Differential gear ratios, spools, tire size, lift questions.

[argonaut]

So I did a little off-road driving in my stock Blazer for the first time last weekend. It was a moderate trail but afterward I got to thinking about my diff gear ratios, front locking options, tires sizes and lift heights.

Doing a little reading on here leads me to believe that with my 350/350/205 combo that it would have come stock with 3.07 gears front and back. Sounds pathetic. Is this correct? I was assuming they wouldn't put less than 3.73 ratio in a truck. Anyway I'll have to verify this myself when i get back home from this business trip.

Was also thinking about putting a mini-spool in my Dana44 front. Are spools really that bad for turning on the dirt and rocks?

My intentions for this Blazer are to give it a 4" lift and run 33" tires on it and stick with the 1/2 ton drivetrain. plans are for a mix of on road and off-road driving. This will not be a dedicated trail rig.

With this in mind I'm looking for expert opinions/recommendation on
1) gear ratio for off-road performance and on-road mileage
2) mini-spools, just how hard is the turning on dirt and rocks on the trail?
3) What is the least lift I can get away with and still off-road with 33" tires? I'll be running 33x10.5 Swampers on 15x8.5 wheels.
4) with a tuff country lift, should I be looking at getting the 6" rear lift springs in lieu of the 4" on the Blazer?

 

[bigblock72]

With this in mind I'm looking for expert opinions/recommendation on
1) gear ratio for off-road performance and on-road mileage
2) mini-spools, just how hard is the turning on dirt and rocks on the trail?
3) What is the least lift I can get away with and still off-road with 33" tires? I'll be running 33x10.5 Swampers on 15x8.5 wheels.
4) with a tuff country lift, should I be looking at getting the 6" rear lift springs in lieu of the 4" on the Blazer?

1: With 33s 4.10s work pretty well, if 35s are in the future then go with 4.56s (be honest with yourself).

2: Spools and front ends don't work well together at all. It's next to impossible to steer with the front end locked together plus you'll be breaking axles left and right. Speaking of axles make sure you have the later front shafts with the bigger 297 series u-joint, most of the first gens came with the smaller 260 axle joints.

3: You can fit 33 10.50s with 2 inches of lift with the right wheels. 33 12.50s will require a little trimming of the fang especially with wheels wider than 8 inches.

4: If you're only going with 33s there is no reason to lift it any higher than 3-4 inches. But like the gearing be honest with your long term goals on tire size as it will save you a lot of money in the end.

 

[argonaut]

Well the main thing is I don't plan on upgrading the axles anytime soon. So i figure that limits the tire size and type of wheeling I'll do. I'd also like to be able to tow my race bike with the blazer.

So I'm figuring 33" is the best compromise on tires size for mixed use.

I'm a little scared though. If I'm only getting 13-14mpg now with a 350, 3.07 gears and 32x11.5 tires, then I'd hate to see what 4.10s are going to do to the mileage!

 

[Big Blzn]

I have a '72 K5 and for awhile I ran 33" tires with the half ton gear and about 4" of lift. Then I moved up to 35" tires and had some minor rubbing on the front of the rear wheel well. I then moved the front axle forward an inch and the rear axle back an inch. I tend to carry about 500 lbs of gear when I go off roading if camping is involved and I rarely rub now unless it is a hard bump on compression. On my half ton axles I had a limited slip in the rear and open d44 up front. Never had any breakage issues. I did, however, put a 14bff in and and 8 lug d44 up front. I went from 3.08 gears to 4.10 with the axle swap and it made a world of difference. I am quite a bit slower on the freeway with the deeper gears though. IMO, if you have any/many plans to drive the rig on the freeway with 33-35" tires, the 4.56 gears will be to low to keep up with even the 18 wheelers in the slowlane with only a 3 speed tranny.

 

[bp71k5]

x5 on the "spool in the front advice". I have a real hard time turning on dirt with my front locked in. It's completely impossible on the street. Although unlocking the hubs might make that easier for the street, it's still pretty difficult in the dirt without hydro-assist.

With an auto trans and no overdrive, my experience is 35's + 4.10s = OK
If you have or ever plan to have overdrive or a manual, 4.56 was a decent choice for me.

 

[Greg72]

Everyone's got opinions....so here are a few of mine.

If I were building a nice streetable K5 like you're talking about (35" tire max) here's how I'd do it:

ARB front / ARB rear - Hands down these will be the MOST street friendly of all the locker / ltd slip options. Most expensive too....sorry!

Chromo-shafts and u-joints (if needed) to upgrade the 1/2 tons... start with just a good quality Spicer joint and see how they do, if you need more strength for your wheeling style, you can always go to CTMs later on.

I'd think long and hard about a 700R4. The overdrive will be a godsend for your highway mileage, and the extra low 1st gear (3.06) is substantially better than the 2.48 gearing in the TH350 or TH400. Combined with the NP205 case, most people call this the "poor mans doubler"... you'll get really nice crawl out of a very simple setup.

Axle Gears - Work it backwards from the highway speed you want to travel, and the final tire size you choose. Keep the engine operating at it's torque peak (RPM) for best mileage. For a smallblock this will probably be in the 2500 - 2800RPM range. My guess is that 4.56 will be the correct choice. You'll LOVE the extra power that you get from deeper gearing when you take off from the stoplight. Overdrive on the top end will give you the best of both worlds.

 

[GRINCH]

I concur with Greg... Well sorta..

