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2001 7700 gear change

 
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Old 04-15-2019, 09:21 PM
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2001 7700 gear change

I am acquiring my dad's 2 wheel drive 2001 f150 7700 and his 2001 5th wheel trailer . It is in mint condition with 160000 km. I want to change the gears from 373 to 430. I am having a hard time finding a place that can calibrate the speedometer. I,m in Edmonton Aberta.
 
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Old 04-15-2019, 10:13 PM
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You don't need to calibrate anything unless you change the diameter of the rear tires.
 
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Old 04-16-2019, 05:18 PM
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As long as the drive shaft changes the revolutions per minute, whether it's a tire size change or a gear ratio change, the speedo will have to compensate for the change in rev's.
 
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Old 04-16-2019, 05:43 PM
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The calibration is done in the PCM Id word block, not in the dash or anywhere else, ...unless the speedo is cable driven.
You better look at your owner manual for the equipage of the trucks and the Gross Combined Weight rating of each.
Then weigh both the truck and the trailer loaded as you would use them.
If the total weight of the truck and trailer comes up greater than the GCWR for either truck, your over loaded.
A 4;30 gear does not make up for 'all' the difference.
Good luck.
 
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Old 04-16-2019, 09:21 PM
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Originally Posted by rtpalin View Post
As long as the drive shaft changes the revolutions per minute, whether it's a tire size change or a gear ratio change, the speedo will have to compensate for the change in rev's.
That would be relevant if the sensor was on the driveshaft, but instead it is on the differential housing and reads axle rotations which will not change unless the tire height is changed from the original Ford value for the stock size tires.
 
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Old 04-17-2019, 09:44 PM
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So Sam I Am are saying that it does matter what gear ratio I have in the rear diff the will always be correct.

Rick
 
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Old 04-18-2019, 01:02 PM
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Unless you change tire size, changing rear gear ratio will not change speedometer reading.
 
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Old 04-18-2019, 01:11 PM
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Originally Posted by Sam I Am View Post
Unless you change tire size, changing rear gear ratio will not change speedometer reading.
Completely incorrect information. The sensor is reading the tone ring not the ring gear. You need to calibrate for gear changes and tire sizes. That's why there is a line item and source code for this programming.
 
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Old 04-18-2019, 06:59 PM
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Originally Posted by ford390gashog View Post
Completely incorrect information. The sensor is reading the tone ring not the ring gear. You need to calibrate for gear changes and tire sizes. That's why there is a line item and source code for this programming.
You're wrong.
The PCM is fed a value of rotations of the wheel/tire/axle/tone ring/etc. for the speedometer information which will not change unless the tire height changes.
It is all bolted together and all turns the same # of degrees in a revolution, not sure what it is about that you are misunderstanding.
 
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Old 04-18-2019, 09:36 PM
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The speedometer reads off of the tone ring in the rear axle. The tone ring is bolted to the carrier that only rotates once per tire revolution regardless of what you gear ratio is. Changing gears doesn't affect the speedometer, only tire size does.
 
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Old 04-18-2019, 11:32 PM
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Originally Posted by 00t444e View Post
The speedometer reads off of the tone ring in the rear axle. The tone ring is bolted to the carrier that only rotates once per tire revolution regardless of what you gear ratio is. Changing gears doesn't affect the speedometer, only tire size does.
Right, I think that you may have explained it better than I did.
On previous trucks not of this generation, the cable driven speedometer which these trucks do not have was driven off a gear on the output shaft of the transmission linked 1:1 with the driveshaft. This speedometer gear spun a cable to turn the speedometer gauge mechanically. On this type system, anything that altered the distance covered per driveshaft rotation would alter the speedometer reading, such as gear change or tire height change.

But like I tried to explain, this generation of trucks (we are posting in the 97-03 F150 section) Uses a sensor in the axle housing to count rotations electronically. This signal is fed through the PCM and then to the speedometer gauge electronically then translated to needle motion at the gauge by small cowboy wizards that only speak Portuguese.

Since the tone ring that the sensor reads turns at the same RPM as the tire/wheel/axle/etc. the driveshaft is now out of the equation, gear ratio is irrelevant, and the only common change that will affect the speedometer reading on the truck that is the subject of this post is the tire height.
If you keep the same height tires you do not need to alter any PCM programming.
Gear it 4.30, Gear it 5.38, gear it whatever you want and send it.
 
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Old 04-19-2019, 02:20 PM
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Thank you all for the information. As for the trailer and truck, I have bought it from my dad who has been towing the trailer with this truck for almost 18 years. The truck hitched up weighs 6650 lbs and the trailer weighs 7450. I have never been able to a GCVW for the 2001 F150 7700.
 
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Old 04-19-2019, 10:08 PM
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Sam........... how many different model years does that cover ? Did they change something it 2004 or 2009 ?
 
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Old 04-19-2019, 11:42 PM
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This reply is not intended to debate the question of gross towing weight.
In the 2001 owner manual pages 176 -178 shows the highest gross weight as 13,500 lbs. for 3.73 equipped trucks with 5.4L motor that likely had a 4r100 transmission.
The rest of the equipage combinations are in 11,500 to 13,000.
Changing rear gear to a lower ratio helps but that's not all there is to engineering a truck for safe towing.
The weights you give is already at 14,000 GCW..
Just to make you a where there are safe engineered ratings no matter what your dad did. He may have not known or chose to ignore it.
It's up to you to decide based on info for your trucks equipage.
.
On speedo indications, on some vehicles the speed sensor at the rear might count the ring gear teeth passing by it . If that is the method, changing gears changes the number of teeth counted thus changes the speed indication.
If a timing tooth wheel is used and timing count remains the same no matter what ratio, then yes the tire size is the only factor..
With an electronic dash, the computer 'drives the speedo with 'derived' pulses.
This data signal is set in the program software Id Block that has all the other build data for that truck. It is adjustable by a dealer if they know or will change it for you..
The changes to this method was in a time when more data control of functions was being added for the future.
On my 02, the speedo reading is 2mph fast from the factory, not that it matters that much. Truck is approaching 299,000 miles.
Good luck..
 

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