IRS rear end question

SoCalDoug · Post by **SoCalDoug** » Thu Oct 03, 2002 10:22 am

Anyone know the difference(s) between the "early" and the "late" IRS rear ends?

i'm building my first rail and have a torsion tube from a 68 (im guessing here, there is a "68" stamp in the middle of the tube where it narrows), and control arms, spring plates, torsion bars, backing plates, brake assy's, and drums, etc from a 73 or later (this estimate was based on measuring the torsion bars).

the torsion has had the horns and pivot points removed. pretty much a bare tube with the shock towers and front tranny mount left on it. i figured i would get some aftermarket pivot points and a jig and go that route. horns shouldnt be a problem either...

thanks!
doug

Post by **Marc** » Thu Oct 03, 2002 10:31 am

Only difference that I'm aware of is that the early ones used double springplates and 4-bolt control arms (like all IRS Type IIIs have) and the later stuff has single springplates and 3-bolt control arms. I think that the change came late in 1971.

SoCalDoug · Post by **SoCalDoug** » Thu Oct 03, 2002 10:47 am

hmmmmmm....

i sure wouldnt mind having the double spring plates.

my biggest curiosity i guess, other than total travel, would be the width from end to end.

it appears that when i jig up the new pivot points and replacement frame horns, the pivots hit/overlap the frame horn tubes by about 1/2 inch. the jig was made on a late model irs rear end, and the replacement frame horns are basically 1.5"x.095" pipe that goes straight back from the torsion to the rear tranny mount (first it goes down a little, then straight back).

IF for some reason, the early torsion was slighly "shorter" in total width (between the cover mounting faces), that would explain why the frame kit manufacture claims they should fit together... and mine doesnt.

thanks for the thoughts!!!
doug

SoCalDoug · Post by **SoCalDoug** » Thu Oct 03, 2002 10:49 am

I found another 1/8" error on each side!

when i put the new pivot points on the jig, i placed one of the large washers on each side. i just found in one of my books that the washers BOTH go on the outside of the control arm bushing. this would move each pivot point out about 1/8" (a step in the right direction i guess)

doug

All_talk · Post by **All_talk** » Thu Oct 03, 2002 1:03 pm

Go here and check out there IRS conversion pages
http://www.blindchickenracing.com/How_t ... ersion.htm

You?ll see that the inner IRS pivot brackets cut into the stock frame horns, if your replacement horns are in the same location you may have the same problem.

Gary