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Apr 17, 2007 | 01:13 AM

Sandidande

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Senior User

Joined: Jul 2006

Posts: 448

Likes: 1

From: La Mesa (East San Diego)

Went from dum to dummer

Hi Folks,

I wrote a new thread last night asking for some explanations on rear end gearing and nominal cruise RPMs for my truck restoration.

The answers were great and the points I got helped completely to answer all the questions I had. However now it seems I have a new problem and I could use your good expertise again.

Remember, I have the 1951 Ford F-1 that now has the newly rebuilt Ford FE 390HP engine and C6 tranny.

But I lied and told you all I have a 9 inch rear end. After looking on a super web site from kevmustang (?) about Ford 9 inch rear ends, according to his description and photos, I actually have a 9 3/8 (9 1/2) inch rear end. The photo's of his and mine are unmistakably the same.

Here is my new problem: I computed using the gearing calculator one of you sent, that it would be perfect to put a 2.72:1 ratio in the rear end. BUT, I can't find ANY info on these rear ends anywhere! There is a tag on the differential but I'm going to have to get under there this weekend to clean it off so I can read it. So, maybe I'll have more specific info on the rear end by then if youneed it.

Can you guys give me some info and some pointers on this rear end?

Thanks again,

Big Dan

Apr 17, 2007 | 02:45 AM

NumberDummy

Ford Parts Specialist

Joined: Nov 2006

Posts: 88,826

Likes: 790

From: Simi Valley, CA

Quote:

Originally Posted by Sandidande

Hi Folks,

I wrote a new thread last night asking for some explanations on rear end gearing and nominal cruise RPMs for my truck restoration.

The answers were great and the points I got helped completely to answer all the questions I had. However now it seems I have a new problem and I could use your good expertise again.

Remember, I have the 1951 Ford F-1 that now has the newly rebuilt Ford FE 390HP engine and C6 tranny.

But I lied and told you all I have a 9 inch rear end. After looking on a super web site from kevmustang (?) about Ford 9 inch rear ends, according to his description and photos, I actually have a 9 3/8 (9 1/2) inch rear end. The photo's of his and mine are unmistakably the same.

Here is my new problem: I computed using the gearing calculator one of you sent, that it would be perfect to put a 2.72:1 ratio in the rear end. BUT, I can't find ANY info on these rear ends anywhere! There is a tag on the differential but I'm going to have to get under there this weekend to clean it off so I can read it. So, maybe I'll have more specific info on the rear end by then if youneed it. Can you guys give me some info and some pointers on this rear end? Thanks again, Big Dan

The ring gear is 9 3/8" but the parts are listed under the 9 inch rear axle parts lists. This rear end (very desirable to some) was used in some 428 equipped cars 1966-70, and 1968/72 F100 Camper Specials, and optional on other F100's. It has 31 spline axles. Two ratios were offered: 3.25-1 and 3.50-1. WEY or WFF should be the Ford rear axle codes that appear on the rear end tag. More than likely the rear axle you have came from a 1966/70 Ford, 66/68 T-Bird, or an F100~68/72.

Last edited by NumberDummy; Apr 17, 2007 at 02:52 AM.

Apr 17, 2007 | 08:07 AM

75F350

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Joined: Jul 2006

Posts: 6,948

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The unfortunate part is that the gears fromt he 9" will not interchange with the 9 3/8" rear axle. I understand the centeer sections will go into the 9" housing, (same bolt pattern), but to install the 9 3/8" carrier into the 9" housing requires some notching to get her to fit. You are very limited to gears selection, as most gears were more abundant for truck applications.. I do recall some car applications from merc / lincoln applications, so you may find some in the 2 3/4 ratios.
The reason I mention the possible (lack) of imterchangability is this. Since the 9 3/8 carrier will bolt into the 9" housing with a little modification, why wouldn't the opposite be true. Maybe if you find it difficult to find gears for your ride, it might be possible to build a 9" center section, and install it into your existing housing. I know the 9" has the ratios you are looking for. I have been looking, and looking, and looking, and can't find any reason why this would not work. If you are set on that ratio, and are unable to find a r /p set in that ratio for the 9 3/8 center section. It might be possible to build just a 9" center section, so you don't have to shell out the dough for a complete rear axle assembly.

Apr 18, 2007 | 01:47 AM

Sandidande

Thread Starter

Senior User

Joined: Jul 2006

Posts: 448

Likes: 1

From: La Mesa (East San Diego)

Hi Bill!

Thanks for all your help in educating me about Ford Differentials. It's been 25 years since my last restoration project, and now I remember why! This on has been 100% easier because of the internet/ebay, etc. I got under the truck tonight because I was dying of curiosity and unearthed the tag on my differential. This is what I found:

It was labelled: "WDT-F1" on the top row, then "2 80 6GC 215" on the bottom.

I think if the web page tables I found are correct, that means this rear end is out of a 1966 to 1970 Ford Car of Mercury; has a non-locking gear ratio of 2.80 to 1; and was the 215 unit produced in the third week of July 1966!

So, I guess all this was fo rnothing because that was the lowest ratio (highest gearing) they made. So I can't improve on it.

I can't help but wonder if hearing the big 390 HP roar through the side pipes on the freeway the other day didn't just sound like "more" because I'm used to my little Ranger with a 3 litre, insulation and air conditioning.

So, anyway, I'm going to leave it alone. It sounds like this is a really strong differential and that's what I'm looking for.

Thanks for all the good advice!

Big Dan