How hard is it to change ratios in an 8-3/4"?

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Bill Crowell

Bill Crowell

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Right now I have 3.73:1 Dana Power-Lock positraction innards, and man! does the engine ever rev high on the freeway! I had that ratio installed because I intended to go to the strip, but so far I haven't got the car sorted out well enough to do that, so I've been daily driving it.

I'd like to buy and install a non-posi 2.76:1 ring and pinion just for highway use, but I really have no idea about how to install it! Would you guys please take pity on me and tell me, just briefly and in general terms, what is involved in switching ratios?

Should I buy a fully pre-assembled 2.76 one-legger center section? Would I then be able to easily swap center sections if/when I ever decide to get some time slips? Again, I apologize for my ignorance. Thanks very much.
 
In an 8.75, it's pretty easy to swap one 'chunk' for another. If you're looking at swapping ring and pinion on the existing setup, it gets involved (doable but not worth it in my opinion).
 
Bill Crowell said:
Should I buy a fully pre-assembled 2.76 one-legger center section?
Click to expand...

That is by far the easiest in your scenario.

Swapping gears in a center section requires a couple specific tools (I made mine), getting the pattern correct ect.
 
I would look for a 3:23 sure grip chunk. You will probably be disappointed with the 2:76 one wheel wonder.
 
Bill Crowell said:
Right now I have 3.73:1 Dana Power-Lock positraction innards, and man! does the engine ever rev high on the freeway! I had that ratio installed because I intended to go to the strip, but so far I haven't got the car sorted out well enough to do that, so I've been daily driving it.

I'd like to buy and install a non-posi 2.76:1 ring and pinion just for highway use, but I really have no idea about how to install it! Would you guys please take pity on me and tell me, just briefly and in general terms, what is involved in switching ratios?

Should I buy a fully pre-assembled 2.76 one-legger center section? Would I then be able to easily swap center sections if/when I ever decide to get some time slips? Again, I apologize for my ignorance. Thanks very much.
Click to expand...
By what you have said you must have a dana 60 housing in your car now not a 8 3/4 mopar housing. totally different housing, innards do not exchange from dana to 8 3/4.You would have to change housing to get the gear ratio you want. The dana only goes down to 3:54 ratio.
 
"totally different housing, innards do not exchange from dana to 8 3/4."

Sabre67, what you say is correct insofar as the currently available parts are concerned, but long ago, before Chrysler adopted the clutch-actuated Sure Grip posi, Dana made a special posi diff (the "Power-Lock" or "Power-Lok", not sure) for the Chrysler 8-3/4" rear end, and it did come in a 3.73 ratio because that's what all the hot rodders used back then. Chrysler stopped using it when they went to the Sure Grip, but until then it was the only 8-3/4" posi diff that the factory offered. I'm not sure whether the Power Lock or the Sure Grip is better, but the Power Lock is certainly no slacker. I picked up a 3.73 center section NOS in 2003. It is not clutch-actuated like the Sure Grip, but I forget exactly how it works at the moment. Maybe some of the more knowledgeable guys on here would want to discuss that.
 
"You will probably be disappointed with the 2:76 one wheel wonder."

Toolmanmike, I am sure you are correct as far as acceleration is concerned, but what if I were totally unconcerned about it? What if I only cared about gas mileage and low freeway cruising RPM? (After all, when I wanted acceleration I could always re-install the 3.73.)
 
Frankly, i'd just live with it and drive a little slower on the freeway if that's what bothers you..............
 
Bill Crowell said:
"totally different housing, innards do not exchange from dana to 8 3/4."

Sabre67, what you say is correct insofar as the currently available parts are concerned, but long ago, before Chrysler adopted the clutch-actuated Sure Grip posi, Dana made a special posi diff (the "Power-Lock" or "Power-Lok", not sure) for the Chrysler 8-3/4" rear end, and it did come in a 3.73 ratio because that's what all the hot rodders used back then. Chrysler stopped using it when they went to the Sure Grip, but until then it was the only 8-3/4" posi diff that the factory offered. I'm not sure whether the Power Lock or the Sure Grip is better, but the Power Lock is certainly no slacker. I picked up a 3.73 center section NOS in 2003. It is not clutch-actuated like the Sure Grip, but I forget exactly how it works at the moment. Maybe some of the more knowledgeable guys on here would want to discuss that.
Click to expand...
So what rear axle do you have?
 
