351 Rear End

[Valhallo]

Looking around on some of the other mustang forums I frequent, I have found it to be a matter of some debate as to whether or not the 8" rear end was used in the same cars that were equipped with a 351 Cleveland motor, but it seems to me that it was done becuase, well, my car is an 8" rear 351C. Is that some freak incident, or some previous owner who messed with my VIN or info decals? My door decal has an axle code 2 and my VIN shows a 351C, but everyone is telling me that's not possible. Anybody who can clear this up?

The reason I got started in researching this is because I am planning on swapping to a trac-loc 3.25 rear. Looks like It may be a more expensive project than I had anticipated. :s

 

[72HCODE]

if you want to be sure of the original configuration you could order a Marti report on your car.

There were some order options for 71 and 73 that could of gotten your car delivered with a 8" rear instead of a 9" rear in a 351C engine configuration. I do not remember the specifics offhand but the same thing happened with the C4 transmission. Most 71-73 came with either a C6 or FMX transmission but there were some freaky option combinations that gave some cars a C4 transmission.

Due to the number of changes to the body itself as far as brackets for options and the different wire harnesses that options required what might of happened was the body for a I6 250 or a 302 was taken off one line and placed on the 351C line to complete assembly.

there is nothing wrong with the 8" rear it is very strong and can take the 351C power. People just flock to the 9" you can swap out the 8" if you want.

I have seen at least 15 different Engine Harnesses and wiring variations for te 71-73 line of cars, any time an option was added to a car it usually required a different engine harness or dash harness to allow the option in the car. the same with the body. like if you had dual exhaust, or rear sway bar, or competition rear suspension, rear fold down seat then it also depended on if the car was early 71 late 71, early 72, late 72, or 73 because the government required changes for new regulations.

so lets say you wanted a loaded sportsroof 351C but it was just a 2V motor, and you didn't want any of the performance parts, standard suspension and 1 exhaust pipe, and it was late 72 which was the big detune thanks to the idiots in Washington DC. well, ford may of gone to the I6 line and pulled out a chassis that had the correct wiring configuration and put it on the 351 mach 1 line for completion of the order. you would of not known anything if you bought the car in the 1970s about them doing that unless you wanted a specific combination of parts and knew what to look for. the 8" would of been fine in that configuration. Now if you had ordered a HO big block car there would of been no way they would of left it leave the factory with a 8" rear.

so it is possible the car was born with a 8" rear. again you can confirm this with a marti report. It is possible in the past the car had a rear axle swapped as well these cars are almost 40 years old a lot can happen in 5 years much less 40.

 

[hyena429]

Yup..I agree...A marti report will tell you everything you need...Who knows whats been added too your car over the years or took away!!..I use to be told all the time that my power windows where not stock...Had to get a marti report to make sure they was,,lol....So i never trust what anyone tells me is stock on there mustang with out the report too prove it...Our cars could be made out of 2 or 3 or more diffrent mustangs..hehe..You just dont know till you get the vin check...the break down sheet is worth the extra too if you car come with alot of odd or rare options...It will show how many made like it.

 

[Don65Stang]

The Marti Report, as best I can tell, only gives Axle ratios not if it had an 8" or a 9" in it. The Axle ratios can be different for an 8" vs 9". For example an 8" has a 2.79 ratio while a 9" came in a 2.75 ratio. Some ratios were the same for either rear other ratios were slightly different.

 

[cobra3073]

As Don inferred, your door tag (#2 for Axle) is valid for a 2.75:1 ratio Nine (9) inch rear. The 8 inch would have been a 2.79:1 for the equivalent ratio.

In short, there is no "disconnect" between the door tag and your having a 351C engine in your Mustang.

The following link has some very good information on rear ends and may assist you in your quest.

http://www.fordification.com/tech/rearends_ford08.htm

BT

 

[Valhallo]

As Don inferred, your door tag (#2 for Axle) is valid for a 2.75:1 ratio Nine (9) inch rear. The 8 inch would have been a 2.79:1 for the equivalent ratio.

In short, there is no "disconnect" between the door tag and your having a 351C engine in your Mustang.

