Broken Diff

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nqkjw

nqkjw

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Broke the diff in my barracuda at the strip last night.

Probably a little early posting this as i haven't stripped it down but looking for advice on whether to upgrade or not.

The car -
69 notch barracuda 440 powered street'n'strip car
Trans - 727 reverse pattern manual with 4000 stall
Race weight 3430lb
303 rwhp

The diff -
8 3/4 741 case with spool,3.55 gears and Currie 30 spline billet axles.

It's either stripped the gears on crownwheel/pinion or sheared the pinion I feel.

Last night it was running 12.1s in the 110s
Traction was off with 60fts in the high 1.7s whereas it's usually mid to low 1.6s.

I have enough parts here to get it together again which is what will happen in the short term but will it break again or was I just unlucky?

Everyone is Ford 9" over here and admittedly aftermarket parts are easy and relatively cheap for them.
8 3/4 and parts are uncommon and rare but not hard to get direct from the US although freight costs load up prices a lot.

There is a 493 stroker at maybe 600-650hp on the way so ultimately can I make an 83/4 survive or should i just look at going straight to a Dana 60?

Any comments greatly appreciated.
 
8 3/4 will hold up fine to that h.p level. Another 100 and I'd want a Dana
 
just a note...if you broke the rear while in low gear...

check the spraq in the trans...
 
You could have broken a cap also which would have led to broken teeth. Is the housing backbraced? That will help and a steel cap or two won't hurt either. As far as 9"s go, you're probably better off with what you have. The only way a 9" is better is if you throw pretty much all of it away and replace it with aftermarket EVERYTHING. Going to a Dana 60 is actually a reasonable upgrade.
 
I have only stripped gears in my 8n 3/4, and only 3 of those in the last 25 years. I was told that it was only because they were set up wrong(Iv'e never set a set up I don't know how). I think it's because I buy my 741s/391s/clutch sg out of 45 year old dodge trucks. I have never seen a broken pinion in any 8n 3/4. when I find a 742 489 I sell them because I trust the 741s for what I do, and people pay good money for the 742 and 489s. my currant car runs mid13s, but Iv'e had cars that ran in the low 12s with 741s.If you broke the Pinion can post pitcher of it, just so I can say I seen one?
 
herschel said:
I have only stripped gears in my 8n 3/4, and only 3 of those in the last 25 years. I was told that it was only because they were set up wrong(Iv'e never set a set up I don't know how). I think it's because I buy my 741s/391s/clutch sg out of 45 year old dodge trucks. I have never seen a broken pinion in any 8n 3/4. when I find a 742 489 I sell them because I trust the 741s for what I do, and people pay good money for the 742 and 489s. my currant car runs mid13s, but Iv'e had cars that ran in the low 12s with 741s.If you broke the Pinion can post pitcher of it, just so I can say I seen one?
Click to expand...

I just seen the part where your going 600hp-650, I have seen pic's in magazines with a clear view of cars with there 8n 3/4 leaving line with the front wheels 5ft in the air. but it' s probably time for a dana 60.
 
I've just drained the oil.
No peices came out but i can stick my finger in the hole and there's a lot of pices in there so I'm thinking stripped gears.
Just gotta get motivated enough to pull it out now!
 
My buddy has a 493ci 440 with a solid cam,aluminum heads,Victor intake and 1050 he broke his gears on the ring gear. But he went from 488s to 430s and hes been fine his car is a street/strip car also..

So I would say a 8 3/4 would hold up to a 493ci with 600-650hp..
 
Will the stock gas tank fit with a Dana 60? Is there anything else that needs to be changed to fit the big axle in there?
 
What gear were you in when it broke? If it was in first, you need to pull the transmission and inspect the sprag at the rear of the case.
 
furd 9" aren't what the are talked up to be. I pulled the center out of mine (it was installed in the car when I bought it) to change r&p. When I pulled the spool out, the casting was broke around the small pinon support bearing. Luckily my buddy had another yet stronger case so we were able to put it back together. l replaced all the bearing in it also.
 
If your going 600-650hp a Dana would end your worries...period.If all you can find or afford is a 9 inch?Build whats best for you.Maybe see if you can find a .489 case and build it with a spool(4.30,s)My narrowed 8 3/4 .489 case with spool and Strange axels has held up well so far.If it starts breaking,I will go Dana,8)
 
CUDA69 said:
Will the stock gas tank fit with a Dana 60? Is there anything else that needs to be changed to fit the big axle in there?
Click to expand...

yes we do it all the time


pettybludart said:
If your going 600-650hp a Dana would end your worries...period.If all you can find or afford is a 9 inch?Build whats best for you.Maybe see if you can find a .489 case and build it with a spool(4.30,s)My narrowed 8 3/4 .489 case with spool and Strange axels has held up well so far.If it starts breaking,I will go Dana,8)
Click to expand...

and i was also gonna mention he is only running a 741, should be running at least a 742 or 489 case...

