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So I'm building an IRS and designed my lower wishbones with some of the same size tubing as the Kinetic wishbones I bought for the front. I was hoping to re-use my 5/8" rod ends from my old suspension, but tapping a 5/8" hole in the end blocks looks.. not awesome. Worried about it opening up the hole over time, so I thought I'd post some photos and get your input.

Here's what it looks like when mocked up. The chamfered edges can be a bit deceiving, but basically you're looking at a 5/8" hole tapped in a 3/4" block, which will be welded into the 2" x 1" tube. One idea I had is to drill a hole through the 2" side of the tube, directly above and below the center of the block and plug weld it. At least that way the block should be well constrained inside the tube and hopefully resist ovaling out.

Since this is a lower wishbone these joints will be seeing axial compression and tension, as well as bending in both the vertical and horizontal.


Thoughts? Am I over thinking it or am I being too cheap in trying to re-use these rod ends?

If that is what you want to do, insert the block to protrude 1/8" for a weld bead around the end of the tube and plug weld if you are still concerned. You could have used thicker pipe or rod and rectangular notched the tube center to accept it. I think Jack used the 1x2 because it was convenient for fitting the miata lbj.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I don't like the change from Jack's ball joints to rod ends. Look up "rod ends in bending". Rod ends do not like loads that are not concentric with the threads.

As for the insert. 360 degree weld around it should suffice. Plug welding as an addition is good practice as MV8 suggested,

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Thanks guys, that makes me feel better. To be clear the rod ends are still on the inboard end of the arms just like Jack's. The difference is that both tubes are 2x1" on my design, and welded into the 'vee' is a cup that will accept the new balljoint. I think the bending forces on the rod ends will be similar to the front in that they are helping take the weight of the car, as well as taking front-rear loading during acceleration and braking (because they aren't a true 2-force member like a radius rod).

At least I know the front suspension has held up to a few years of autocross very well, and those arms were done in a similar way - albeit adapted from Jack's kit and so using the standard 1/2" rod ends. Now I've ditched the bike engine in favor of a rear-mounted electric motor and more torque across the entire range of speeds the car sees while on track. And hopefully no more disqualifications for going over 92 decibels.


Partial CAD model for reference:

If you attach the lcaps with bolt-on brackets, there is no need for sphericals since the brackets can be shimmed. Lighter unsprung wt, less expensive, less corrosion, less wear.

A single leg can carry the weight with the other as an adjustable length locator in tension/compression. Attaches to the load bearing leg with a fabricated clevis end and pipe insert through the load bearing 11ga 1x2.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Sorry, my bad assumption. Carry on

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Unless Jack has changed from what is shown on his drawings, his tubing is 1 x 2.5 x .065. You appear to be using 1 x 2 x .120. This allows Jack's smaller 1/2 rod ends to be inserted into a meatier 7/8 thick block, and leaves your design with just 1/3 the minimum thread wall as Jack's. While it only impact part of the thread, and you can use the welds to 'reinforce' it, your tubing is also massively (unnecessarily) stronger... Likely to the chassis' detriment in an 'incident'.

Even if you wanting to reuse the 5/8 rod ends, for both cost and simplicity, I'd probably switch to the same dimensional material as Jack's to both double the minimum thread wall and give the chassis a fighting chance..

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie