JL re Shock Absorbers in 1978

[Tom R.]

Joe:

While studying build sheets for 1978, I've come across a set of broadcast codes called out when a non-FE7 with L82 and P255/60 R15 tires were ordered. Build sheets call out CK (front) and CL (rear).

According to 1978 build sheets, all FE7 equipped Corvettes call out CK (front) and CE (rear) and we have those part numbers as listed in numerous past NCRS threads.

According to 1978 build sheets, all base suspension Corvettes with L48 and P225/70 R15 call out CH (front) and CJ (rear) shocks.

Also in 1978-79, 18 different coil spring configurations (and therefore broadcast codes) were called out that in addition to vehicle weight + option weight, a weighting was assigned for whether the vehicle was to be equipped with RPO QGR (P225/70R15) or RPO QBS (P255/60R15) P series tire.

The AIM for both years call out these Part#s:

• For 1978 FE7 front shocks, AIM specifies GM# 4984577
• For 1978 FE7 rear shocks, AIM specifies GM# 4984578
• For 1979 FE7 front shocks, AIM specifies GM# 4984577
• For 1979 FE7 rear shocks, AIM specifies GM# 22012402

In my judging over the years, I've been conflicted over FE7 shock numbers because the AIM and our threads have listed 4984578 as rear shocks. But I know from top flight and Bowtie judging that 22012402s were installed on 1978 FE7 equipped vehicles.

I'm drawing the conclusion that the FE7 rear shock 4984578 is the CL broadcast code when P255/60R15 tires were ordered with L82. These same vehicles were equipped with GM# 4984577 front shocks (CK). As a result, 1978 Corvettes were equipped with two different heavy-duty shocks and by 1979, only one was used when FE7 was ordered.

When FE7 was ordered with either engine configuration, it called out the CE broadcast code and 22012402 was installed.

In this analysis, broadcast codes called out on build sheets are driving this analysis but I'm curious what your database shows, of which you have referenced in previous threads on the discussion of FE7 threads.

Below, I've included two snippets from 1978 Pace Car build sheets. The first is VIN 2324, non-FE7 with L82 and P255s. The second is VIN 2212 with FE7, L82 and P255s.

VIN 2324_suspension.jpg

VIN 2212_FE7.jpg

[Joe L.]

Re: JL re Shock Absorbers in 1978

Joe:

While studying build sheets for 1978, I've come across a set of broadcast codes called out when a non-FE7 with L82 and P255/60 R15 tires were ordered. Build sheets call out CK (front) and CL (rear).

According to 1978 build sheets, all FE7 equipped Corvettes call out CK (front) and CE (rear) and we have those part numbers as listed in numerous past NCRS threads.

According to 1978 build sheets, all base suspension Corvettes with L48 and P225/70 R15 call out CH (front) and CJ (rear) shocks.

Also in 1978-79, 18 different coil spring configurations (and therefore broadcast codes) were called out that in addition to vehicle weight + option weight, a weighting was assigned for whether the vehicle was to be equipped with RPO QGR (P225/70R15) or RPO QBS (P255/60R15) P series tire.

The AIM for both years call out these Part#s:

• For 1978 FE7 front shocks, AIM specifies GM# 4984577
• For 1978 FE7 rear shocks, AIM specifies GM# 4984578
• For 1979 FE7 front shocks, AIM specifies GM# 4984577
• For 1979 FE7 rear shocks, AIM specifies GM# 22012402

In my judging over the years, I've been conflicted over FE7 shock numbers because the AIM and our threads have listed 4984578 as rear shocks. But I know from top flight and Bowtie judging that 22012402s were installed on 1978 FE7 equipped vehicles.

I'm drawing the conclusion that the FE7 rear shock 4984578 is the CL broadcast code when P255/60R15 tires were ordered with L82. These same vehicles were equipped with GM# 4984577 front shocks (CK). As a result, 1978 Corvettes were equipped with two different heavy-duty shocks and by 1979, only one was used when FE7 was ordered.

When FE7 was ordered with either engine configuration, it called out the CE broadcast code and 22012402 was installed.

In this analysis, broadcast codes called out on build sheets are driving this analysis but I'm curious what your database shows, of which you have referenced in previous threads on the discussion of FE7 threads.

