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desertjoe 
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 Topic: Allison trans to a short deck 454 BBC,,,?
Posted: 06 Jan 2024 at 8:47am |
I recently aquired a tall deck 427 BBC with an Allison transmission that came out of a 2003 School bus with only 60K miles. The compression checked out from 145 to 155, I had plans for this BBC but it being a tall deck doesn't lend itself to my plans,,BUT I am interested in doing a change over of the Allison into my 1988 GMC C3500 with the 454 BBC short deck that currently has a T400 that "May" be needing some help inside,,?? Does anyone know if GM ever put the allison behind the short deck BBC and would it entail a difficult changeover?
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Codger
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Posted: 06 Jan 2024 at 8:57am |
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All of the tall deck engines I've seen have an SAE flywheel housing adapter on them. The low deck blocks have the Chevy pattern cast into them. There are companies that make adapters out there to change from one to the other, but I don't know about the flywheel/torque converter setup as have never been involved.
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DaveKamp
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Posted: 06 Jan 2024 at 9:11pm |
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Which Allison, Joe? Many of the school bus Allisons were the 545... if so, you might be better to look for a 4L80E...
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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SteveM C/IL
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Posted: 06 Jan 2024 at 10:14pm |
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the back of the blocks should be the same. If allison has an adapter no reason it can't switch to the std block
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Coke-in-MN
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Posted: 07 Jan 2024 at 1:18am |
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Was driving a Ford with a small CAT engine and Allison 5 speed - problem is no one works on those any more . Ford dealer said no one of their mechanics could work on it and they did not have test gauges or knowledge on it . Finally one old mechanic who only worked a few days a week said he could look at it as it was upshifting to quick - he got it about right but he said it was luck not knowledge that made it better .
Now it's if it can't be hooked to computer , no one knows how to fix it .
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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desertjoe
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Posted: 07 Jan 2024 at 9:48am |
Hey Coke,,you do have a point there,!!After I retired from the Refinery, I was offered a position at the local Chevrolet Dealer and now remember an issue with there NOT being a Technician that knew anything about an Alison trans in a school bus Nor the equipment to analyize the issues with the trans, The School System had to trailer that big old bus all the way to Alburquerque for the repairs!
Hey Dave Kamp,,From what little I know about the 4L60E or the 4L80E,, I have read the 4L80E is heavier Duty of the two. I'm curious about the final gear ratio in the 4L80E and WHO supplies the electrical adapters for use on my 1988 GMC?
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DaveKamp
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Posted: 07 Jan 2024 at 8:46pm |
4 = 3spd with overdrive L = Longitudinal (not transverse) driveline 80 = GVWR class 18,000lbs E= Electronic controls
4L60E is rated for 6000lb GVWR class.
The 4L80 is the successor to the TH400, just has an additional overdrive ratio.
The 4L80E has a brother called the 4L85E, which is rated to 690ft-lbs input, and GVWR of up to 18,000lbs
Shift pattern on all is same. You have a 1-2 solenoid, and a 3-4 solenoid. 1-2 3-4
1st on off 2.48:1
2nd off off 1.48:1
3rd off on 1:1
4th on on 0.75:1
making an adaptation isn't a big deal. What trans is in your '88?
Here's a stand-along dude:
Edited by DaveKamp - 07 Jan 2024 at 8:55pm
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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desertjoe
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Posted: 07 Jan 2024 at 9:34pm |
Hey Dave Kamp,,the trans in the 88 GMC is a TH400 which is in itself plenty Stout enough behind the Big Brutus 454,,but I noticed a time or two that it tends to hesitate a little before it engages at first start,,,after that it operates as suppossed to and shifts solidly from the 1st to 2nd and 2nd to 3rd. I would love to have the 4L80 for its overdrive for some relief on the gasoline consumption that I'm told will be of great concern,,,, 
Was going to check out that link you sent but it would not open,,,,
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Coke-in-MN
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Posted: 07 Jan 2024 at 11:41pm |
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Have the 4L80 in my 2000 GMC 3/4 ton PU - has the tow/haul feature with electric lockout on shifter (push button in end of lever) , when hauling skid loader on trailer used it and or when camper on truck and headwind or hills .
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Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something.
"Challenges are what make life interesting; overcoming them is what makes life meaningful."
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DMiller
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Posted: 08 Jan 2024 at 5:33am |
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If set a 545 next to a T400 the similarities will be stark and showing as are the same family.
Problems as noted is few to any shops rebuilding these anymore and the truck trans output is wrong spline wrong u-joint for lighter equipment.
I second the 4L80E but requires a processor, a speed and throttle position sensor and various other small parts to make work. That and the converter is a lockup type.
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DMiller
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Posted: 09 Jan 2024 at 5:14am |
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Most common issue on a T400 is the modulator, bad vacuum from the engine, bad line allowing lower value, ruptured diaphragm, stuck plunger from sitting.
Those transmissions were pretty well bulletproof. Converters would fail first or leaks would cook them.
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desertjoe
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Posted: 09 Jan 2024 at 8:36am |
Well, DMiller,,I agree with you on the TH400 as GM has chosen to use it for all sorts of their heavy haulers as well as their dedicated High Performance vehicles like the COPO Camaros and others still use the TH400. The TH400 in the one ton has been setting for some time and most likely needs oil and filter change as well as new modulator and possibly a new vacuum supply line,,,for starters...  ,,,,maybe an overdrive,,,? 
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Codger
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Posted: 09 Jan 2024 at 8:58am |
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Put a gear vendors on the truck and be done with it. No complicated anything but require driveline work one time. Use the overdrive when needed only and they install easily.Seen a lot of GVW with them in use and they seem to hold up quite well. Available used often too.
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