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B body rear end/third member question ?

pearljam724

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Excuse me, I’m not a rear axle expert. What is the highest geared rear end/third member that was typically available for a 10 bolt 8-3/4 rear end b body ? Last I remember, I have a 2:73 or 2:74, something like that, lol !
I’m interested in looking into swapping out for a higher gear ratio for better highway speeds. For example, on a 70 mph road, it’s more practical if I do 60 mph because my car feels like it needs one more higher gear. At 60, it cruises at 2K rpm. But, to go any faster. I would need to hold pedal to the floor and keep it there.
What I’m wanting is to slip in another third member that would allow me to do 65-70 mph while dropping the rpm’s from 2K to 1500. I have a LA 360, 904 auto tranny. The car will easily exceed 60 mph, but I would have to be pedal to the metal.
 
3.23 was the highest gear available I believe
 
According to the tech archive at Moparts:
"Gear ratios available on the 8-3/4" axle through the years include:
2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17,
5.57" (I don't know how old this list is).
Looks like Richmond Gear only goes to 3.23.

Bry
 
According to the tech archive at Moparts:
"Gear ratios available on the 8-3/4" axle through the years include:
2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17,
5.57" (I don't know how old this list is).
Looks like Richmond Gear only goes to 3.23.

Bry
Thank you, so I will take that as 2.76 being the answer.
 
Maybe a overdrive unit ?
Your rear gear set is basically the best for highway driving
 
Maybe a overdrive unit ?
Your rear gear set is basically the best for highway driving
Not it today’s world, lol ! I get out on big interstates and people are running me over at 60 and it seems like it’s too taxing on the engine if I try to stay at 70. Maybe the transmission isn’t automaticity shifting up to the highest gear at that speed. At 60, it runs fine at 2K rpm. Any faster consistent speed I would need to hold it to the floor. It’s not an engine issue for sure. It seems to me, if it were the best highway third member. The engine would be running between 1500 and 2000.
 
Last edited:
2.94... not 2.93. Also a 2.76 available. I have a 2.94 in the Bee that I threw in back in '79 when we blew the OE 3.23 one Friday night. It was easier in those days to just hit the junk yard and get another entire assembly, springs and all, and give the lady that owned the yard your old one as an even trade for weight! The only thing we paid for was radiators that she kept locked up in a milk truck.. 25 bucks ! ;)
 
2.94... not 2.93. Also a 2.76 available. I have a 2.94 in the Bee that I threw in back in '79 when we blew the OE 3.23 one Friday night. It was easier in those days to just hit the junk yard and get another entire assembly, springs and all, and give the lady that owned the yard your old one as an even trade for weight! The only thing we paid for was radiators that she kept locked up in a milk truck.. 25 bucks ! ;)
I hear ya dad, I wish I could find a third member locally. I’d pay up to $300 for a descent one. I’d like to have a 3.23 to swap around when I feel like it. I’m 99.9% sure it’s a 2.76 I have, that sounds right. I looked at it once, but can’t remember for sure.
 
I hear ya dad, I wish I could find a third member locally. I’d pay up to $300 for a descent one. I’d like to have a 3.23 to swap around when I feel like it. I’m 99.9% sure it’s a 2.76 I have, that sounds right. I looked at it once, but can’t remember for sure.
You need to figure out what gears you have now and go from there. You can either find a tag on one of the pumpkin bolts or lift up the rear end and "count" the gear based on available options. The "most highway" gear for a 8-3/4" rear end is 2.76. You've obviously got a gear with a higher number. 3.23 or even 3.55 gears won't have the engine screaming like you say......so either somebody put some 3.91 or 4.10 gears in your car at some point OR you've got a transmission/torque converter issue...maybe just low fluid? Does it ever feel like the transmission is slipping?
 
