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Doesn't mean anything about the ratio or type of differential inside that 9-inch 3rd member. The alpha-numerics are simply engineering casting numbers and dates when the case and the pinion support housings were cast.
Originally, there would have been a tag affixed to one of the (10) studs that holds the 3rd member to the rear end housing. This tag would have contained the information about the differential type and the gear ratio. If the tag is missing, it means someone has removed the 3rd member from the housing at one time but, didn't bother to put the tag back on before tightening all (10) of the nuts.
The only sure way to know what differential type is there and what ratio it is would be to remove the 3rd member and visually identify what's in there.
If you do take the 3rd member out but don't know an open (single track) differential from a Traction-Lok, you can post a photo of it and I can identify what it is.
As far as determining the ratio, all you have to do is count the number of ring gear teeth and the number of pinion gear teeth. Divide the number of ring gear teeth by the number of pinion gear teeth and that will give you its exact ratio --none of this lift up the rear end, count the number of driveshaft revolutions vs. wheel/tire revolutions. That method can easily be inaccurate. Actually counting ring & and pinion teeth is fool-proof with no margin of error or guessing and the result will be exact.
Doesn't mean anything about the ratio or type of differential inside that 9-inch 3rd member. The alpha-numerics are simply engineering casting numbers and dates when the case and the pinion support housings were cast.
Originally, there would have been a tag affixed to one of the (10) studs that holds the 3rd member to the rear end housing. This tag would have contained the information about the differential type and the gear ratio. If the tag is missing, it means someone has removed the 3rd member from the housing at one time but, didn't bother to put the tag back on before tightening all (10) of the nuts.
The only sure way to know what differential type is there and what ratio it is would be to remove the 3rd member and visually identify what's in there.
If you do take the 3rd member out but don't know an open (single track) differential from a Traction-Lok, you can post a photo of it and I can identify what it is.
As far as determining the ratio, all you have to do is count the number of ring gear teeth and the number of pinion gear teeth. Divide the number of ring gear teeth by the number of pinion gear teeth and that will give you its exact ratio --none of this lift up the rear end, count the number of driveshaft revolutions vs. wheel/tire revolutions. That method can easily be inaccurate. Actually counting ring & and pinion teeth is fool-proof with no margin of error or guessing and the result will be exact.
Doesn't mean anything about the ratio or type of differential inside that 9-inch 3rd member. The alpha-numerics are simply engineering casting numbers and dates when the case and the pinion support housings were cast.
.........
The only sure way to know what differential type is there and what ratio it is would be to remove the 3rd member and visually identify what's in there.
If you do take the 3rd member out but don't know an open (single track) differential from a Traction-Lok, you can post a photo of it and I can identify what it is.
.........
Actually counting ring & and pinion teeth is fool-proof with no margin of error or guessing and the result will be exact.
Thank you. Next question: How does one go about checking fluid level / filling if necessary?
Thank you. Next question: How does one go about checking fluid level / filling if necessary?
Fill/sight plug will be on the left side of the 3rd member.
NOTE: Early 9-inch 3rd members didn't have a fill/sight plug on them. The plug would have been on the backside of the rear end housing (pre-Bumpside era). Later 9-inch 3rd members have the plug on them and no plug on the back side of the rear end housing (from later into the Slick era through the Bullnose era).
"DIF" is where the parts were cast: Dearborn Iron Foundry.
The code on the warranty plate may correctly indicate what is presently inside the rear end housing and, it may not. If the I.D. tag is missing from the 3rd member, good chance the 3rd member has been taken out of the housing. Gears could have been changed, differential type could have been been changed, even the entire 3rd member itself could be something different than what the truck originally came with.
Fill/sight plug will be on the left side of the 3rd member.
NOTE: Early 9-inch 3rd members didn't have a fill/sight plug on them. The plug would have been on the backside of the rear end housing (pre-Bumpside era). Later 9-inch 3rd members have the plug on them and no plug on the back side of the rear end housing (from later into the Slick era through the Bullnose era).
"DIF" is where the parts were cast: Dearborn Iron Foundry.
The code on the warranty plate may correctly indicate what is presently inside the rear end housing and, it may not. If the I.D. tag is missing from the 3rd member, good chance the 3rd member has been taken out of the housing. Gears could have been changed, differential type could have been been changed, even the entire 3rd member itself could be something different than what the truck originally came with.
Perfect, I will have to look when I get that side cleaned up better, there was like 2" thick of mud/gunk covering the entire rear.
Here is the back side of mine after some cleaning:
Is this a '67 model truck? I see a fill/sight plug on the back of the housing --towards the lower right side.
Just got home and crawled under for a look:
Yea it ia a 67' "on paper", but I'm starting to figure out that the f in f100 on mine must stand for Frankenstein. As I also have a 71' engine running a 68' distributor hmm.
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