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  #1  
Old 08-17-2008, 03:23 PM
coronetcustom coronetcustom is offline
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Default busted rear?

hello all,
i think i broke something while trying burn some rubber.
i used little brake and gave some gas, car shook a lot. i did quick check on engine and gearbox(727 automatic), they seemed to be ok. i drove car real slow and gently half a mile to my garage. when near home, i tried accelerating with more gas and felt a small shock, like if rear wheels ran over a plank or something. i re-tested and same happened again, i pressed down brakes bit faster and could feel the same thing.
i checked shaft ends and could not see damage or slack. i raised rear up and rotated wheels. i could not hear, see or feel anything unusual.
i got 8 3/4 banjo type rear axle assembly. car is from 1971, but i don´t know more info about rear end.
any suggestions?
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  #2  
Old 08-17-2008, 03:34 PM
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ehostler ehostler is offline
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Is it an open rear or a sure grip? If it is an open, you may have broken a tooth or two on a spider gear.
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Old 08-17-2008, 03:49 PM
John Kunkel John Kunkel is offline
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Did you have the shifter in D when attempting the burnout? (if so, shame on you)

Does the car accelerate from a stop OK in D? If the car is sluggish when accelerating from a stop in D but is OK in "1", you busted the sprag in the transmission.
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  #4  
Old 08-17-2008, 05:24 PM
coronetcustom coronetcustom is offline
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i had shifter on 1st on burnout. when i drove car to garage i had shifter on 2. will do more tests tomorrow. don´t know what is open rear or sure grip. what does "sprag" do? is it easy to fix?
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  #5  
Old 08-17-2008, 10:39 PM
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ehostler ehostler is offline
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Open rear = peg leg (power is sent to one tire and the other goes along for the ride)
Sure Grip = Limited Slip Differential (power is sent to both tires)
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  #6  
Old 08-19-2008, 11:28 PM
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pishta pishta is offline
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did the same on a 7 25 sure grip, pinion took a shark bite out of my ring gear. Would actually roll, but would not take any power as it would skip when it got to the damage. Smelled like a dead body when I opened it up, very strange.
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  #7  
Old 09-01-2008, 01:39 PM
coronetcustom coronetcustom is offline
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Default culprit found

problem turned out to be broken u-joint(front) and completely(but neatly) torn engine mount rubber pad. lucky i broke u-joint at same go. it had deep grooves from needle bearings on all points and cups, might have failed while doing 60 on highway. will also replace rear u-joint tomorrow. seems like all is well. i´m not sure about what to say to question about type of rear, open or sure grip.. both wheels spin on gravel and wet tarmac, but on hot, dry tarmac mostly draws line with passenger side wheel
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  #8  
Old 09-01-2008, 02:54 PM
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pishta pishta is offline
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u-joints, the fuse of the driveline. Least expensive and easiest to replace! And if your worried about your rear end breaking, just get one of these.
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  #9  
Old 09-06-2008, 08:24 PM
dodger1 dodger1 is offline
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Lucky you! U-joints are cheap and easy. Regarding the rear axle description, we can sometimes forget that not everyone is familiar with the nicknames we give to lots of gearhead things. Ed used one (peg-leg) to describe open rear, neither of which may make sense to you, but the description of how they work is fine. Other terms for limited-slip differentials include Positraction (Posi), a GM tradename but often used as a generic description for any limited-slip diff. Auburn also makes limited-slip diffs for many axles - works on a different principle but gets the same result. Easiest way to check for the presence of a limited-slip is to lift the axle enough to clear the ground, and manually turn one wheel. If the opposite wheel rotates in the same direction, you have a limited-slip (or locked) differential. If the other wheel rotates in the opposite direction, you have an open differential.
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  #10  
Old 09-06-2008, 11:00 PM
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Ray Bell Ray Bell is offline
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Even better...

Jack one wheel, have the car in neutral, if you can't turn the wheel it's a limited slip, if you can it's an open or normal differential.
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  #11  
Old 09-07-2008, 10:34 AM
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JVMopar JVMopar is offline
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Word of caution

Never attemp a burnout in D. When the shifter is in D the sprag at the rear of the transmission case is holding when you start to rev the engine and load the drivetrain. Then when the tires break loose and the drivetrain unloads all it's stored energy it will shock the sprag and cause it to spin loose in the case which isn't good. The factory sprag is only pressed into the transmission case. They do make a bolt in sprag to take care of this problem.

Leaving it in 1st doesn't use the sprag. Since you don't use it you won't wreck it.
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  #12  
Old 09-07-2008, 10:46 AM
Century Cp Guru Century Cp Guru is offline
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JV Mopar that Post is so wrong.When the Shifter is in D its in first Learn alittle about TFs before you speak.
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  #13  
Old 09-07-2008, 11:03 AM
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JVMopar JVMopar is offline
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I think you need to take a look at the component application chart in a factory service manual before you make a post like that. If you knew anything about TF's you'd know that the sprag is only holding in drive. It is not used in the manual 1st.

In manual 1st the low/reverse band is applied to hold. Instead of the sprag.

And sprag failures are common in the drag race world where high loads on the drivetrain are unloaded instantly. That's why the aftermarket makes a bolt in sprag so it can't spin in the case. It's a common upgrade during rebuilds.
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  #14  
Old 09-07-2008, 12:26 PM
Century Cp Guru Century Cp Guru is offline
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No Kidding No Matter what you Never Use 1st gear to Do a Burnout.
But with a Good Manual Valve Body most are Built with NO BAND Aplly on
deceleration.
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  #15  
Old 09-07-2008, 02:40 PM
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JVMopar JVMopar is offline
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Yes your right with a manual valve body it's better to do your burn out in second gear. This will avoid a sprag failure and ultimately possible front drum failure from overspeeding the assembly.

But with a stock valve body which from what I can determine this guy has. Then using Low or maual 1st is the safest way. The low/reverse band will help protect the sprag and front drum.

Here is a site with a good discription and good info http://board.moparts.org/ubbthreads/...=1&Search=true
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  #16  
Old 09-07-2008, 05:08 PM
John Kunkel John Kunkel is offline
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Quote:
Originally Posted by JVMopar View Post
Then when the tires break loose and the drivetrain unloads all it's stored energy it will shock the sprag and cause it to spin loose in the case which isn't good. The factory sprag is only pressed into the transmission case. They do make a bolt in sprag to take care of this problem.
In reality, sprag failure seldom involves the outer cam spinning in the case, the most common failure involves the rollers and springs which is why the bolt-in sprag is no panacea for sprag failures.

The pic below shows a failed bolt-in sprag with the bolts clearly visible.
Attached Images
File Type: jpg Sprag.jpg (48.4 KB, 12 views)
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  #17  
Old 09-07-2008, 07:17 PM
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JVMopar JVMopar is offline
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That's what I derived from that other site I posted. I guess I've always heard about the sprag spinning in the case and not the tips rolling over and letting the rollers loose.

I'll be the first to admit that I don't know everything. You learn something new everyday.
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