THIRD MEMBER

The rear end parts used in Hipo cars were originally Galaxie parts. 1/2 ton trucks would be the same in 65. In 66 some cars and trucks had a 9 3/8 rear end. Although they look similar, the only thing that is the same is the third member to axle housing gasket. They are 31 spline units and I see them all the time on Ebay represented as a 9 inch rear end. I do not know how they get away with it as the buyer gets screwed every time.

-Fred-

Keep in mind that this thread is related to third members only and not the axle housings. The Mustang axle housings are unique. Only the Galaxie and truck third members are at issue here. All Galaxie and truck 9 inch third member parts are usable all the way down to a six cylinder vehicle.

-Fred-

Ring gear sizes can get confusing at times. By the time you are done reading this post you will be even more confused but possibly also enlightened as to Fords terminology. All of the following information is based on the Ford parts books. Yes, there is an 8 3/4 ring gear listed from 1957 to 1961. After that the same gear is listed as a 9 inch. An example is a B7AZ 4209 K which is a 4.11 ratio. It starts off as an 8 3/4 until 1962 where it becomes known as a 9 inch. There are several other examples as well. To confuse things even more there was an 8 3/4 rear end in a 69 Galaxie but it was of the integral carrier type with a rear inspection cover. I know there are some sources that list the 8 3/4 rear end for 1965 and 1966 however there is no mention of an 8 3/4 ring gear for 1965 and 1966 in the parts book, only 9 inch. How are we doing now?

-Fred-

Here is more fuel for the fire. The 8 3/4 and 9 inch gears are interchangeble both directions. Most people are unaware of the fact that there are actually three different axle housings listed for 65 and 66 Hipo Mustangs. C5ZZ 4010 A is 65 only. C5ZZ 4010 B is 66 until 10/1/65 and C5ZZ 4010 C is from 10/1/65. The C5ZZ 4010 C one is the one commonly referred to as the later 66 housing as it looks totally different from the earlier ones. I have had both 65 and early 66 housings and I did not see what if any difference there is in them. A discussion about this would be best in another topic. Ford did not change the axle housing to accomodate the 8 3/4 or 9 inch sizes as the are interchangeable. I had mentioned the 9 3/8 rear end third member as appearing similar to the 9 inch. It does use the same housing gasket as a 9 inch and when you look at the gasket you will notice an extra relief cut in the top and bottom. That is to clear the 9 3/8 ring gear. You actually could put a 9 3/8 third member in your Mustang by match grinding the gasket relief pattern to your housing. Of course your 28 spline axles would not work with the 31 spline differential and the really low basement gears that were available for a 9 3/8 was a 3.50 ratio.

-Fred-