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Quad Box Pucking Oil

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Good friend has B with TRQ 720 trans. It takes spells of leaking trans. oil out the clutch housing. Leak doesn't seem to be related to outside temp or oil temp or amount of time truck has been running but will stop when truck is shut off. He is running 90 wt. oil same as I run and I don't having any leaking problems.

Anybody got any ideas???

Thanks,

Tom

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Good friend has B with TRQ 720 trans. It takes spells of leaking trans. oil out the clutch housing. Leak doesn't seem to be related to outside temp or oil temp or amount of time truck has been running but will stop when truck is shut off. He is running 90 wt. oil same as I run and I don't having any leaking problems.

Anybody got any ideas???

Thanks,

Tom

Hi Tom,

The TR 72 series transmissions have an internal oil pump that operates when the input shaft turns. The oil passages in the transmission lubricate the front bearing to the input shaft. When the input shaft is not turning (as when engine is stopped) there is no oil flow and the leak will stop. What I am saying is the front seal to the transmission is bad.

Rob

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Hi Tom,

The TR 72 series transmissions have an internal oil pump that operates when the input shaft turns. The oil passages in the transmission lubricate the front bearing to the input shaft. When the input shaft is not turning (as when engine is stopped) there is no oil flow and the leak will stop. What I am saying is the front seal to the transmission is bad.

Rob

That trans has no front seal it has a reverse thread om the input shaft.

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Which leads one to assume the front bearing may be getting loose and wearing out the oil return thread. Or something is restricking the oil flow from the pump intermitenly.

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Tom tell your friend to check the vent on top of the transmission if it is clogged up it can cause it to leak, the same can also apply to rearends. Block

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I put a new pinion seal in my rear..now it does puke out the vent cap?

Actually the pinion nut was loose one notch, so it leaked(cause the bearings were loose). I put a new seal and tightened it up again. No leaks there, but the vent has constant stream coming from it.

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Is the bottom section too full? When was the last time you drained out the excess? The top sections like to leak down into the bottom on these rears so the bottoms get too full and leak.

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Can't recall if I've pulled the sight level plug out of rear. Might have?

Why would it blow it out the top of the vent plug if it had just a bit too much? Think it would be leaking at the axle long before it ever got to the vent cap?

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Good friend has B with TRQ 720 trans. It takes spells of leaking trans. oil out the clutch housing. Leak doesn't seem to be related to outside temp or oil temp or amount of time truck has been running but will stop when truck is shut off. He is running 90 wt. oil same as I run and I don't having any leaking problems.

Anybody got any ideas???

Thanks,

Tom

Is the bellhousing coming loose from the engine block? Looseness here will cause intermittent misalignment of the input shaft, possibly wearing the oil return threads. Also if this is the case, the next thing that'll happen is it'll rip the center out of the clutch disc(s) from the misalignment & flexing.(I've seen this happen several times, it seemed to be a "Mack disease" back in the days of B models & early DM's.)

Watch the seam where the bellhousing attaches to the block as a helper depresses the clutch pedal repeatedly, if it's loose you'll see a slight opening & closing of the mating surfaces.

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Freightrain, it was just a suggestion. Ive drained bottoms that were a gallon or a gallon and half too full. It could just be a bad vent too letting oil out.

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Is the bottom section too full? When was the last time you drained out the excess? The top sections like to leak down into the bottom on these rears so the bottoms get too full and leak.

I believe Freightrain has a single axle rear with the front mounted carrier, so the upper & lower compartment thing does not apply here.

The tandems (CRD92 & 93, CRD 112 & 113, CRD 95 & 96) would be the ones with the upper & lower compartments.

I was always told that the upper & lower compartments (and the small compartment on the power divider, if equipped) should be filled initially, then during regular PM's just the bottom should be checked.

Filling upper & lower at each PM is how you wind up with an overfull condition.

Drain out the excess? Think about that for a moment- if you fill the compartments properly at the initial fill, where would excess oil come from? Answer: from adding to the upper compartment each time it's checked.

Makes no sense to keep adding oil to the top compartment & draining it out of the bottom.

If there is a severe leakdown from top to bottom it usually means the carrier mounting bolts inside the side cover are loose & should be tightened.

