9"
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Freshman User
Joined: Dec 2001
Posts: 34
Likes: 0
From: Mesa, AZ
9"
I just bought a donor car (78 Merc Marquis) for the 9" rear end and possibly the 460. I have no use for the C6 behind it.
My question is I asked on the tranny rear end forum about the 9" and was told I have an "open" differential. What does this mean? I was asking for any info I could get from the tag which reads
WDC-EL 7KC 2.50 - 9 040A
I am looking for the gear ratio and the "type" of differential.
Any Help??
My question is I asked on the tranny rear end forum about the 9" and was told I have an "open" differential. What does this mean? I was asking for any info I could get from the tag which reads
WDC-EL 7KC 2.50 - 9 040A
I am looking for the gear ratio and the "type" of differential.
Any Help??
Senior User
Joined: Mar 2000
Posts: 113
Likes: 0
From: Connecticut
9"
Originally posted by pademc
I just bought a donor car (78 Merc Marquis) for the 9" rear end and possibly the 460. I have no use for the C6 behind it.
My question is I asked on the tranny rear end forum about the 9" and was told I have an "open" differential. What does this mean? I was asking for any info I could get from the tag which reads
WDC-EL 7KC 2.50 - 9 040A
I am looking for the gear ratio and the "type" of differential.
Any Help??
I just bought a donor car (78 Merc Marquis) for the 9" rear end and possibly the 460. I have no use for the C6 behind it.
My question is I asked on the tranny rear end forum about the 9" and was told I have an "open" differential. What does this mean? I was asking for any info I could get from the tag which reads
WDC-EL 7KC 2.50 - 9 040A
I am looking for the gear ratio and the "type" of differential.
Any Help??
It looks like it's a 2.50 ratio and a non posi rear. usually when they say "open rear" it means it has a modern type driveshaft, not the "closed" type on a pre-48 car. More than likely this donor car was equipped that way with a higher gear ratio was to get some help in the fuel economy dept. with the 460.
Post Fiend
Joined: Feb 2001
Posts: 6,328
Likes: 124
From: Iowa
9"
Dennis
I can't say for sure what they meant, but I refer to an open rear end as a non-positraction, traction-lock etc. (different manufacturers call them by various trade names.) It lacks the clutch packs which apply torque to both wheels rather than just the right side.
There are also locker or spool style rearends which essentially lock both axles together causing them to spin at the same rate, even when going around a corner. These are generally drag race or 4x4 special application differentials though.
This is not a 100% explanation because even an open rear end can, under certain circumstances, apply enough power to both wheels sufficient to leave 2 tire marks on hard acceleration. The left axle doesn't always just follow along for the ride.
I can't say for sure what they meant, but I refer to an open rear end as a non-positraction, traction-lock etc. (different manufacturers call them by various trade names.) It lacks the clutch packs which apply torque to both wheels rather than just the right side.
There are also locker or spool style rearends which essentially lock both axles together causing them to spin at the same rate, even when going around a corner. These are generally drag race or 4x4 special application differentials though.
This is not a 100% explanation because even an open rear end can, under certain circumstances, apply enough power to both wheels sufficient to leave 2 tire marks on hard acceleration. The left axle doesn't always just follow along for the ride.
Posting Guru
Joined: Jul 2001
Posts: 2,119
Likes: 2
From: Southern New Hampshire
9"
The 2.50 should keep a truck moving right along IF you keep the C6.
One good thing is that is a 28 spline unit so a lot of easy to find ratios are available; all years and makes are interchangable as far as the center cection.
If you want to convert to the 5 on 5.5" pattern there are parts that can be swapped but it would be simpler to find a truck 9".
One good thing is that is a 28 spline unit so a lot of easy to find ratios are available; all years and makes are interchangable as far as the center cection.
If you want to convert to the 5 on 5.5" pattern there are parts that can be swapped but it would be simpler to find a truck 9".