I always believed that the clutch type Sure Grip was a Dana Power-Loc unit and the later cone type Sure Grip as a Auburn type unit.
 
694spd said:
I always believed that the clutch type Sure Grip was a Dana Power-Loc unit and the later cone type Sure Grip as a Auburn type unit.
Click to expand...
I stand corrected, I guess I'm not old enough to remember that unit from factory:rolleyes:
 
I have a rebuilt OD unit that would solve that problem for pretty cheap...
3:09 first 30% OD or .70....with 3:73 and a 27" tall tire at 70 mph puts you at say......less than or equal to 2200 rpm.
 
Bill Crowell, I have bought two different carriers (“chunks”) for my 8 3/4 that is in my Duster. Currently it has a 3:23 ratio in it. Now I have 3:55 and 3:91 carriers available. Changing them out takes a couple of hours or a day depending on equipment such as jack stands, ramps, or hoist.

I have considered the purchase of an overdrive unit but right now I don’t want to modify the trans tunnel. The older I get the more attractive the OD unit becomes because I have less desire to wrench on heavy stuff like the carrier units.
 
You can pickup complete center sections in those high ratios pretty cheap. To find the ring and pinion, a rebuild kit etc to then setup the carrier you have would likely be the same amount of money. It isn't hard, just time consuming, and you will need a dial indcator and mount. Swap meets, ready to go they are likely dime a dozen,
 
years ago we needed the demon as a daily driver I got a set of 8 3/4 2:74s one wheel wonder the car is a 1971 demon 340 with 28" tires go around 24 mpg on the freeway it worked well but was hard on the clutch but would do well over 120mph in third gear
 
In my day MANY guys ran the deeper gears for the weekend drags and changed the pumpkin for the daily drive.
I just sold a 741 case 276 open complete center section for $100. There was nothing wrong with it. You can still find them at swap meets and online. Buying and setting up a ring and pinion will cost a lot more. The time needed to swap the center (two hours or less once you get practice) makes it the ultimate "low dollar" fix to your problem. Keep the good center section on the shelf for the racing and buy cheap used ones to run the highway. BTW, if you find you DON'T like the 276 ratio? Sell it or trade for a 3:23. They can be had for about the same price on a 741 case.
 
BTW you asked for the instructions:
#1 Put a floor jack under the rear and raise the car. Jack stands are good for safety. Remove the tires and brake drums.

#2. There are five 9/16 nuts that hold the backing plate to the housing on each side. Remove them. NOTE: On the passenger side, you will find a clip bolted to one of those bolts. don't lose it.

#3. Pull the axles back about 6 inches being careful not to break the brake lines. You sometimes need to tap the backing plate to loosen up the seals.

#4. Remove the U-Joint caps and slide the driveshaft forward in the trans enough to allow it to fall out of the yoke and sit on the floor. Be careful not to let the ends fall off.

#5 There are 10 9/16 nuts holding the "chunk" to the housing. Remove them and then drop the center section. You should have a drain pan under the rear. It may be necessary to wedge a screwdriver between the housing & the unit to break the gasket seal. There are two generally accepted ways to remove and reinstall the chunk. Older guys use a floor jack, but in my day we would crawl under the car with the unit on our chest and "bench press" the 75 pound chunk into place!

#6 Reinstall the drive shaft & u-joint caps.

#7. Reinstall the backing plates and axles. Remember that "clip" on the passenger side that you removed? That is a retainer for the end play adjustment. The bearing retainer on that side is threaded. You can turn it by tapping it with a hammer and screwdriver (yes I'm certain there's a more accurate tool for the job but I've being using the screwdriver for 45 years) Tighten the retainer about 1/4 turn to eliminate any end play (if there is any). Make certain the clip is reinstalled to prevent it from backing out.

IMPORTANT NOTE #1: The older "clutch style" sure grip units had a "thrust retainer" pin that allowed one axle to press against the other for end play adjustment. These pins sometimes fall out when the unit is removed. Without it, you CANNOT ADJUST THE END PLAY! Look carefully into the chunk where the axles go before installing the chunk. If you can see daylight, the pin is missing! Do not install without fixing the problem!

