8 3/4 chunk with no number??
#1650012
07/23/14 10:21 AM
07/23/14 10:21 AM
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Joined: Jun 2005
Posts: 5,102
Western Md.
skicker
OP
"The Champ"
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OP
"The Champ"
Joined: Jun 2005
Posts: 5,102
Western Md.
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I was rummaging thru my gear sets last night thinking about a gear change for the Dart. I have a 3.91 open chunk that has no number on it. (489-741-742) I was told they were the older units and were typical to the 742 cases. Anyone have any info? I'm going to roll a clutch posi unit into it and want to make sure it doesn't have the small diameter pinion. The Dart has slicks and the 340 makes decent power, I don't want to waste time with something that might break. 
...FAFO...
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650013
07/23/14 11:22 AM
07/23/14 11:22 AM
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Joined: Jan 2003
Posts: 74,978
U.S.S.A.
JohnRR
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I Win
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Quote:
I was rummaging thru my gear sets last night thinking about a gear change for the Dart.
I have a 3.91 open chunk that has no number on it. (489-741-742)
I was told they were the older units and were typical to the 742 cases. Anyone have any info?
I'm going to roll a clutch posi unit into it and want to make sure it doesn't have the small diameter pinion.
The Dart has slicks and the 340 makes decent power, I don't want to waste time with something that might break.
I was expecting a picture of the chuck , not the car ...
Are there any numbers or letters at all on the chuck anywhere?
The smallest part of the pinion is where the outer pinion bearing slides on , behind the yoke. The 741 and the 489 use the same bearing, 742 is the same size too, same bearing ??? ... anyway if you are worried about the pinion breaking you'll strip the teeth off the ring and/or pinion before you break the pinion stem itself.
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650015
07/23/14 11:56 AM
07/23/14 11:56 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,040
Lincoln Nebraska
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I twisted the splines on a 741 pinion in the stock car (mild 360/class rules) & no drag race standing starts  . I only saw it when I went to pull the yoke off later on. Maybe it was a one time deal but it kinda made me leery of em for a high powered app
live every 24 hour block of time like it's your last day on earth
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650017
07/23/14 04:00 PM
07/23/14 04:00 PM
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Joined: Jan 2003
Posts: 74,978
U.S.S.A.
JohnRR
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I Win
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Quote:
I will get a pic of the front of the chunk tonight. Reason I ask is that a bunch of years back I snapped a 741 off clean behind the yoke on the pinion shaft. I don't want that to happen again... 
That spot can break on all the 8.75's because they are all the same size there.
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Re: 8 3/4 chunk with no number??
[Re: JohnRR]
#1650018
07/24/14 11:42 AM
07/24/14 11:42 AM
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Joined: Jun 2005
Posts: 5,102
Western Md.
skicker
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"The Champ"
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OP
"The Champ"
Joined: Jun 2005
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Western Md.
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Low and behold after digging thru what was a pretty good build-up of rust I found a line of small numbers. For whatever reason the numbering sequence and placement is entirely different than the other 5 I was comparing it to. Looks like its a 489 case. Plan on rolling an early clutch pak unit in and changing the yoke. The one that's on there is in pretty bad shape. Counted the pinion and ring gear teeth and confirmed it is a 3.91.
...FAFO...
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650019
07/24/14 11:58 AM
07/24/14 11:58 AM
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Joined: Jan 2003
Posts: 2,632
Nashville, TN
MOPARMIKE69
master
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master
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Posts: 2,632
Nashville, TN
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Looks like a really early unit
69 Road Runner vert
69 GTX hard top
70 Road Runner 4 speed
70 Hemi Cuda vert
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Re: 8 3/4 chunk with no number??
[Re: MOPARMIKE69]
#1650020
07/24/14 12:00 PM
07/24/14 12:00 PM
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Joined: Jun 2005
Posts: 5,102
Western Md.
skicker
OP
"The Champ"
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OP
"The Champ"
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Posts: 5,102
Western Md.
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I didn't know if the smaller stamp below the others was a date stamp or not but it looks like it says 1963???
...FAFO...
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650024
07/24/14 05:02 PM
07/24/14 05:02 PM
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Joined: Jan 2003
Posts: 74,978
U.S.S.A.
