What fuel mileage to expect from a 700R4 equipped Blazer?

[mangus580]

After he bought the truck, he monkeyed around with the T-case, shifted into 4-HI, N, and 4-LO, then back to 2-HI, but he didn't know that you had to back up to get the auto-locker hubs to unlock. When he took off on the highway, he noticed that it felt a little more sluggish on the get-up-and-go meter. Then, when he got up to about 30 MPH, he heard a ratcheting noise in the front left followed by a big "POP!", then the power was back to normal, and the noise went away. Now, it does the "ratchet, POP" thing every once in a while right around 30 MPH. I thought it sounded like he blew the hub, so he stopped in at a Pick-N-Pull type place to get some manual hubs, but the only ones that would fit his truck, he couldn't get to come off. So he just got an auto-locker from another truck. Now that he installed the new(old) hub, it makes the "ratchet, POP" noise all the time!

What could the problem be?

New set of Warn manuals are only about $100...

I used to love my auto's... until I started plowing with them!

They are actually pretty simple, but they lock/unlock every time you change direction.

 

[superburban]

The ratchet-POP problem was a real "head-scratcher". It turns out the the passenger side hub was stuck in the locked position, causing the axle to turn, causing the driver's side hub to try to lock, at about 30mph. We took off the passenger side hub, unlocked it by hand, and mashed a bunch of grease back into it, now it works great. No more ratchet-POP!

 

[mangus580]

Just be careful.... GM had a special grease for them. It was said that if their grease was not used they would never work right. I 'might' still have a tube someplace.....

 

[superburban]

We're not too worried about the grease thing. He pretty much just wanted to be able to drive the 30 miles home. He is planning on some manual lockers in the near future.

I finally took some pics:

 

[peyton]

To give you a kind of baseline for mileage, my 86 2wd suburban with 700r4, 4.10 and a normally aspirated 6.5 get 22 on the freeway at 65mph using the cruise control. Around town, it is in the 12-14 range. I calibrated the odometer and speedometer using the freeway mileage markers over a long distance and have since checked it a number of times and believe it to be pretty accurate. My speedometer and odometer both read about 10% low.

Since the frontal areas are the same, a simple weight ratio comparison might give a good estimate for the blazer (given the same ratios, tires, etc.). I suspect with a 700r4 and 3.42 or a 3.73 rear end you could easily get into the high 20's on the freeway.

BTW, he got a very good deal.

Peyton

 

[AJMBLAZER]

Nice. Classic GM peeling paint.

 

[superburban]

I checked the data tag in the glove box, and found that it's got 3.73 gears and 31x10.5 R15 tires.

(I think I told someone that it had goodyears, but they are actually Big O)

 

[superburban]

Update time:

After puting quite a few miles on the truck in the last month, my friend has reported right under 20 mpg (19.5ish).  I showed him how to change the fuel filter without having to crank and crank the engine yesterday (you know, you pull the pink wire on the IP while filling the new filter), so hopefully he can pick up a few more mpgs there too. 

He is really enjoying this vehicle, and is glad that I recomended it.  It is definitely a step up from his 2wd BroncoII!  It gets better fuel economy, has more power, and is about twice the size!

 

[dependable]

Too bad the th700 has durability problems. I recently saw a cucv pickup on craigs list with a 4L80 overdrive automatic... the listing said it used an aftermarket computer chip to enable conversion. Has anybody tried this? The th 700s are not strong enough for sustained use in anything heavyer than a blazer or c-k 10 in my experience. The 4L80 is supposed to be based on the th-400, but I have no personal experience with anything that new.

 

[Croatan_Kid]

It's not just a "chip", it's a complete stand-alone computer that controls the transmission. They are EXPENSIVE! This is why most choose to go with the 700R4, such as myself.

I've been running one in my M1008 for a number of months now with no durability problems. With the amound of aftermarket upgrade available, the 700R4 can be transformed into an entirely different animal capable of holding up to some serious abuse! I know mine has (front and rear lockers, 39" tires) . You shouldn't have any problems with a 700R4 behind the ho-hum 6.2, even a relatively potent 6.2 turbo won't tax one beyond it's capacity. Even if my truck does weigh 6000 pounds, I don't feel that the transmission is the weak link, if anything, it's the transfer case! (which is also reasonably stout)

 

[randyscycle]

On the auto hub issue, I have found that most auto hub problems were due to them being filthy or improperly lubed.

Take them off and apart and clean them very thoroughly. When reassembling them, use only a very light grease like White-Lube. Do not use wheel bearing grease as it is too thick and will cause them to stick and not unlock. They usually function just fine if you do this. The reason they stick so many times is that they don't get used, nor do they get any service, even when the bearings are serviced.

 

[desertfoto]

My new to me, 91 Burb with the 700R4 and 6.2 gets right at 12 MPG. Much lower than I expected but I have some work to do. It has the stock 3.42 gears and 35" Mickey Thompsons. My plan is to drop down to a 33" tire and bump the gears to 4.10. According to the Grimmjeeper gear ratio calculator, with the factory 235/75R15 tires is was turning 1811 rpm at 65. With 4.10s and 33" rubber the same calculator puts the 65mph rpm at 1899 rpm. Right now if I can get to 65 I'm only at 1494 rpm. After that I'll look into maybe a new IP and injectors since they are unknown. The truck has about 155,000 miles. Was considering the 3.73 ratio but the 4.10s get me closest to the factory RPM and I will, on occasion, tow trailers.

Amigo, I get 15 MPG and sometimes better in my 85 K20 Suburban with 4.10 axles if I keep it at 60, but it has 235 85r16's and a SM465 4 speed manual with a 350 gas engine.

 

[tlm47201]

Well, been driving my 09 for over a month now, over 2000 miles. Low oil consumption, and a solid 20 to 22 mpg. My 26k 09 will soon turn 29k. My driving is part hiway, rural and seldom over 60 mph. I even make a "spirited" fire run or two.