Below, I've included two snippets from 1978 Pace Car build sheets. The first is VIN 2324, non-FE7 with L82 and P255s. The second is VIN 2212 with FE7, L82 and P255s.

[ATTACH]30789[/ATTACH]

[ATTACH]30790[/ATTACH]

Tom------


I do not recall what I've come up with previously, but I can't be of too much help here on this issue. A big problem with shock absorbers is that the PRODUCTION part numbers are almost always different than SERVICE part numbers and, in most cases, I have no way to co-relate the two. Often times, the stamped shock part numbers found in a SERVICE parts box will be the same as PRODUCTION, but, unless one happens to know what part numbers are stamped on a SERVICE shock of a particular part number and thereby co-relate the SERVICE part number to a stamped part number, the SERVICE part numbers cannot be co-related to PRODUCTION part numbers.

I can tell you that in SERVICE GM never specified different shock part numbers for 1978-82 Corvettes equipped with 225-70-15 tires versus 255-60-15. They did, however, specify different part numbers for cars equipped with manual transmission versus automatic transmission. Of course, there were also different part numbers for FE-7 versus standard suspension.

[Tom R.]

Re: JL re Shock Absorbers in 1978

I can tell you that in SERVICE GM never specified different shock part numbers for 1978-82 Corvettes equipped with 225-70-15 tires versus 255-60-15.

Ok, I can re-examine the build sheets and see if correlates to some other option. But I think you can tell, some factor is calling out various shock combinations.

They did, however, specify different part numbers for cars equipped with manual transmission versus automatic transmission.

What numbers were specfied for manual versus automatic? Also, look forward to 1979 and describe any similarities or differences. And thanks much!

[Joe L.]

Re: JL re Shock Absorbers in 1978

Ok, I can re-examine the build sheets and see if correlates to some other option. But I think you can tell, some factor is calling out various shock combinations.



What numbers were specfied for manual versus automatic? Also, look forward to 1979 and describe any similarities or differences. And thanks much!

Tom------


It's very possible that in PRODUCTION different shocks were used for the different tire sizes. However, if so, different shocks were not offered in SERVICE for specific tire size applications.

As far as SERVICE shocks, they were as follows (as of 9/79):

front:

78-80 with auto trans (except FE7, L-82)---GM #4975486

78-80 with FE7-------GM #3196957

no listing for manual transmission or L-82

rear:

78-79 with manual trans ----------------GM #4940459

78-79 with auto trans (except FE7, L82--GM #4975487

78-79 with FE7----------------------------GM #4993538

[Tom R.]

Re: JL re Shock Absorbers in 1978

It's very possible that in PRODUCTION different shocks were used for the different tire sizes.

I would have to say based on production broadcast codes, this is indeed the case as you state. The premise of my inquiry is based on PRODUCTION equipped shock absorbers so this aligns with my theory nicely.

After a review, shock selection as called out on 1978 build sheets has no correlation to transmission selection. I have M38 automatics with L82, L48s either. Non-FE7s with P225s called out base equipment (CH).

However, if so, different shocks were not offered in SERVICE for specific tire size applications.

This makes perfect sense as we have seen over the years.

I also see that RPO F51 (heavy duty shock absorbers) PRODUCTION from 1979-1982 specified GM# 4984577 (front) and 22012402 (rear). The 4984577 heavy-duty shock had a long run from 1974 through 1980 as a member of the FE7 suspection option and migrating to the F51 option.

I'm concluding here that FE7 in 1979 used the same shocks as F51. FE7 got heavier duty springs both front and rear.

[Joe L.]

Re: JL re Shock Absorbers in 1978

I would have to say based on production broadcast codes, this is indeed the case as you state. The premise of my inquiry is based on PRODUCTION equipped shock absorbers so this aligns with my theory nicely.

After a review, shock selection as called out on 1978 build sheets has no correlation to transmission selection. I have M38 automatics with L82, L48s either. Non-FE7s with P225s called out base equipment (CH).



This makes perfect sense as we have seen over the years.

I also see that RPO F51 (heavy duty shock absorbers) PRODUCTION from 1979-1982 specified GM# 4984577 (front) and 22012402 (rear). The 4984577 heavy-duty shock had a long run from 1974 through 1980 as a member of the FE7 suspection option and migrating to the F51 option.

