updated pics of my hemtt restoration

[army_greywolf]

I just looked in the manual, yep, latest specs have switched from 10W to 15W40 in ALL HEMTT M977 series ((that includes yours, even the 5 speed)) tranmissions. Furthermore, it includes the two available transmissions used in the PLS.

Food for thought.

One more thing. You want to use a low-emulsion oil aka, do NOT use things like lucas oil stabilizer, in fact no additives of any kind and use ONLY agricultural grade, like something approved for use in John Deeres or Case Tractors, it's the type of oil that won't pick up air bubbles and suspend them that you want to use. Dexron will "foam" at high temperatures, it stands to reason why you are slipping.

 

[army_greywolf]

one last thing...if you made the mistake, its ok, it can be fixed, you will need to flush it, including draining the converter, which can be done on some of the rebuilt models by the drain plug on the converter itself...but not always.

 

[dma251]

Well, this poses an interesting dilemma....

Tell me this - What type of military equipment was the Allison HT750CRD used in?

I've got the Allison literature saying one thing, the military literature saying another.... I guess to start with I need to know what piece of equipment this HT750 came from.... It wasn't any hemtt I've heard of.

Anyone know?

 

[dma251]

Okay, per the Allison HT 750 CRD manual, I can run any dextron III, or C-4 approved 10-40 or 15-40 oil. I use Delo 400 40 weight in the engine as it's a 8V92, but can I use regular Delo 400 15-40 in it? I pulled the specs on the Delo 400, and it has this to say -

Chevron Delo 400 Multigrade SAE 15W-40 meets:​

•​

​

​

​

API Service Categories CI-4 PLUS, CI-4, CH-4,​

CG-4, CF-41, CF, CE1, CD1, SL, SJ, SH1, SG1

Do these indicate C-4 certification?

I know from speaking to the Allison rebuilders that they were adament that whatever I ran be C-4 certified....

If I can find a 15-40w that is C-4, then I will use that and satisfy both Allison's specs AND the military TM's.

 

[army_greywolf]

Let me do some research. I'd like to know what engine was in front of your transmission before the 8V92, the issue is interesting, since that trans lists having several torque converters and configurations based on the engine in front of it. Torque converters in diesels generally have HUGE stators, that's why they overheat at idle.

 

[dma251]

check out what the boys over at Bobistheoilguy forums say...


(by the way, for any of you have the stomach for truly dizzying oil and fluid science with very little talk of the actually vehicle that contains it, this is your place. These guys KNOW oils.... They LOVE oils.... It's quite an interesting culture over there)

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1325798&fpart=1

 

[TBigLug]

Wow, just got done reading through all 327 posts. Sweet job! Hope your tranny woes are fixed once and for all soon!

 

[cranetruck]

.............
One more thing. You want to use a low-emulsion oil aka, do NOT use things like lucas oil stabilizer, in fact no additives of any kind and use ONLY agricultural grade, like something approved for use in John Deeres or Case Tractors, it's the type of oil that won't pick up air bubbles and suspend them that you want to use. Dexron will "foam" at high temperatures, it stands to reason why you are slipping.

The "Premium Tractor Hydraulic" fluid that I decided on for my Allison trans in the xm757 8x8 meets the "C-4" specifications, but has a much lower viscosity rating than the 15W-40, about 6 cps at 100°C (or equivalent to a 10W engine oil).

So what role does the viscosity play here?

 

[rockman]

It sure is interesting reading about auto trannies and MVs. Adding a auto tranny to a combact vehicle certainly addes to the maintenance efforts. Wonder if the benefits paid off by making the trucks easier to drive? Sticking to the deuce 5 speed for now.

 

[cranetruck]

One reason for the automatic (in the m656/xm757 8x8s anyway) was to be able to drive faster off-road and not losing momentum when shifting. The 6-speed Allison in my 757 has very small ratio increments and shifts flawlessly in bumpy hills etc.

