Nomad C4 chassis assembly

[NickP]

Machinery Handbook - 24th edition, says "Allowance For Forced fit - .001 to .0025 per inch with .0015 being a fair average." My question, and Rick will have the answer, is the difference between a fit in aluminum versus steel. If you had some dry ice it might ease the assembly some but again, when the BJ comes up to room temp I don't know what will happen. Is the dimension you have for the control arm an average or a single measurement (not that that really makes a difference)?

[chevynut]

http://econtent.autozone.com:24999/z...e_specific.pdf

Duralast Part No. FA2101 Press-In Ball Joint Service

Applications affected: All vehicles using Ball Joint FA2101: Ford Crown Victoria, Mercury Grand Marquis, Lincoln Town Car (1995-2002) and Ford Mustang (1994-2004).

Description: This ball joint relies on a press (interference) fit within the control arm opening. This means the diameter of the ball joint housing needs to be larger than the inside diameter of the opening in the control arm housing. By OEM design this is a .002” (two thousandths) interference fit. However,most aftermarket balljoints, including Duralast, are manufactured slightly larger than the OEM part, to provide additional interference to compensate for minor wear of the opening in the control arm. "

I think I'm going to press an OEM balljoint out of one of my other lower C4 a-arms and do some measuring. There's always some goddam thing slowing my progress.

[chevynut]

Machinery Handbook - 24th edition, says "Allowance For Forced fit - .001 to .0025 per inch with .0015 being a fair average."

So that would be .003" for the C4 a-arm.

My question, and Rick will have the answer, is the difference between a fit in aluminum versus steel.

Yes, I've been wondering about that myself. I have many hours of polishing in these a-arms and really don't want to break them or I have to start over.

Is the dimension you have for the control arm an average or a single measurement (not that that really makes a difference)?

I've measured both a-arms several times and keep coming up with 2.068" with calipers for the BJ hole. I may re-measure more accurately with a snap gauge and mic but I'm betting it's withing a couple thousandths. The Cerakote is really thin so it's not affecting the measurement much, I don't believe.

[NickP]

There's Cerakote in the hole? As memory serves me, and this was years ago, we were making parts for the Navy (Govt. Contractor) and always, any bore for machined fits, be it Titanium, Aluminum or Steel were not allowed to have any material (Free of Finish) in the receiving bore. I suspect they had a good reason but way over my head.

[WagonCrazy]

Have you sanded down the ceracoat yet? Just to be sure you have the most accurate "stock" opening measurement? Can the a-arm ball joint holes be machined (opened up) ever so slightly so that you have the size of your ball joints? Just thinking it a bit here...

[chevynut]

I have not sanded down the Cerakote and didn't mask it before spraying because I forgot . But it's supposed to be a half a mil thick (0.0005"). I have .014-.021" interference fit depending on the balljoint I use. I don't think the Cerakote is the issue.

[NickP]

I wasn't suggesting that the coating was the issue. I guess my concern would be more from the BJ skiving off the coating (regardless which one is used) and not allowing the BJ to be seated fully in its bore as the material built up at the bottom. I'm certain I'm just overthinking things again. Do you have any other lowers that need BJ's? If yes, maybe press one out and measure it and inspect the hole for issues.

What does the manual say about the process or sizes?

[chevynut]

Okay I just took another lower a-arm with the original GM balljoint and pressed it out. I measured the balljoint body with a 2-3" micrometer and got 2.075-2.078". It seems to have a slight taper to it and the small measurement is the place that hits the a-arm first when installing it. I also measured the hole in the a-arm with a snap gauge and the same mic and got 2.068", which is the same as I got before on my a-arms with the calipers. The bore is not very clean and has scrape marks from pressing the BJ out. That gives an interference fit of .007" to start out and .010" at the fully seated position. That seems fairly reasonable for a press fit.