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I believe Freightrain has a single axle rear with the front mounted carrier, so the upper & lower compartment thing does not apply here.

The tandems (CRD92 & 93, CRD 112 & 113, CRD 95 & 96) would be the ones with the upper & lower compartments.

I was always told that the upper & lower compartments (and the small compartment on the power divider, if equipped) should be filled initially, then during regular PM's just the bottom should be checked.

Filling upper & lower at each PM is how you wind up with an overfull condition.

Drain out the excess? Think about that for a moment- if you fill the compartments properly at the initial fill, where would excess oil come from? Answer: from adding to the upper compartment each time it's checked.

Makes no sense to keep adding oil to the top compartment & draining it out of the bottom.

If there is a severe leakdown from top to bottom it usually means the carrier mounting bolts inside the side cover are loose & should be tightened.

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Ya, it's a single axle double reduction. Seems there is like two compartments, but only cause the upper ring/pinion get oil, then drips back to large bull gear area.

Just seems odd that it now leaks out the vent so much?

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Ofcourse you need to keep adding oil to the top section after the initial fill. Even brand new mack rears leak down from top to bottom so then you end up with an empty top section and power divider and a way over full bottom. If you dont add oil to the tops they will run dry. It doesnt take much, maybe a half gallon every 8 thousand miles or so. We service at 8 and i add about a half gallon to the top and take a half gallon out of the bottom.

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Ofcourse you need to keep adding oil to the top section after the initial fill. Even brand new mack rears leak down from top to bottom so then you end up with an empty top section and power divider and a way over full bottom. If you dont add oil to the tops they will run dry. It doesnt take much, maybe a half gallon every 8 thousand miles or so. We service at 8 and i add about a half gallon to the top and take a half gallon out of the bottom.

Nope! That ain't the way it works.

Even if the oil from the top leaks down while the truck is parked and causes the top to be underfilled & the bottom to be overfilled, as soon as the truck is driven the rotating gears throw the oil back up to the top section again.

Mack recommends that the diff. lube level be checked when the truck just comes in from a run for just that reason - so the oil doesn't have time to leak down & give a false reading.

I've been doing the lube check my way for over 30 years & I've never had a rear end run dry or suffer damage from lack of lube, but I have saved a lot of money by not wasting gear oil by pumping it into the top compartment & draining it out of the bottom.

11_17_1.jpg

Above is the instructions from the Mack maintenance manual regarding rear diff oil levels.

It says that if the oil level is full in the bottom compartment, no further action is necessary. If the oil is not full in the bottom, then fill the bottom & fill the top compartment too.

Nowhere does it say keep filling the top compartment every time & keep draining the excess out of the bottom compartment!

How many gallons of gear lube have you wasted over the years? I've never heard of anything so absurd.

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I have never added oil to the top of a mack rear after the first fill, the oil from the bottom is splashed to the top of the rear and overflows back to the bottom, I beleve it says on the side cover for initial fill only. Gonna take a look in the books just in case, hope I've been doing it right for the last twenty years!!!

Thanks HK I feel beter now.

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I have never added oil to the top of a mack rear after the first fill, the oil from the bottom is splashed to the top of the rear and overflows back to the bottom, I beleve it says on the side cover for initial fill only. Gonna take a look in the books just in case, hope I've been doing it right for the last twenty years!!!

Thanks HK I feel beter now.

Do not add oil to the top after it has been filled one and if you dont check the level on the top you will not think that it is low. When it gets thru drain down to the bottom it still has oil in the top and the sure way to find out is go and pull the side plate and you will have oil in the top.

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Almost every service that we do the truck is hot, and not just warm they just came back from a heavy 5 or 600 miles. The top sections are never even being close to full and the bottoms are way overfull. Theres no where for the oil to come back up in any great amounts on the rears. The only place that it can go through is around the shaft and the oils not going to come in the topsection. They say oil level is correct when oil level in the bevel gear housing is slightly below the threads. Is slightly below where you cant reach it with a finger? For the amount of miles these trucks run everyday we cant take a chance on lubrication problems. Oil is a lot cheaper then a tow from delaware or philadelphia because of a blown rear due to lack of oil.

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Truck stop mechanics just trying to make a living.

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