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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Topic started by: srozell on May 13, 2017, 10:43:11 pm

Title: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: srozell on May 13, 2017, 10:43:11 pm

So as far as I can tell the mounting points for the front springs are in their stock locations. Furthermore, the shackle length appears to be the same, however I pulled some springs off a lifted GMC (4"), and thought they would fit nicely into my Chev and discovered the springs on the GMC were almost 2 inches shorter...

I measured the mounting locations, and sure enough, it was shorter by the same distance on the GMC.

Go figure.

Is this a GMC vs Chevy thing or something else entirely?

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: Engineer on May 14, 2017, 09:18:57 pm

This isn't a Chevy or a GMC thing, this is a bubba thing.

Front springs for all 1973~1987(91) Chevy and GMC 4x4 trucks was 47" eye center to eye center.

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: Irish_Alley on May 14, 2017, 10:00:09 pm

what did you measure? your old springs could appear to be longer due to the arch being flattened

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: srozell on May 14, 2017, 10:57:21 pm

I measured 47" in the chev from the front mount to the center of the rear shackles hanging vertical.  I then measured in the GMC and found it shorter measured the same way, and the springs matched the dimensions on the trucks.

I'm going to go out and remeasure again tomorrow morning because I haven't quite wrapped my head around it. Perhaps it was an "end of a long day so I'm going to screw up more" kind of thing.

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: srozell on May 15, 2017, 12:59:56 pm

It seems I should just quit working when I get tired.

So it turns out it was a mix between bubba and me.

Bubba put on a pair of 45 1/2" springs, which jammed the rear mount for the front spring way forward. Since they were jammed forward, my measurement read 45 1/2 on the GMC instead of 47" I didn't check to see that the mount was in the vertical position when I measured.

(https://myuglytruck.files.wordpress.com/2017/05/20170515_105257.jpg)

I'm getting the local spring guy to make me up some real springs for the front. I really hate when people do things dumb.

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: Engineer on May 15, 2017, 09:15:14 pm

Sounds like Somebubba took a set of stock or similar springs and had arch added without "springing" the money to have a new main leaf made. The main leaf on a 6" front spring needs to be about 3" longer than stock to account for the reduction in span by drawing up a stock spring.

"Building" a set of "custom" springs requires more than just a little engineering.

Title: Re: 1980 GMC K20 vs CHEV K20.. front spring length difference.
Post by: srozell on May 16, 2017, 03:59:13 am

Yep. You're probably right.

I get the new springs tomorrow, and I can finally replace the original "shocks" my chev has! I can't wait to see how it rides.

I haven't even got the 35's on yet and my wife is giving me the stink-eye. It's gonna be AMAZING!