Issues with 2.56 ratio diffs

[Majorrdad]

Having a bit of a nightmare with a HMMWV project. Had a company restoring my M998. Apparently when the HMMWV was test driven there was no oil in the transfer case (218 NP) Tried to test drive after adding oil and there were so many growling noises had to put the vehicle on a lift and begin to isolate particular problem areas. Replaced Transfer case with a new NP 218. Found most of the additional noise coming from the Front Diff. No tags on the front or rear so pulled the cover and counted teeth. 2.56 ratio. Replaced front diff with remaned diff. Noise greatly reduced in front. Now rear diff makes a loud whirring noise upon deceleration. The Transfer case seems to operate properly in High Range. H/L may be working properly, at this point not sure. The issue seems to be in Low range. When the Transfer case is placed in low, you can put the transmission in Drive with no throttle applied and it will creep forward and stop completely. Shift the transmission in reverse it will creep back and stop completely. It seems like something in the Torsen is locking up. Anyone with any Idea on how to check this out please let me know. Again the Transfer case is new and the Front Differential is a new re-manufactured unit.

Thanks,

Julian King

 

[papakb]

Isn't the standard HMMWV diff gearing 3.08? If you've got 2.56 gears in the front case they're fighting each other big time. I think 2.56 gears were used in the H1s.

Kurt

 

[86humv]

Early trucks used 2.56, then later 2.73, then up armored used 3.08's.

 

[papakb]

Mornin' Greg, If we've got 2.56 gears they why are we sooooooo sssslllloooowwwwww? Wouldn't 3.08s slow us down even more?

Kurt

 

[DatGuyC]

Mornin' Greg, If we've got 2.56 gears they why are we sooooooo sssslllloooowwwwww? Wouldn't 3.08s slow us down even more?

Kurt

because we also have something like 1.98:1 reduction at the hubs. The 3.08's were used in trucks with the 4l80e so they have overdrive.

 

[Majorrdad]

Early versions of the HMMWV had the 2.56 ratio. One of my old Motor Sargent's said the trucks were to run the autobahn, however, with the 3L80 if you're looking for that additional 10-15mph need the NP242 and the 4L80E transmission. Will be checking to night the rear differential to see if possibly a 2.73 was installed. This vehicle went through a number of upgrades, has the 6.5L de-tuned engine. Could possibly be the carrier bearing.

 

[Retiredwarhorses]

I would bet all these trucks have 2:56.... I have rebuilt so many diffs I lost count, they have all been 2:56
my 98hummer has 2:56

the new diffs have a tab on them with the ratio...this way you don't have to open them up to read the numbers on the main hear.
I did have a 97 hummer come into the shop that had a 2:73

 

[Majorrdad]

Had things checked from underneath. Found the brakes sticking. Rotors and brake shoes are new. If I lift the brake pedal with my foot the brakes will free up. The maintenance team feel that I need to get in some mud and try and break the new Transfer case in. Does anyone have any ideas on why the brakes would stick and free up when the brake pedal is lifted up. The spring is on the pedal.

Hope everyone has a good day.

 

[Retiredwarhorses]

did they install the correct the hydroBoost if it was replaced? I would remove the lollie pop from the brake pedal and see if it moves freely and is not binding as well. That brake pedal should swing free, there are plastic bushings on the cross bolt that the pedal pivots on. You can't overtighten the that bolt as it is shouldered.
By removing the hydro boost lollie pop from the pedal you can check all this.

as Far as the tcase goes..get it up on a lift, perform same test, disconnect the drive shafts at the tcase one at a time and perform same....for that matter, disconnect drive shafts and see if the tcase will turn in low, if not...you tcase is toast.
You said it was a new Tcase....I haven't seen a new 218 in many many years...rebuilt yes. New...No.
the np218 is very simple tacase, Any competent mechanic can split the case and rebuild one.
your diffs and geared hubs can also be checked while the truck is on the lift...I assume these crack mechanics put Gear oil in your geared hubs and diffs?

