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Stock shocks should be 12.75" compressed and 21.38" extended, and be bayonet stud top, and eye on the bottom. Here's the Monroe chart showing all the shock numbers, end types, and dimensions.


Based on the chart your stock shock also has a 3/8" stud on top that's 2.125" long, and a 5/8" end on the bottom with a bushing 1 5/16" wide.
S4 top stud, and L1/CP3 bottom.
You can look down the chart to find another shock that got a longer extended length with the S4 top, and L1/CP3 bottom, and get the part number.
I've found the fastest way to work through this chart is scroll down looking for S4 top number, and then look at extended length. Once you find the length you think works, then look at the bottom number. Other bottom numbers that will work are LS49, LS55, LS79, and LS85. All have the same 5/8" eye, but are slightly different widths that will still bolt up fine.
Other top numbers that will work are S34 and S42. slightly longer length studs.
There's over 100 pages there, but I've yet to not find another shock that would work.
 

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Discussion Starter · #28 ·
Figured I would post my experience with the 3” springs from mcveigh. I had to get longer shocks ( the monroe number I mentioned). Had to cut 3/4” off my driveshaft and always watch the passenger spring shackle it did flip on me today. The driveshaft while on the lift goes so far forward it knocked the rubber out my trans seal (4 speed t10). I will post how it rides when the shocks get here.
 

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Cocke County, TN. 55 Bel Air Sport Coupe
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What is wrong with these springs? Are they too short? Never heard of the shackle flipping by itself.
 

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Discussion Starter · #30 ·
I think due to the arch. The shackle flips forward so u have to pull it back with a pry bar when letting it down off the rack. Its not a big deal. i was disgusted about having to shorten my driveshaft. Buying longer rear shocks was not that bad thanks to the chart 1971BB427 posted. I still think its worth it to not have air shocks. Do you guys think caltracs will clear the spring arch?
 

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I'd contact Caltrac and get some dimensions from them on the height of pivot points front and rear. Then you can use a straight edge to measure front and rear height along your spring arc to know if they'll work or not.

I personally don't have an issue with air shocks IF the Tri Five has a retrofit top shock crossmember. But with stock shock top mounts even overload shocks with their lighter springs can eventually work their way through the trunk floor. I've used air shocks on 4 different cars I used for drag racing to adjust the preload on the rear tires. I always run independent lines to each side so I can vary the pressure. Never depend on them for stance so they are kept at minimum 25 psi most the time. But at the track I've occasionally doubled that on the right rear to make the car launch well, and straight.
My '39 Chev coupe has them presently, but my Austin gasser uses QA1's and ladder bars, so I adjust the coilovers for trips to the drags.
 
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