78 blazer rearend not the same..

[Firebirdjones]

I assume at least somebody here already knew that. Boy I sure didn't.

I scored a nice front and rear diff out of a 78 blazer with positraction and 3.73 gears, all new drums, rotors, pads and shoes, wheels cylinders, calipers, all new ball joints and tie rods, center link, brake hoses, wheel bearings,,,,you get the idea. They are brand new inside and out.

I get ready to install the rearend first and found out the shock mounts are staggered. No big deal, I'll just flip one and reweld it....

Not that easy. Not only does my 72 have the rear shocks mounted in front of the housing, but they are further inboard too. So I had to cut and move both shock mounts. It gets better....

I did some more measuring and found out the spring perches are moved outward about 1 1/2" on the 78 rearend. Overall the rearends are the same width but evidently GM decided they wanted more stability and moved the springs outboard slightly.

Sooo, after more cutting and rewelding I have the spring perches where they need to be. I spent all day on that so I didn't get a chance to drop the rearend in the truck. Maybe tomorrow.

Oddly enough, I measured everything on the front diff and it all appears to be identical to the original, springs are in the same places, same shock mounts etc....but I'll probably install the front diff at a later date when I have more time for a front end alignment.

Just thought I'd share.

[red71cheyenne]

Good to know info. Glad you found it out before I did!

[Firebirdjones]

Sure thing. I am surprised there isn't someone here who has tried this swap already.
You also get an upgrade on rear brakes (or at least my setup did) with 11x2 3/4" shoes vs the stock 11x2" shoes on my 72 blazer. So the drums are naturally bigger as well.

I took some shots I'll have to post later. I'll need to retune the trans tables for the gear swap, that will take some driving time.

[Firebirdjones]

Here you go, finished it up this morning.

I spent alot of time working my trans shift tables and rpm settings to suit my driving habits. Knowing the gear change to 3.73's was going to change the VSS output readings and skew my shift points, I was a little disturbed about that.

Turned out all I had to do was go into the speedo calibration and input the new gear, hit calibrate, and it automatically adjusted all my shift tables. That was the easiest part of the whole swap
It still shifts at all the same rpms and throttle angles I had set, it's just a lower mph to compensate for the gear change.

Had to move the shock mounts inboard and face both of them forward.



Then found out I had to move both spring perches inboard too,,,ugh



But it all worked out and fit like a glove Now this 6.0 runs with a little more pep in it's step....maybe too much, I see parts breakage a problem now

[red71cheyenne]

Excellent info and pics! What 6.0 combo are you running? 4L60 or?

[Firebirdjones]

Originally Posted by red71cheyenne

Excellent info and pics! What 6.0 combo are you running? 4L60 or?

It's a 2004 6.0 with an LS6 cam and a custom SD tune, and a built 4L60E behind it.

[mcmlxix]

Nice.. I just picked up a 6.0L for mine... how did you run the belt for the AC? Did you swap out the tensioner?

[Firebirdjones]

I used an AC relocation kit from Kwik Performance to move the compressor up top. It won't fit on the bottom with the factory bracketry, hits the frame.
The relocation kit gives you a new belt number that runs the entire system with one belt, since the AC no longer runs on a seperate belt.

[mcmlxix]

I almost recognized the kwik kit. I searched your other threads but most of the pics are gone... I want to add a York style compressor for on board air (fill tires / run air tools) and I can make it fit in the same spot... I was looking for pictures and ideas on how to run the belt and where to place a tensioner and idler pully...

[Firebirdjones]

Originally Posted by mcmlxix

I almost recognized the kwik kit. I searched your other threads but most of the pics are gone... I want to add a York style compressor for on board air (fill tires / run air tools) and I can make it fit in the same spot... I was looking for pictures and ideas on how to run the belt and where to place a tensioner and idler pully...

Yeah I have an issue with photobucket deleting pics after a while, wrong setting or something, I don't know. I would assume these pics here will also disappear after a couple of days.

