Military 1985 Blazer confusion

[K5dreamer]

Hey all,

The deal on the 72 blazer i was looking at is falling through, but ive found a backup plan im starting to look into.

A 1985 ex military blazer with the 6.2L diesel and apparently a TH400 trans? The specs ive found thus far indicate that the 85 blazer came with 10 bolt front and rear diffs, and the th350 or 700R4 trans as far as automatics. however ive seen multiple military trucks for sale that claim dana axles and TH400 transmissions, so im confused.

Does anyone know what options a 1985 military diesel blazer came with? the cost is very agreeable, and i like what ive read about the 6.2L diesel so far, as far as its mileage and power.

The advertized cost for the truck is 2500 obo, but i have yet to see what kind of shape its in. I wanted that full convertable first gen, but i just dont have the time this winter to do the drivetrain overhaul it needs.

Thanks in advance.

-erik

 

[tRustyK5]

The M1009's have the 6.2. TH400, NP208, 10 bolts front and rear with 3.08's. They also have a goofy 12/24 volt electrical system.

Rene

 

[dremu]

Hey all,

The deal on the 72 blazer i was looking at is falling through, but ive found a backup plan im starting to look into.

A 1985 ex military blazer with the 6.2L diesel and apparently a TH400 trans? The specs ive found thus far indicate that the 85 blazer came with 10 bolt front and rear diffs, and the th350 or 700R4 trans as far as automatics. however ive seen multiple military trucks for sale that claim dana axles and TH400 transmissions, so im confused.

Does anyone know what options a 1985 military diesel blazer came with? the cost is very agreeable, and i like what ive read about the 6.2L diesel so far, as far as its mileage and power.

The advertized cost for the truck is 2500 obo, but i have yet to see what kind of shape its in. I wanted that full convertable first gen, but i just dont have the time this winter to do the drivetrain overhaul it needs.

Thanks in advance.

-erik

The CUCV Blazers are the only Blazer that came with a TH400. They also have 10-bolts front and rear; the CUCV trucks (pickups) had the D60/14BFF combo.

VEEEERY few options, comfort-wise ... no AC, no carpet (rubber floor mat), pretty basic -- duh, military

Power train is the J-code 6.2 with a TH400 and 3.08:1 gears on the Blazers on the aforementioned 10-bolts. (The others were 4.56:1 on D60/14BFF or D70 for duallies.)

Depending on condition, 2500 could be high or low. I paid $2300, I think, for mine with very little rust, in black and white paint (ex-PD after the Army) and intact and running, with crappy brakes but nice interior.

And oh yeah, tRusty's right ... WEIRD electrical. You can convert to 12V fairly easily, if you're not intent on keeping it stock.

-- A

 

[Metrodps]

The M1009's have the 6.2. TH400, NP208, 10 bolts front and rear with 3.08's. They also have a goofy 12/24 volt electrical system.

Rene

If you do get one here is the right way to fix the 12/24 system. http://www.roscommonequipmentcenter.com/news_notes/nn10.pdf
These guys do it for the government and have perfected it. It is also a good read for information any way also. You can look at the other project they have done by going here http://www.roscommonequipmentcenter.com

 

[K5dreamer]

thanks everyone, good to know the parts im dealing with, i also had heard something about hydroboost brakes, and the military trucks came with them, and if i wind up putting a small lift kit and bigger tires on the truck that might be a good thing to have, any thoughts?

also, is there an obvious visual difference between the standard vacum boost brakes and the hydroboost brakes? im guessing no big vacuum brake booster, but i dont know what the hydroboost system looks like.

or did all military trucks have them?

-erik

 

[K5dreamer]

also, regarding the transmission, i realize the TH400 is stronger than the 700R4, but that overdrive would be nice.

Does the military blazer with the 400 sacrifice the good mileage the civilian trucks seem to have gotten? if so, how difficult would the swap be to put in a 4x4 case 700R4 in the 400's place?

 

[tRustyK5]

The hydroboost is easy to identify, as you guessed no big booster by the MC...just some steel hydraulic lines.

The TH400 does suck up a bit of power and a bit of fuel mileage, but with a set of 33" or larger tires low 20's shouldn't be too hard to get. The 6.2's fuel efficiency is tied directly to cruise rpm. If you can get it turning about 1800 rpm at highway speed you should see 22-23. At 2500 rpm mileage will be closer to 16-17 mpg. Pretty much 100 rpm = 1 mpg (@ 65 mph)

As you can see even just going up one tire size could result in a gain of 2 mpg....

