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My ’71 coupe is numbers matching except for the rear differential. It has 9/20/1977 stamping on the case, which I think it means that it would have originally been on a 1978 car.
I currently have the trailing arms off of the car and sent them to Bairs for rebuild. Now that everything is apart I can see that the spring looks really tired and the leaves appear to be fanning out/misaligned. The spring that is on the car now is 2-1/4” wide. I’m wondering if this is the wrong width spring for a 1978 rear diff and therefore allowing leaves to fan out. Can someone that is familiar with 1978 springs help me determine which width spring I need to buy? I want to make sure that a 2-1/2" wide spring will fit on this somewhat early 1978 rear diff.
I think you are correct in your assumption: When I bought my ‘75, the original rear end housing was toast because the stub axles had worn into the case. I found a complete 1979 rear end on craigslist and swapped in the differential and spring. The ‘75 used a 2.25” wide spring where the ‘79 uses a 2.5” wide spring. Not sure what year they changed, but an extra .25” of width would certainly allow the leaves to move around.
Hi Rick,
The leafs are splayed because it's the 4 bolts that keep them aligned when the spring is installed.
The spacing between the 4 bolts (2 forward of the spring and 2 to the rear of the spring) that mount the spring to the differential cover is wider on 77+ covers.
There are spacers available that allow you to use the 2 1/4" spring on the later cover if you wish. (Paragon 13023K)
If you decide to replace your spring you may want to keep it or sell it because often people are looking for original rear springs so they can restore the proper ride height to the rear of their car.
Regards,
Alan
Hi Rick,
The leafs are splayed because it's the 4 bolts that keep them aligned when the spring is installed.
The spacing between the 4 bolts (2 forward of the spring and 2 to the rear of the spring) that mount the spring to the differential cover is wider on 77+ covers.
There are spacers available that allow you to use the 2 1/4" spring on the later cover if you wish. (Paragon 13023K)
If you decide to replace your spring you may want to keep it or sell it because often people are looking for original rear springs so they can restore the proper ride height to the rear of their car.
Regards,
Alan
I wasn't aware that I could buy a spacer. Perhaps I should consider buying that spacer and keeping the original spring because of your other point about ride height. If I were to go with a new 2-1/2" spring, will I find that the rear is too high? I don't think I'd like the look if the rear was too high. Some like the "rake", but I'm not one of them👍
Hi A,
What the rear ride height will be with a new spring depends on the specifications for the spring you buy.
I'm not a fan of simply using longer spring to trailing arm bolts… that cures the symptom but not the cause of the problem.
Regards,
Alan
In 78 the standard spring is a nine leaf spring which measures 2-1/2 inches. The optional spring (FE7) has six leaves and is 2-1/4 inch wide. The use of the narrower FE7 spring required the placement of spacers .
I wasn't aware that I could buy a spacer. Perhaps I should consider buying that spacer and keeping the original spring because of your other point about ride height. If I were to go with a new 2-1/2" spring, will I find that the rear is too high? I don't think I'd like the look if the rear was too high. Some like the "rake", but I'm not one of them👍
You can probably make a couple of spacers (one in front of the spring and one to the rear) from some 1/8" aluminum plate. I would make them long enough to extend an inch or more past the bolts and just tall enough to contact the differential and the spring retaining plate.
Not tall enough and they may slip out, just tall enough will allow them to be wedged in and not likely move.
Thanks to all that responded. After digesting all of this, I thinking that it may be best just to buy or make a spacer and reuse the spring that is in the car now so I don't end up with an undesirable ride height.
Hi Rick,
You might look into buying the proper spacer set that's available.
They're the correct thickness and are shaped so that they can't move out of position….. they have a slight 'curve' at each end so the 4 spring mounting bolts hold them in position.
Regards,
Alan
When I swapped in the 2.5” spring, the ride height did in fact change. In order to get the proper height, the two smallest leaves had to be removed. I now have a 7 leaf rear spring, but the ride height, handling and ride do not seem compromised in any fashion. Per Alan’s note, the spacer seems to be a better option (to me)...
Correct rear leaf spring width
