Differential HAMMER!

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Differential HAMMER!

Post by marks454ss on Sun Jan 04, 2015 8:11 am

During my recent back surgery I had a garage install my 3:55 gears. I never got to see the inside but was told it's a 67 12 bolt posi unit. Broke it in by the Richmond gears paperwork and have about 300 miles on it since I changed the oil. Yesterday I ran it for about 5 miles at 75 in a 70 zone for the first time. Drove an additional 10 miles at 60 on the way home. When I turned into the neighborhood, about 30 ft after straitening out I hear 2 BANGS that sounded like you hit the housing with a 3 pound hammer. Never going over 20mph, I turn left onto the next street and again after straitening out 2 more bangs. Turn left onto my street, same thing! Let car sit about 1/2 hour and get neighbor to come over and walk beside car to verify if it is indeed rear end. Now it won't do it but he said he heard it when I was 2 streets over. Anybody have any ideas as to what I should be looking for when I pull the cover? I'm more familiar with the 9 inch Fords (put a Detroit locker in my 73 Mustang).
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Re: Differential HAMMER!

Post by Joe73 on Sun Jan 04, 2015 8:55 am

Every time I've had that happen (three times for me) it was the cross pin that slid out of the unit. Meaning the cross pin bolt broke and allowed the cross pin to slide in and out. When it comes out it hits the diff housing with a bang. Pretty scary. Both times I oblonged the posi unit which needed replacing. Now when putting in the cross pin bolt I dont rely on the goo that comes on its threads when new for locking. I like to clean it real good with brake cleaner, put some loctite on and then torque it to spec.
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Re: Differential HAMMER!

Post by ant7377 on Sun Jan 04, 2015 10:29 am

Same thing happened with my 73 monte. DONT DRIVE IT! When it let go it destroyed everything in there. Get it towed to whoever put it together for you. Like Joe said the bolt came out for the crosspin. That bolt should be replaced as well when taking out the carrier.
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Re: Differential HAMMER!

Post by marks454ss on Sun Jan 04, 2015 10:35 am

Thanks guys. Would the oblonged hole be obvious in the unit?
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Re: Differential HAMMER!

Post by ant7377 on Sun Jan 04, 2015 10:37 am

Should be. The amount of force of the cross shaft wacking the inside of the housing is incredible. Im sure that noise was very loud.
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Re: Differential HAMMER!

Post by Joe73 on Sun Jan 04, 2015 10:49 am

ant7377 wrote:Should be. The amount of force of the cross shaft wacking the inside of the housing is incredible. Im sure that noise was very loud.

Yes, the hole in the carrier should be oblonged if not cracked. When this happens the carrier is usually gone and 2 out of three time for me the cross pin knocked a few teeth off my pinion.
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Re: Differential HAMMER!

Post by ant7377 on Sun Jan 04, 2015 10:52 am

Also have it flatbedded back to the shop. The c clips broke on mine and the axles started to come out while it was on the trailer going to the shop from it swaying. Dont know if they broke yet on yours but FYI.
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Re: Differential HAMMER!

Post by marks454ss on Mon Jan 05, 2015 9:32 am

Researched some carriers. OUCH!
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Re: Differential HAMMER!

Post by mc71454 on Tue Jan 06, 2015 6:22 pm

marks454ss wrote:Researched some carriers. OUCH!

Mark,

As already been said, it is very likely the Pin. I use open carriers with Powertrax Lock Rite Lockers in 3 cars. The open carriers are cheap and sometimes free and the Locker is $330. Might be an economical alternative.
I use them because they act like a spool on the straight away, no slipping or inconsistent launches as the clutches wear or get real hot. Never mind the "Cone" types which are not for use at the strip.

Tom



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Re: Differential HAMMER!

Post by dynchel on Tue Jan 06, 2015 9:45 pm

mc71454 wrote:
marks454ss wrote:Researched some carriers. OUCH!

Mark,

As already been said, it is very likely the Pin.  I use open carriers with Powertrax Lock Rite Lockers in 3 cars.  The open carriers are cheap and sometimes free and the Locker is $330.  Might be an economical alternative.
I use them because they act like a spool on the straight away, no slipping or inconsistent launches as the clutches wear or get real hot.  Never mind the "Cone" types which are not for use at the strip.

Tom



I also have a powertrax locker (but I have the more expensive one, can't remember the name). It works very well, and was easy to install for anyone with some mechanical ability.  My only complaint is it does make some loud noises at slow speeds when it engages/disengages.
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Re: Differential HAMMER!

Post by marks454ss on Wed Jan 07, 2015 9:21 am

Again. Thanks guys! This looks like the best alternative. Hoping to get the car hauled to the garage that installed my ring and pinion and see what they are willing to do about this. I'm thinking though they will try to put it on me. (small garage) Either way I'm going to get this thing back on the road.
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Re: Differential HAMMER!

Post by pila on Wed Jan 07, 2015 10:22 am

They may fix it in the end..that's what product liability insurance if for. People make mistakes sometimes, and always will ...

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Re: Differential HAMMER!

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