I re-measured my a-arms and depending on where I measure I get 2.066-2.068", about the same as the other one I just disassembled. Some of this variance is likely the Cerakote (.001" or so) and some is due to small burrs in the bore. It's probably 2.068" nominally. Wish I knew what the design size is supposed to be.

The Delco BJ I got measures 2.084-2.086" again slightly tapered. That gives an interference fit of .016-.018".

The BJ I originally got in my rebuild kit measures 2.091-2.092" with almost no taper. I'm not sure why it measured larger this time but I didn't re-check with the calipers. That gives an interference fit of .023-.024".

Here's a couple pics....the BJ on the left is the one from my rebuild kit, and the center one is the Delco part. The hole in the polished a-arm is nice and clean (Nick, the a-arms are a pair I got from you ):

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[chevynut]

C-4 Lower ball Joint part problem....

---

"I am in the process of replacing the lower ball joints on my 84 Corvette. I got new joints from NAPA and I measured them before I installed them.
I found the new joints to be .015 larger than the ones that I removed.
I also measured a set of TRW and Moog ball joints and found them to be the same as the NAPAs. I am hesitant to try to press these into the control arms, because I don't want to damage the bores. What am I missing. The control arms did have Z51 stamped on them, but the parts stores all claim the 84 up use only one type of joint. Any help would be appreciated.
Dave "

http://www.corvetteforum.com/forums/...t-problem.html


"David B05-15-2008, 09:16 AM

Here's the latest episode of "Dave vs Ball Joint".

The control arm hole is approx. 2.063" id.
Original (removed) joint is approx. 2.075" od.
Aftermarket joint is approx. 2.091" od.

I'll have a GM joint tomorrow (Fri.)

Sat. I'll install whichever new joint is smaller od.

I'll put joint into freezer (to shrink) and use a bearing heater stuck into control arm hole (to expand), and go for it.

I'm an industrial mechanic/electrician and deal with press fits, tapered shafts, etc., but I've never dealt with anything that looked this simple but was this much trouble, AND I HAVE THE WHOLE REST OF THE CAR TO DO!!! before paint.

Thanks All for the advice. I'll post the results...good or bad.
It looks like I'll be wearing you all out with my rebuilds!"


"David B05-18-2008, 08:40 AM

I won!!!

Lightly sanding paint on joint's mating surface didn't help. Putting joint into freezer didn't help. Sticking top of bearing cone heater into hole in control arm didn't help. I had to simply force bearing tool (surprised I didn't break it), remove it, heat arm with torch (I don't really think torch helped either!), beat joint to realign it, use tool again, repeated procedure until joint was finally seated. I'm sure I had 4 or 5 hours in simply installing the lower joint. I'll install upper joint today.

When I decide to lower front ride height, will I have to go through this again, or worse?

Thanks to everyone!!! :thud:"



http://www.digitalcorvettes.com/foru.../t-101728.html


Seems like there would be lots of complaints on the internet about this, but I can only find a couple. From everything I read, everyone says just force it in.

[Rick_L]

A few comments but nothing to change the basics.

The Machinery Handbook general recommendation of .001"-.002" of interference per inch of diameter agrees with every other authoritative recommendation I know of.

That said, if aluminum is one of the materials, you might want to want the interference on the tighter end of the range because aluminum is not as stiff as steel. Also if the assembly was to be used at an elevated temperature (and this one is not), you'd want to have a tighter fit to overcome the higher thermal expansion rate of steel - if the part with the bore is aluminum.

Having more interference than the general recommendation could have negative consequences. The control arm hole could possibly split if the wall was thin enough. It could take more force than typical installation equipment could produce, or more than you have. This could also be a safety hazard if something broke (including the installation equipment, perhaps especially). Also as already seen, installation or removal may tear the aluminum, which is going to reduce the interference, defeating the intention of using a "more is better" approach to the fit.

If it was mine, I'd remove the coating trying not to remove metal. Removing metal runs the danger of a hole that's not as round as it once was. Then I'd seek some ball joints that are close to OEM diameter.