Unfortunately I can't directly link pictures to the site, as most sites are that way.

I haven't seen a york style compressor so I'm not sure what you are dealing with. But if it takes a 6 rib surpentine belt it might be do-able. That bracket kit from Kwik is made specifically for Sanden compressors, and even a specific model number at that. So I'm not sure what you might have to do to make that work.

[LS6 XAA]

many people have dealt with this problem ! a perch relocation and shock mount relocation is all that's necessary... move perch's inward just about half the width of the perch it's self the shock mount on drivers side needs to be welded on axle tube on the same side as passenger side shock mount ur post is of great value and the pics tell the story... I just hung a new axle with 3:73's under my 70 k5 last week.

U said ur perch's were moved out ward? hmm on my axle they were moved inward and I had to swap out e brake cables, the donors were to short, it was a not as easy I thought at first but turned out to be quite simple... as for the brake cables r concerned, let common sense do the work along with needle nose vice grips

I can post a pic with a tape measure pulled across rear end housing for exact perch relocation for u timid fellows,if it will be of any help since the old housing was modified

[LS6 XAA]

Oddly enough, I measured everything on the front diff and it all appears to be identical to the original, springs are in the same places, same shock mounts etc....but I'll probably install the front diff at a later date when I have more time for a front end alignment.

I read just what u explained about the front axle for dana 44. corp 10 bolt may be same to ? any one... thanks for this great info and pics maybe some one can post a pic or video diy step by step on the rear end mod's
Firebirdjones : can u explain how u setup the relocation angle for the perchs, I never did the mod my self as far as the cutting off and moving, the po did it on the axle I removed and the donor axle had had this mod done to it all ready. my donor had a 4" susp lift & one perch broke of when I pulled it so I re welded it back on to match the other perch using a bubble level. I read to use a angle finder but decided to do it my way lol

[Firebirdjones]

I probably didn't explain that very clearly, as I had to read it again myself a couple of times

On the rearend, the spring perches on the 78 rearend are moved outward (toward the backing plates), about 1 1/2 inches,,,or about half of the spring perch width as you mentioned. So I moved them inward

I'm sure GM did this for more rear stability, just not sure when that change was made. I would assume with the square body change in 73....

I used an angle finder to reweld the perches at the same angle I removed them from. I compared that to the original 72 rearend in my blazer and they are setup at the same angle, so all driveline angles are unchanged.

Really very simple to do, just a little extra work that I wasn't expecting.

The front dana 44 diff from the 78 measures exactly the same as the dana 44 currently in my 72 blazer. So apparently GM didn't make any changes up there. That will be a simple swap with basic hand tools, but it will require a front end alignment when I'm done. So for right now I haven't tackled that until a make an appointment for the alignment rack.

[Blazed72]

What do you have to get an alignment for? Are they just checking the toe in/toe out?

[Firebirdjones]

Yeah basically. This other front diff I have sitting here is brand new with ball joints, tie rods, u-joints, rotors, calipers etc....

Basically a complete new front suspension ( but with my old springs). So just to be sure everything is set where it should be, I'll bolt it all in and take it to the alignment rack first thing. Make sure I don't ruin a $500 set of tires.

[Blazed72]

Gotcha, Didnt know if you were checking caster. Have you ever set the toe at home? Its pretty easy and you dont have to pay someone.

[hgs_notes]

The 12 bolt is plenty strong for the 6.0. The new trucks with the 6.0 are not running dana 60's or 14 bolts, most are comparable to a corp 10 bolt. The swap to heavier axles is mainly done by guys that have 37" or larger tires. The 12 bolt compares pretty well with a ford 9" except for it using c clips to hold the axles in, and there are kits available to eliminate those.

The rear section of frames on the 73 and up trucks are wider, but the front is the same, which is why so many people will use the newer 2wd front crossmember for swapping to disc brakes. They are easier to find than 71-72.

Nice truck and nice shop. Wish I had that kind of space and a lift.