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Burn Out Help: 2.76 gears in an 8.75 rear end

watermelon

watermelon

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Hi All,

I have a 66 Coronet with a 727 driving a 8.75" rear end with 2.76 gears. All tires are BF Goodrich's 235/60R15.

My kids and I did out first burn out in the car and the sucker produced a nice cloud of smoke.....all be it on one wheel. It was fun any how.

Well, now we want to see two rear wheels smokin.

I like the fact that the car can hang with modern freeway traffic speeds so I like the 2.76. However, we want to see two patches of rubber.

I am guessing I have to change out the 2.76er for some type of locked diff setup I think.

What do you recommend?

Also, I may be dropping the 727 for a Keisler 5 speed eventually (can't get them out of my mind even with all the current bad buzz surrounding them). So I want something that will burn two wheels, maybe increase the launch speed a bit, hang with freeway traffic, fit into the 8.75 housing, and take into account a 5-speed manual transmission at some point in the future.



thanks,

watermelon
 
A Sure Grip unit can be installed with any gear ratio in your chunk.

It might be pricey, though. I think they are about $300, and probably another $300 labor for someone to set it up for you.

2.94 is areal common final drive gear, and might be just a bit easier to launch, while not affecting highway running too much.

Then there's 3.23- probably the easiest factory SG rear to find used.

Not surprising to find decent ones for around $250.

The manual trans conversion will probably cost you in the ballpark of 5K, unless you get REALLY good deals and do the work your self.
 
.............and to add to the above, doing one-wheel burnouts with an open axle is REALLY hard on spider gears.
 
thanks for the replies.

i did some craigslist prowling and found a complete 8.75 center section with a posi clutch type sure grip and 3:23 gears with 489 case for sale "in great shape"...$400ish.

i looked at my casing and found out i have a 741. i may go and check this out.

what do i look for in terms of condition on these things? i am guessing chewed up teeth is a no-no but anything else?

also, will this work with my drive shaft, axles, n other stuff?

any special tools? what else should i have on hand before i attempt the swap?



thanks for the help,

watermelon
 
Not an expert but I look for metal slivers in the case and check for pinion play while holding the ring gear and slap a little grease on the gears and turn it backwards a few times and check the coast pattern and then do the same forward and make sure it has a nice contact patch. Listen to the bearings while you turn it and listen for a sandy or growling sound. These arent good.
 
get a detroit true trac, fits right in and its a helical setup so no clutch discs.
 
That sounds a bit high, unless it's ultra clean.

You should be able to do the swap with typical hand tools.

Might need a gasket set, although some guys just use silicone.

Careful with the axle shafts and the seals.
 
Nothing wrong with a 741 case. (unless you've got 600+HP)

742 is the hardest to find gears for.

If you can find any case, good, clean, correctly set up chunk with an SG unit and any of those popular gearsets (2.94, 2.23, 3.55) for about $300, You'll be fine.
 
thanks all,

what do i need to consider when going from a 741 case to either a 742 or 489?

i would like to just change the "pumpkin" (i learned that today :) ) and stick with my driveshaft and axles.




watermelon
 
Nothing really, except maybe the size of the u-joint.

There are two different sizes.

There should be a "conversion" joint available, if you need it, that has one set of bearings the larger size, and one the smaller.
 
65 Plymouth Satellite 426 said:
Dump That 741 Case And Gears! Go To The 742 Case And Put A Sure Grip 3.55 In It! Then You'll See Smoke!
Click to expand...


I like the 3:55 gear overall too! Good Call. It will be a night and day improvment over your current "ONE TIRE FIRE" :angryfire: But what do I know.. I have a 3:73 which whines like a prom queen on Sat morning at 55mph it's pushing 4k

I will offer you one piece of advice. It's your car and if you want to burn up tires to help hold off the next impending Ice Age .. Do it !

Enjoy your car find the right advice that fits your goals and go with it

Happy Twisting!
 
i just went from a 741 non sure grip case to a 489 case with a detroit true trac and it bolted right in and the drive shaft bolted right on i didnt have to modify anything or change anything easy swap
 
[QUOTE=Printdoc But what do I know.. I have a 3:73 which whines like a prom queen on Sat morning at 55mph it's pushing 4k.

Seems like you either have REALLY short tires or a tach that's not reading correctly

Quick calculation with a 28" tall tire, 3.73 ratio, 55 mph = 2461 rpm

Formula is: RPM= MPH X Gear ratio X 336
Tire Daimeter
 
coloradodave said:
[QUOTE=Printdoc But what do I know.. I have a 3:73 which whines like a prom queen on Sat morning at 55mph it's pushing 4k.

Seems like you either have REALLY short tires or a tach that's not reading correctly

Quick calculation with a 28" tall tire, 3.73 ratio, 55 mph = 2461 rpm

Formula is: RPM= MPH X Gear ratio X 336
Tire Daimeter
Click to expand...

Dave

It's possible my tach might be off but keep in mind I'm running a 727 not a 5 speed

Thanks again I'll check my tach when I go thur the roadrunner this winter for PM
 
Hi,
This formula is based on a 1:1 transmission high gear, stick or auto (not including any slip). Gets you close.
 
If you are goin with a 5 speed I would say 3.91 or 4.10 with a sure grip. You could also find a truck with a tow package and dana 60 it should have 4.10s. Then narrow it and you are good to go.
 
This is outstanding.

I was just about to start a thread asking what gear ratios will produce what kind of RPM at highway and city driving speeds once I swap my 727 for a four speed. Dave's handy-dandy formula is EXACTLY what I needed.

Thanks!!
- Steve -
 
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