Tranny shifting
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Junior User
Joined: Jan 2002
Posts: 52
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From: Roseville US
Tranny shifting
I have a 93 Bronco and my (e4od) tranny does not down shift worth crap when trying to pass. I have 36 inch tires and 3.55 gears..Is there a computer chip or some adjustment you cam make to help this problem?
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Tranny shifting
Kemical is right. 3.55's and 36" tires mess with your shift points because the engine never reaches the rpms it needs to, to trigger the sensors in the tranny to downshift. The average small block V8 (302's and 351's) optimum rpm or "power band" is between 2000 and 2800 rpm. You will get different opinions on this point by a few hundred rpms but the fact remains that if your are cruising down the highway at 60-70 mhp and only turning 1300-1500 rpm while it may seem better for fuel mileage, it makes the engine and tranny work harder when the power is needed for things like passing and towing. Since your tires are so much larger in diameter than the stock tires, they are covering a lot more ground with each revolution hence the truck is moving faster at lower engine rpm.
Many lift-kit manufacturers and differential parts suppliers have calculators for correct differential gearing on their websites. Randy's Ring and Pinion has several different calculators. Superlift actually gives you the mathematical formula for figuring this yourself on their site under tech questions or FAQ, can't recall which.
Many lift-kit manufacturers and differential parts suppliers have calculators for correct differential gearing on their websites. Randy's Ring and Pinion has several different calculators. Superlift actually gives you the mathematical formula for figuring this yourself on their site under tech questions or FAQ, can't recall which.
Senior User
Joined: Jul 2001
Posts: 189
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Tranny shifting
My recomendation is that you go with a set of 4.11 gears, and if you really have to a set of 4.30's. I installed a set of 4.56 gears and that was the worst mistake i ever made. The truck ran at 3,000 rpm going 80 on the freeway, gas mileage really sucked, not to mention the high rpms made the truck run hotter on the freeway. Once the gears have been changed then adjust your speedometer to correct the shift points.
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Tranny shifting
[updated:LAST EDITED ON 04-Nov-02 AT 07:31 PM (EST)]Found the mathematics for calculating gears. For non-overdrive transmissions:
MPH x (gear ratio i.e. 3.55) x 336
----------------------------------------------
RPM
For overdrive transmissions:
MPH x (gear ratio) x (overdrive ratio i.e. 0.75) x 336
-----------------------------------------------------------------------
RPM
Plug in the numbers that you know and solve for the variable. I know, I know too much math and Algebra to boot! But you can use this to figure out rpm, gear ratio, tire size, etc. depending on what numbers you already know.
Trucks with overdrive have the added benefit of being able to handle slightly taller gears and still be better off on mpg on the highway because of the overdrive being factored into the equation.
MPH x (gear ratio i.e. 3.55) x 336
----------------------------------------------
RPM
For overdrive transmissions:
MPH x (gear ratio) x (overdrive ratio i.e. 0.75) x 336
-----------------------------------------------------------------------
RPM
Plug in the numbers that you know and solve for the variable. I know, I know too much math and Algebra to boot! But you can use this to figure out rpm, gear ratio, tire size, etc. depending on what numbers you already know.
Trucks with overdrive have the added benefit of being able to handle slightly taller gears and still be better off on mpg on the highway because of the overdrive being factored into the equation.
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
Tranny shifting
The REAL reason the trans doesn't shift right is that it doesn't know the correct speed from the VSS in the rear axle. Anytime you change your tire size, you throw it off a little, but going to 36s
has thrown it for a LOOP!
You need to adjust the "conversion constant" in the Programmable Speedometer/Odometer Module so that it will put out 8000 pulses per mile to all the other accessories that use the vehicle speed input (cruise control, EEC for transmission functions on electronic autos only, 4WABS, and overhead console on '95-6 EB Broncos). There's a mechanical method using the switches on the back http://www.fleet.ford.com/truckbbas/non-html/1997/c40_ps.pdf but it's not accurate to the 2nd decimal like the electronic method. If this link http://bbs.off-road.com/ubbthreads/showflat.php?Cat=&Board=offroadfordbroncolate&Numb er=935351&page=0&view=expanded&sb=5&o=&fpart= isn't allowed, e-mail me & I'll hook you up to a post on the Off-RoadBBS in which I detail the procedure & give all the necessary formulas.
has thrown it for a LOOP! You need to adjust the "conversion constant" in the Programmable Speedometer/Odometer Module so that it will put out 8000 pulses per mile to all the other accessories that use the vehicle speed input (cruise control, EEC for transmission functions on electronic autos only, 4WABS, and overhead console on '95-6 EB Broncos). There's a mechanical method using the switches on the back http://www.fleet.ford.com/truckbbas/non-html/1997/c40_ps.pdf but it's not accurate to the 2nd decimal like the electronic method. If this link http://bbs.off-road.com/ubbthreads/showflat.php?Cat=&Board=offroadfordbroncolate&Numb er=935351&page=0&view=expanded&sb=5&o=&fpart= isn't allowed, e-mail me & I'll hook you up to a post on the Off-RoadBBS in which I detail the procedure & give all the necessary formulas.
Thread Starter
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Junior User
Joined: Jan 2002
Posts: 52
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From: Roseville US
Tranny shifting
I was thinking of swithching out with a friend. He has a f150 with 4.11's a he does not like it so he said he would just switch axles with me Good Idea????
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Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
Tranny shifting
That won't really fix it. You need to reset the PSOM. After that, you might not need to do anything to the axle.
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New User
Joined: Apr 2002
Posts: 17
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Tranny shifting
i forget the name of it but there is a cable conected to your throtle that tells your tranny how to shift. make shure its snug. its an easy adjustment. when it has play your tranny doesnt want to down shift. worth the look.
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