Thread Starter
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Freshman User
Joined: Dec 2001
Posts: 34
Likes: 0
From: Mesa, AZ
9"
So is the general concenus is to ditch the merc 9" and get one from a pickup??
Thanks for all your input guys. I'll have to think about this. Will reply soon. In the mean time is anyone looking for a good 460?
Thanks for all your input guys. I'll have to think about this. Will reply soon. In the mean time is anyone looking for a good 460?
Post Fiend
Joined: Feb 2001
Posts: 6,328
Likes: 124
From: Iowa
9"
Dennis
I wouldn't ditch the merc rear if it happens to be the correct width. If not, the 57-72 F100 9 inch couldn't be easier to install.
Purple
No 'fenders does not need a 460 thankyou
John doesn't need one either. He just thinks he does. Nobody here needs one in fact. OK, maybe Carl does for his snowplow trucks but even he could probably get by with an injected and blown 351W like 'rage.
I wouldn't ditch the merc rear if it happens to be the correct width. If not, the 57-72 F100 9 inch couldn't be easier to install.
Purple
No 'fenders does not need a 460 thankyou
John doesn't need one either. He just thinks he does. Nobody here needs one in fact. OK, maybe Carl does for his snowplow trucks but even he could probably get by with an injected and blown 351W like 'rage.
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Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
9"
Dennis,
I think what transmission you use might be a factor in whether to use this rear end or not. If you go with an automatic, you will be okay, but a standard shift will not work well with a rear end ratio of 2:50. That ratio is so tall, you will have to slip the clutch to take off. Of course, you could always change the ring gear and pinion to a higher number ratio. With a straight stick you probably need at least a 3:00 to 1.
I think what transmission you use might be a factor in whether to use this rear end or not. If you go with an automatic, you will be okay, but a standard shift will not work well with a rear end ratio of 2:50. That ratio is so tall, you will have to slip the clutch to take off. Of course, you could always change the ring gear and pinion to a higher number ratio. With a straight stick you probably need at least a 3:00 to 1.
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Thread Starter
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Freshman User
Joined: Dec 2001
Posts: 34
Likes: 0
From: Mesa, AZ
9"
Vern
The more I read about my "new" 9' the worse it becomes. I have a T-10 hooked to a 351W and I wanted to use the 9" in place of the original rear that's in place now. I have the C-6 that's still attached to the 460. I guess I'll try and sell the engine and trans and find a 9" from a pickup like I should have done in the first place. Thanks for the input
The more I read about my "new" 9' the worse it becomes. I have a T-10 hooked to a 351W and I wanted to use the 9" in place of the original rear that's in place now. I have the C-6 that's still attached to the 460. I guess I'll try and sell the engine and trans and find a 9" from a pickup like I should have done in the first place. Thanks for the input
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
9"
Dennis,
Take into consideration what you will be doing on the front end also. The passenger car nine inch will have a much friendlier bolt pattern (5 on 4.5) than the truck rear (5 on 5.5) as far as wheels are concerned. If you are going with the stock pattern up front, then the truck rear might be better. I had a 77 Trans-Am four speed with the big block 400 years ago and made the mistake of putting a 2:47 to 1 rear end in it (the guy I bought it from told me it was a 3:23). I have no doubt whatsoever that the car would have gone over 150 MPH easily if I had the guts to do it, but taking off was like taking off in second gear. I eventually had to change the rear again.
Take into consideration what you will be doing on the front end also. The passenger car nine inch will have a much friendlier bolt pattern (5 on 4.5) than the truck rear (5 on 5.5) as far as wheels are concerned. If you are going with the stock pattern up front, then the truck rear might be better. I had a 77 Trans-Am four speed with the big block 400 years ago and made the mistake of putting a 2:47 to 1 rear end in it (the guy I bought it from told me it was a 3:23). I have no doubt whatsoever that the car would have gone over 150 MPH easily if I had the guts to do it, but taking off was like taking off in second gear. I eventually had to change the rear again.
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