Blazer, Rearend swapping guru's step in...

[Firebirdjones]

I've searched and searched and I know this has been discussed before. I can't find a sticky on it and really feel the need for one.

I'd like to start my own personal spread sheet of sorts to lay this all out.

Rearends like the 14 bolts and dana's are popular swaps among the offroad community but there are housing width differences, spring perch width differences, and then there are rearends that are supposed to be a drop in bolt up application.

Who has done these swaps? Who knows what falls in and what requires fab work? What did you use? What years to look for?

Differences in brake sizes?

Is a semi float 6 lug an easier swap than an 8 lug full floater? Where are they found (vehicles) and what years?

I know there are some smart guys in here that have been through some of this. Any information is appreciated.

[drunkbus]

There are some 14 bolts with the correct spring perch width but will still need new shock mounts. I had a 14 bolt out of a late 70's 1 ton crewcab and the spring perch width was correct for my Blazer.

[Firebirdjones]

Originally Posted by drunkbus

There are some 14 bolts with the correct spring perch width but will still need new shock mounts. I had a 14 bolt out of a late 70's 1 ton crewcab and the spring perch width was correct for my Blazer.

I've heard that, so I crawled under my 79 1 ton and sure enough, the spring perches are the same width as my 72 blazer. Draw backs are the enormous brake drums that won't accept a 15" wheel not to mention 8 lugs, and a 1350 series U-joint, all things to think about for the swap.

I wonder if a semi float 14 bolt with it's 6 lug axles would solve some of those issues? Smaller brakes? I'd love to hear about it.

[Yukon Jack]

I put a ff 14 bolt in my 70 K5 - it came from a 78 3/4 ton 4x4. Here is a link to a thread and page 2 discusses my swap.

[Firebirdjones]

Originally Posted by Yukon Jack

I put a ff 14 bolt in my 70 K5 - it came from a 78 3/4 ton 4x4. Here is a link to a thread and page 2 discusses my swap.

Now these issues are some of the things I'm talking about.

You had to relocate the spring perches on this application, but I'm told (and I verified) that there are 14 bolts with correct spring perch location.
My 79 1 ton 14 bolt FF spring perches measure exactly the same dimensions as the 12 bolt in my 72 blazer. So technically it's a simple bolt in (just have to relocate the shock mounts).

Now since that's the case, why are so many people buying 14 bolt FF's and having to relocate spring perches? There has to be a year break or model difference where GM changed the locations for what ever reason. Maybe the style you had is more plentifull and people would rather relocate spring perches than try to hunt for the version I have in my 79 1 ton?? That's what I'm trying to figure out.

The U-joint issue is an easy one as adapter joints are out there (all 14 bolts I've seen use a 1350) Darn adapter joints in my area are $50 a piece though (just bought one for a different project) In the end I'd rather have a driveshaft made that uses 1350 joints and enjoy the added strength (local shop builds them for $300).

The other issue I see in your thread are those enormous brake drums (my 79 1 ton has them). I assume using a different wheel wasn't a big deal for you so easy problem solved.
I'd like to know if a semi float 14 bolt would have a smaller brake drum package? I'm thinking yes since it's a 6 bolt axle flange and more of a 3/4 ton application. If so,,,,then this already sounds more like a better fit for my 72 blazer but housing width has to be the same.

Don't know if such a 14bolt exists.....

[jonesky2]

Originally Posted by Firebirdjones

Now these issues are some of the things I'm talking about.

You had to relocate the spring perches on this application, but I'm told (and I verified) that there are 14 bolts with correct spring perch location.
My 79 1 ton 14 bolt FF spring perches measure exactly the same dimensions as the 12 bolt in my 72 blazer. So technically it's a simple bolt in (just have to relocate the shock mounts).

Now since that's the case, why are so many people buying 14 bolt FF's and having to relocate spring perches? There has to be a year break or model difference where GM changed the locations for what ever reason. Maybe the style you had is more plentifull and people would rather relocate spring perches than try to hunt for the version I have in my 79 1 ton?? That's what I'm trying to figure out.

The U-joint issue is an easy one as adapter joints are out there (all 14 bolts I've seen use a 1350) Darn adapter joints in my area are $50 a piece though (just bought one for a different project) In the end I'd rather have a driveshaft made that uses 1350 joints and enjoy the added strength (local shop builds them for $300).

