Author Topic: JL8 vs HD service package 4-wheel disc 12-bolt rear axle  (Read 1929 times)

Jon Mello

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JL8 vs HD service package 4-wheel disc 12-bolt rear axle
« on: May 04, 2013, 03:57:07 AM »
Because of some discussion that was starting to take place in the Heavy Duty GM 12-bolt axles thread, I was asked to get a new topic of discussion going comparing the production JL8 rear axle assembly used in 206 Camaros built in '69 to the Heavy Duty service package 4-wheel disc axle sold over the GM parts counter. Consider this thread the proper place for that discussion.

Here is a small bit of rear axle part number data, courtesy of Bob Morton.



Jon Mello
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Re: JL8 vs HD service package 4-wheel disc 12-bolt rear axle
« Reply #1 on: May 04, 2013, 04:08:01 AM »
Thanks Jon!

Does anyone know of or have any documentation re the number of plates and spring pressure differences in teh posi units between the two rears?   Bob Christianson told me the differences.. and I made notes.  but can't find my notes..   From my memory, there is a significant difference in the number of plates and the Service Package rear posi has much higher spring pressures...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

Jon Mello

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Re: JL8 vs HD service package 4-wheel disc 12-bolt rear axle
« Reply #2 on: May 04, 2013, 05:18:42 AM »
Robert (sixteengrandsedan56) sent me this photo of his HD service package 4-wheel disc rear axle showing the inner guts. I suspect he will check in on this thread and fill you in on more details...
Jon Mello
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Re: JL8 vs HD service package 4-wheel disc 12-bolt rear axle
« Reply #3 on: May 05, 2013, 01:08:44 AM »
I located some of my notes from my last discussion wtih Bob Christensen re the Service Package rear end.   It has been many years since Bob owned that car, and raced it in T/A and IMSA, but his memory is fantastic.  I talked to him 3 or 4 yrs ago by phone (he now lives in KY).   At that time he told me the standard 12 bolt rear Posi Unit had a breakaway torque of 50 ft lbs, whereas the Service Package Posi unit had 4X that amount (200 Ft-lbs), using 22 plates and larger heavier springs in the unit.  He ran his own '69 Z28 from '69 to '74, in regional SCCA, T/A, and IMSA GT, and also ran the Bolus/Snopes Camaro with Bob Mitchell (another Huntsville, AL racer/engineer).   They finished 4th and 5th respectively in class at Sebring 12 hr race in '71.   Bob Mitchell finished 2nd in class in '70 at Sebring.   They both were very good engineer/racers and raced and competed for close to 10 yrs from late '60's to late '70's.   Both bought new '69 Camaro Z28 cars and immediately converted them for competition.   I have a few parts from Bob C's Z28 (the SP rear and the original 1st day takeoff exhaust manifolds.. :).   I'd love to flesh out the specs on those service duty rears if anyone else has any info.   The one I have needs to be setup - has 4.11 gears and the original posi and two sets of axles and caliper mounting brackets, but no brake parts.   I have mid 60s' Corvette brake parts that I would like to build up the rear as close as possible to original spec A(with the parts I have).
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan