Locker or sure grip for 8.75? What are you running in your hot street/strip car?

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blufie

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I posted this under different topic but no replies so trying different title and more specifics...

I need new third member... Car is 450ish HP automatic in 68 cuda... foot braking it. Plan is to occasioanly drive it street and to track for summer drags. Broke the rear Monday at around 4500rpm on hard first gear pull (on street and I think tires were still spinning a bit when it broke). I know I am going to have to tear the trans down (again) but not sure what to do with the rear end.

I don't know the exact HP or torque on this car yet but I thought I would be safe with a good 8.75. Maybe not? Am I nearing Dana 60 territory? Either way should I be considering a locker since I street drive some or would a good sure grip still be the choice? Not sure I could live with a spool but have no experience with them. Would rather only built this once so would prefer quality over initial cost.

I appreciate any info on what others are running and experiences/suggestions from the real world.
 
A well built 8 3/4 should handle your HP. have you taken the rear apart to see what broke. Did you break it in low gear? If so you probably broke the sprag in the trans.
 
If you are at the point where you are wrecking 8 3/4s in an auto car, its time to step up to a Dana 60.

A locking differential will not drive as well as a conventional limited slip type differential.

Just how bad depends an on driver impression. I think locking rear ends on the street totally suck, others think they are OK. Impossible to say what you would think.
 
Hmm,the locker in my trucks front axle doesnt do so well on pavement. It needs a slippery surface or the tires howl around corners. Im thinking a locker would be fine if there were some means of disengaging it for normal cruising /driving,like in my truck. Maybe an air locker?

If your 8 3/4 blew up Im thinking it was pretty tired already.Hardly ever hear about a failure.
 
needsaresto said:
Hmm,the locker in my trucks front axle doesnt do so well on pavement. It needs a slippery surface or the tires howl around corners. Im thinking a locker would be fine if there were some means of disengaging it for normal cruising /driving,like in my truck. Maybe an air locker?

If your 8 3/4 blew up Im thinking it was pretty tired already.Hardly ever hear about a failure.
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Air lockers are sweet.
 
SGBARRACUDA said:
A well built 8 3/4 should handle your HP. have you taken the rear apart to see what broke. Did you break it in low gear? If so you probably broke the sprag in the trans.
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Yes, it was in low and agree on he sprag. Diff and trans coming out today so may know more later.

needsaresto said:
Hmm,the locker in my trucks front axle doesnt do so well on pavement. It needs a slippery surface or the tires howl around corners. Im thinking a locker would be fine if there were some means of disengaging it for normal cruising /driving,like in my truck. Maybe an air locker?

If your 8 3/4 blew up Im thinking it was pretty tired already.Hardly ever hear about a failure.
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It was an original unit but seemed solid. The other (more likely) scenario is that when I changed to the 1350 pinion I didn't get the preload correct and it started the failure cascade.

I have never heard of an air locker but will look into it.

Thanks for the replies so far...

Would be interested to hear what more people have used when setting up their street/strip. I read a few other threads that suggested it was easy to spend as much on a beefy 8.75 as you would on a decent Dana... and then still break the 8.75 but I wouldn't think <500 hp would be enough for a slushbox foot braked <3000lb car.

I will post more details on the damage when I get them.
 
An 8 3/4 with a sure grip should hold up just fine behind a 500 hp auto car. I have seen 4 speed cars runing mid 11's do just fine wth an 8 3/4.
 
An 8 3/4 built right is plenty for what your putting throught it,i have one with Moser axles and 4.30's with a spool and billet yokes,i previously had a 489 3.91's and trac-loc,handles everything my stroker or 360 can throw at it,wheels up off the line..:-D:-D
 
I think the cost comparison between building the Dana 60 vs. and 8 3/4 is usually if sombody doesn't already have a housing. If you look at having a strange 60 built vs. buying a 8 3/4 housing and outfitting it then it is probably better to do the 60.

I think since you already have the housing you would be better off rebuilding what you have.

Best of luck!
 
Well, the rear is out. Not as much damage as I thought. Ring and Pinion seem ok, even spider gears not too bad (a little worn) but I did find some metal shards on the ends of the Yukon axles and in the case housing.. not many but a few...

So not really sure what I did to it now. Any ideas... I will pull it apart tonight but expected much worse. Tranny sounded like it was turning the drive shaft but car not wanting to move and growling when rpms applied after the bang.

