Safe highway cruising speed
Lead Driver
Joined: Oct 2018
Posts: 7,893
Likes: 2,371
The 400 was not a great engine but if you rebuilt it half decent you should be able to drive it any legal speed with no issues at all. holding it at 3500 all day should be no problem.
You won't find in the owners manual where gear ratio it gives you a top speed limit . just drive. I'd worry more about poor handling than anything else, fuel economy wasn't the only reason the speed limit was 55 safety had a lot to do with it and they were right.
You won't find in the owners manual where gear ratio it gives you a top speed limit . just drive. I'd worry more about poor handling than anything else, fuel economy wasn't the only reason the speed limit was 55 safety had a lot to do with it and they were right.
Thread Starter
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Mountain Pass
Joined: Jul 2017
Posts: 229
Likes: 27
Ok, got home. My tires are 265/75R16. Which by the Google conversion chart=31.6"
https://photos.app.goo.gl/ULKisXjyQqKNVYCS8
Here is a picture of my door tag--https://photos.app.goo.gl/9tYVbLzJPYfVAqVe8
If I am reading it correctly, it is a 23 axle (per the above link)=3.31 ratio
https://photos.app.goo.gl/ULKisXjyQqKNVYCS8
Here is a picture of my door tag--https://photos.app.goo.gl/9tYVbLzJPYfVAqVe8
If I am reading it correctly, it is a 23 axle (per the above link)=3.31 ratio
More Turbo
Joined: Feb 2021
Posts: 525
Likes: 84
So I have a conundrum - are 3.73 gears something that was offered in Ford 9" third members? My 75 F100 has that, according to the PO and in 4th at around 2500 RPM, I am at 63 MPH which seems to indicate I have 3.73 gears... Obviously I'd need to lift it up and do the chalk on tire vs chalk on driveshaft to be certain (wont happen for a while though) but figured I'd poke around...
Laughing Gas
Joined: Feb 2011
Posts: 996
Likes: 318
Based on numbers looks like you'd be around 2500 RPM at 70 but someone else can confirm. I personally would try to keep it around 65 on an interstate but 70 shouldn't be any problem. On todays highways though going 65 in the slow lane is too slow for most other drivers. Good luck! Sounds like a nice trip
https://spicerparts.com/calculators/...rpm-calculator
https://spicerparts.com/calculators/...rpm-calculator
Mountain Pass
Joined: Apr 2021
Posts: 140
Likes: 12
From: Bay Area
Based on numbers looks like you'd be around 2500 RPM at 70 but someone else can confirm. I personally would try to keep it around 65 on an interstate but 70 shouldn't be any problem. On todays highways though going 65 in the slow lane is too slow for most other drivers. Good luck! Sounds like a nice trip
https://spicerparts.com/calculators/...rpm-calculator
https://spicerparts.com/calculators/...rpm-calculator
Hi @Mark8man,
is your 77 came with ac from factory? if the answers is yes can you please send me a picture of the crankshaft pulley, my truck is missing the A/C crankshaft pulley.
Thank you,
New User
Joined: Mar 2021
Posts: 7
Likes: 0
So I have a conundrum - are 3.73 gears something that was offered in Ford 9" third members? My 75 F100 has that, according to the PO and in 4th at around 2500 RPM, I am at 63 MPH which seems to indicate I have 3.73 gears... Obviously I'd need to lift it up and do the chalk on tire vs chalk on driveshaft to be certain (wont happen for a while though) but figured I'd poke around...
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Fleet Mechanic
Joined: Sep 2013
Posts: 1,504
Likes: 8
From: Indian Falls, New York
Never. Again. Ever.
There was so much bug splatter that the chrome mirrors were black and it broke both headlight doors and 4 mount points on my grille from wind resistance. Oh and I smoked the wheel bearings out of the front so bad that when I pulled the rotors off the grease was hard and crumbling in my hands.
These trucks will do 80 on the highway just fine as long as its setup so its not screaming high rpms.