 

[rockman]

Bjorn, interesting performance note on your 757. It also makes sense when the driver had to double clutch the prime movers. Since these trucks are slightly underpowered, keeping momentum is important. Is your 757 road worthy and in service now?

 

[cranetruck]

Yeah, it's pretty much ready for the road, but I have reservations about the tires.... they do hold the pressure, but there are lots of "weather cracking" visible.

 

[Jones]

This is per Fort Eustis;
The decision to go to automatic transmissions a while back was based on a very simple principle. Most new 88Ms these days have never driven a stick in civilian life and would have to be trained on proper shifting and clutch techniques. It takes lots of experience to master when it's right to upshift and downshift depending on vehicle, vehicle load, driving surface and conditions. Add to that the fact that sometimes military operations are in off-road conditions which throws a whole different set of conditions/rules into the mix.

I'm a dyed-in-the-wool manual transmission fan and cut my teeth on non-synchro transmissions and even a few Model Ts but I have to say;
Automatics are a set-it-and-forget-it proposition. The trans decides when to upshift and downshift and when it does, the transition is usually in the tenths of a second range-- invaluable if you're operating in sand, snow or mud where bogging down during a shift could cost you momentum.
Trust me, there's nothing like missing a shift and winding up out of gear on a grade when you were really counting on engine braking to get you safely to the bottom with the rest of the traffic, instead of in your own express lane.

Once you get shift linkage adjusted, automatics pretty much just want to be operated within their own comfort range and to be kept in clean fluid and filters.
Most problems are a the result of overheating (get sufficient cooling), dirty fluid (pay more attention to regular maintenance), or mis-handling (pay more attention to proper operating practices).

My personal experience is that Allisons are some of the more dependable transmissions and they've been around long enough to get most all of the bugs worked out.
When I selected one for the baby HEMTT the complete package was dirt cheap; the truck dismantler said it was because " the darned theings never break-- the only time we sell one is when somebody wants to up-grade from a stick".

 

[dma251]

Obviously having owned two other MV's with manual trannies, I have been on both sides of the manual/automatic street. Here's the thing -

You really should drive a hemtt. These trucks are so easy to make go so fast! It really is nice to jump up in the cab with coffee mug in hand, wind through the woods, and then jump on the freeway for a run up to about 70 mph, and all the time never have to stand on a clutch pedal, or put your mug down to throw a shifter... It's an effortless truck to drive.

Now I am not saying I don't enjoy driving a truck like my old 5-ton, because that's a blast too, but in a much more "driver-involved" way. When I wanted to drive my 5-ton, I knew I was gonna be working for it. Smiling all the way, but still exerting a bit of effort and strategy.

Also, it should be noted that everyone that I've heard from that drives hemtts, has complimentary things to say about the shifting of the hemtt. Not sloppy or poorly timed shifts, but crisp and right where you want them. Once I can get past first gear, mine is the same way. A pleasure.

 

[rockman]

Guess I need to start saving for one..thanks for the note

 

[dma251]

I drove the hemtt over to the shop today for the tranny removal. First gear was slipping so bad it made it necessary to creep up the 15% grade leaving my neighborhood in 8-LOW in reverse to preserve the 1st gear clutches.

As soon as I made it to the top I turned around and cruised about 20 miles to the shop with no troubles.

Darn, I sure missed driving it this last couple months. It drove like a dream once the trans was fully warmed up and probably hit about 70 mph on the straight stretches outside town.

With diesel prices low for now, I am gonna start driving this to work a couple times a week!

Here's the video from today.

[media]http://www.youtube.com/watch?v=itHKsm0m-gc[/media]

 

[rivired]

and i though a deuce was alot of machine to work on lol

 

[rivired]

that was an awesome vid..i LOVE the sound a of a detroit!

 

[madsam]

Nice...

 

[EZFEED]

What a monster.......pass up everything but a refuling station! Must be quite a rush to manuever that thing through traffic!