help! how do i decifer the gear ratio of my rearend

65Truck_Nut · Post by **65Truck_Nut** » July 7, 2007, 9:29 pm

the numbers are 7L28 and a sun dial looking circle with 1 in the 10 oclock position and a 3 in the 12 oclock and a 5 in the 3 aclock and a 7 in the 6 oclock and 9 in the 8 oclock position and a M with a Cc and 79 I know theres probably a code book but i dont have access to one and was hoping for someone who has one to respond thanks guys ,Byron

dotcentral · Post by **dotcentral** » July 7, 2007, 9:45 pm

I think what you found are date of manufacture info for the axle.

Does your axle have a metal tag on it? There would be an axle code number on that. They are usually missing.

Any idea if your axle would be original? If so, do you still have a metal plate riveted to your door? It would have the VIN #, plus a series of other numbers. The last 2 numbers on the 1st line would be the axle code. On mine it is 17, which = 3.25.

If you post the numbers, someone can probably decode the axle and other info for you.

65Truck_Nut · Post by **65Truck_Nut** » July 8, 2007, 12:09 am

Ok heres the goal I have a 65 that had a 6 banger with a 3 on the tree and i put a 302 with a granny 4 speed in it .I found out that standard trannys (unless they are 5 speed or overdrive) are all 1 to 1 gear ratio in high gear. and im taching about 3,000 rpms at 65 and would like to bring that down a tad maybe 24k or 25k so im concentrating on rear gears since i cant afford a 5 speed right now. the tag is missing on the rearend . it is out of a 67 model pickup thats all i know, its on the ground at a friends house. We jacked up my 65 and turned the wheel and counted the revolutions of the drive line and wheel. its about 1 and 1/4 turns of the shaft to 1 wheel I was told its probably a 3:55 ratio whid pretty much standard for ford 1/2 ton trucks I may have to get a car 3rd member or I was told that a 65 through 72 pickup with a big block automatic would have the higher ratio rearend. Ill start looking for ones with tags. Thanks for the help,Byron

6166 Junkyard Dog · Post by **6166 Junkyard Dog** » July 8, 2007, 6:24 am

amost every 61-66 on a Ford 9" would be a 3:70,,, that ws stock from the factory 3:50's where used in the 68-72's , 3:54 where used in the spicer rear ends that where heavy duties, if you find the tag it will say the rear end ratio on it

Ford4jack · Post by **Ford4jack** » July 8, 2007, 7:44 am

If your rear axle is a ford 9'' you should be able to find something like a 3.00 center for a decent price.
Had a 3.70 stock in mine ( 6cyl 4 sp) and it felt like I was making grandma jog until I went with a 3.00 gear.

This should not be an issue but be sure to count the axle splines if you go to swap out center chunks

The metal tag should be on one of the center carrier bolts.

Not sure what year they changed 68? but ford 9'' truck rear axles went with wider brakes before the made the housing & spring pad location wider in 73 If I remember correctly.

BigTim · Post by **BigTim** » July 8, 2007, 9:39 am

Also if you know for sure the MPH, RPM, and tire diameter you can use a gear ratio calculator found on the internet to figure out what ratio you are running.

Here is a nice one to try http://www.et-studios.com/motorsports/gears/gears.html.

If you have a 26 inch tire and your tach and speed are right this says you have a 3.50/1 ratio

Truckrat · Post by **Truckrat** » July 8, 2007, 10:20 am

Guys, 3 grand at 65 is pretty noisy, and uses more gas at 3 plus bucks a gallon, so no doubt a higher gear is preferable. And yes they did widen the axle saddles in 73 with the groove side trucks(opposite bump side). As has been said, count your splines on the end of an axle before you spend time and effort pulling a 3rd member out. If you get one out of a car, more than likely it will be a 28 spline axle. Most trucks are 31 spline, but there are exceptions. Also a car will have the smaller bolt pattern, so you would have to use the whole brake drum assembly to use them. If you can find a 70s truck with a 460 and c6 in it, you might find a higher gear than used in the earlier 6 cylinder trucks. Generally the automatic trans trucks were geared higher. As far as being sure of what you have, counting the teeth of the ring and pinion inside the 3rd member is your best bet if you don't have the tag on there. What I thought was a 3.00 or 3.25 turned out to be a 2.75 when I counted the teeth on the R & P.
I am hoping the tag on the axle of my 74 is still on there, but since it is a 390/C6 truck, I figure it will be a 3.25 or 3.50. We'll see.
Hope you find what you need. Oh yeah, You may want to check under late 60s thru 80's e150 vans as well. They had 9 inch axles, too. Good hunting! TR

65Truck_Nut · Post by **65Truck_Nut** » July 8, 2007, 12:28 pm

I have a uncle who once pulled a axle out of the long side of a 65 galaxie and stuck it into his 58 ford 1/2 ton truck rearend, and used the car tire and wheel. he might have plugged the brake off on thet wheel since it was a quick fix more less to get it home, i think, but it worked on that ocassion. but ford changed things alot so I may be biting off more than i can chew trying to find one of those.

