Rear Leaf Spring Question

[tismy55]

So if you use just the springs would it line up with the 72 axle

[Chulisohombre]

If using the stock axle and and spring in the stock hanger and shackle it should line up directly above the perch. It may have a ill movement to line up perfect but shouldn't have to angle the spring to sit on the perch like if you had a later year axle. If its that far off you have wrong axle and will have to move the perches to get it under the springs correctly. After 40 years anything could have been changed in the drivetrain.

[tismy55]

Thats so true I will measure the perches tomorrow and the springs while they are mounted in the hangers to get an overall measurement to see if a different rearend will work.

[Jdubs71]

Your spring perches should be 40.5" from center pin to center pin. If your spring perches are different then you may have a later model axle 73 and up.

[tismy55]

Do you know what the 73 up width are, It seems like my rear end axle is not wide enough,It is not reaching the springs on both sides

[Jdubs71]

If your axle has 42.5" on centers then you likely have a 73 and up rear end. Are you sure you have 69-72 blazer frame?

[tismy55]

I think you are right I don't think I have a 72 frame,I know the rearend and front axle are from a 72 .Now that I think about it The front leaf springs were 44" but I had to use 47" because the 44's were to short. I measured the rear end it is 40.5

[Jdubs71]

Post some pics of your frame and we'll be able to tell you for sure

[tismy55]

would a 78 rearend be the same width as a 73 ,I will take some pics and upload

[Jdubs71]

If they're are both 12 bolt rear ends then the spring perch width will be the same and the axles will be interchangeable.

[Chulisohombre]

73-91 I believe they are the same width spring perch wise. So a ten bolt rear should fit as well. If you had to use the later model springs it does sound like someone switched to a later frame. Glad he got the widths for you.

[tismy55]

when one uses blocks to raise the frame do you change springs as well or do you use original spring and just add a leaf. I bolted the spring into the hangers and measured ,center to center 41-1/4" I see imprints of a block that was used on the bottom of the spring.

[Chulisohombre]

Block just sits under original spring in between that and the perch and is sanwiched together with longer u bolts.

[tismy55]

All I have to do now is move each axle perch over 3/8" from where they are now and should work fine.

[Jdubs71]

I recommend buying lift springs and doing away with the blocks. Its safer and if you buy good springs its usually a better ride. They can be costly though.

[tismy55]

I found some raised springs but first I have to move both perches on the axle 3/8" so they will line up with the springs I have.

[Jdubs71]

It sounds to me like your trying to line up the perches with the springs? I could be getting it wrong, but if that is the case you don't want to do it that way. You want your rear axle to be perfectly centered under the frame. Weld your spring perches on the axle where they go, evenly spaced, and then bolt your springs to the perches.

[tismy55]

I installed the springs in the hangers & bolted them down ,then I measured center to center it was 41-1/4" ,then I measured the axle perches they were 40-1/2" leaving 3/4" that in turn moves each perch outward 3/8" .the rear end should still be centered shouldn't it. If not how would you do it. Thanks for your help by the way.

[Chulisohombre]

You need to move the perches to fit yes. Have you verified what frame is under the truck yet? From the way you described it it seems to have a later frame from the width. The springs can move slightly in the hangers but not
That much and still be Strait. If you're carefully you can reuse the stock ones but it may be better to get New Ones welded on.

[Chulisohombre]

How was this put together before you switched springs? The bushings will move some to bolt it up. I hate not being in front of something trying To give advice. So hard without swing it
In person how far it's off.

[tismy55]

I purchased it as being a 72 blazer frame, however when I went to bolt the front up the leaf springs were to short, so I had some 73 front springs that fit. I was told 72 & 73 Rear springs were the same. I bolted up the rear springs to the hangers and raised the rearend to bolt it up got one side on the perch but the other side was 3/4" off .I tried moving the spring over but it wouldn't move that far. I guess it is a 73 or newer frame. but according to the stats the rearend of a 73 perches are 42-1/2" and mine measure 40-1/2 , I measured across my rear springs they are 41-1/4 center to center. I don't know if a wider rearend will work or not. So I figured I would move the perches on the 72 rearend out 3/8" on each side .That way it would bolt up to the springs and should stay in the center. Is there another way to center the 72 rearend that you can think of

[Chulisohombre]

Sounds like that will work. You want to measure center of the center pin on both springs to make sure the center holes on the perches line up perfect. Another problem you may have is the body mount locations to drop your blazer onto the frame. I'm guessing those will need work too.

[tismy55]

the body mounts I guess have been done ,the body was bolted to this frame when I purchased it. Thats why I thought the frame was a 72. when I purchased it It had no front or rear axles. I found a guy parting out a 72 and purchased the axles front and rear from him. So I know the body and the axles are from a 72.??? the frame not a clue I may get a 78 blazer rearend ,I found one at a local wrecking yard and try that. I'm not sure of the gear ratio if they will be compatible front to rear.Also with a wider rear may stick out farther than the front axle.

[Chulisohombre]

At least that part is good. The 78 axle if under a blazer or pickup and is halfton should be the same width. It will just have the perches in the correct location for the later frame. Then the shocks should bolt in correctly as well. I believe width is 68 inches wheel mounting surface to the other side wms.

[tismy55]

I will let you all know if that works. Stay tuned