JohnRR
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Quote:
Quote:
Make sure you read and understand the instructions on how to properly change the pinion yoke on the "489" case third members (IE pinion shaft crush sleeve preload)  If you do not know how or have the proper tools to do that correctly take it to a shop that does
John, I will check what the letter is this evening.
Cab, I have been spoiled on this. When I was dirt racing with a 9" the builder always set it up with a crush sleeve, then removed it and replaced it with the correct shims. Yoke changes were simple and painless. Guess I'm back to having to be careful again. I have done it in the past but may need to read up on it again as a refresher course. 
the problem with the 489 is you can't pull the crush sleeve out from the yoke end , you have to pull the carrier and the pinion to change it .
2 reasons why 489's are the least desirable , the cone type sure grip and the crush sleeve .....
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Re: 8 3/4 chunk with no number??
[Re: JohnRR]
#1650026
07/25/14 12:36 AM
07/25/14 12:36 AM
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Joined: Jan 2011
Posts: 492
Kansas
BEINGmeISaCRIME
mopar
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mopar
Joined: Jan 2011
Posts: 492
Kansas
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Quote:
Quote:
Quote:
Make sure you read and understand the instructions on how to properly change the pinion yoke on the "489" case third members (IE pinion shaft crush sleeve preload) If you do not know how or have the proper tools to do that correctly take it to a shop that does
John, I will check what the letter is this evening.
Cab, I have been spoiled on this. When I was dirt racing with a 9" the builder always set it up with a crush sleeve, then removed it and replaced it with the correct shims. Yoke changes were simple and painless. Guess I'm back to having to be careful again. I have done it in the past but may need to read up on it again as a refresher course.
the problem with the 489 is you can't pull the crush sleeve out from the yoke end , you have to pull the carrier and the pinion to change it .
2 reasons why 489's are the least desirable , the cone type sure grip and the crush sleeve .....
Thank goodness they came up with the solid spacer for the 489 cases. Cone style sure grip = 
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Re: 8 3/4 chunk with no number??
[Re: DoctorDiff]
#1650028
07/25/14 09:23 AM
07/25/14 09:23 AM
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Joined: Jun 2005
Posts: 5,102
Western Md.
skicker
OP
"The Champ"
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OP
"The Champ"
Joined: Jun 2005
Posts: 5,102
Western Md.
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Ding Ding Ding
Cass is right. I found a date on the ring gear last night. After checking the case for condition I remembered where this set came from.
These were removed from a 74 Snow Commando p/u that was nearly rusted in half. Took them out thinking there would be a posi unit there and instead ended up with the 3.91 open rear. The date on the ringear is 6/25/73.
I looked over the 741 case 3.91's as well last night.
Something I found that was interesting was the part # stamping on both sets of 3.91 gears in two different number cases.(741-489) was the same.
2070228 391-1 MS 291
Date on the ring gear in the 489 set was 6/25/73.
Date on the ring gear in the 741 set was 6/28/70.
Just thought it was strange...
...FAFO...
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Re: 8 3/4 chunk with no number??
[Re: skicker]
#1650029
07/25/14 03:30 PM
07/25/14 03:30 PM
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Joined: Jan 2003
Posts: 74,978
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 74,978
U.S.S.A.
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Quote:
Ding Ding Ding
Cass is right. I found a date on the ring gear last night. After checking the case for condition I remembered where this set came from.
These were removed from a 74 Snow Commando p/u that was nearly rusted in half. Took them out thinking there would be a posi unit there and instead ended up with the 3.91 open rear. The date on the ringear is 6/25/73.
I looked over the 741 case 3.91's as well last night.
Something I found that was interesting was the part # stamping on both sets of 3.91 gears in two different number cases.(741-489) was the same.
2070228 391-1 MS 291
Date on the ring gear in the 489 set was 6/25/73.
Date on the ring gear in the 741 set was 6/28/70.
Just thought it was strange...
Ring gears don't care what size the pinion stem is , the ring and pinion tooth count is still the same so both rears having the same part number is not strange.
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I've drag raced the snout out of a 741 with 3.91 gears in my 1969 Dart GTS with a 440 and a 727 on slicks, it is tougher than the stock 489 chunks as far as I'm concerned 
