9 inch housing help

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Heardatbeat

Well-known member
Joined
Nov 22, 2016
Messages
162
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Location
Washington
My Car
1971 Mach 1
Good afternoon everyone. I got a '71 Mach 1 that the previous owners swapped an 8 inch in place of the original 9 inch (learned from help here and the Marti Report). Well I finally got a good deal on a 9 inch from someone local to me all he knew was that it was from a pickup $150 for the housing, center and axles. After some cleaning I found the bucktag and found out it came from a 70's F-100 it measures 61 inches from flange to flange. After some more help from one of the 7123 FB groups I found out the spring perches are on the top instead of bottom because pickups had the leaf spring on top as opposed to the leafspring coming from the bottom on a Mustang. So my question to ya'll is can anyone measure their original 7123 9 inch housing diameter please? I want to know if it's going to be similar enough for minimal work. I know I have to cut the perches and re-weld them to the bottom. I'm also concerned about the staggered shocks plate. If the housing is bigger the plate theoretically should not bolt up right?

 
Measure the outside diameter of the axle tubes at the Mustang spring perch location, probably not the same width as the F150. Then measure from the inside of the front spring plate mounting holes to the inside of the rear holes. If the axle tube diameter is larger than the inside-to-inside spring plate hole dimension you'll have a problem. You'll also need to take into consideration the  spring perch widths and the Mustang leaf widths. It's not easy to cut the spring perches off clean enough to reweld them. A guy I used to know that rebuilt and narrowed 9-inch axles used a cutoff wheel to remove as much of the weld as possible.

Up to '72 the width of the axle flange-to-flange was 61.25", the same as '71 to '73 Mustangs. Starting in '73 the F150s were 4 inches wider.

 
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Measure the outside diameter of the axle tubes at the Mustang spring perch location, probably not the same width as the F150. Then measure from the inside of the front spring plate mounting holes to the inside of the rear holes. If the axle tube diameter is larger than the inside-to-inside spring plate hole dimension you'll have a problem. You'll also need to take into consideration the  spring perch widths and the Mustang leaf widths. It's not easy to cut the spring perches off clean enough to reweld them. A guy I used to know that rebuilt and narrowed 9-inch axles used a cutoff wheel to remove as much of the weld as possible.

Up to '72 the width of the axle flange-to-flange was 61.25", the same as '71 to '73 Mustangs. Starting in '73 the F150s were 4 inches wider.
The housing diameter measures 3.25 inches where the spring perch sits. The length of the bare housing is 61.25. 

 
If the bare housing flange to flange is 61.25" you likely have a '73 and up rear end, which will have an axle width of 65.25". '71 to '73 Mustangs have a housing width of about 57" and an axle width of 61.25". The bolt pattern for a '70s F150 wheel is 5 lugs on a 5-1/2" bolt circle, the ones for a Mustang are 5 lugs on a 4-1/2" bolt circle. 

What is the tag number?

If you want to swap in a stronger rear axle you should look for an 8.8" Explorer rear axle. They have 31 spline axles and are stronger than the 9-inch rear ends with 28 spline axles that came with our cars. They have the same bolt pattern on the wheels and they have disc brakes. They have one drawback and that is they are about 1.5" narrower than '71-73 axles, but that can be compensated for by spacers or wheel backspacing.

Rear axle upgrade/swap - Engine, Transmission, Drive Line, Etc - 7173Mustangs.com

Rear end (suspension and wheels) - Engine, Transmission, Drive Line, Etc - 7173Mustangs.com

 
If the bare housing flange to flange is 61.25" you likely have a '73 and up rear end, which will have an axle width of 65.25". '71 to '73 Mustangs have a housing width of about 57" and an axle width of 61.25". The bolt pattern for a '70s F150 wheel is 5 lugs on a 5-1/2" bolt circle, the ones for a Mustang are 5 lugs on a 4-1/2" bolt circle. 

What is the tag number?

If you want to swap in a stronger rear axle you should look for an 8.8" Explorer rear axle. They have 31 spline axles and are stronger than the 9-inch rear ends with 28 spline axles that came with our cars. They have the same bolt pattern on the wheels and they have disc brakes. They have one drawback and that is they are about 1.5" narrower than '71-73 axles, but that can be compensated for by spacers or wheel backspacing.

Rear axle upgrade/swap - Engine, Transmission, Drive Line, Etc - 7173Mustangs.com

Rear end (suspension and wheels) - Engine, Transmission, Drive Line, Etc - 7173Mustangs.com
That's cool! I wouldn't mind switching to disc brakes. Especially if it's oe. Well some fabrication needs to be done to this one so maybe I'll sell it and get a 8.8 instead. I'm sure I won't have trouble selling the 9 inch. Starting from a blank slate would you rather get an original 9 inch or the 8.8 swap?

 
If you're not doing a concourse restoration I would go with the 8.8, stronger, disc brakes (easy to get repair/replacement parts), 3.73 gears, and they were available with traction lock. I have a 9-inch with a Detroit Locker and 3.73 gears and have been considering swapping to the Explorer rear end, just for the disc brakes, if I find one for the right price. I like the idea of being able to go to a parts store and buy brake pads or a caliper kit without having to worry about what will fit a conversion kit.

 
I have had my 8.8 in my mustang for probably 13-14 years. I love it.  You can pick them up cheap from wrecking yard easily for $150 or less. Get the driveshaft too. I took explorer rear section of drive shaft and front section of my mustang driveshaft and had a driveshaft shop make me a custom driveshaft.  Definitely worth the time and money to do this swap. The  ranger station .com is good place for 8.8 info too. 

