My 68' F100 was powered by a 6 cyl with a 3spd on column. It now has a FE motor of unknown size. (390 rebuild on the way) I am going to go from a T-18 to C6 trans very soon. I am looking for a good gear ratio for a daily driver that will not be used much for heavy loads or towing. What might the original ratio be in a 9" rear? The rear end has no tags and appears original. I plan on rebuilding the rear this fall and am trying to plan for cost.

68' F100 2X4 T235/75R/15 tires

Thanks-Robert

 

John
jowilker@nc.freei.net

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

Rob 68 and John! I’d like to piggy back on this one if I may! I am in the same situation i. e. former 6 cyl with a basically stock Fe of unknown vintage with a C6 and 9 inch. My differential is devoid of tags and the chalk mark on the drive shaft and counting revolutions didn’t help figure out the ratio. I don’t want to pull the differential just now, it ain’t broke and the weather is too hot to work on anything outside. I would change the differential to avoid having to set up gear contact patterns after replacing the ring and pinion. Just easier for me! The truck has 265-75 R15’s on now and seems to pull okay! Engine rpm at 2800 to 3000 keeps me in freeway traffic and no flashing lights in my mirror. The engine has a 4bbc, dual exhaust and I am told also has a “rv” camshaft. I have no clue how fast I am going. I need advice on what size tires/differential ratio/engine rpm would be comfortable at 65 mph for a basically stock FE motor. I rarely drive faster and most of my 60 mile daily round trip commute is on secondary roads. I do like a zippy takeoff but do not want to spin the motor past 3000 rpm at 70 mph. I have read that the C6 can accommodate different internal ratios for first and second gear. This would allow quick takeoff and still maintain a peaceful rpm in high gear. I plan on installing 265-60 R15’s when the current set wears out.
William in Atlanta

 

William, I had some different setups at one time, and kinda determined this:

There were two basic engine offerings in mid sixtys, 240 I6 & 352 V8. I believe the 240 only came with a manual tranny (could be wrong) the 352 both sd & auto. The 352 1/2 ton had a standard 3.25 ratio with the sd, & 3.00 with auto. The 240 had a 3.75

Your truck should pull a 3.00 with no problems at all and a 2.75 for more mpg. You will loose a little pazzase with the 2.75 but empty running you shouldn't have any problems at all.

It may have been Barry that posted a check for rearend ratio, and I believe it was like this.

Jack one wheel off the ground and rotate it one turn and count the turns of the driveshaft. Do the standard wheel chocking for safty sake. :-)

If that isn't correct we'll hear about it.

I was very fortunate to find a member on the list that had a 2.75 gear that he traded for one of my 3.25s for.


John
jowilker@nc.freei.net

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

[FONT COLOR="#0000ff" SIZE="+1" FACE="Veranda"]
I believe Ford Offered many engine/tranny/gearing combos. I can only say with certainty in 67, but it's my understanding for 65 and 66 as well, that the F100/250's came standard with a 240 and you could get an auto with that engine at least in the 2wd's. The standard 67 F100 combo was a 240, 3spd Ford Manual and a 3.70 9" rear gear.

However, Ford had several specific option combo's which could be had in 1967. There were several ratios one could order depending on which engine (240, 300, 352), which tranny and which rear end housing you wanted (9", dana 44 or dana 60). Ford had standard or recommended ratios for each combo. For instance: if you ordered an F100 with the optional 352 equipped with a Ford 9" and the tranny you wanted was either 3-spd Ford, 4-spd Warner T-18 or a Cruise-O-Matic Auto then Ford recommended either 3.25, 3.50 gears). This is not to say that other combos weren't possible.

In reality, what could be had then is all kind of academic now because your truck has whatever it has. Further, when you consider that PO's may have changed it becomes hard to predict what's under the truck now. BTW-the chalk mark method should work for you to determine the ratio. In case anyone is interested, I spent a little time since this afternoon expanding my site to include a some info on "how to determine rear gear ratio." Look under the technical info link on the main page. Feedback always appreciated.
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[FONT COLOR="#ff0000" SIZE="+2" FACE="Bassett"]Stock Man[/FONT]
[FONT COLOR="#0000ff" SIZE="-1" FACE="Tahoma"]
1967 F250 4wd Mini Fire Truck
1967 F-250 FE 390 4wd LWB Styleside
1966 F-250 I6 240 2wd LWB Flareside
http://www.hometown.aol.com/tbeeee

 

>Jack one wheel off the ground
>and rotate it one turn
>and count the turns of
>the driveshaft. Do the standard
>wheel chocking for safty sake.
>:-)
>
>If that isn't correct we'll hear
>about it.
>

I think you have to multiple your answer by 2 using this method. With one wheel up, my shaft turned three times for every two turns of the wheel, exactly. I counted 'em all the way up to 27 and 18. Without the massaging of the numbers that's a 1.50. Think about how a differential works and it makes sense.