F 9"
 

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805moparkid said:
yes we do it all the time




and i was also gonna mention he is only running a 741, should be running at least a 742 or 489 case...

F 9"
Click to expand...

how much clearance do you have between the diff and tank? and is the axle in the stk location or moved back?
Nice lookin rear end .:bootysha::toothy10:
 
Dana's are plentifull in p/u trucks. You will need to narrow the housing and change the spring perches but there are still tons around.
 
scamp 408 said:
how much clearance do you have between the diff and tank? and is the axle in the stk location or moved back?
Nice lookin rear end .:bootysha::toothy10:
Click to expand...

axle and tank is in the stock location, some times they rub depending in the cover we use...
 
I'd sell the 8 3/4 with all my parts for it, so I could buy a Dana 60. If you some how manage to break the Dana 60, the only thing left is a Rockwell.
 
Like mentioned above. A 60 with an aftermarket cover can get close to the tank.

I have the factory Dana 60 cover and XHD springs in the factory location (68 Barracuda). My clearance is fine.
 
Stripped the ring and pinion.

Short term I've got a 3.55 489 case LSD I'll just whack in for now.

I've also got a 3.23 open 741 case so medium term I'll get some better gearing (3.73s?) and spool that up.

Long term I guess I've got to go Dana 60.I'd rather Dana 60 as opposed to 9" because I like to be different.The $$$ aren't that big an issue.

nnobbr.jpg


just a note...if you broke the rear while in low gear...

check the spraq in the trans...
Click to expand...

Yep!!! Will certainly speak to my tranny builder.He was actually out there and saw me break LOL.

Will the stock gas tank fit with a Dana 60? Is there anything else that needs to be changed to fit the big axle in there?
Click to expand...

I've got a flat trunk floor and trunk mounted fuel cell so i can fit ANYTHING in there.
The only thing I need to clear is twin 4" over the diff tailpipes.

If your going 600-650hp a Dana would end your worries...period.If all you can find or afford is a 9 inch?Build whats best for you.Maybe see if you can find a .489 case and build it with a spool(4.30,s)My narrowed 8 3/4 .489 case with spool and Strange axels has held up well so far.If it starts breaking,I will go Dana,
Click to expand...

$$$ aren't really a problem as I stated above and I really don't mind breaking stuff.I've been doing that all my life LOL.
4.3s are too stiff for me atm.I don't have enough rpm.I have had 3.91s in there and it went no better.Just over revved over the line.It's only got 5200 useful rpm and I'm running a 28" tyre.
Ultimately I guess it's gotta be a Dana 60.

Dana's are plentifull in p/u trucks. You will need to narrow the housing and change the spring perches but there are still tons around.
Click to expand...

Not in Australia!!! But i'll turn up something.

Thanks for all the interest and comments.It's pretty well confirmed what I was expecting but it's good to get other opinions.
Any more certainly welcomed!!!
 
What shape is the pinion bearing in?
Something looks like it moved, odd it took inner diameter teeth off of the ring gear.
What shape are the bearing races in?
 
Bearings are all fine.
They were new when I assembled the spooled diff.
But you're right.
Something did move.
The bearing adjuster on one side (the part that screws into the cap and carrier) was blown out.The lock tab still had it in it's correct place but the bottom was blown out.
Whether this has caused things to move and the failure or whether the failure blew the adjuster out is hard to say.

Anyway,she's up and running again with posilok 3.55 489 centre.
It's booked in early new year to have the tranny pulled and disassembled.
My tranny mechanic was out there when I broke the diff and he doesn't feel I'd have hurt the tranny (it was built for the 493 stroker that's coming and is guaranteed to handle 800hp) but he said it'd be wise and good insurnce to check it.The box has done over 200 runs so he's interested to see inside it anyway.
 
As stated, a cap may have broken allowing the ring gear to move away from the pinion and the rest is history! I am using a 8 3/4 in a Dart Sport but only for one more go round! When it breaks...and it will, a Dana will be installed. ALSO your trans needs to come apart! DO NOT RUN THIS CAR UNTIL YOU CHECK THE ROLLER CLUTCH! Bad things happen to the trans case/legs/ankels etc. if you do not check the trans! If you don't believe me google 727 trans explosions! Pix will help you decide what you should do! I'm sure someone in the forum has pix to pass along to you!
 

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Yeah,cars parked up till the trans comes apart.
It's booked in for abt 10th January - 1st job when they reopen for the new year.
 
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