 
I have had my 8.8 in my mustang for probably 13-14 years. I love it.  You can pick them up cheap from wrecking yard easily for $150 or less. Get the driveshaft too. I took explorer rear section of drive shaft and front section of my mustang driveshaft and had a driveshaft shop make me a custom driveshaft.  Definitely worth the time and money to do this swap. The  ranger station .com is good place for 8.8 info too. 
Right on! Yeah I already sourced one out. 230. I'll have to ask about the drive shaft. Thanks for the good info. Now I just need to sell the 9 inch. I'm sure I won't have trouble with that. 

 
i have been watching some of Kenny Brown's presentations online. He does not like the 8.8 disc brake rears for performance applications. He said since the axles are retained by the C clips you have the side to side play in the axles. In fact my X wife complained about our 1984 mustang making a clunking noise when new. It was the axles shifting back and forth.
Kenny Brown builds most of the current racing mustangs. What he said was that every time the axles shift it pushes the piston back on the caliper so when racing you have to pump the brakes every time you use them. He much prefers to use 9" with disc brakes over the 8.8". The 9" disc brake rears were in Lincolns, higher end Granada and Mercury Monarch and do fit in mustangs. That is the direction I am going to go with my track car.. He also said to never use drilled and slotted rotors. They use only slotted to let the gas out said that drilled always break when racing and using heavy braking. They make a paint you put on the outer edge of the rotor that changes color showing the highest temperature the brakes work at. Then you select the right type pad based on the temp. They also bleed the brakes after every time on the track to get the heated up broken down fluid out of the calipers. He said that no fluid made does not break down due to the high temps when racing, they do get red hot lots of times boils the fluid.

 
i have been watching some of Kenny Brown's presentations online. He does not like the 8.8 disc brake rears for performance applications. He said since the axles are retained by the C clips you have the side to side play in the axles. In fact my X wife complained about our 1984 mustang making a clunking noise when new. It was the axles shifting back and forth.
Kenny Brown builds most of the current racing mustangs. What he said was that every time the axles shift it pushes the piston back on the caliper so when racing you have to pump the brakes every time you use them. He much prefers to use 9" with disc brakes over the 8.8". The 9" disc brake rears were in Lincolns, higher end Granada and Mercury Monarch and do fit in mustangs. That is the direction I am going to go with my track car.. He also said to never use drilled and slotted rotors. They use only slotted to let the gas out said that drilled always break when racing and using heavy braking. They make a paint you put on the outer edge of the rotor that changes color showing the highest temperature the brakes work at. Then you select the right type pad based on the temp. They also bleed the brakes after every time on the track to get the heated up broken down fluid out of the calipers. He said that no fluid made does not break down due to the high temps when racing, they do get red hot lots of times boils the fluid.
That's some really good info. I have been reading about the 8.8 inch and the inherent problems with the C clips. There is a solution out there that gets rid of the C clips entirely. I know most of us build our cars for that 10 percent. But I'm trying to sway from that and build for the 90 percent. Which is just a badass street car. I'm not a professional driver by any sense of the word and I don't need drilled or slotted rotors. If I was going to use mine for the track I would definitely be building a track car but since it's just going to be a street bruiser I don't think the C clips will be too much of a problem and if it does the C clip eliminator seems to fix that issue. 

 
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I haven’t had any problems with c clips with mine.  I have been running around 600hp through over the last few years and no issues. Brake pedal is always good.  The one thing you will want to do is weld the axles tubes to the center section. They are pressed in from factory and can twist if not welded. 

 
I haven’t had any problems with c clips with mine.  I have been running around 600hp through over the last few years and no issues. Brake pedal is always good.  The one thing you will want to do is weld the axles tubes to the center section. They are pressed in from factory and can twist if not welded. 
Thanks. I'll make sure to do that. Do you have staggered shocks on yours?

 
No I don’t. I have standard shocks. I took out factory u-bolt plates/ shock mounts and cut off the angled part that mounts the shock. I then welded that angled piece to a piece of 1/4” steel plate and drill holes in it for my u-bolts. The shop that made my driveshaft also custom made u-bolts too. 

 
No I don’t. I have standard shocks. I took out factory u-bolt plates/ shock mounts and cut off the angled part that mounts the shock. I then welded that angled piece to a piece of 1/4” steel plate and drill holes in it for my u-bolts. The shop that made my driveshaft also custom made u-bolts too. 
I was going to try to keep the staggered shocks so I'll probably try to have some fabbed up so I can keep them.  Do you got any photos of your set up? I would love to see some shots of how it's all mounted up. 

 
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You should be able to keep the staggered shocks. You just need to cut the mounts off the stock spring u bolt plates. The axle 8.8 is a different size tube than the 9 inch.  That’s why you need to transfer the shock mounts to new flat steel plate. 

I will look around for some pics but I can’t find any at the moment. I may be able to go out this weekend and get a couple. 

 
You should be able to keep the staggered shocks. You just need to cut the mounts off the stock spring u bolt plates. The axle 8.8 is a different size tube than the 9 inch.  That’s why you need to transfer the shock mounts to new flat steel plate. 

I will look around for some pics but I can’t find any at the moment. I may be able to go out this weekend and get a couple. 
That would be awesome. Nice car by the way! That burnout was badass!

 
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