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Learn from my lesson: early Allison weak spot


Ken_P
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I have a 2004 Silverado 2500HD with the Duramax/Allison combo. Towing a few months ago (30’ fifth wheel RV) and pulling a grade. Top of the hill, let off, and heard a very ominous “thump thump thump”. Coasted into the rest stop at the bottom of the hill and found that all the fluid was leaking out of my truck’s transmission.

 

Since it was a Saturday night, I had it towed to a shop and the rv towed to our site.

 

Upon tear down, it turns out the transmission tail shaft housing was cracked circumferentially over the top 180 degrees. A little research indicated that this is a weak link on the 4wd trucks because this housing supports the entire weight of the transfer case.

 

The aftermarket makes several braces that link the transfer case to the main case of the transmission, and Chevy redesigned the tail shaft housing  a few years later with extra ribs to strengthen it.

 

I also learned a second, extra expensive lesson. In removing that tail shaft housing, you are also removing the transmission output shaft. It is an intermediate style shaft that slides onto the next shaft with a spacer slid onto splines on the intermediate shaft. That assembly can only be assembled vertically, to ensure alignment. The repair shop I found discovered that lesson after it was reassembled. The owner was honest with me about how it all went together, and thought he had it, but misalignment caused a gear to chip and wrecked my planetary gears as a chunk of metal traveled through!!! So, now I have a freshly rebuilt transmission! 🤦‍♂️ 

 

2 key points: 

- there is a weak link in the early Allisons, even with a stock truck

- the transmission cannot be reassembled in the truck!

 

Learn from my $$$ lessons.

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Edited by Ken_P (see edit history)
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Bummer......thanks for the heads up.......just ordered one. I replaced my transfer case at the dealer three years ago......and they installed a rebuilt one with the same flaw.......nice.

 

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They replaced the tail housing of the transmission when they did the transfer case? The part in question is below.

 

The piece I’m talking about is the back end of the Allison. On 4wd trucks, it has a bearing and six holes to accept the studs from the tcase. It also has the transmission mount - the tcase floats.

 

Not a problem on 2wd trucks because the Allison tail shaft housing just has a bearing and seal for the driveline.

 

@edinmass - check your rear driveshaft ujoint on the tcase end. Mine was very bad, and had apparently been so for a while. My transmission shop just got another early Duramax in with the same ujoint bad and a broken tail shaft housing. Our theory is that the tcase vibrates excessively, which throws out the ujoint, thus exacerbating the tail housing problem until it fails.

 

- or I’m too heavy footed 🤣 -

 

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Edited by Ken_P (see edit history)
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I should rephrase.......they installed a new transfer case and didn’t install the brace.........my truck only had 30k on the clock (2005) when the transfer case failed. Obviously they knew the truck was basically new........and would see hard service. Interesting that I had not read about the issue in the trucks forums..........

Edited by edinmass (see edit history)
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1 hour ago, Robert Street said:

Just a curious observation but isn’t that truck overwhelmed with a 31 fifth wheel?  Just asking

Robert


I have hauled 27k with one..........had a tranny kit installed. No problem. This is 48 feet.

 

 

Inside.......two Pierce cars, an eight and a twelve, and a bunch of parts.

 

 

 

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Edited by edinmass (see edit history)
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42 minutes ago, edinmass said:


I have hauled 27k with one..........had a tranny kit installed. No problem. This is 48 feet.

 

 

Inside.......two Pierce cars, an eight and a twelve, and a bunch of parts.

 

 

 

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Ed yours looks like a one ton dually. I was thinking I was reading about a 3/4 SRW.  I couldn’t even think about towing your trailer with my one ton!  Plus Maryland DOT would probably run me down and deadline me as payload numbers and GCVW  and license are way over my one ton placard.

Robert

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Robert....in the future......get a triple axel.....they stop 200 percent better(much safer), and are more stable. Also makes dealing with flats easy. My other trailer..........34 foot tag.

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Edited by edinmass (see edit history)
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1 minute ago, edinmass said:

Robert....in the future......get a triple axel.....they stop 200 percent better(much safer), and are more stable. Also makes dealing with flats easy. My other trailer..........34 foot tag.

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I’m down in DelRay now and I’d love to have a triple but.....  it would easily fit in the car cottage but Maryland would lock me and my one ton up!

Robert

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24 minutes ago, Robert Street said:

Maryland would lock me and my one ton up!

Robert


So glad I can keep my registration in Idaho- it’s actually legal to pull an rv followed by a boat! Granted, way less traffic out there!

 

The 2500 SRW is a good compromise - it tows an rv or my 24’ car trailer but I can drive it easily to work, and park in tight spaces. When I get settled post-military in a few years, a one ton dually is in the cards.

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I’ve seen those RV’s and boat or car trailer combos and shake my head!  A couple years ago a friend was in his Class A pusher and towing a 28 car trailer and Maryland DOT nailed him for 1,600 in fines plus he had to obtain a class A CDL before he was legal in Maryland roads. He is a Delaware resident and tagged Delaware and had been pulling through Maryland for years but never been stopped by Maryland DOT previously.

I like my one ton SRW diesel for same reasons as you do. Parking being primary. But payload is reduced a bunch with SRW so nothing trailered over 9,999 GVW

Robert

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Laws are clear, if you PRIVATE and legal in you state, your legal in every state. The Federal DOT rules apply interstate. If commercial......all bets are off. I carry a copy of the rules......I don’t stop at scales. 

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1 hour ago, edinmass said:

Laws are clear, if you PRIVATE and legal in you state, your legal in every state. The Federal DOT rules apply interstate. If commercial......all bets are off. I carry a copy of the rules......I don’t stop at scales. 


i have also had to start carrying the federal motor carrier book mainly because in Maryland the Maryland motor carrier book doesn’t exempt private car trailers and I have been given the hard stuff several times but always finally released. The Maryland book clearly indicates that Maryland has adopted the federal exemption section which clearly exempts our car carrier trailers. 
The friend I was referring to above had two problems. 1.  He like all of us are legally required to stop at Maryland scales. Read the scale signs closely as it says All vehicles over 5T must stop at scale. No mention of commercial or trucks only. I hear Pennsylvania is close to copying that and when I tow west I believe it’s Illinois I’ve seen that wording but their pounds is 26,000 GCVW. I’m 25,000 GCVW so ok there!  The other problem he had was he was observed running a scale and when stopped they learned his class A pusher was registered in his business but the trailer was in his private name/address.  His GCVW was way over 26,000 so was in CDL requirement.  For Delaware tax reasons he was better obtaining his CDL. 
The local state highway scales really give me a fit but when clear of them and over on I-95 or I-70 I am green lighted 99% of time as those scale guys know their exemptions.

I and others have met with Maryland legislators about the book not including our private under 10,000 GVW car trailer exemption but to no avail.

Robert

Edited by Robert Street (see edit history)
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