I really like the Eaton E-lockers. (No Compressor needed or leaks) The are open or locked. Plus cheaper than the ARB's. However they won't warranty them if running larger than stock tires. (Not to worry anyway)

700R4's can be built to hold up to the abuse.

If you are redoing the front axle.. Gears and Lockers. Why not upgrade to the 30 Spline axle shafts. GM ran them in the Blazers and Burbs from 89-91.

Trust Greg on the ratio...

How do I know..

Until I rolled it, I ran a 90 with Eatons front and rear, a well built 700R4. I had 4.10 gears which were great with my 33's but when I jumped up to my 37" creepys the 4.10's weren't the best option. I also ran them with 35's.

I never broke any U-joints or axle shafts, even running the 37's. Of course you need to know when not to use the skinny pedal

 

[Greg72]

Oh..... I change my vote. eLockers instead of ARBs.

My response was rushed and I forgot about those as an option. Totally agree, much simpler to have an electric connection than to plumb for air (unless you want onboard air for some other purpose).

 

[argonaut]

Hmmmm, 700R4 is very very enticing. I'm guessing the easiest way to install the longer transmission is to move the engine forward which really shouldn't be too difficult. if I was too look into picking up a cheap 700R4 to rebuild myself what years/models/spec should I be looking for? I've heard some versions were stronger than others.

The first thing I need to do before diving into the axles and suspension is pull the motor-trans-transfer case and do a rebuild. Valve guides are worn and with the lack of maintenance I've found on other parts of the truck my guess is that the transmission has probably been neglected its entire life. That said she still runs pretty and drives pretty well for a neglected 37 year old truck. SO while I'm doing that perhaps I should look at replacing the tranny.

 

[Greg72]

..my guess is that the transmission has probably been neglected its entire life. SO while I'm doing that perhaps I should look at replacing the tranny.

You are dancing so close to the "Might As Well" expression I can practically see the words in the air next to you in a little cartoon dialogue bubble!

 

[argonaut]

Haha, if i had more cash to throw around I would certainly be throwing around "might as wells" left and right!

But for now I've limited myself; no axle swaps, no motor swaps. I know, I know, where is the fun in that!?! But this is my first 4x4 so the truck will have to grow at the same rate as my desire and abilities do.

 

[Greg72]

FWIW -> I've never enjoyed driving my truck as much as when it was still on 1/2 ton axles and 35" tires.

Probably the best setup it ever had for street driving was:

1/2 tons
35" radial tires
ORD rear shackle flip
4" ORD custom front springs (very soft)
Front sway bar (with ORD disconnects)

It ran straight and true down the road, it was comfortable and didn't rattle me to death. The swaybar took the "spookiness" out of the soft front springs in the sweeping corners.

Don't assume that you absolutely HAVE to go 1-Tons / Doubler / BBC to have fun... The build should be structured around the tire size that you choose, it's really that simple. If you keep the tires under about 37" diameter you make your life a whole lot simpler and can re-use almost everything you currently have.


"Functional is the new hardcore"


In 2010, you'll be hearing this expression a lot more.

 

[Big Blzn]

FWIW -> I've never enjoyed driving my truck as much as when it was still on 1/2 ton axles and 35" tires.

Probably the best setup it ever had for street driving was:

1/2 tons
35" radial tires
ORD rear shackle flip
4" ORD custom front springs (very soft)
Front sway bar (with ORD disconnects)

It ran straight and true down the road, it was comfortable and didn't rattle me to death. The swaybar took the "spookiness" out of the soft front springs in the sweeping corners.

Don't assume that you absolutely HAVE to go 1-Tons / Doubler / BBC to have fun... The build should be structured around the tire size that you choose, it's really that simple. If you keep the tires under about 37" diameter you make your life a whole lot simpler and can re-use almost everything you currently have.


"Functional is the new hardcore"


In 2010, you'll be hearing this expression a lot more.

That is probably the best advice I have heard on CK5 in a loooooong time. Imagine how much money and labor we all would have saved by using this logic.

 

[argonaut]

My thoughts exactly!

 

[Greg72]

If you liked THAT one....here's another one that is just as important:

"Don't change the direction of the build DURING the build"


I've lost my a$$ on parts that I bought because I kept changing my mind about how I wanted to build my truck. I bought Doublers (Ford & Chevy drops), sold Doublers , Bought transmissions, sold transmissions.... all in the pursuit of a "holy grail" combination of parts.

The truth is that for a lot of us the "target" changes as we go along. In your case, it sounds like you know that you want a good all around truck that you can occasionally enjoy offroad.... if that goal doesn't change and become "hardcore wheeler" on you, then it sounds like you've got a plan to get there pretty quickly.

More pics by the way.

 

[champsjimmy]

Front sway bar (with ORD disconnects)

It ran straight and true down the road, it was comfortable and didn't rattle me to death. The swaybar took the "spookiness" out of the soft front springs in the sweeping corners.

Greg - what sway bar did you use?

 

[Greg72]

Just a '73+ Blazer Swaybar and spring plates with custom bushing hangers mounted to the front frame crossmember...

Very simple OEM parts with very little fabrication required.

 

[champsjimmy]

Doh! - I had a '77 parts Blazer I got rid of!

 

[argonaut]

Greg,
Can you post some photos of that sway bar and its mounting? I haven't see the blazer setup, only the 2wd.

 

[argonaut]

Oh, and here are some pics of my Blazer as it sits today:

No rust in the floors!

Mostly stock under here:

And a few with the 33x10.5 Swampers that are to large to run with the stock list. The right rear hits the front of the fender on larger street bumps.