8 3/4 geared to low. Whats compatable?

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KIII

KIII

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1973 DDS 340, 727 trans, 8 3/4 (2070741) Here is my problem; My rear end gears seem to be real low. My tach is broke but I know its way to low. Even kids and people who know nothing of cars ask me why it doesnt shift. I new to Mopars and I dont know how easily rear end gears can be changed. I think the car was set-up not to drive on freeways. I dont think the previous owner used it daily. My son takes it to school every nite. Question#1. How hard is it to change out rear end gear? #2. Will a Duster 8 1/4 fit? Thnx. Oh yeah, does the 727 only shift 3 times?
 
Sounds like you have some pretty tall gears(4.56)Yes it only has 3 gears LOL.You can buy gears from a few places..Dr.Diff,Strange,Moser,s.You can also swap the whole center section of the rear out.Sounds like you want a 3.23 gear for daily driving/highway.:D
 
KIII said:
1973 DDS 340, 727 trans, 8 3/4 (2070741) Here is my problem; My rear end gears seem to be real low. My tach is broke but I know its way to low. Even kids and people who know nothing of cars ask me why it doesnt shift. I new to Mopars and I dont know how easily rear end gears can be changed. I think the car was set-up not to drive on freeways. I dont think the previous owner used it daily. My son takes it to school every nite. Question#1. How hard is it to change out rear end gear? #2. Will a Duster 8 1/4 fit? Thnx. Oh yeah, does the 727 only shift 3 times?
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a 727 is a three speed automatic.

why would you want to go from an 8 3/4 to a 8 1/4? thats going backwards.

just change the center section to a more street friendly gear. its not hard to do. just make sure your set up will run ok with a different gear.
 
If it is not shifting with the 4:56 gears I would be looking at the transmission. Unless you are already in high gear and it sounds as though you should be shifting again. Does your transmission shift into all 3 gears?
 
sorry it does say it only shifts 3 times....just change the center section.
 
I have an open 741 3rd member with 3.23 gears that I would send to you for cheap. Gears are like new. PM me if interested. You can honestly swap 3rd members in your driveway in a couple of hours.
 
it could be that the kickdown linkage is not right.... if that is the case, it will damage your transmission.
 
I've got a set of 3.91's in my 8.75 Tru Trac and it will shift through ALL 3 gears in a very short distance going at a slow pace. If you are getting 3 obvious shifts then yes you will want some taller gears for the road. The question i would have is the rear you have is it a sure grip? Keep that portion if it is. To change the ring and pinion is more of a chore that most novices dont want to tackle much less have the tools to accomplish the task. Swapping the whole chunk can be done in the drive as was stated earlier. When you pull the old one there will be a number stamped on the ring. Let us know what that number is. Just in case do remember, the ring bolts are LEFT hand.
Small Block
 
Badart said:
I have an open 741 3rd member with 3.23 gears that I would send to you for cheap. Gears are like new. PM me if interested. You can honestly swap 3rd members in your driveway in a couple of hours.
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how cheap is cheap??
 
If your transmission is shifting three times, it is not a 727. The 727 transmission is a three speed automatic transmission that only shifts twice.
 
Small Block said:
I've got a set of 3.91's in my 8.75 Tru Trac and it will shift through ALL 3 gears in a very short distance going at a slow pace. Small Block
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My 904 does the same thing and hits 3rd within maybe 50 feet. No problem as the KD is always looking for a sudden foot stomp.

If that 8 3/4 is a suregrip you may be able to sell it "for cheap" to a guy like me who runs the 1/8.
 
StrokerScamp said:
If your transmission is shifting three times, it is not a 727. The 727 transmission is a three speed automatic transmission that only shifts twice.
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I thought it shifts 4 times :D

I get a laugh out of reading 1970 car mags, they usually make little reference to 3.91--4.10 gears not being highway friendly. Comparing a 1971 3.55 gear 383 Road Runner to a 4.10 gear 440 6 pack Road Runner they go on to say how both cars about about even zero to 60 but 90 to 110 the 440 car is much safer at those speeds compare to the 3.55 gear 383 car.

Then the oil company have ads saying how their 260 pump fuel is like racing fuel, just cheaper and made for cooler temps, like early morning starts

How much things have changed from 1970
 

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My 727 only shifts 2 times. :dontknow:

1-2 and 2-3 :D

I would install a center section with 3.23 or numerically lower gears for the type of driving you are doing. It will last much longer and burn much less fuel.
 
dartnabout said:
If it is not shifting with the 4:56 gears I would be looking at the transmission. Unless you are already in high gear and it sounds as though you should be shifting again. Does your transmission shift into all 3 gears?
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Yes, all 3 gears in about 40 yards.
 
Before you go nutz buying stuff, why not jack up the rear end, and calculate the rear gear ratio. You will also determine if your 8 ¾ is a Suregrip or open differential.
Here is a simple method: http://www.slantsix.org/forum/viewtopic.php?t=36418

I have 3.55:1 gears in the Dart, and it turns 3000 rpm at 60 mph, this rather busy compared to today’s slow turning sub 2000 rpm overdrive equipped cars at the same speed. Back in the day this engine speed was considered normal, thrashing down the freeway.
 
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