Cant get over 45-50 mph
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Elder User
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From: Peoria, Arizona
Cant get over 45-50 mph
Hello all,
I have this 1982 F-100 that I dropped a 302 from an 85 into. I retrofitted duraspark II onto it got a new carb and all in all revamped everything not inside the engine.
My problem is that it has plenty of power in first and good power in second but as soon as I drop it into third I lose almost ALL of the power from the truck. The same but worse in 4th. Its all it can do to maintain speed. Its an RTS tranny from 84 or 85. My father in law vouches that the tranny was fine 6 years ago.
It has to be a gearing problem? Is the engine possibly just a dud?
This is so disheartening. I thought I was done with the thing.
please help
-David
I have this 1982 F-100 that I dropped a 302 from an 85 into. I retrofitted duraspark II onto it got a new carb and all in all revamped everything not inside the engine.
My problem is that it has plenty of power in first and good power in second but as soon as I drop it into third I lose almost ALL of the power from the truck. The same but worse in 4th. Its all it can do to maintain speed. Its an RTS tranny from 84 or 85. My father in law vouches that the tranny was fine 6 years ago.
It has to be a gearing problem? Is the engine possibly just a dud?
This is so disheartening. I thought I was done with the thing.
please help
-David
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From: Virginia
What engine did the truck originally have? What is the rearend code on the door jamb. Have you put a timing light on the engine and revved the engine to see if the timing is advancing?
Also pull the aircleaner off, and after the engine is warmed up, make sure the choke door is fully open.
Also pull the aircleaner off, and after the engine is warmed up, make sure the choke door is fully open.
Post Fiend
Joined: Dec 2007
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From: Lost
I think Franklin is on on the right track here, especially if the F100 had a 300 I6. The low end torque of the 300 allowed it to overcome gearing that is rather tall, where the 302 just can't manage to pull the truck at the same low rpm as the 300 did.
A 300 could easily power a truck down the road with rear gearing in the 2.5:1 range, even with a OD trans, while a 302 will struggle with anything more than 2.75:1 and no OD. Ford tended to use around a 3.50:1 rear gear ratio for a 302 with an OD trans, just so the truck could pull itself down the road.
A 300 could easily power a truck down the road with rear gearing in the 2.5:1 range, even with a OD trans, while a 302 will struggle with anything more than 2.75:1 and no OD. Ford tended to use around a 3.50:1 rear gear ratio for a 302 with an OD trans, just so the truck could pull itself down the road.
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Elder User
Joined: May 2009
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From: Peoria, Arizona
It originally had a 300-6 in it. It did its 260k miles and died honorably.
The door jam says
Axle - 174
and the rear says
DMDC 1k09
47 9 S3225
I will double check my timing and look for the choke door.
Thanks!
The door jam says
Axle - 174
and the rear says
DMDC 1k09
47 9 S3225
I will double check my timing and look for the choke door.
Thanks!
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
Axle code doesn't quite make sense, most are 2 digit codes.
The axle tag has a missing number, but it looks like a 2.47:1. (Bottom line should have a "2" close to the bolt hole)
If that is a 2.47 rear gear, and you have a 4OD manual trans, there's your problem. Even without OD, a 302 will struggle to pull the truck with that tall of a rear gear.
I'd reccomend looking for a 3.25 or 3.50 rear gear to replace the 2.47.
The axle tag has a missing number, but it looks like a 2.47:1. (Bottom line should have a "2" close to the bolt hole)
If that is a 2.47 rear gear, and you have a 4OD manual trans, there's your problem. Even without OD, a 302 will struggle to pull the truck with that tall of a rear gear.
I'd reccomend looking for a 3.25 or 3.50 rear gear to replace the 2.47.
Post Fiend
Joined: Dec 2007
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From: Lost
Assuming it's the 82 F100 in your sig, it likely has a 9". Just for the record, 8.8" has a rear cover that bolts on, while the 9" comes out the front of the housing. Was that tag on the front, or rear of the axle housing?
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Elder User
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From: Peoria, Arizona
It has no rear cover. so it has to be a 9"
Also I had my lady pace me and I'm actually hitting around 65 so... I guess I have to play with the speedo gears as well.
Thanks!
Surfing Ebay now...
Also I had my lady pace me and I'm actually hitting around 65 so... I guess I have to play with the speedo gears as well.
Thanks!
Surfing Ebay now...
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Post Fiend
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From: Lost
I'd hold off on the speedo gears until after the rearend swap. You *might* get lucky and find the rearend ratio that just happens to match the speedo........
65 is pretty decent for a 302 and 2.47. I had a 78 F150 that had a 351M/3spd/2.47, and it would easily run 70 MPH in 2nd gear. Kinda handy, since it wouldn't stay in 3rd....... After I replaced the trans, it would get well over 20 MPG on the highway, unloaded. Loaded, 3rd was *almost* unusable at less than 60 MPH, and the MPG went into the single digit range.........
65 is pretty decent for a 302 and 2.47. I had a 78 F150 that had a 351M/3spd/2.47, and it would easily run 70 MPH in 2nd gear. Kinda handy, since it wouldn't stay in 3rd....... After I replaced the trans, it would get well over 20 MPG on the highway, unloaded. Loaded, 3rd was *almost* unusable at less than 60 MPH, and the MPG went into the single digit range.........
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Elder User
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From: Peoria, Arizona
Do you all know which 9 inch rear ends would fit right into the 82 f100? If I can just find a cheap rear end it will save me the hassle of having to buy and install the gears.
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9 inch rearends are cake to work on. Nothing like being able to remove the entire 3rd member and put it on a bench to work on it. Check Ebay for used gear sets; they pop up on there all the time, and finding used gear sets in good shape for a 9 inch is easier than any other axle out there. I just looked and found a new set of 3.50 gears for $118, and a used set for $50.
None of the junk yards around me have any older trucks at all after the cash for clunkers scam a while back, and it may take you longer to locate an entire axle that has the gears you need instead of just doing a gear swap. If you are dead set on finding the whole thing the most common applications are F-100-250 from 1982 down to the 60's, spring width shouldn't be a problem.
None of the junk yards around me have any older trucks at all after the cash for clunkers scam a while back, and it may take you longer to locate an entire axle that has the gears you need instead of just doing a gear swap. If you are dead set on finding the whole thing the most common applications are F-100-250 from 1982 down to the 60's, spring width shouldn't be a problem.
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From: Virginia
Any early 80's 9 inch will fit of course-the whole unit will fit if you wanted to do that.
All other 9 inch rearend center sections will work IF the spline count on the axles are the same. There was a 28 spline version and a 31 spline version.
If you do find a 28 spline center section, and want to use it, you can get a machine shop to open the hole larger where the axle slips through, and then use your old 31 spline spider gears.
My 80 4x4 was 31 spline. I am not sure what the f100 2wd's were.
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