 

[Majorrdad]

Thanks, Retiredwarhorses,

Believe it or not it is a new 218 which was still coated in cosmoline. The group I have working on the vehicle now are active duty (OMS technicians) moon lighting on the side in the evenings. We know the original T-Case was test driven DRY (15 miles by their own omission) and we suspect the differentials were too, however, they caught it (due to the roar) put oil in them then shipped it here. Have to be careful what I say, in that, the company is a vendor on this site. What I think is happening since the T-Case is so tight, in low range with the brakes sticking when I lift up on the brake pedal the vehicle will roll. Planning to test it on muddy terrain to see how the TC performs this afternoon. Thanks for the input on the bushings, will check that as well. The hydro boost wasn't replaced.

 

[Retiredwarhorses]

I worked all weekend with active duty army mechanics on a no start issue on a hmmwv, they were freaking clueless.
so I don't hold out much hope that this vendors are much better....

if if I read this correclty, they drove this truck 15miles with no fluids in the tcase and diffs, if it were me, it would all be replaced. And as I said...check your geared hubs.
This pipe dream about needing to go muddling is funny....so if I get read this correcly, the tcase is binding so bad in low gear that the trucks stops, but romping in the mud will fix it....LOL

thats a new one....I would do what I said about about seeing if the tcase turns freely while on a lift. If,you proceed with your plan....you risk grenading the tcase which very well will render it not rebuildable.

 

[Majorrdad]

No, the original vendor doing the work didn't put the fluids in. The OMS shop where I live has been doing the work on my other HMMWV and have it 100% mission capable. When the HMMWV in question, the one I'm having problems with came in, there was dexron fluid on the bed of the truck. We pulled it off and checked all the fluids. That is when we discovered the dry transfer case. The dexron fluid was coming out of the Steering pump. There were Plastic shavings in the pump form where it had been drilled for the snorkel vent tube. At this point the differentials and transfer case have been replaced. Last night with the hmmwv on the left, we verified that the vehicle would go into reverse and fwd in low range without stopping. If the engine was turned off and restarted and shifted to drive or reverse the wheels would start turning and stop, lift the brake pedal and they would start turning freely. Repeated the same proceedure on the ground with the same results. In low range everything is rolling freely now as long as I lift the brake pedal, so replacing the bushings in the pedal as you recommended. The only issue I saw last night was slight wheel hop in low range which I thought to be normal since we were on asphalt. Was thinking it would now be a good idea to test the low range in a low traction environment. Since we now know the transfer case rotation is stopping due to the braking, do you still think it is a bad idea to test it off road?

Thanks,

Julian

 

[Retiredwarhorses]

Not sure what you mean about drilling the PS pump....nothing gets drilled for the fording kit...unless you men the PS cap which get at vent. Since it's the brakes causing the wheels to stop turning....as it should, and it's spinning when off, then the issue is when the pump is supplying pressure as it should when the engine is running, so I would lean towards a plumbing issue on the pump, steering gear, cadillac valve or the wrong or bad hydroboost....post some pics of the Hydroboost and master cyl.

 

[Majorrdad]

 

[Retiredwarhorses]

i see you have a milemarker winch plumbed in...make sure it's bled out, and plumbed up correctly. The install instructions call specifically for certain port on the manifold to go where it need too...that manifold appear to be for a rear winch.
do you have a front and rear winch?

 

[Majorrdad]

Just got in from the mud exam, New Transfer Case worked well in H/L and L. had some whinning in L. The winch is mounted on the front.

 

[patracy]

FWIW, I just did a diff replacement on my M1038. It too had 2.56 gearing in the diff. According to CSI, that's all they've ever came up with. But they believe that 2.56's are pretty much the standard. If you have a A1/A2 variant with a 4L80e, you likely have a 2.73. (If was a 93 or later typically) They've not seen a 3.08 outside an armored variant.

 

[Expendable]

NA H1s had 2.73s, TD H1s got 2.56s. NA was avail until 1998 for H1s.

 

[Majorrdad]

Wheel hop very bad left side