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Old 10-02-2016, 12:42 PM   #1
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8.2 governor question.

I've just bought a 1990 Chevy bus with a DD 8.2 Fuel Pincher. On the 500 mile drive home the bus ran fine, pulled well, and maxed out speed at 40 MPH for the entire 15 hour ride home. Foot to the floor the bus pulls hard until it reaches 40 then its like I took my foot off the pedal. The School district I bought the bus from said they disengaged their governor, as a double certainty I physically ripped the linkage from their governor to the throttle linkage off. I'm thinking that they set the engine governor low. I have ordered a shop manual and its on the way, and I will be looking into a tachometer tomorrow when I finally get off work but my question is this: How do you adjust the max RPM governed speed? I saw a tutorial about the 6v71 motor, but there just isn't much out there about the 8.2. I know the dangers and the need for the tach, but I really think that the bus has something that is keeping it from revving high enough to pull itself on the road. On big down hills it would overspeed up to almost 60 mph, but on flat ground or hills, 40 mph is all it would do. I also understand that its probably geared very low, its a school bus and eventually i will be changing out the rear axle, but for the short term I want to make sure i can at least drive this thing on public roads without being a danger to other motorists!

Also, I want to clarify some terms "no load rpm" "low idle" "High idle" these terms confuse me. In my mind Idle speed is what the engine runs at when your foot is off the pedal. A "high idle" would be a switch or other means to bump the idle speed up a couple hundred rpm for some reason (pto, keep the ac working, or spin the alternator to power a load like emergency lights, winch, etc)

this "no load" stuff makes no sense. At what rpm should i cruise on the interstate at, what is the redline, what is the idle speed. Those are terms i Understand.
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Old 10-02-2016, 01:46 PM   #2
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Good afternoon. I to have an 8.2 Detroit 1986 version and I to can only do 45-49 mph without touching my governors.
I have the at-545 which is another speed issue to a point and my biggest speed restraint is my rear end gearing of 6.50.
A little history of mine with the governor is that the head mechanic at the bus barn told me I could adjust or do away with them/it but I would burn the rear gears up and with the governor's as is Is the 8.2 fuel punchers sweet spot for max longevity.
A little more about what I have figured out along the way.
My 8.2 still has the factory build tags on the valve cover and this is a little of what it says.
Min. Idle RPM-700
Max RPM no load 3050
Max output 170 hp at 3000rpm
No load means there is nothing accepting or looking for output from the engine? Kind of like the engine sitting on a stand in a shop running with no tranny/pto or anything connected or for us the tranny in neutral.
My ideas to get my bus at least to 55mph is to change my 9r20 de mountable tubed rims to 10r22.5 tubeless rims and tire which should get me at least to 50-mph until I find my rear gear replacements?(have been trying for awhile) and I just found some 9r22.5 tubed tires that will save me from finding new rims.
For the rear end I have not found anything comparable to mine for either a total swap or just a differential change or just a ring and pinion change but I try looking all the time?
Gearing sizes I have learned?
I have 6.50 and even though hooked to the fuel pincher I can pull a trailer with a car and no changes (done)
If I change the gears into the 5 range then I gain a little more highway speed but
lose some towing/uphill/pull strength.
If I change into the 4 range then I gain a good bit of highway speed but lose all towing strength and any uphill/pull strength.
All of this is keeping the engine and tranny in its sweet spot.
The sweet spot is where the engine was designed to be to give max life for its intended use.
That's where mine was designed at and my calculations were to keep it there cause most get around 500,000-700,000 if taken care of and mine just hit 200,000 so even though it's underpowered I decided to design around my well maintained power plant instead of the money to replace it?
Some 8.2's were designed for 250hp instead of the fuel pincher 170hp?
If you and your resources can prove that's it's he same block and configuration just a blocker plate or smaller injectors or something like that please let me know.
If that's the case then I need to look more into my at-545 tranny. I already know the heat kills them and at one point I had a gear ratio vs RPM chart from this forum on them? But can't seam to put it in front of me?
Good luck and please post your decisions you make cause I am floating in the same slow boat to travel AMERICA.
I live in NC and the bus is one speed or another going to Texas
If it happens at 49 then I grew up and I always loved the back roads and once I cross that Texas line I know I have no backroad problems
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Old 10-03-2016, 02:33 PM   #3
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Quote:
Originally Posted by Transporter2112 View Post

Also, I want to clarify some terms "no load rpm" "low idle" "High idle" these terms confuse me. In my mind Idle speed is what the engine runs at when your foot is off the pedal. A "high idle" would be a switch or other means to bump the idle speed up a couple hundred rpm for some reason (pto, keep the ac working, or spin the alternator to power a load like emergency lights, winch, etc)

this "no load" stuff makes no sense. At what rpm should i cruise on the interstate at, what is the redline, what is the idle speed. Those are terms i Understand.
No load max rpm= Put your foot to the floor in neutral, AKA redline

Low idle= base idle speed of the engine, anywhere from 600-1000 rpm

High idle= 1.5-2 times as fast as low idle. Used for warm up, faster air build time, to prevent wet stacking, etc.


