Technical 9” 3rd member

So I picked up this 3rd member from a guy, it was advertised as a 4.4:1 ratio. I couldn’t pass on it for the price. Looks to be in good shape. Coming to closer inspection I see that it is stamped with a 42-10 ratio, witch should be 4.2 ratio. I’m curious about these oddball ratios and not a whole lot of information on them from the searching I’ve done. I plan on trying this 3rd member out with my gasser build. BBC 454 with TH400 tranny and roughly 30-31” tires. What do you guys know about these?

 

Early Bronco 6 cly. ?

 

ring gear is from 1971 or later, according to the engineering number

might work ok, I'd probably check the tooth contact pattern, inspect the bearings, and replace the differential with a locker or spool or something, depending on intended use

 

Early Broncos had either 4.11 or 4.56.

Ford had a 3.91 and 4.30 for their hipo ratios but they should be in a N case carrier.
Could be someone put that together from spare parts.

 

Have you counted the teeth?

 

Definitely a locker or spool in the future. I may just run it though

 

That's why I placed question mark. Goggle can not always be trusted. That said. There are several other people asking the same question in regards to 4:20 gears. So they are out there.

 

Not yet lol.

 

I will count the teeth when I get a chance.

 

For some reason, that seems to light up a memory of being a 2.75:1 gear.

That would be 44-teeth on the ring, and 16-teeth on the pinion.

 

^^^^^ That did come up during the short while I googled 4:20 Ford gears.

 

That 4210 is part of the engineering number. You should have counted the teeth before you bought it.

 

If it is a 2.75:1 gear set, I have a 2.50:1 gear set, if you want to make it worse.

 

That case isn't very strong, it has just the single web. I wouldn't spend any money on it to use in a gasser, it won't last long launching a big block.

 

Judging only by how thin the ring gear is, I'm betting it is a 2.87 or 300:1. Definitely a single spinner because the ring gear bolt area is flat instead of bumpy. I'll go one further and guess it is 28 spline, only because they are more common.

I don't swear my information is 100% accurate, because sometimes I'm full of shit, but I bet it's pretty close.

Hang on to it, you will need it for something someday.

-Abone.

 

Yep, the 'basic' part number, probably found on all ring gears regardless of ratio, although I suspect this particular number is for 9" axles only.

The 'D' is the decade ('70s), '1' is the year (in this case, '71), the 'A' is generic Ford, and the 'W' is axle/driveshaft group. Then the 'standard/basic' part number from within that group, and lastly the 'A' is the first revision.

If it was a body part, it would be six numbers instead of four for the 'basic' number, with the first two identifying the specific model (Ford, Mustang, Fairlane, 2-dr, 4-dr, etc), and may have a color indication after/in place of any revisions.

Some mechanical parts (primarily distributors and carbs) would have the basic part number, then an additional number denoting the specific application, either stamped in or on a separate tag. Some OEM-installed engines/transmissions would also have a partial VIN stamped on them, but not all.

Also keep in mind that Ford didn't change casting or part numbers yearly; they merely denote the first appearance of that particular part. As long as the part was substantially unchanged, a part would keep the same number.

 

As has been said the D1AW 4210 A is the engineering number that tells me it was designed in 1971. Probably used for several years thereafter until the next redesign. The C6AW number was designed in 1966 and used for many years and the case was done in 1967 etc. Count the teeth and divide by pinion teeth. From looking at it its probably a 2:75 or so gear from a 70's ford car and not a locker.

 

Ive found 390 and 411 ratio 9 inch in old late 50's and early 60,s stick shift cars & trucks. the auto trans had 300 and a six auto a 350. the FE stick trucks had 325 ratio.

 

If they were 4:11 or lower, that ring gear would be awfully dam thick...

 

I see a bunch of rust in photo 3. I wouldn’t use them.

 

We ran a 7.33 gear in a circle track car, it was real thick !

 

Never heard of a 4.4:1 ratio, so the selling was all wet. Count the teeth.

 

would not run as is for that ride - never seen a 9" with that type of webbing but, I am no expert - kevinstang.com is good source for Ford differential info

 

People have different ideas of what a gasser is.

 

I’ve got a 4:11 in a locker third member if you’re interested.
I even have a 4:56, too.
r


Sent from my iPhone using H.A.M.B.

 

I was after some 4:11 gears . I saw the 4.4 and 4.2 ratio and thought I’d give it a go. Obviously I know nothing about them I think I did alright for $120

 

There may be another stamping on the ring gear designating the tooth count.

 

IMO you got hosed...not the gear you were told it is, weak single rib case, open differential....not even worth $50 bucks

 

If there 28 spline axles your 454 is going to make short work of them, even shorter if you have slicks. The C7AW case is probably the weakest one in the 9 inch pecking order also.
One good thing is your using an automatic.