Lower Control Arm Pivot Shafts

[RRChris]

I purchased new lower control arm shafts as I am chasing a knock in the front end. The fit of the shafts in the new LCA bushes (rubber), when I did it 18 months ago, was not an interference fit anymore. So I have decided to invest in new shafts. and bushes again.
Have gone to do the job, and now find that the new shafts where they mount in the k frame have some slop. The old shafts here are snug. Measuring the diameters on both old and new, near the shoulder, there is about 15thou (0.40mm) difference in size - with the new ones smaller than original. I would have thought the new ones should be the same, if not a fraction bigger. Even adjacent the pivot shaft nut they are 6thou (0.17mm) smaller.
Has anyone else experienced this with new pivot shafts? I can't believe that simply tightening these up on the pivot shaft nut will solve the problem given the amount of load that goes though this point with the torsion bar load and car weight.
Am I over thinking it? Is there a way around the problem (if it is a problem)? Or simply tighten up on the nut?

 

[AR67GTX]

Whose pivot shafts are you using? I replaced mine for the same reason a couple of years ago with PST ones and there were some dimensional differences with the originals, the details of which I don’t recall exactly. But the did tighten up and work fine.

 

[ZR9B]

1 of mine are on the small side where it goes through the k member. I haven't removed it yet to see where the problem is and I guess it could be the k member hole. Hmmm

 

[gkent]

Since these are tapered, as long as they will seat in the K once the nut is tightened you will be fine. But if the shoulder of the shaft prevents it from seating then you're screwed.

 

[zyzzyx]

Being a retired Machinist, all I can say is that if the sizes are not within 0.001 (one thousandth) of the originals, they're junk,
and should be returned. They need to be a press-fit into the LCA inner bushing sleeves, and they need to be snug in the K-frame.
I've heard of the new bushings being oversize, and that's not acceptable either. Working with aftermarket parts, you always
need to measure everything so you know what you've got. There's no other way to do this.

 

[themechanic]

This guy had a lot of issues installing aftermarket pivot shafts and bushings.

 

[wvmarv]

This guy had a lot of issues installing aftermarket pivot shafts and bushings.

It would help if he had a ******* clue what he's doing.

 

[PRND21]

Skybe? Scibe? Huh?

 

[RRChris]

Whose pivot shafts are you using? I replaced mine for the same reason a couple of years ago with PST ones and there were some dimensional differences with the originals, the details of which I don’t recall exactly. But the did tighten up and work fine.

Don't want to mention company names just yet as I has written back to the supplier and manufacturer regarding the issue. When I have an outcome I am happy to share then.

 

[RRChris]

Being a retired Machinist, all I can say is that if the sizes are not within 0.001 (one thousandth) of the originals, they're junk,
and should be returned. They need to be a press-fit into the LCA inner bushing sleeves, and they need to be snug in the K-frame.
I've heard of the new bushings being oversize, and that's not acceptable either. Working with aftermarket parts, you always
need to measure everything so you know what you've got. There's no other way to do this.

I agree with you regarding the tolerances - as an engineer it didn't make sense to me, but I wanted to make sure I wasn't missing something. The old saying of ask questions first before firing off.
For the life of me I cannot understand why it is so difficult to make aftermarket parts that fit!! These are really simple tolerances. Hopefully I get a positive response from the supplier and manufacturer.

 

[RRChris]

Since these are tapered, as long as they will seat in the K once the nut is tightened you will be fine. But if the shoulder of the shaft prevents it from seating then you're screwed.

Taper diameter is too small, already on the shoulder. As you said - screwed!!

 

[zyzzyx]

The sad part is that there seems to be no quality control at all! Someone made the parts, (A thousand of them?) and
no one checked them. Then they got shipped to the vendor and he didn't check them. Then he sold them to you.
No one gives a Rat's *** anymore.

 

[RRChris]

Unfortunately the manufacturer claims the supplied parts dimensions are to their drawings. Seeing their drawing they are.
Still does not explain why they are under size.
I am reaching out to PST (who is not the manufacturer in question) for some help. Hopefully they have the right sizes.
I have attached a sketch with my dimensions. Can anyone here confirm if these are correct (Dimension A and B), or if I have something unusual

 

[RRChris]

So, I think I am finally coming to the end of this journey.
Summit Racing really went all out to help me on this. However, the manufacturer has drawings that confirm the dimensions of the parts they supplied. Despite this Summit is refunding my money without question - I cannot complain about Summit's customer relations.
James (and Dan) at PST have also been super helpful. They have confirmed that the larger end of the taper is actually 24mm, 0.2mm larger (8 thou) than my 50 year old original. This will give something for the shaft to pull up into the taper. Thanks James and Dan at PST my order will go in tonight.