IMPORTANT NOTE #2: If your rear has been modified to run the new "Green bearings" you do not need to worry about the end play adjustment.

#8 Reinstall brake drums and tires and fill rear with new oil.
 
Last edited:
Bill Crowell said:
Right now I have 3.73:1 Dana Power-Lock positraction innards, and man! does the engine ever rev high on the freeway! I had that ratio installed because I intended to go to the strip, but so far I haven't got the car sorted out well enough to do that, so I've been daily driving it.

I'd like to buy and install a non-posi 2.76:1 ring and pinion just for highway use, but I really have no idea about how to install it! Would you guys please take pity on me and tell me, just briefly and in general terms, what is involved in switching ratios?
Should I buy a fully pre-assembled 2.76 one-legger center section? Would I then be able to easily swap center sections if/when I ever decide to get some time slips? Again, I apologize for my ignorance. Thanks very much.
Click to expand...

iF you lived a lil closer, I'd swap you anything you want for those; 3.55/3.23/2.94/2.76/2.45...
But here's a tip, if you're just cruising it;
grab a complete 7.25, and driveshaft. You can have that under there in a jiffy, and barely get dirty..
 
As mentioned above buy a complete working unit. setting up gears is not for a amateur (no offense). I have 2 3rd members for mine. A 2.94 gear for cruising and a 3.55 when I go to the track. I can swap them out in about 45 minutes
 
gregpurcell said:
BTW you asked for the instructions:
#1 Put a floor jack under the rear and raise the car. Jack stands are good for safety. Remove the tires and brake drums.

#2. There are five 9/16 nuts that hold the backing plate to the housing on each side. Remove them. NOTE: On the passenger side, you will find a clip bolted to one of those bolts. don't lose it.

#3. Pull the axles back about 6 inches being careful not to break the brake lines. You sometimes need to tap the backing plate to loosen up the seals.

#4. Remove the U-Joint caps and slide the driveshaft forward in the trans enough to allow it to fall out of the yoke and sit on the floor. Be careful not to let the ends fall off.

#5 There are 10 9/16 nuts holding the "chunk" to the housing. Remove them and then drop the center section. You should have a drain pan under the rear. It may be necessary to wedge a screwdriver between the housing & the unit to break the gasket seal. There are two generally accepted ways to remove and reinstall the chunk. Older guys use a floor jack, but in my day we would crawl under the car with the unit on our chest and "bench press" the 75 pound chunk into place!

#6 Reinstall the drive shaft & u-joint caps.

#7. Reinstall the backing plates and axles. Remember that "clip" on the passenger side that you removed? That is a retainer for the end play adjustment. The bearing retainer on that side is threaded. You can turn it by tapping it with a hammer and screwdriver (yes I'm certain there's a more accurate tool for the job but I've being using the screwdriver for 45 years) Tighten the retainer about 1/4 turn to eliminate any end play (if there is any). Make certain the clip is reinstalled to prevent it from backing out.

IMPORTANT NOTE #1: The older "clutch style" sure grip units had a "thrust retainer" pin that allowed one axle to press against the other for end play adjustment. These pins sometimes fall out when the unit is removed. Without it, you CANNOT ADJUST THE END PLAY! Look carefully into the chunk where the axles go before installing the chunk. If you can see daylight, the pin is missing! Do not install without fixing the problem!

IMPORTANT NOTE #2: If your rear has been modified to run the new "Green bearings" you do not need to worry about the end play adjustment.

#8 Reinstall brake drums and tires and fill rear with new oil.
Click to expand...


After you do it a couple of times, swap time drops to under an hour.
Rather than crawling under, removing the plug, squirting in the fluid and replacing the plug, I jack one side up a little. Then squirt the fluid into the axle tube. Then stick the axle back in.
 
I always pull the axels all the way out so they are not resting on the oil seal
 
fishy68 said:
As mentioned above buy a complete working unit. setting up gears is not for a amateur (no offense). I have 2 3rd members for mine. A 2.94 gear for cruising and a 3.55 when I go to the track. I can swap them out in about 45 minutes
Click to expand...
Oh yea! When you do this a number of times, it can get done fast. From opening the tool box to close of the box is an hours job. When you know what your doing by a few tries/times doing it.
I’d get it done in an hours time from box opening to close.
 
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