Chassis Swap vs. Upgrade for 80-82
Thread Starter
Race Director
Joined: Mar 2017
Posts: 11,989
Likes: 4,537
From: Virginia
Chassis Swap vs. Upgrade for 80-82
TL/DR: I am about to have a spare 79 chassis, and two spare 79 3.55 iron diffs (hopefully at least one of them is in good enough shape to reuse or rebuild). Is there any reason not to use this chassis under my 80?
Long version: The 80 chassis is made from slightly thinner steel to save weight. That also means it is less stiff. I'd like to run an iron diff in my 80, which means shortening the driveshaft. I'd also like to raise the diff, per what @wheresmyhorsepower is doing in this thread:
https://www.corvetteforum.com/forums...ised-diff.html
It seems like a lot of work to mod my 80 chassis to save a bit of weight. Is there any reason not to just build up the 79 chassis, add the gussets per the Chevy Power Book, and be ready for a high-mount diff and better aftermarket support for suspension mods? Am I missing anything?
Long version: The 80 chassis is made from slightly thinner steel to save weight. That also means it is less stiff. I'd like to run an iron diff in my 80, which means shortening the driveshaft. I'd also like to raise the diff, per what @wheresmyhorsepower is doing in this thread:
https://www.corvetteforum.com/forums...ised-diff.html
It seems like a lot of work to mod my 80 chassis to save a bit of weight. Is there any reason not to just build up the 79 chassis, add the gussets per the Chevy Power Book, and be ready for a high-mount diff and better aftermarket support for suspension mods? Am I missing anything?
Instructor
Joined: Apr 2006
Posts: 109
Likes: 23
From: Duvall WA
Bikespace - I’ve messed with the differences between these frames.
They are pretty much interchangeable, especially if You are able to do
some light welding. The welded transmission cross member brackets
with the “ears” to put the long bolt through that holds the crossmember
on both LH & RH sides are located different 1979-older vs. 1980-82.
The center tab under the differential is slightly different if I remember?
Note: If You are going to use an aftermarket transmission cross member
the 1979-and older are different than 1980-82 just buy the matching year.
I am guessing that You plan to use the “aluminum batwing” differential
cross member and bolt in the stronger 1979/older cast iron differential??
I think You are on the right path to get the proper 1/2-shaft geometry with
a LOWERED-CAR. Shorting (raising) the frame mount “tabs-ears” for the batwing
1/2 to 3/4” should keep the drive-shaft half-shafts at the originally designed
angle, thus less wear on the differential yokes and less alignment “toe-change”
with a lowered car when the suspension is compressed & rebounds, that
causes some unwanted “rear-steer” twitchy-feel.
Recapping - You are correct that the 1980-82 frame is lighter gauge steel.
I believe that the 1979 frame would be a better frame to modify.
They are pretty much interchangeable, especially if You are able to do
some light welding. The welded transmission cross member brackets
with the “ears” to put the long bolt through that holds the crossmember
on both LH & RH sides are located different 1979-older vs. 1980-82.
The center tab under the differential is slightly different if I remember?
Note: If You are going to use an aftermarket transmission cross member
the 1979-and older are different than 1980-82 just buy the matching year.
I am guessing that You plan to use the “aluminum batwing” differential
cross member and bolt in the stronger 1979/older cast iron differential??
I think You are on the right path to get the proper 1/2-shaft geometry with
a LOWERED-CAR. Shorting (raising) the frame mount “tabs-ears” for the batwing
1/2 to 3/4” should keep the drive-shaft half-shafts at the originally designed
angle, thus less wear on the differential yokes and less alignment “toe-change”
with a lowered car when the suspension is compressed & rebounds, that
causes some unwanted “rear-steer” twitchy-feel.
Recapping - You are correct that the 1980-82 frame is lighter gauge steel.
I believe that the 1979 frame would be a better frame to modify.
Instructor
Joined: Apr 2006
Posts: 109
Likes: 23
From: Duvall WA
One last thought - The 1980-82 cars drivers-side floor pan was slightly deeper (lower) to accommodate
the driver LH electric seat option, thus maybe check clearance in this area when “cross-breading”
the body & frame.
the driver LH electric seat option, thus maybe check clearance in this area when “cross-breading”
the body & frame.
Thread Starter
Race Director
Joined: Mar 2017
Posts: 11,989
Likes: 4,537
From: Virginia
Bikespace - I’ve messed with the differences between these frames.
They are pretty much interchangeable, especially if You are able to do
some light welding. The welded transmission cross member brackets
with the “ears” to put the long bolt through that holds the crossmember
on both LH & RH sides are located different 1979-older vs. 1980-82.
The center tab under the differential is slightly different if I remember?
Note: If You are going to use an aftermarket transmission cross member
the 1979-and older are different than 1980-82 just buy the matching year.
I am guessing that You plan to use the “aluminum batwing” differential
cross member and bolt in the stronger 1979/older cast iron differential??
I think You are on the right path to get the proper 1/2-shaft geometry with
a LOWERED-CAR. Shorting (raising) the frame mount “tabs-ears” for the batwing
1/2 to 3/4” should keep the drive-shaft half-shafts at the originally designed
angle, thus less wear on the differential yokes and less alignment “toe-change”
with a lowered car when the suspension is compressed & rebounds, that
causes some unwanted “rear-steer” twitchy-feel.
Recapping - You are correct that the 1980-82 frame is lighter gauge steel.
I believe that the 1979 frame would be a better frame to modify.
They are pretty much interchangeable, especially if You are able to do
some light welding. The welded transmission cross member brackets
with the “ears” to put the long bolt through that holds the crossmember
on both LH & RH sides are located different 1979-older vs. 1980-82.
The center tab under the differential is slightly different if I remember?
Note: If You are going to use an aftermarket transmission cross member
the 1979-and older are different than 1980-82 just buy the matching year.
I am guessing that You plan to use the “aluminum batwing” differential
cross member and bolt in the stronger 1979/older cast iron differential??
I think You are on the right path to get the proper 1/2-shaft geometry with
a LOWERED-CAR. Shorting (raising) the frame mount “tabs-ears” for the batwing
1/2 to 3/4” should keep the drive-shaft half-shafts at the originally designed
angle, thus less wear on the differential yokes and less alignment “toe-change”
with a lowered car when the suspension is compressed & rebounds, that
causes some unwanted “rear-steer” twitchy-feel.
Recapping - You are correct that the 1980-82 frame is lighter gauge steel.
I believe that the 1979 frame would be a better frame to modify.
Thanks for the tips!
I think the power seat option started in 81, and all 81 and 82 cars have the low floor under the driver seat. My 80 has the standard floor pan.