The following link has some very good information on rear ends and may assist you in your quest.

http://www.fordification.com/tech/rearends_ford08.htm

BT

Yeah, I went out and used the ID tag on the differential case, and it is in fact a 9inch 2.75 (conventional?) I had actually just used the link you posted for me via google! Now I'm not worried about the 8 vs 9 inch, I just have to put a 3.25 ratio and limited slip in.

Speaking of - would that be something that would be a dumb idea to find scrapped? There are a couple of parts cars around me, and a yard I found with several 71-3 generation mustangs.

 

[Ponydrvr72]

Hello, did the axle have a differential tag, is it a 9" diff housing? if it is it may be a 8.75". 8"-9" pumpkins look very similar. what the guys are saying about options availability is true, you could get a 8" axle for the 71-73 but usually for V-6, 302. but with a gas crunch on anything was possible, Not to mention when the vehicle got to the dealer. I've bought a few gear sets over the years from dealerships going out of business that had stacks of higher ratio gears that were removed from factory fresh cars/trucks at the customers request who were looking for better economy.

 

[72HCODE]

I can tell you a scraped 9" Plus rebuild, gear swap, and new locker is going to cost just as much as a ready to go drop in 9" axle.

the new ready to go 9" rear ends are much stronger then original and you can get them built stronger with a daytona nose and nodular steel center case.

 

[Ponydrvr72]

I can tell you a scraped 9" Plus rebuild, gear swap, and new locker is going to cost just as much as a ready to go drop in 9" axle.

the new ready to go 9" rear ends are much stronger then original and you can get them built stronger with a daytona nose and nodular steel center case.

Aint that the truth! and unless you like to collect tools,don't bother thinking of doing it yourself, the tools alone will be over a grand unless you have them already. inch pound torque wrench,1/2" 200 pd. torque wrench,press,breaker bar,clutch pack measuring tool,calipers,bearing splitter,bearing puller,bench mounted carrier holding device, Etc... almost went through a divorce over that build:s:s

 

[cobra3073]

As Don inferred, your door tag (#2 for Axle) is valid for a 2.75:1 ratio Nine (9) inch rear. The 8 inch would have been a 2.79:1 for the equivalent ratio.

In short, there is no "disconnect" between the door tag and your having a 351C engine in your Mustang.

The following link has some very good information on rear ends and may assist you in your quest.

http://www.fordification.com/tech/rearends_ford08.htm

BT

Yeah, I went out and used the ID tag on the differential case, and it is in fact a 9inch 2.75 (conventional?) I had actually just used the link you posted for me via google! Now I'm not worried about the 8 vs 9 inch, I just have to put a 3.25 ratio and limited slip in.

Speaking of - would that be something that would be a dumb idea to find scrapped? There are a couple of parts cars around me, and a yard I found with several 71-3 generation mustangs.

No, trying for a "junk" carrier is NOT a problem and keep in mind that you do not necessarily need the whole pumpkin (just the carrier). You should also note that you are NOT limited to 71-73 Mustangs, as any 28 spline Ford 9 inch vehicle will suffice.

Using the link I sent you, all you have to do is find a Ford vehicle with the appropriate tag denoting a Nine inch locking differential ith 28 inch splines and drop the carrier assembly.

Again, you will have to ensure that it is a 28 spline and not a 31 spline, thereby making it a "drop in" for your 28 spline axles. Quite frankly, I have pulled many junk yard carriers to interchange during my more active racing days while stationed overseas.

Review the link for the cars that you are looking at and hopefully the tags will still be on the differential for the vehicle that you are looking at as a donor. If the tag is there, it is more than likely that the original ring, pinion and traction lok is still there.

Hope this helps!

BT

 

[Jeff73Mach1]

Let me chime in with this. Converting a center section from 28 spline to 31 splkine or vice versa is as simple as replacing the 2 side gears and the hat with the proper one. Even with new parts this is a 125.00 or less and the work can be done without taking the gear off or disturbing backlash or pinion settings.

I have a rebuilt 3.50 and a nice 4.11 both 28 spline and trac lok I'd sell for a reasonable price plus shipping but man are they a pain to ship!

