned, yours should be fine though a bit stronger than the original since it's thicker.

I've attached a picture of what I mean the cap around the bushing tube.

[RoddyMac]

Thanks for the dimensions.  I had drawn in the thickness of material as 3/32" but the dimension tolerance I had set was 1/16", hence the thickness showing up at 1/8".  But, even at 3/32" it's thicker than stock.  I'll correct the end radius and look into the "wraps".  Now I need to find a laser cutter who can cut me a set.....

Rod

[jbcollier]

The steel pivot tube is 1.25" OD 0.095" wall seamless tubing 1.25" in length (standard size, available off the shelf).  Early arms just have the arm welded straight to the pivot tube.  Later arms have a reinforcement strip which wraps around the rear of the pivot tube and overlaps the arm, strengthening the joint.

[BDA]

I think the thing critical about the radius dimension is that a washer fit under the bolt or nut of the trunnion. I wouldn't sweat differences in the radius beyond that.

"Strap" would be a better term instead of "cap." 

[RoddyMac]

John
In the past I've had DOM tubing machined out to the correct ID. But, when I was going through all my off-cuts of DOM I found some tubing that I had picked up for something else which matches what you've stated. The anorak fact of the day is Lotus had been using the same dimensioned bushing since at least the start of the Lotus Eleven production run. Unfortunately I've returned the Eleven factory drawings to my friend so I can't quote the original Metalastik part number. 

And thanks for the clarification on the "straps".  I had a look at what Kelvedon supplies for their "race" wishbones for the Elan, and it looks like they've incorporated the "strap" into the flange portion of the wishbone (the flange continues around the bushing tube).  I wonder how many failures Lotus had before they went with the "strap".  I recall my Elan +2 having them on the rear lower wishbones, but they were brazed (bronzed) together.