The other issue I see in your thread are those enormous brake drums (my 79 1 ton has them). I assume using a different wheel wasn't a big deal for you so easy problem solved.
I'd like to know if a semi float 14 bolt would have a smaller brake drum package? I'm thinking yes since it's a 6 bolt axle flange and more of a 3/4 ton application. If so,,,,then this already sounds more like a better fit for my 72 blazer but housing width has to be the same.

Don't know if such a 14bolt exists.....

From what I have gathered the 1 tons have the correct spacing on spring perches. But everything else (3/4 ton) you have to move them. 14bff from a 1ton thats not a dually or C&C are harder to come by.

Just do the disk brake swap.. pretty straight forward and a big improvement also gets rid of those huge drums

[Firebirdjones]

Good info, now if someone could just supply years and break downs with specifics it would help greatly.

Disc brake swap wouldn't be an option for me. It opens up to many other issues. Brake lines, different proportioning valves, E-brake, and I'm sure more that I'm forgetting. Just don't want to go there.

[Mike C]

67-72 4x4 trucks have 40.5" spring centers. The 2x4 have 42.5" spring centers. 73-87 trucks, 2 and 4 wheel drive have 42.5" spring centers. Except the one ton trucks. Ton trucks have 40.5" spring centers. But you have to work on the shock mounts.

42.5" spring center axles are much more common than the 40.5". Which means cheaper. And most people who are converting to heavy duty 14 bolt are capable or willing to have the spring and shock mounts relocated.

I put a semi-float 8 lug 14 bolt in my Jimmy by relocating the spring perches and using the original shock mounts off the 12 bolt after building a jig to line everything up. Not a big deal. And IMO, the giant brakes and huge u-joints are a plus, not a drawback.

But if you don't want to convert the front or buy new wheels, etc. The semi-float 6 lug 14 is the way to go. But you have to do spring seats and shock mounts. Another option is a semi-float Dana 60 that was available on '67 and maybe some '68 trucks. But it is uncommon.

[Mike C]

And a lot of one ton trucks had Dana 70 rear axles and not 14 bolts which is the case of my 86 4x4 dually.

[Firebirdjones]

Originally Posted by Mike C

67-72 4x4 trucks have 40.5" spring centers. The 2x4 have 42.5" spring centers. 73-87 trucks, 2 and 4 wheel drive have 42.5" spring centers. Except the one ton trucks. Ton trucks have 40.5" spring centers. But you have to work on the shock mounts.

42.5" spring center axles are much more common than the 40.5". Which means cheaper. And most people who are converting to heavy duty 14 bolt are capable or willing to have the spring and shock mounts relocated.

I put a semi-float 8 lug 14 bolt in my Jimmy by relocating the spring perches and using the original shock mounts off the 12 bolt after building a jig to line everything up. Not a big deal. And IMO, the giant brakes and huge u-joints are a plus, not a drawback.

But if you don't want to convert the front or buy new wheels, etc. The semi-float 6 lug 14 is the way to go. But you have to do spring seats and shock mounts. Another option is a semi-float Dana 60 that was available on '67 and maybe some '68 trucks. But it is uncommon.

That nails down the spring perches Thanks. Relocating the spring perches and shock mounts isn't a big deal for me, I just did the 12 bolt in my 72 blazer because I used a rear out of a 78.

I assume even though these spring perches on the 14 bolts slightly differ (73-87 2x4 and 4x4 at 42.5"/ and 1 ton trucks having the 40.5" spring perches) All the 14 bolts still have the same axle flange to axle flange width (both full float and semi float)???

[Ridnhi]

Totally off the topic but I will be heading o Prescott tomorrow and will be staying until friday. PM sent

[Ridnhi]

I'm in down town Prescott right now walking through shops and saw a white over white 70-72 blazer looked sweet! Wouldn't mind meeting up.
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[Mike C]

Axle widths can and do vary depending on the donor. Especially the '88 and up trucks which is where a 6 lug semi-float would be found.

[coyote72]

I swapped a 14 bolt into mine I'm not sure this is the right way to get the link but I had a build post from a ways back

http://67-72chevytrucks.com/vboard/s...d.php?t=429715


That's how I did mine

[WarBeard]

Everything you will ever need to know about our friend the 14 bolt.

http://www.pirate4x4.com/tech/billavista/14b_bible/

[tismy55]

will a 78 4x4blazer rearend & leaf springs fit my 72 blazer 4x4 ? thanks

[Mike C]

Leaf springs fit, perch spacing is wrong as noted above at 42.5" instead of 40.5". Perches and shock mounts need to be redone.