6166 Junkyard Dog · Post by **6166 Junkyard Dog** » July 8, 2007, 12:42 pm

I hate to tell somebody wrong but hear it goes 28 spline axles where used on Ford Trucks from 1957-72 BUT On some of the 68-72 trucks did have 31 spline In which are hard to find and most of your 73-79 trucks did have 31 splines so if anybody say that the trucks all had 31 spline THEY ARE WRONG, WRONG, WRONG!!!!!!!! There is no listing of 31 spline axles from 1957-1967 If look back in some previous posts about axles that I did it gives you the full run down

6166 Junkyard Dog · Post by **6166 Junkyard Dog** » July 8, 2007, 1:53 pm

had to look back but if you go to July 29th 2006 Topic is Rear Brake Drum Upgrade you will see all the axles on what years fits what from 1948-79 trucks that I posted before

dotcentral · Post by **dotcentral** » July 8, 2007, 2:51 pm

65TruckNut your 67 axle is probably a 28 spline. Might want to count them to make sure. You could probably get a 3.25, 3.00, 2.75 out of a truck or a car 9" from a salvage yard if they have anything more than 15 years old. Not real hard to swap the whole center section, but definitely messy and requires a set of jack stands and a good floor jack helps for lowering and lifting the heavy center section into place.

I've seen a lot of F100's with 3 speed column shift manuals with base V8's (352's or 302's) and they have all had 3.25 gears. Seemed like the 6's had the 3.70 gear. I figured that was the base gear, but might be something to do with geography?

65Truck_Nut · Post by **65Truck_Nut** » July 8, 2007, 3:23 pm

well i took my truck for a drive and i was wrong at 65 mph the 302 is taching 2,700 rpms which isnt as bad as i thought. I guess the 18 inch glasspacks dumping on the ground 1 foot behind the cab might have some influence on my assement of the situation LOL I measured my tires there 28 inches in diameter .I found a post from last year that gave all the ratios useing a 26 inch diameter tire but i need to find the formula for calculating the ratio of my 28 inch tires. I wonder if i bought a new ring and pinion from lmc with a 3.00 ratio if i would get it down to around 2,400 rpms at 65?????

dotcentral · Post by **dotcentral** » July 8, 2007, 3:37 pm

Based on that link it should do what you are wanting.

You could probably get a good used ring & pinion set in a center section for a lot cheaper than LMC would sell you the ring & pinion. Plus it would be already setup. I bought a different ratio but a complete center section for $75.

65Truck_Nut · Post by **65Truck_Nut** » July 8, 2007, 3:41 pm

duh!!! Big Tim gave me a link to the calculator for gear ratios. By the way thanks big tim!! looks like with a 28 inch diameter tire and 3.00 rear gears will put me at 2,000 rpm at 56 mph which might be what im looking for since speed limit in our hilly section of Arkansas is 55 anyway i might be able to ride cumfy at 60 to 62 with no problem.

64 f100 · Post by **64 f100** » July 8, 2007, 10:44 pm

What you really need is an overdrive transmision, and leave the 3.70's in.

Rich

64 f100 · Post by **64 f100** » July 9, 2007, 5:50 am

There is an axle code on the data plate, usually on the drivers door. This will tell the original ratio, but you will have to have someone look the number up. generally, the alxes were 3.25 3.70, 3.89, 3.50, 4.11.

Rich

fmartin_gila · Post by **fmartin_gila** » July 9, 2007, 6:03 am

If your not going to be too hard on it, the T5 tranny is the best IMHO way to go. Will drop RPM and noise a considerable amount. Will give you a better starting gear and allow you to have OD, and just leave the rear alone. I move along at 60 MPH at about 1500, the 223 seems to like it(my cheapo tach may be off some).
Fred

wbulick · Post by **wbulick** » July 9, 2007, 3:00 pm

[quote="6166 Junkyard Dog"]had to look back but if you go to July 29th 2006 Topic is Rear Brake Drum Upgrade you will see all the axles on what years fits what from 1948-79 trucks that I posted before[/quot

Anybody have a link to that? I can't pull it up for some reason and that would be handy to have.

GLindley · Post by **GLindley** » July 9, 2007, 3:38 pm

Wbulick, try ->HERE<- and scroll down to the 4th response.

banjopicker66 · Post by **banjopicker66** » July 9, 2007, 4:20 pm

Since you live in hilly Arkansas, I would recommend AGAINST anything lower than a 3.25.
You will find that a 3.00 or lower will really dog your little 302 out, as it does best at higher RPMs than a 300 six.

help! how do i decifer the gear ratio of my rearend

help! how do i decifer the gear ratio of my rearend

rearend ratio