 

[Ponydrvr72]

Let me chime in with this. Converting a center section from 28 spline to 31 splkine or vice versa is as simple as replacing the 2 side gears and the hat with the proper one. Even with new parts this is a 125.00 or less and the work can be done without taking the gear off or disturbing backlash or pinion settings.

I have a rebuilt 3.50 and a nice 4.11 both 28 spline and trac lok I'd sell for a reasonable price plus shipping but man are they a pain to ship!

Those plastic milk crates work well for that. on the 28 to 31 conversion, what you mentioned is the cheap part, the axles on the other hand,,,, you may want to upgrade the yoke for bigger joints. I've got a 78 F-150 parts truck with a 31 spline set up, been thinking about pulling it out and restore it into a 79 F-100 I have with a 28 spline open rear end that sits behind a C-6/429.

 

[73vertproject]

Let me chime in with this. Converting a center section from 28 spline to 31 splkine or vice versa is as simple as replacing the 2 side gears and the hat with the proper one. Even with new parts this is a 125.00 or less and the work can be done without taking the gear off or disturbing backlash or pinion settings.

I have a rebuilt 3.50 and a nice 4.11 both 28 spline and trac lok I'd sell for a reasonable price plus shipping but man are they a pain to ship!

Any idea what the 3.50 would cost including shipping to 89445 Winnemucca, Nevada? The rear end is next on my project list now that the Cleveland is in and running great.

 

[Don65Stang]

Let me chime in with this. Converting a center section from 28 spline to 31 splkine or vice versa is as simple as replacing the 2 side gears and the hat with the proper one. Even with new parts this is a 125.00 or less and the work can be done without taking the gear off or disturbing backlash or pinion settings.

I have a rebuilt 3.50 and a nice 4.11 both 28 spline and trac lok I'd sell for a reasonable price plus shipping but man are they a pain to ship!

Any idea what the 3.50 would cost including shipping to 89445 Winnemucca, Nevada? The rear end is next on my project list now that the Cleveland is in and running great.

Try http://uship.com. I used it and it was fantastic.

 

[Jeff73Mach1]

I'd take $400 for the gear, even though it cost me close to 700. it has less than 1500 miles on it and looks pretty much perfect. Let me know if you want a picture and I'll unwrap it and send you a few.

As to the axles . . . 31 splines can be shortened with a chop saw, so if you find decent axles at a salvage yard you can often reuse them, but my point wasn't to go upgrade your rear end, it was that if you find a nice center section that is a good deal, the 28/31 spline issue is not that big a deal

 

[73vertproject]

Thanks, Jeff. After taking close to a year and a half to rebuild the Cleveland, I'm leaning WAY toward having most of the restomod done by the local guys (that do a good job) at $65 an hour. Can you give me a guestimate as to what it would cost me all together to get that rear end to me? I have the stock 2.75 gears/axle/pumpkin/etc. Any idea how much work would it be for my shop to swap what you're offering with my stock setup? Thanks in advance if you have some estimates - I'm pretty clueless about rear ends.

 

[73mach1]

Doc it's a pretty easy swap,just pull the axles out a little bit then the center section and put the new one in.You should be able to do it in an hour or less .

 

[Jeff73Mach1]

It is not a hard job, but I imagine most shops will charge you two hours for the work. Jack up the rear end of the car place on jack stands. Remove rear wheels, remove brake drums. Through the access hole remove 4 bolts on axle retaining plate on each side. Remove rear U-joint and swing driveshaft to the side. Remove nuts from the axle housing surrounding the carrier. Use a rubber mallet to crack carrier seal from housing and let gear lube drain into appropriate container. Pull axles out a couple of inches with the understanding that you may now lose some gear lube-if you get it on brake pads they are ruined so use care. Once rear end is drained remove center section, clean face of housing put a bead of sealant or a new gasket on the studs and reverse everything up til now. Finally remove fill plug from new center section and fill with gear lube and posi additive up to the fill plug. Once everything is back together and donedrive in an open parking lot in a figure 8 pattern about 10 times to fully circulate all additive to the trac loc clutches and you should be done.

I think I paid $70 to have the last one I bought shipped. I imagine I can do it for that or a little less.

 

[73vertproject]

Great! Sounds like a plan. Thanks for the PM, Jeff!