60 mph at 2K is nothing .......a 3:55 gear would be winding close to 3K
 
I think that we have gotten used to low rpm cruising with our newer cars. Overdrive often has us turning under 2000 rpms at 70.
Remember, before oil prices and gas prices jumped in the early 70s, there were no overdrive transmissions. People just accepted a 2800 rpm speed at 65 mph. People didn't know any different. The engine can take it....It is not abuse, it was designed to operate at that speed. It is US that changed. WE have a hard time dealing with the high rpms, the vibration and noise because cars have been made more and more comfortable and fuel efficient since the early 1980s.
 
If you have to have the pedal to the floor to go faster than 60 mph, you either have some very steep gears or some really short rear tires. I'm ok cruising down the highway at 3K in my non overdrive cars.
 
If you think 2 k at 60 mph is too many rpm, wow. At 2k it should at the bottom of torque curve. With a 2.76 gears it would accelerate like a pig. Your way over thinking this.
 
run taller tires
Excellent suggestion, I put 15’s on. But, the tires I chose aren’t very high and I wish I had chosen a taller tire for looks alone. Very good point, I know that. But, it slipped my mind until you mentioned it. Thank you

FA4EE4AA-6840-4469-B4E8-4C325DE0036A.jpeg
 
If you think 2 k at 60 mph is too many rpm, wow. At 2k it should at the bottom of torque curve. With a 2.76 gears it would accelerate like a pig. Your way over thinking this.
I don’t think 2K is too high at 60. I made the point that’s why I stay there. If I try to go above 60, that’s where the problem is. Long story, but I believe I have a small intake manifold leak at the firewall. I’m leaking oil down to the tranny and after I retorqued the manifold bolts and many observations, that’s around the time it started to leak oil. That’s probably the over 60 mph problem. The car runs great under 60 mph. But, I won’t know for sure until I address the intake manifold.
 
You need to figure out what gears you have now and go from there. You can either find a tag on one of the pumpkin bolts or lift up the rear end and "count" the gear based on available options. The "most highway" gear for a 8-3/4" rear end is 2.76. You've obviously got a gear with a higher number. 3.23 or even 3.55 gears won't have the engine screaming like you say......so either somebody put some 3.91 or 4.10 gears in your car at some point OR you've got a transmission/torque converter issue...maybe just low fluid? Does it ever feel like the transmission is slipping?
I know it’s a 2.76, I found the tag several months ago.
 
Not it today’s world, lol ! I get out on big interstates and people are running me over at 60 and it seems like it’s too taxing on the engine if I try to stay at 70. Maybe the transmission isn’t automaticity shifting up to the highest gear at that speed. At 60, it runs fine at 2K rpm. Any faster consistent speed I would need to hold it to the floor. It’s not an engine issue for sure. It seems to me, if it were the best highway third member. The engine would be running between 1500 and 2000.
In today's world you are right. In 67 when I bought my first new car, it had a 3:23 sure grip. With the stock tires it was dead on 25 mph for every 1000 rpm. Today my 2009 Challenger with a 3:91 and a 6-speed is running in 6th gear and 75 mph at 1800 rpm.
 
In today's world you are right. In 67 when I bought my first new car, it had a 3:23 sure grip. With the stock tires it was dead on 25 mph for every 1000 rpm. Today my 2009 Challenger with a 3:91 and a 6-speed is running in 6th gear and 75 mph at 1800 rpm.
Yep, what engine transmission and gear ratio that was practical in 1969. Isn’t practical in many conditions today. I have a Ford F 150 with a 5.4 liter. It also does 2K rpm at 65-70 mph. That’s with hardly pushing the throttle pedal.
 
I think that we have gotten used to low rpm cruising with our newer cars. Overdrive often has us turning under 2000 rpms at 70.
Remember, before oil prices and gas prices jumped in the early 70s, there were no overdrive transmissions. People just accepted a 2800 rpm speed at 65 mph. People didn't know any different. The engine can take it....It is not abuse, it was designed to operate at that speed. It is US that changed. WE have a hard time dealing with the high rpms, the vibration and noise because cars have been made more and more comfortable and fuel efficient since the early 1980s.
Well said
 
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