I'm concluding here that FE7 in 1979 used the same shocks as F51. FE7 got heavier duty springs both front and rear.

Tom-----


I feel very confident that F51 and FE7 used the same shock absorbers.

[Tom R.]

Re: JL re Shock Absorbers in 1978

Reading a footnote in the 1978 Corvette MVMA Specifications Form (Motor Vehicle Manufactuers Association) for Suspension and for shock absorber it states:

Spring rates and shock absorber equipment may vary when engine, transmission or gymkhana suspension options are used.

The MVMA also states that spring were computer selected by size and rate according to vehicle weight including optional equipment. The MVMA is the packet of information owners get when they make the request through the GM Heritage Center. The particular issue date of this document is 10-77 and revised 2-78.

Interesting looking at the additional weights from RPOs, A/C when equipped with L82 was a +67 while L48 was a +63 pounds. However, L82 engine added an additional +20 pounds. Must have been the duct work and mandated emission control equipment.

[Terry M.]

Re: JL re Shock Absorbers in 1978

Tom,
Even the early C3s hade a note in the MVMA spec sheets that the springs were "computer selected." I have always wondered what that meant.

FWIW: My 1995 Caprices have the same note on the VIS (Vehicle Information System) papers. By 1995 it might have had more meaning that it did for my 1970 -- but I really doubt it.

[John H.]

Re: JL re Shock Absorbers in 1978

Even the early C3s hade a note in the MVMA spec sheets that the springs were "computer selected." I have always wondered what that meant.

Terry -

The federal MVSS regulations beginning in 1968 mandated control of bumper height requirements within a specified "window" of maximum-to-minimum height of the portion of the bumper which would be impacted by the test device used to certify the 5-mph bumper system.

That's when the number of springs "exploded" to accommodate all the different combinations of tire sizes and options that affected front and rear trim heights, causing springs to be "computer-selected" based on keeping the impacted face of the bumper within the MVSS "window" for that particular vehicle.

We changed a lot of "B"-body Impala/Caprice springs in Heavy Repair using height gages to buy off the bumper heights for the first month of production until Engineering got the tire size and option weight/spring height and load rate numbers corrected in the computer.

Corvette wasn't affected as much as the full-size cars, as there was a far smaller number of variables to deal with than on the full-size cars, but the front springs WERE "computer-selected" to keep the front bumper height within the MVSS "window".

[Terry M.]

Re: JL re Shock Absorbers in 1978

Thank you John for supplying my daily dose of learning for today.

[Tom R.]

Re: JL re Shock Absorbers in 1978

And I'm delighted you early C3/C2 guys are contributing to this late model discussion thread! John's kernels of knowledge are truly insightful and appreciated. Seems like everything streams back to a federal regulation and so it goes with shock selection!

[Joe L.]

Re: JL re Shock Absorbers in 1978

Terry -

The federal MVSS regulations beginning in 1968 mandated control of bumper height requirements within a specified "window" of maximum-to-minimum height of the portion of the bumper which would be impacted by the test device used to certify the 5-mph bumper system.

That's when the number of springs "exploded" to accommodate all the different combinations of tire sizes and options that affected front and rear trim heights, causing springs to be "computer-selected" based on keeping the impacted face of the bumper within the MVSS "window" for that particular vehicle.

We changed a lot of "B"-body Impala/Caprice springs in Heavy Repair using height gages to buy off the bumper heights for the first month of production until Engineering got the tire size and option weight/spring height and load rate numbers corrected in the computer.

Corvette wasn't affected as much as the full-size cars, as there was a far smaller number of variables to deal with than on the full-size cars, but the front springs WERE "computer-selected" to keep the front bumper height within the MVSS "window".

John------


Yes, adherence to tight bumper height requirements definitely was the reason for the larger number of springs. As far as springs go, Corvettes were not heavily affected by the "plethora of springs phenomenon" and from 1972 through the 1982 model year there was never more than about 10 front springs used for any particular model year and usually less. There were much fewer rear springs used in any particular model year.

Beginning in 1975 GM used a very creative means to adjust the rear ride height without using a multitude of spring part numbers. What they did was to have 5 slightly different length outer spring bolts available for the assembly line to use selectively to adjust rear ride height. Most of these bolts were never available in SERVICE, though.