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Old 01-02-2013, 10:00 PM   #1
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Cat 3126 governor

Does anybody know how to get rid of the governor on a Cat 3126 engine. The bus seems to not have enough power, and it tops out at 55-60 mph. I talked to a bus driver, and he said that they have governors on them.
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Old 01-03-2013, 10:41 AM   #2
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Re: Cat 3126 governor

You should be looking more at your rpm's and rear gear ratio. Where are the rpm's when it tops out?
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Old 01-11-2013, 08:40 PM   #3
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Re: Cat 3126 governor

I have no idea what the RPMs are, my dad drove it home cause he has a CDL A. He said he had it to the floor, and it topped out at like 55 mph. Is there anyway to make it go any faster. I would like to go at least 65, to go the speed limit on the interstate. I thought about changing the rear gear ratio, but thats expensive and time consuming.
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Old 01-11-2013, 08:52 PM   #4
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Re: Cat 3126 governor

A wild guess, the answer is no. Its more than likely governing out at its specified rpm, which is what you want. I cant suggest anything until you find out what rpm its turning at top speed...sorry.
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Old 01-11-2013, 10:26 PM   #5
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Re: Cat 3126

The Cat 3126 engine is not a very powerful engine and does not make high horsepower. The govenor is to control engine operating conditions to about 2250 RPM. The top speed is determined by the rear axle gears. The higher the ratio, the lower the top speed. To determine the rear axle ratio, raise one side of the bus so the wheel may be turned. The park brake needs to be released so the wheel can be turned. With a chalk or marker, place a mark on the raised wheel pointing at the earth under wheel. Make another mark on the driveline about 6 inches long near the rear ujoint, horizonal. Turn the raised wheel slowly while watching the driveline mark. When the wheel makes a single revolution, the driveline turns should be remembered.
Many buses and trucks have a 5:1 gear ratio. A good ratio for hiways is 3:73 down to 4:10. Most rear gears can be changed to satisfy any application.... Frank
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Old 01-11-2013, 10:51 PM   #6
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Re: Cat 3126 governor

How much would it cost to change the rear end ratio. I know that it wont be cheep. Also would it be possible to do it on my own, or should i take it somewhere to have it done. Would a programer such as this one from TS performance be a good upgrade? http://www.tsperformance.com/MPHD_tuck.html
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Old 01-12-2013, 08:53 AM   #7
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Re: Cat 3126 governor

The 3126 is an electronically controlled engine. It can have a vehicle speed governor programmed into it. The only way to know for sure is to take it to a Cat service center and have them hook it to a computer and look.
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Old 01-13-2013, 06:53 PM   #8
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Re: Cat 3126

Quote:
Originally Posted by frank-id
The Cat 3126 engine is not a very powerful engine and does not make high horsepower. The govenor is to control engine operating conditions to about 2250 RPM. The top speed is determined by the rear axle gears. The higher the ratio, the lower the top speed. To determine the rear axle ratio, raise one side of the bus so the wheel may be turned. The park brake needs to be released so the wheel can be turned. With a chalk or marker, place a mark on the raised wheel pointing at the earth under wheel. Make another mark on the driveline about 6 inches long near the rear ujoint, horizonal. Turn the raised wheel slowly while watching the driveline mark. When the wheel makes a single revolution, the driveline turns should be remembered.
Many buses and trucks have a 5:1 gear ratio. A good ratio for hiways is 3:73 down to 4:10. Most rear gears can be changed to satisfy any application.... Frank
I have seen 7.2 Cats running 330HP in RV's and 275 in trucks. The one I drive every day is 250HP, power peak is 2200, governor is 2600. A 7.2 Cat with no OD trans and fullsized 22.5" truck tires wants a 4.11 axle gear...maybe 4.30's if it's really low-power.
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Old 01-15-2013, 04:41 AM   #9
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Re: Cat 3126 governor

agree with last post.
axle or pot should be changed out is my guess as many of the newer ones are geared to go no more than 60 mph. If bus is a pusher, conventional axle can be installed if flipped and plug holes changed...
My 3208 Cat is underpowered in the rocky mountains, esp when full of car parts and towing box trailer with same...
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Old 02-20-2013, 08:10 PM   #10
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Re: Cat 3126 governor

Quote:
Originally Posted by superdad
The 3126 is an electronically controlled engine. It can have a vehicle speed governor programmed into it. The only way to know for sure is to take it to a Cat service center and have them hook it to a computer and look.
I spoke to the head maintenance guy at the nc school bus supply today, and state law in nc is that all school buses be governed at 45mph. He said to bypass this take it to CAT to be reprogrammed as stated above. I'd lose my mind going 45 everywhere lol
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Old 02-21-2013, 01:09 AM   #11
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Re: Cat 3126 governor

Quote:
Originally Posted by richlindquist
Quote:
Originally Posted by inkblots84
I. poke to the head maintenance guy at the nc school bus supply today, and state law in nc is that all school buses be governed at 45mph. He said to bypass this take it to CAT to be reprogrammed as stated above. I'd lose my mind going 45 everywhere lol
This surprised me, so I had to look it up, what do you know it really is the law! You would think that the people they trust with the safety of their children would be able to understand a speedometer.