Of course, the larger a tire you use with those 3.08's the more sluggish that 6.2 is going to feel.

Rene

 

[K5dreamer]

actually thats great to know, i was planning on eventually running a 4in lift and 35's on it. ive got the camaro for speed, so a slightly sluggish torquey truck that dosnt kill the wallet at the pump (diesel is up to 2.70 around here vs 2.30 for regular gas) is exactly what im lookin for, and the 55-60 mph range is exactly what i commute at

 

[mrk5]

I bought a military K5 in a closed bid auction for $1100. Still have the truck today, but without the 6.2L.

With the stock axles, 6.2L, and 33s I was getting right around 20mpg, and it didn't seem to matter if I was pulling our pop-up camper or driving in the mountains.

The only thing I will warn you about is that according to the diesel mechanic I was using, the military is pretty hard on those diesel engines. I ended up replacing all the injectors and the injection pump. The truck only had 45,000 miles on it when I bought it, but I'm guessing a ton of hours were on the engine just idling. Plus my truck had set alot. When they replaced the injection pump the mechanic find a nice nest of dead mice on the intake valley pan.

I wish I still had the 6.2, but it reached a point where it needed a rebuild and that's pricey on a diesel. I wouldn't not buy the truck because of the 6.2, but just be prepared for possible issues.

It does have hydroboost brakes. When other people have driven my truck they are very impressed with the difference in the breaks. I would pick up a power steering cooler for it, though.

The rear 10bolt in mine had the gov-loc setup. That's a version of limited slip that a lot of people don't like, but if you're only doing mild wheelin' with 35s I'm sure you'll be okay.

We also ended up rebuilding the trans shortly after we bought it.

I would just make sure you check the truck out good. I think it would be really nice if you could have a good diesel mechanic check it out. Let you know if you might need to spend some money on the motor. Back in 2000, the injection pump cost me $800 and the injectors were $25ea.

 

[tRustyK5]

IP's and injectors can be had for a lot less if you know where to look. I got my IP and 8 injectors rebuilt for $347 total including shipping from www.accuratediesel.com

Rene

 

[mrk5]

When I had the 6.2 diesels were like pure f'n majic to me. So I had to pay someone else to do the work. One of those, "if I knew then what I know now."

 

[tRustyK5]

Yeah, if it weren't for CK5 I never would have attempted to do the whole diesel swap in the first place...

Rene

 

[K5dreamer]

well, seems that murphy likes kickin me in the balls. first the 72 was leaking like the titanic, now the 85 had a hackjob diesel to carbed 305 swap done, well if nothing else i learned alot about the CUCV's, this really is a great forum

ah well, now onto a 1971 jimmy thats caught my eye

 

[jdemaris]

The TH400 does suck up a bit of power and a bit of fuel mileage, but with a set of 33" or larger tires low 20's shouldn't be too hard to get. The 6.2's fuel efficiency is tied directly to cruise rpm. If you can get it turning about 1800 rpm at highway speed you should see 22-23. At 2500 rpm mileage will be closer to 16-17 mpg. Pretty much 100 rpm = 1 mpg (@ 65 mph)
Rene

I disagree a with some of that. I've got six diesel Blazers (that run) - some with the 700R4, two with T-400s, some with manual trans. With the two K5s that have T-400s - one has a mechanical governor and the other is vacuum modulated via a VRV valve on the fuel-injection pump.
The RPMs are very important, as you said. But so is rolling-resistance. The oversize tires roll harder - and even though they drop RPMs, fuel mileage still goes down - not up. At least where I drive.
For example, take my 83 4WD 6.2 diesel with T-400 trans and 3.08 axles. With the oversize tires - 31-10.50-15" - it will get 19 MPG at it's absolute best on a flat highway at 65 MPH. Same trip with stock 235-75-15" tires and it gets 21.5 MPG. Same vehicle pulling a 20' camping trailer. I made a 2000 mile trip through Canada twice - once with the oversize tires and once with the standard - with the 31-10.50-15"s I averaged 12.1 MPG for the entire trip. With the standard 235-75-15"s I averaged 13.2 MPG.
On another Blazer - an 86 4WD with the 700R4 trans and 3.08 axles - on a flat highway - it gets 23 MPG with stock tires - and 20 MPG with the oversize 31s. I also found that when empty and using the big tires - in hilly areas (my area is all hills) I get slightly better fuel mileage with the torque-converter lockup wire-harness unplugged. That, because - with the 31" tires and lockup-overdrive - the 6.2 labors too much on uphill grades. If it had a turbo - and thus more power - things might be different.
With my 82 K10 4WD 1/2 ton pickup - with a 6.2 and NP833 overdrive manual trans and 3.08 axles - same results. It can get 24.5 MPG with stock tires and 21 MPG with the 31s. Now maybe - in an area that is all flat driving - the results may differ?

