RPMs going 65-70
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Laughing Gas
Joined: Jan 2023
Posts: 1,172
Likes: 114
RPMs going 65-70
I have a 88 f150. It’s a 302 paired to a AOD. It’s got a 3.55 rear end. It’s running 2200 rpm going down the freeway at 65-70. I thought with that setup it was supposed to be 1500-1800?
It’s also got 31x10.5r15 tires.
It’s also got 31x10.5r15 tires.
Tuned
Joined: Dec 2005
Posts: 400
Likes: 57
From: Saskatchewan
The oversize tires should lower the RPM's from stock size. You can do some math and calculate the RPM based on gearing and tire circumference. Research the trans to find out the ratios for each gear and calculate the RPM's you should turn for whatever speed you want.
Logistics Pro
Joined: Nov 2013
Posts: 3,928
Likes: 1,198
From: Mojave, Ca
That is high. Perhaps a previous owner swapped the rear end or the rear end gears. Crawl under your truck and try to read the stamped metal tag bolted to the differential cover. It should say something like 3 55 or 3L55 if it's limited slip. I bet it's say 4 10 thou.
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Laughing Gas
Joined: Jan 2023
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The calculation for that is the attached photo of the calculator. I did 265 tire that’s what Google said was the equivalent of 31”. But if I do it with 4:10 gears it says 1500. The tach is accurate at idle.
So I’m confused with it being 2200. But I’ve counted the shifts and it reaches overdrive.
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Logistics Pro
Joined: Aug 2010
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From: Chillicothe
These seem low to me, but i have the five speed ro my rpms are higher anyway since the od isnt as deep.
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Logistics Pro
Joined: Aug 2010
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From: Chillicothe
So either it really isnt gettin to 4th and maybe you are feeling the converter lock in 3rd and thinking it is reaching 4th Or
Someone put 4.56s in it and your tach is off a fuzz above idle
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Laughing Gas
Joined: Jan 2023
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So, how would I be able to tell if the trans is locking into 3rd or OD? RPMs go down a lot when it goes into “overdrive” if it is OD.
Both of those rpm’s look right wether it is a 4.56 or not shifting. I’m driving so I’m not paying attention to the tach that much, so I could’ve been wrong and it was 2300, and not 2200.
Edit: next time I drive it can I just put it into the second Drive gear without OD and see if it’s acting different. Will it still go into lock up in 3rd? If it has a tag, that’s says 3.55?
Both of those rpm’s look right wether it is a 4.56 or not shifting. I’m driving so I’m not paying attention to the tach that much, so I could’ve been wrong and it was 2300, and not 2200.
Edit: next time I drive it can I just put it into the second Drive gear without OD and see if it’s acting different. Will it still go into lock up in 3rd? If it has a tag, that’s says 3.55?
Lead Driver
Joined: Sep 2002
Posts: 9,540
Likes: 2,032
From: North Texas
If TV cable too tight, it may not shift into OD. Also, it has mechanical lock for converter when stock. You can run an open converter in them too. Too many unknowns with your current combo.
My 302/AOD with a 4.10:1 and 275/60R15 does about 2300rpm last I recall.
Stock gauges are not super accurate.
Pop diff cover and count what is in there when you have free time.
My 302/AOD with a 4.10:1 and 275/60R15 does about 2300rpm last I recall.
Stock gauges are not super accurate.
Pop diff cover and count what is in there when you have free time.
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Laughing Gas
Joined: Jan 2023
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I got some, what does it take to do that?
I was belong someone doing their 84 Chevy I believe. He had to take some c clip things out and take the whole brake drum assembly off. But that was a Chevy and he was doing a disc brake conversion.
It’s got axle code 19 in the door.
I was belong someone doing their 84 Chevy I believe. He had to take some c clip things out and take the whole brake drum assembly off. But that was a Chevy and he was doing a disc brake conversion.
It’s got axle code 19 in the door.