Rich
You must not have done much driving in nc.. I am not surprised at all! People here (in the RDU area anyway) drive crazy.. And stupid. And if it rains? All hell breaks loose!! Snow? Forget it. I love to drive in the snow (I'm originally a new englander) but I won't step foot into that mess here

Just a side note, bus guy also said the cats are notorious for leaking oil. Supposedly they pretty much all do to some degree (they don't have blue birds here), but cats can be the worst. According to him they were originally designed for large marine use like yachts, but reconfigured for buses which I thought was pretty neat.
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Old 02-22-2013, 03:43 PM   #12
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Re: Cat 3126 governor

I found an online service manual, and the speed is limited when the bus is bought, and all it takes it to take it to a Cat dealer and they can reprogram the max speed for $50. It seems totally worth to me.
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Old 08-04-2015, 02:34 PM   #13
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I found an online service manual, and the speed is limited when the bus is bought, and all it takes it to take it to a Cat dealer and they can reprogram the max speed for $50. It seems totally worth to me.
Sorry to bring a thread back from the dead. I have a 3126 bus that also wont go over 55-60mph, did you have any luck at the CAT dealer making it go faster?
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Old 08-08-2015, 11:43 AM   #14
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Sorry to bring a thread back from the dead. I have a 3126 bus that also wont go over 55-60mph, did you have any luck at the CAT dealer making it go faster?

That member hasn't been on here for over a year.
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Old 08-08-2015, 12:20 PM   #15
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Sorry to bring a thread back from the dead. I have a 3126 bus that also wont go over 55-60mph, did you have any luck at the CAT dealer making it go faster?
Porkchopsandwiches wrote Allison a very nice letter requesting permission to have 6th unlocked on his MD3060, explaining why he wanted it, etc. If your 3126 has an electronic Allison, contact them.

But, remember you *are* driving a school bus sold at the end of it's useful life, and its not an MCI or Eagle motorcoach.

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Old 08-08-2015, 01:28 PM   #16
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Bottom line, buses don't need to go over 60mh.

More power for hill climbing is a different story.

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Old 07-22-2016, 12:58 PM   #17
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I could only hit 65 mph on the ride home with my purchase. It seemed that if I kept the hammer down it would overheat and I would have to was it back to 55 for the light to go out.
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Old 03-19-2017, 01:50 AM   #18
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Thumbs up

I sure am glad people on these forums don't get their panties in wads over non-issues like "necrobumping".

It's good to be part of the 3126 club. Mine's the "e" (electronic) version and hooked up to an Allison MD3060. The previous owner passed on his immaculate service records, which contain an entry from a non-CAT technician (if I remember correctly) that reads "6th gear unlocked". To perform this change, I believe nothing more is necessary than proprietary CAT software and a connector. You could probably have it done for free, when having other maintenance done by someone familiar with the CAT software.

With the seats in, I reach 75 mph on flat roads and Indiana-grade inclines.
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Old 08-25-2018, 04:51 PM   #19
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long resurection.. I just bought a .. 2003 Freightliner FS65 wiht a CAT 3126 behind an Allison 2500 PTS transmission. wont go back and pick it up for a couple weeks though. I do have my CDL btw.. I drive school bus in Wisconsin Ironically.
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Old 05-18-2020, 08:00 PM   #20
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Hello friends! I am Dylan Galicia I have a 2001 Thomas Saf-T-Liner school bus with CAT 3126 7.2 engine with Allison MD3060 transmission I bought it in NC a year ago and traveled from there to Guatemala, C.A almost 3,0048 miles, without any problem. After introducing myself I want to help with the issue of the maximum speed provided by this vehicle: indeed you can only go 55 mph with 5 speeds, if you want to go faster you must enter the ECM through special equipment for this. I did it and I was able to go at 65 mph, it is very dangerous for your safety and those who travel with you, for the engine and transmission as well. The reason for the risk in the engine is that CAT maintains a maximum of 2640 rpm so bringing the vehicle to 65 mph is being at the limit of engine turns; The transmission also suffers from this situation, not to mention that diesel consumption is excessive, plus the premature wear of all engine and transmission components. I reprogrammed the speed to 55 mph again because in my country you have many mountains and extreme roads in which you can circulate calmly at 55 mph (flat road) at most. This is not to discourage you, I am going to share the knowledge that the person who sold me the school bus changed me: He said that the Allison 3060 transmission (If you have this transmission this information can be useful) of 5 speeds can be programmed to have 6 speeds in any Allison agency or if you know someone who has access to the code to unlock this speed and who has the tool to carry out the programming. With this procedure you can go to 65 mph below the maximum limit of the engine rpm, you save or maintain the consumption of the vehicle and you do not demand more work from the engine and transmission, that if you and those who accompany you are at risk of having an unfortunate accident. I hope my contribution will be of help to everyone.

Kind regards from Guatemala, C.A.

Dylan Galicia.
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