Dan Blackwell

 

[FONT COLOR="#0000ff" SIZE="+1" FACE="Veranda"]
Not to be a smart alec, but (1) what ratio is actually in your truck? and (2) do your caluclations "add up" with what the data plate said should be in there for the rear axle ratio?
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[FONT COLOR="#ff0000" SIZE="+2" FACE="Bassett"]Stock Man[/FONT]
[FONT COLOR="#0000ff" SIZE="-1" FACE="Tahoma"]
1967 F250 4wd Mini Fire Truck
1967 F-250 FE 390 4wd LWB Styleside
1966 F-250 I6 240 2wd LWB Flareside
http://www.hometown.aol.com/tbeeee

 

(1) what ratio is
>actually in your truck?
>and (2) do your caluclations
>"add up" with what the
>data plate said should be
>in there for the rear
>axle ratio?
>[/FONT]
>

Stockman, I gotta admit I've done some assuming and the real answer to your question is that I don't know. The door plate lists the axle code as "17" which, according to the table in the Chilton's book I have, wasn't available 'til '69 and which is ID'd as a 3.25. The "07" code that is listed for '67 and '68 is for a 3.00. I've looked high and low for a tag on the case but it just isn't there. DB

 

[FONT COLOR="#0000ff" SIZE="+1" FACE="Veranda"]
A code "17" (sounds like cop lingo) between 1966/69 was the 3.25 to 1 ratio Ford 9". I see you counted carefully when you checked so I don't doubt your results. Absent an error from the factory, I'd have to say that the rear gear was probably changed in your truck. There is really no way to know for sure without taking things apart (and even then you may not learn anything more). Did the speedo read accurately before you performed the tranny swap?[/FONT]

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[FONT COLOR="#ff0000" SIZE="+2" FACE="Bassett"]Stock Man[/FONT]
[FONT COLOR="#0000ff" SIZE="-1" FACE="Tahoma"]
1967 F250 4wd Mini Fire Truck
1967 F-250 FE 390 4wd LWB Styleside
1966 F-250 I6 240 2wd LWB Flareside
http://www.hometown.aol.com/tbeeee

 

Can't really say about the speedo before my tranny swap. I usually ran around 60 on the "I" going to work and kept up with some traffic. A few more eased around me and some shot past like bullets so I always figured it was close.

I'm going to get a new rear end next Sat, supposed to be a 2.75. I can choose one from a '80 or one from a '76. The guy says he has in his "notebook" that either one will work on a '67-'72. Anyway, I may take mine apart after I swap 'em out. Never having done that before, I'll learn something. I don't know if I'll find out the ratio, but I'll definitely learn something. DB

 

[FONT COLOR="#0000ff" SIZE="+1" FACE="Veranda"]
Excellent! You can be a case-study for us all. Before the drop the rear end, try the estimation method one more time, only this time do it once your method and then once the way I suggest on my page. When you take it apart, just count the teeth on both gears and divide the number of ring gear teeth by the number of pinion gear teeth and you'll have your ratio. I will be curious as to your findings.
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[FONT COLOR="#ff0000" SIZE="+2" FACE="Bassett"]Stock Man[/FONT]
[FONT COLOR="#0000ff" SIZE="-1" FACE="Tahoma"]
1967 F250 4wd Mini Fire Truck
1967 F-250 FE 390 4wd LWB Styleside
1966 F-250 I6 240 2wd LWB Flareside
http://www.hometown.aol.com/tbeeee

 

>I believe Ford Offered many engine/tranny/gearing combos. I can only say with certainty in 67, but it's my understanding for 65 and 66 as well, that the F100/250's came standard with a 240 and you could get an auto with that engine at least in the 2wd's. The standard 67 F100 combo was a 240, 3spd Ford Manual and a 3.70 9" rear gear.
>
>

Thom, maybe I need to clean up my wording a little too. I ment to imply that the most common combos were I-6 with straight drive, 3.75 rears and 352 for the V-8 and again mostly with sd, with 3.25 and a few Autos with 3.00.

I had my two trucks, one a sd, the other an auto, plus some donors and put together my thoughts from what I gleaned there, and what made sense in my mind. The 3.25 was a base line rear, but because of the auto structor a 3.00 was used. The I-6 with less ability had the 3.75 to compensate.

Then you have the other combo's to factor in. I did think it was interesting that your source listed the rear at 3.70 and I had a tag with 3.75. There couldn't have been much difference in the two unless your refference is not a 9 in.

Giveing you something to chew on while the pastors message is sinking in today. ;-)


John
jowilker@nc.freei.net

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

[FONT COLOR="#0000ff" SIZE="+1" FACE="Veranda"]
I have a few ford publications which were my source, but remember, I was only being specific to 67. It all gets confusing because yu have to consider which engine, tranny and diff. housing. Interesting is the fact that the 2.75 or the 3.00 aren't even on the menu in 67 according to one of my sources. However, I do see 3.00 gears in the parts manual as being available in trucks equipped with a Ford 9" for each year from 65 through 72. 3.00 seems to be the tallest gear factory installed in the trucks. I'm curious what the model number was on the tag that showed 3.75. I didn't see that one, but I recall a 3.73 available for both teh Dana 60 and 44. More fat to chew.
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[FONT COLOR="#ff0000" SIZE="+2" FACE="Bassett"]Stock Man[/FONT]
[FONT COLOR="#0000ff" SIZE="-1" FACE="Tahoma"]
1967 F250 4wd Mini Fire Truck
1967 F-250 FE 390 4wd LWB Styleside
1966 F-250 I6 240 2wd LWB Flareside
http://www.hometown.aol.com/tbeeee

 

>then once
>the way I suggest on
>my page.

Wife let it roll down the driveway while I counted. Two complete turns of the wheels (valve stem at the bottom) with exactly six revs of the shaft (piece of tape facing straight towards me). Dad never told me anything about having the rear end swapped out before, but it wouldn't be a real big surprise if he had. Anyway, this one's a 3.00.

DB

 

Dan which engine and tranny is this behind.

I am gonna guess FE & auto.


John
jowilker@nc.freei.net

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.