 

[tRustyK5]

I was generalizing...and you brought up several good points.

It's all the variables that can either make or break your fuel mileage, but in general if the 6.2 is turning lower rpms on the highway (and not lugging) it will get better fuel mileage.

My own truck managed a best of 16.3 mpg on the freeway. It actually gets that mileage regularly, but no better. This is with 5" of lift, rolling on 39.5" bias ply TSL's and spinning at 2600+ rpm at 65.

I just got the 5 speed in it, so we'll see how much better it gets turning 1900 rpm at 65 with same tires. 20 would be nice, but my gut tells me I'll need some smoother rolling radials to really see the most improvement.

I do maintain that the TH400 eats power and mileage, even though it's a great tranny. Another CK5er local to me here has a 2WD 3/4 ton Suburban with a 6.2. With 4.10's his mileage was 13 or 14 (31" tires IIRC). He went through the trouble of installing some 3.21's and saw the same mileage. He then installed an SM 465 and gets almost 20 now.

Rene

 

[jdemaris]

I was generalizing...and you brought up several good points.
It's all the variables that can either make or break your fuel mileage, but in general if the 6.2 is turning lower rpms on the highway (and not lugging) it will get better fuel mileage.
Another CK5er local to me here has a 2WD 3/4 ton Suburban with a 6.2. With 4.10's his mileage was 13 or 14 (31" tires IIRC). He went through the trouble of installing some 3.21's and saw the same mileage. He then installed an SM 465 and gets almost 20 now.

Rene

I've got two 6.2 diesel Suburbans - and 87 Chevy and an 89 GMC - both 3/4 ton, both 4WD, and both with T400 trans., both with standard 235/85-16" tires (31.7" diam.), and 3.73 axle gears. Both get the same fuel mileage - 13 MPG on average all-around driving, 17-18 MPG on most highway trips, and 19 best mileage on a flat highway at 65 MPH.

 

[cityfarmer2]

On the Hydroboost remeber the military used Dot 5 Brake fluid runs about $80.00 a gallon, something to consider

 

[jdemaris]

also, regarding the transmission, i realize the TH400 is stronger than the 700R4, but that overdrive would be nice.

Does the military blazer with the 400 sacrifice the good mileage the civilian trucks seem to have gotten? if so, how difficult would the swap be to put in a 4x4 case 700R4 in the 400's place?

You're not going to see much of a difference in fuel mileage with the overdrive with the 3.08 axles. I've got several K5 Blazers with 6.2s, 3.08s, and T400s, and also a couple the same but with the 700R4. At 65 MPH, there's a 1 - 2 MPG difference in ideal flat-highway driving. But,where I live, in the hills? Almost no difference, not even on the Interstate, and the T400s are nicer to drive. That is, unless you unhook the wire-harness from the 700R4. My 86 K5 cannot maintain 65 MPH on the nearby Interstate - i.e. it downshifts on long uphill grades. With the harness unplugged though, and the lockup converter not working, it drives much better.
I've gotten 23 MPG with the overdrive on flat runs at 65 MPH, and 21 MPG with the T400s. Around town, all my 6.2 K5s get 16 MPG, and all my 6.2 Suburbans get 13 MPG.

 

[dremu]

On the Hydroboost remeber the military used Dot 5 Brake fluid runs about $80.00 a gallon, something to consider

You can flush the silicone fluid out and use DOT3 ... the cops who had my M1009 before me did just that. $15 or so for a gallon of DOT3 is worth it to blow that purple crap out

-- A