Got the rear fixed!

[Outlaw72]

I plan to do a write-up on this build as a contribution to the site. Maybe something you guys can sticky. I see tons of questions regarding rear-ends in the drivetrain forum and it might have some pointers others can follow. This was a complete bulletproof 12 bolt truck build I did myself. They are still weak rears and there is no proof that this one will hold to my future plans but we will see.





4.56
studded mains
solid pinion spacer - no crush collar
welded axle tubes
girdle cover
3 in axle studs

Everything is complete except for the axle studs. I need to buy a 9/16 drill bit and make the holes a lil wider and the moroso studs will press in.

[Outlaw72]

Here are a few before pics ...

[usernamessuck]

Awesome!

[Super73]

So what makes these 12 bolts weak?

[Outlaw72]

Believe it or not the 8.5 10 bolt is a stronger rear than a truck 12. Keep in mind there is a difference between a truck 12 and a car 12.

The truck 12 has a 1.4XX pinion shaft diameter and the 8.5 10 bolt has a 1.6XX pinion shaft diameter. The car 12 also has this 1.6XX pinion shaft diameter. Therefore, the truck 12 is weaker in the pinion shaft.

Also, the truck 12 has a 3/8 ring gear bolt as opposed to the 7/16 ring gear bolt of the 8.5 10 bolt. This is a weak point also.

This doesn't mean it's a weak rearend, it just means theoretically and on paper it is not quite as strong.

I guess I should elaborate on my statement of "weak"....I wasn't trying to say the 12 bolt truck is weak. Otherwise, I would not have spent the money to beef it up. It was more of a test for me to see how well a strong one will hold up in extreme nitrous situations and 1.5X possibly 1.4X 60.ft times. A low 1.5 60ft. for me is right around the corner and I want to know how strong they really are with almost full lwb weight on top of them.

[BADGMC]

Chances are you'll strip the teeth off the gears again as a result of the pinion trying to climb up the ring gear on the launch. The case just doesn't have the beef to resist flexing which allows this to happen. 4.56 and lower ratios are famous for this since the pinion has very few teeth. Why don't I see any mention of aftermarket axles or at least c-clip eliminators in your list of parts as you're going to need them.

[Outlaw72]

You are right....that will probably end up being the result again. As I mentioned earlier, it is just a test case and I had X amount of dollars to spend. I was not going to spend 14-1500 dollars to make a solid unit if it is just going to break again so the money was spent to strengthen the carrier area as much as possible. Axles were the only thing spared and since it is driven on the street often, I kept the c-clips in it as well as the old carrier. If the 30 spline stock axles break, then I'm cool with that. I will clean it up and throw some axles in it and see how much longer it will last. If I am going to spend that kind of money, I will build a complete 9 inch and be done with it. I'm just trying to see how much abuse one will take before I buckle up and throw a 9 inch in it.

[GMC70c20]

just to throw this out there A guy I work with runs 10.80's in his nova with a 8.5 10 bolt rear.

[Outlaw72]

There are several guys here running in the 8's on a 10 bolt 8.5 @ 3200 lbs.

[djracer]

I run a 9 inch because its easy to deal with and much cheaper to get some one to set up your gears in his shop instead under your truck.

[Super73]

I took and hacked a Ford 8.8 center section and slid my old 7.5" 10bolt tubes in it after laything them down. This was for my 01 Camaro. It allowed me to keep the ABS and traction control. I also got rid of the Torque Arm and made the LCA's in to a short ladder bar (Pete Z-bars).

I did all this as I was worried aobut breaking the small 10 bolt in my camaro being a 6 speed and 510rwhp. Sold the car shortly after.


Now I have heard you can convert the truck 12bolt rear to a car 12 bolt rear. Is this true? Would that be worth it?

[Outlaw72]

Originally Posted by Super73

I took and hacked a Ford 8.8 center section and slid my old 7.5" 10bolt tubes in it after laything them down. This was for my 01 Camaro. It allowed me to keep the ABS and traction control. I also got rid of the Torque Arm and made the LCA's in to a short ladder bar (Pete Z-bars).

I did all this as I was worried aobut breaking the small 10 bolt in my camaro being a 6 speed and 510rwhp. Sold the car shortly after.


Now I have heard you can convert the truck 12bolt rear to a car 12 bolt rear. Is this true? Would that be worth it?

In my opinion, no...it would not be worth it and this is why.

First you are gunna have to find a 12 bolt car center (unless you already have one) and this will require the purchase of a complete housing (most likely).

Second, you will have to buy all new guts because you cannot interchange the guts. Hence the exact reason parts are sold specifically for car or truck.

I think I would rather fab a 9 inch together and be done with it. Seriously

In the case of your 8.8, now that would be a great idea IMO for the simple fact if you look hard enough, you can find an 8.8 for free. The 8.8 is extremely strong and would be worth doing for an F-Bod.

[Outlaw72]

Originally Posted by djracer

I run a 9 inch because its easy to deal with and much cheaper to get some one to set up your gears in his shop instead under your truck.

Yes....one of the many advantages of the 9 is to just pull the pumkin and throw it on the bench. I use to charge only $100 for 9 inch set ups.

[djracer]

I have guys that will do that for me for free. getting one of them to come lay in my shop floor well that would be another story!.

