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Discussion Starter #1
I've successfuly used the threaded rod (all-thread) method a few times over the decades to compress the front springs on 105/115 cars. But today I had one of the rods fail on its fourth compress cycle. Luckily I had made a point of keeping hands and other body parts out of the potential line of fire, so no injury or damage. But pretty dramatic.

I was using 3/8-12 acme threaded carbon steel rods from McMaster. Not sure why the rod failed when it did; maybe damage due to contact with the spring pan, or I didn't grease it enough, or just one too many times exceeding its tensile strength.

This leaves me with one more spring to compress, so I'm going to try the same size acme threaded rod, but in alloy steel this time, with over double the rated tensile strength. Will get the replacements in 3 days and try again.

Be careful out there.
 

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But Mad North-Northwest
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Yikes! Glad you weren't hurt. The rod actually snapped?

I was literally doing this job two days ago. I can't imagine you were anywhere near the tensile strength of the rod if I'm doing my math right. Even lowly grade 2 rod is still 57,000 PSI yield strength. Coarse thread 3/8" rod has a cross sectional area of 0.077 sq. in. So even a single rod should be able to support 4400 lbs, and you had at least two rods in play.
 

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My experience with parts from McMaster Car has been good but who knows where the stuff was made. This highlights the difference between specification and quality.
 

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But Mad North-Northwest
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The pan bolts are 10mm. 3/8" is 9.5mm.

M10 threaded rod is tough to find in the US, and would only give 10% more cross sectional area.
 

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Discussion Starter #8
OK, after taking a break from it, I went back and did the forensics. Clearly operator error. I was puzzled at first that I could only find one piece of the rod, the bottom piece. Then took a closer look at the scene -- the outer tie rod is not installed yet, and the compressor rod had found its way into the ball joint bore of the steering idler arm. I was turning the rod from the bottom, so as the spring compressed, the rod must have gotten itself into a tighter and tighter angle between the idler and the dog bone, and eventually failed right at the bottom edge of the dog bone:

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Lower piece:

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Clearly my screw-up for not noticing the rod going into the idler bore, and for continuing to crank on it as the load increased. Now I have to figure out how to get the rod out of there -- must be under considerable load still. Hopefully I didn't b*gger up the taper bore of the idler too badly.

Like I said, be careful (and observant) out there.
 

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But Mad North-Northwest
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10,484 Posts
Oof. That's pretty random. Again, glad you weren't hurt.

This is really one of those jobs where I wish I had the factory tool. It's not too bad with short springs, but with stock springs the threaded rod method takes FOREVER.
 

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Cutting wheel. Cut a wedge so it doesn’t jam. Maybe a grinding wheel would be safer still. Cut 50-75% of width only and it will probably fold on itself enough to relieve any pressure.
 

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Push hard and live
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Low tensile strength Home Depot all-thread isn’t up to the job. I bought some hardened, high-tensile 10mm threaded rod from McMaster Carr, cut four pieces to the right length, and welded on a nut to one end of each. I use my 1/2 impact wrench, some wheel bearing grease, and it’s a very quick job.

However, even the high-strength rod has a limited life. After maybe 20 uses, they need to be replaced.
 

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Discussion Starter #13
Once again, a bit of luck seems to have saved me from my own ineptitude . . . Got the upper rod half out without a fight -- backed the nut off, then wiggled the steering wheel (center tie rod is installed) and it loosened up. And the idler seems to have survived, though I need to spend a little more time with flashlight, mirror, etc. to make sure. To DPeterson3's point, I don't have a welder, but jammed two nuts onto one end of each rod and then drilled and pinned one with a roll pin. Works well, at least when I'm paying attention.

1626203
 

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Push hard and live
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MIG welders are cheap, and a critical shop tool. So are a good compressor and air tools.

Using two jamb-nuts is a great way to find yourself reassembling your jack screws in the middle of the job.

might a pin through a nut weaken both the nut and rod?
 

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Discussion Starter #16
Good question regarding the hole through the nut and rod. My theory is that the jam nuts share the load and so that weakness isn't critical, but I have no analysis to support that.. At least in this experiment the tool didn't fail at the pinned nut. And yes, the welder and compressor are on the long-term wish list. Biggest impediment is clearing enough crap out of the garage to make room.
 

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Good question regarding the hole through the nut and rod. My theory is that the jam nuts share the load and so that weakness isn't critical, but I have no analysis to support that.. At least in this experiment the tool didn't fail at the pinned nut. And yes, the welder and compressor are on the long-term wish list. Biggest impediment is clearing enough crap out of the garage to make room


ALL YE SPRING COMPRESSOR TYPES- May I suggest a quick and dirty safety tip for anyone doing this task, regardless of method employed. I used it upon my initial Alfa front spring R & R years ago. This after hearing a horror story from the late Gary Valant (of VALCO Alfa Romeo) when he got to remove an errant coil spring embedded in a nearby wooden overhead garage door. I have since seen other cautious folks use it too.

PLEASE, take an extra couple of minutes to cinch a suitable retaining strap or "tether" of some sort around the topmost spring coils and then to the upper body mount to prevent said compressed spring from exiting into your face or upper torso, etc. in case of an accident. This might not prevent hand or lower arm contact in the case of an unintended escape, but will likely contain the spring to the wheelwell area. A short finger is better than no finger.
 

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Oof. That's pretty random. Again, glad you weren't hurt.

This is really one of those jobs where I wish I had the factory tool. It's not too bad with short springs, but with stock springs the threaded rod method takes FOREVER.
The factory tool is available at Centerline for $400
Front Suspension Tool | Centerline International. It's also available at OKP.

So yeah $400 now go found out what your ER co-pay is and make your plans accordingly. You may also want to establish a personal $ number for how much you are willing to pay to avoid having a high speed piece of metal pass through your body.

Bye
 

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But Mad North-Northwest
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Honestly, no, it's not worth $400 for me to buy the tool. It would be faster to use, but I'm not convinced there's a significant safety difference assuming you're using the proper rods and pay attention.

I'm using 10.9 M10 threaded rod with 10.9 extended length flange bolts myself. It's slow to do but with at least two rods on there that spring and pan aren't going anywhere.

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