Pulling trans now.

I will just rebuild a solid 489 center with good gears and put it back together... oh and go through the trans again :-D.

I really appreciate the replies as it is giving me confidence to go forward with what I have! Less bucks too!!
 
blufie said:
Well, the rear is out. Not as much damage as I thought. Ring and Pinion seem ok, even spider gears not too bad (a little worn) but I did find some metal shards on the ends of the Yukon axles and in the case housing.. not many but a few...

So not really sure what I did to it now. Any ideas... I will pull it apart tonight but expected much worse. Tranny sounded like it was turning the drive shaft but car not wanting to move and growling when rpms applied after the bang.

Pulling trans now.

I will just rebuild a solid 489 center with good gears and put it back together... oh and go through the trans again :-D.

I really appreciate the replies as it is giving me confidence to go forward with what I have! Less bucks too!!
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Look at the ends of the axles.I'll bet the splines are spun off due to not enough spline engagement. Seems like a common problem when replacing axles with aftermarket. They just dont seem to be the right length.
 
I haven,t heard anything good about the Yukon axels for 8 3/4,s.Heard there too short,not 28 inches.Maybe you should measure and post there length?

P.S Sounds like your clutch pac is worn(slipping)Is it clutch or cone type sure-grip?
 
That 8 3/4-489 you've got should stand up to a 500HP auto car no problem. Go through it with a fine tooth comb and if in doubt throw it out. Pay particular attention to the housing bearing saddles and have the caps die checked for cracks. If you're running the cone type check that they haven't worn to much into the housing and if it's the clutch type replace the discs and plates. Then drive her like ya stole her.
I'm running dam close to 500 thru a 742 and haven't broke er and that's with the occasional stickies bolted on. (drives the street stang drivers nuts when they're spinning and I'm not)
http://www.moparts.org/Tech/Archive/axle/13.html

Terry
 
Sounds more like you broke the transmission. Possibly the one of the planetaries if 2nd didnt work. Ive done that just driving normal in a car that had a big block, weighed 4300lbs, and uased a 150hp NOS plate. Sometimes they just reach the end and pop.

If it's the rear, I only use the Detroit Tru Trac now. It's about $100 more than the new Aubrns, but they are trash along with most cone types. The True Trac will never need rebuilding and you wont break it, plus, it will never loosen over time and abuse. But you need to run Green axle bearings as they do not use a floating spacer for the end play.
 
SGBARRACUDA said:
Look at the ends of the axles.I'll bet the splines are spun off due to not enough spline engagement. Seems like a common problem when replacing axles with aftermarket. They just dont seem to be the right length.
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We have a winner - axles. The drivers side axle was only engaged by 1/3 inch (and that part is now stripped bare). Probably the same for the psgr side. I have a 741 case out of a 71 Dart so think it has clutches but they are probably toast now as well.

pettybludart said:
I haven,t heard anything good about the Yukon axels for 8 3/4,s.Heard there too short,not 28 inches.Maybe you should measure and post there length?

P.S Sounds like your clutch pac is worn(slipping)Is it clutch or cone type sure-grip?
Click to expand...

The Yukon axles measure 25 1/2 inchs from the mount plate, and 27 1/2 inchs from the back of the axle. Looks like I needed at least another inch on both sides. That is pretty crappy. I bought them from Mancini (before I found this site and heard some of the quality issues posted) but I at least expected them to be the correct length :angry7:. The problem with that sentence is expect... if you don't measure... you lose.

Edit... I just noticed that I have the early style 2 piece split spline rear and Mancini reccomends that you need to order a diff part # (longer axles) with this combo. I may have made this mistake myself.

So.. SGBARRACUDA - still have the 489 case for sale :happy10:?

Thanks again for al the help and replies / sugestions. The teardown was needed anyway since I needed to replace my sprag and I had a broken sealing ring in the tranny that was causing converter drain so once I build the rear and tranny back I should be solid for a while.

One more question: If I get an auburn style posi (or similar) in the new rear, I wonder if I can still use these axles?? Since I only had 1/4-1/3 of an inch engaged (and stripped on one side) If I got a full inch or better engaged in a new setup they might still be serviceable. Guess I will do some close measuring during the rebuild.
 
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