[71Dragtruck]

Another thing is aftermarket parts availability, compare a list of parts available for a truck 12 compared to a 9", even a car 12 for that matter. My new 9" won't have a single Ford part in it, except for being based on one of their rearend designs, to call it a Ford rear is a very large stretch. I have this coversation with a guy all the time who's also hung up on go with a 12 bolt opinion, and it goes the same way every time. I have way too much money tied up in my truck 12 now and it is still way too weak for my application, and I have no plans of sinking a single nickel into it ever again.

[Outlaw72]

Originally Posted by 71Dragtruck

Another thing is aftermarket parts availability, compare a list of parts available for a truck 12 compared to a 9", even a car 12 for that matter. My new 9" won't have a single Ford part in it, except for being based on one of their rearend designs, to call it a Ford rear is a very large stretch. I have this coversation with a guy all the time who's also hung up on go with a 12 bolt opinion, and it goes the same way every time. I have way too much money tied up in my truck 12 now and it is still way too weak for my application, and I have no plans of sinking a single nickel into it ever again.

Yea....I hear ya. That's why I didn't spend a ton of money. I didn't build this rear originally. I would have never put Richmonds in it to begin with. So, the $600 I just spent will be all I spend. I refuse to beat a dead horse to the ground. If it breaks again, I already have a 9inch ready for some trailing arm plates and coil over brackets. Axles and pumkins will be so easy to come by so, my backup plan is already in place. Just thought I would spend a little money on it once and see what happens. Frankly, I would kinda like to know how much abuse a stronger one will take. Just for the sake of information.

I set up gears in many different rears, built PTO's for big trucks and driveshafts for a while before I changed profession. Now I'm a software engineer. The last two rears I put together for friends was an 8.8 that is cutting 1.2XX 60ft times and a 9inch that is pulling the same 60ft. I only charged my buddy $50 to set up his 9 inch. They are so easy it is unbelievable. I will not do another one on my back. If you look close, you will notice even mine is up on a bench out of the truck.

[Super73]

Speaking of weak rears though, the 7.5" 10bolt being the time bomb that it is, lasted a long time in my buddies 10 second Camaro. It seems the M6's are much more brutal on them than the autos. He was cutting consistant high 1.5's on the motor and low 1.4's on the bottle.

Now I know weight was really helping there (his car being 3,200 with out him), but my truck last time weighed was only 3,840 with me in it. I have since:

Swaped from 7" steel wheels to 6" front and 12" rear drag lite
Removed front bumper and frame stubs
Pulled heater box and plumbing for it

Have yet to:
Remove power steering and install Vega steering box
Swap to manual brakes from my boosted set up
Buy glass hood.

I suspect I'll be a little bellow stock F-body weight when done.

[djracer]

you will have to do more than that to get below 3200!

Originally Posted by Super73

Speaking of weak rears though, the 7.5" 10bolt being the time bomb that it is, lasted a long time in my buddies 10 second Camaro. It seems the M6's are much more brutal on them than the autos. He was cutting consistant high 1.5's on the motor and low 1.4's on the bottle.

Now I know weight was really helping there (his car being 3,200 with out him), but my truck last time weighed was only 3,840 with me in it. I have since:

Swaped from 7" steel wheels to 6" front and 12" rear drag lite
Removed front bumper and frame stubs
Pulled heater box and plumbing for it

Have yet to:
Remove power steering and install Vega steering box
Swap to manual brakes from my boosted set up
Buy glass hood.

I suspect I'll be a little bellow stock F-body weight when done.

[Super73]

Stock 4rth gen f-bodies weigh about 3400-3500 depending on options, buddies car had some weight taken out.. That's what I'm shooting for for now..

[djracer]

I wish I could afford an aluminum 598 short block!

[Outlaw72]

Super....can you point me in the direction of any articles talking about putting an 8.8 in an fbody? That's an idea I may have to use for my 02 TA!

[Super73]

There is no article persay.. What I did was took a 8.8 apart. Cut off the axle flanges..

Take the 10 bolt and make a jig. Take 2 pieces of flat stock for the tube ends. Drill th 4 holes in to the flat and bolt it up. Take a piece of square tube and cut the bottom and top to length and weld it to the inside of the flat stock. There is your width.

Take and make a couple arms that come off the square tube and come in contact with the axle tubes about 4-6" in from the axle end. This will support the axle tubes when you weld on the new ends.

Cut the tubes off the 10 bolt fairly close to the center section.

Take and ID measurement of the 8.8 tubes. Lathe the 10 bolt tubes down to that. Now the 10 bolt tubes should be able to slide in to the 8.8 tubes, this adds strength (one thing to know though is the 8.8 tubes get smaller towards the center section).

Weld up the seems.

I opted for 9" ends to get rid of the c-clips. You can weld them up at this time.


Now, I did not use a TQ arm. Call Madman (LS1 tech sponsor) and order up some Pete Z bars. You need to have a hotchkis like square tube control arm though. They come with brackets that weld to the rear and have a tube that bolts to the control arm. It turns your LCA in to a ladder bar basically.

They allow you to adjust pinion angle with the new top bar.

No more TQ arm allows for a larger drive shaft..


Doing this changed the instant center of gravity and antisquat dramatically. The rear would rise and hook way hard on the street..

[Outlaw72]

Interesting....

[Outlaw72]

I have a fab guy that can prolly do just that...I bet I can find a trashed 8.8 for free.

[Outlaw72]

Well...the rear is back in the truck.....looks like everything worked out okay. Ran into a few snags with the new axle studs but we are good now.

Note to self.....try not to put gear oil in when it's in the 30's outside.