How fast should your bus run? Depends on what limit you hit first.

1)You could be gear limited, meaning that your final drive ratio is too high and the engine is redlined.

2)You could be governor limited. Meaning there is a speed limiting governor that will kick in keeping you slow.

3)Or you could be power limited. Meaning that the engine isn't making enough power to keep accelerating.

Odds are, it's one of the first two.
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Old 10-04-2016, 05:16 PM   #4
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It is definitely hitting the no load max rpm. The question i have now is: Did the previous owner, Wayne County Schools monkey with the no load max governor. I cannot find the gear ratio of my drive axle so until I get a tachometer I don't know if I'm cruising at 40 mph at 3050 rpm as stated on the valve cover, or if I'm cruising along at 2000 rpm. Either way I am pretty certain that i am running at whatever the max no load rpm is. Any suggestions on tachometers?
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Old 10-04-2016, 09:18 PM   #5
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Update, either the engine governor (no load max) is set low, or there is some other speed governor on the bus. I have used a gearing calculator and come up with some numbers. I know my tire size, transmission final drive ratio and the stated no load max rpm of 3050. Using these numbers if I hit my max speed of 40 mph at 3050 rpm then my rear end ratio is 9.44. I seriously doubt that my bus has a rear end ratio that low. So I need to figure out how to disable any speed governor that the school district installed, or turn the engine governor back to where it belongs. Any thoughts?
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Old 10-04-2016, 09:54 PM   #6
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what I wonder is what transmission you have.. if its an AT545 it should be shifting 3 times... 1-2,2-3,and 3-4 Im wondering if you are never getting into your final gear...

have you looked to find a tag on the transmission?

second thing is to make sure if that transmissio has a shift cable that its not broken, disconnected, or pulled too tight... I know the AT545 doesnt like a broken shift cable.. it will fail to make all of its shifts..

in the worst case you may have a 4th clutch engagement issue... at least i think thats the clutch which needs to grab for 4th gear... someone more versed on the 545 can tell me...

lets play for a moment here..

lets say your calculations came up correct for what you were attemting.. assuming a 545 would be a 1:1 ratio you got 9.44 for a gear ratio..
say that transmission failed to shift to 4th gear and stayed in 3rd.. it has a 1.41 ratio in 3rd..

you would have a 6.69 gear.. still far fetched..

lets say the transmission was really buggered up and stayed in 2nd gear... a 2.25 final ratio..

that gives you a "4.19" gear.. 4.10 maybe?

just throwing ideas out...

-Christopher
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Old 10-05-2016, 12:55 AM   #7
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Good thinking, but I believe my transmission is functioning correctly. I do believe it's the Allison 545 and have counted the shifts. It does indeed shift into 4th gear, no strange noises or slipping noticed. It pulls well until i reach 45 indicated on the speedometer, 40 GPS, then it really feels as if I've let off the throttle. It doesn't slowly loose power like a normal vehicle does when you max it out with a gradual decline of acceleration, it pulls until the governor kicks in. I used to drive over the road tractor trailers for Warner and the trucks were governed at 70 MPH. This feels exactly the same. So either: the school system installed some speed limiting governor that was not properly disconnected when I purchased the bus, or: they turned the mechanical engine governor down to some lower RPM setting and I'm not getting full revs. I've ordered a tach so hopefully it can shed some light.
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Old 10-07-2016, 08:25 AM   #8
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Most likely there is a road speed limiter. It could be attached on the side of the governor, or anywhere where it will intercept your throttle input so it can back it off once it hits 40 mph. Remove the air cleaner and look around. Take some pictures if you have to. Also, check the speed rating on your tires and make sure you don't exceed that.
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Old 10-07-2016, 03:26 PM   #9
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If anyone has a mechanical 8.2 I would love to see a picture of the governor's so that I have a better idea of which one is which and what to adjust/disconnect?
I and my computers still suck at posting pics?
I can takes pics of mine and post in my album but that's about it.
I have several things interconnected with my throttle cable including a homemade plate with a cable extension a couple of springs out to other things and anchor plates but to me it looks like it is mounted on top of an inline butterfly valve for something?
Thanks
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Old 10-23-2016, 11:01 PM   #10
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Year: 1990
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Chassis: Ward?
Engine: 8.2 liter ?
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I have an 8.2 but don't know what a governor looks like.

I have rebuilt many car engines over the years... I know which end of the screwdriver to hold... but I am a greenhorn around diesels. I'm in the middle of a conversion on a 1990 Ward (AmTran) with an 8.2. I can take a couple of pictures but seriously... I don't know what I'm looking at.

Ross
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