Gear Change

[noco-k5]

Curious as to others opinions on what to do with my 70 Blazer. I just had a friend help install a front diff from an 84 Blazer onto my 70 so I now have front disc brakes. The stock 3.07 gears aren't cutting it and I would like some sort of limited slip or locker in the back. I want to keep the stock ralley wheels so would like something I can run six lug wheels on. It's my understanding the 14 bolt semi float rear ends out of some vehicles will swap and are 6 lug? Or can you make the 12 bolt that's on their pretty strong fairy cheaply? My truck sees 80 percent street duty so I don't need to go crazy but I would like at least 3.73's or maybe 4.10's just looking for the cheapest way to do it. Any advice?

[red71cheyenne]

I would gladly trade you rear ends out of my 69. It is either a 3.73 but I am thinking its closer to 4.11. I know that at hiway speed, I am running almost 3K rpm. Other than that, not sure what to tell you on rear ends. I know that most of the newer ones(95 and up) six lug is common. Only problem is the metric or whatever the lugs are.

[noco-k5]

Originally Posted by red71cheyenne

I would gladly trade you rear ends out of my 69. It is either a 3.73 but I am thinking its closer to 4.11. I know that at hiway speed, I am running almost 3K rpm. Other than that, not sure what to tell you on rear ends. I know that most of the newer ones(95 and up) six lug is common. Only problem is the metric or whatever the lugs are.

That's definitely the flip side of the coin, but the thing is a dog with a 290 horse crate 350 and 33's with the 3.08 gears.

[red71cheyenne]

What tranny are you running? Just curious if that could have something to do with its sluggishness. Initial drive ratio's could be part of the problem. I have an SM465 and T-221 in mine and of course I don't even use first gear. You can walk faster than it is. I will be swapping in a 3:08 gear set eventually.

[Firebirdjones]

Originally Posted by noco-k5

That's definitely the flip side of the coin, but the thing is a dog with a 290 horse crate 350 and 33's with the 3.08 gears.

I ran this exact combo for a while (mild 355/350 turbo and 3.07 gears with 33" tires).

It really wasn't all that horrible around town,,,it wasn't something that would set the stoplights on fire, but it still drove nicely. The best part was cruising at 70 mph at only 2400 rpms. and it got me 13 mpg city and 16 mpg highway.

I can understand wanting more squirt though. I did eventually switch mine to 3.73's after the overdrive install.

Your dilema really depends on what you have available to you. The 14 bolt semi float is a nice swap, comes in 6 lug, and is the same overall housing width. The problem though is even if you are lucky enough to find one with the same spring perch width, you'll still have to move the shock mounts so it does require a little fab and welding work. There is also the dilema of finding one with exactly the gear you are looking for and in a decent price range that makes the swap feasable. But they are out there, just have to start hitting the junk yards. I'm actually on the hunt for one myself

The factory 12 bolts aren't bad pieces, just a tiny pinion (1.438") is the real weak link. I opted to keep mine for the time being until I find a suitable 14 bolt semi floater,,,then I may swap, but it's not a necessity.

To do a gear swap in the 12 bolt you are looking at about $200 for the gears, another $100-$150 for a setup kit with bearings, and depending on which style of posi unit you want will change the price a bit. I wanted an Eaton clutch style posi (about $450) so that's what I went with. In the end about $7-800 for all new parts and that doesn't include paying someone to set it up which is easily another $150-$200 (I do it myself)

When you look at it that way,,,,then finding a 14 bolt semi float rear should be much more friendly on the pocket book. I can't see a used one costing that much.