Thread Starter
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Mountain Pass
Joined: Jul 2017
Posts: 229
Likes: 27
Based on numbers looks like you'd be around 2500 RPM at 70 but someone else can confirm. I personally would try to keep it around 65 on an interstate but 70 shouldn't be any problem. On todays highways though going 65 in the slow lane is too slow for most other drivers. Good luck! Sounds like a nice trip
https://spicerparts.com/calculators/...rpm-calculator
https://spicerparts.com/calculators/...rpm-calculator
Cross-Country
Joined: Apr 2021
Posts: 67
Likes: 11
From: Dayton, OH
Using this chart and a $40 Tach from Advanced Auto I determined I have 4.10 gears. Handy little chart for sure!ENGINE RPM @ 60 MPH:::::::::::::::::::::::::::::::::::::::::::::::
-----,------------------ TIRE DIAMETER (INCHES) ----------------------
RATIO|.26....27....28....29....30....31....32....3 3....34....35....36....38....40
-----|-----------------------------------------------------------------
2.73 | 2117 2038 1966 1898 1835 1775 1720 1668 1619 1572 1529 1448 1376
2.90 | 2249 2165 2088 2016 1949 1886 1827 1772 1720 1670 1624 1539 1462
3.07 | 2380 2292 2210 2134 2063 1996 1934 1875 1820 1768 1719 1629 1547
3.21 | 2489 2397 2311 2232 2157 2088 2022 1961 1903 1849 1798 1703 1618
3.31 | 2567 2471 2383 2301 2224 2153 2085 2022 1963 1907 1854 1756 1668
3.40 | 2636 2539 2448 2364 2285 2211 2142 2077 2016 1958 1904 1804 1714
3.54 | 2745 2643 2549 2461 2379 2302 2230 2163 2099 2039 1982 1878 1784
3.73 | 2892 2785 2686 2593 2507 2426 2350 2279 2212 2148 2089 1979 1880
3.90 | 3024 2912 2808 2711 2621 2536 2457 2383 2312 2246 2184 2069 1966
4.09 | 3171 3054 2945 2843 2748 2660 2577 2499 2425 2356 2290 2170 2061
4.56 | 3536 3406 3283 3170 3064 2965 2873 2786 2704 2627 2554 2419 2298
4.88 | 3784 3644 3514 3392 3279 3174 3074 2981 2894 2811 2733 2589 2460
5.12 | 3970 3823 3686 3559 3441 3330 3226 3128 3036 2949 2867 2716 2580
-----,------------------ TIRE DIAMETER (INCHES) ----------------------
RATIO|.26....27....28....29....30....31....32....3 3....34....35....36....38....40
-----|-----------------------------------------------------------------
2.73 | 2117 2038 1966 1898 1835 1775 1720 1668 1619 1572 1529 1448 1376
2.90 | 2249 2165 2088 2016 1949 1886 1827 1772 1720 1670 1624 1539 1462
3.07 | 2380 2292 2210 2134 2063 1996 1934 1875 1820 1768 1719 1629 1547
3.21 | 2489 2397 2311 2232 2157 2088 2022 1961 1903 1849 1798 1703 1618
3.31 | 2567 2471 2383 2301 2224 2153 2085 2022 1963 1907 1854 1756 1668
3.40 | 2636 2539 2448 2364 2285 2211 2142 2077 2016 1958 1904 1804 1714
3.54 | 2745 2643 2549 2461 2379 2302 2230 2163 2099 2039 1982 1878 1784
3.73 | 2892 2785 2686 2593 2507 2426 2350 2279 2212 2148 2089 1979 1880
3.90 | 3024 2912 2808 2711 2621 2536 2457 2383 2312 2246 2184 2069 1966
4.09 | 3171 3054 2945 2843 2748 2660 2577 2499 2425 2356 2290 2170 2061
4.56 | 3536 3406 3283 3170 3064 2965 2873 2786 2704 2627 2554 2419 2298
4.88 | 3784 3644 3514 3392 3279 3174 3074 2981 2894 2811 2733 2589 2460
5.12 | 3970 3823 3686 3559 3441 3330 3226 3128 3036 2949 2867 2716 2580
Mountain Pass
Joined: Apr 2021
Posts: 140
Likes: 12
From: Bay Area
Here you give you all an update,
I drove yesterday 250 miles to Bakersfield, I made safe and strong, 65MPH at 3200 RPM, I keep my speed 60 to 65MPH.
This is my first long trip since I Owen this truck.
Question to you all, why is the stick rattle once I reach 55mph, what I was doing is to put pressure to one side to stop the noise.
If anyone can share with me, what should I do to stop that noise.
Thank you you all.
I drove yesterday 250 miles to Bakersfield, I made safe and strong, 65MPH at 3200 RPM, I keep my speed 60 to 65MPH.
This is my first long trip since I Owen this truck.
Question to you all, why is the stick rattle once I reach 55mph, what I was doing is to put pressure to one side to stop the noise.
If anyone can share with me, what should I do to stop that noise.
Thank you you all.