Abraham Lincoln
Feature Winner
Who needs skills All i need is Logic
Posts: 141
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Post by Abraham Lincoln on Feb 9, 2012 14:00:15 GMT -5
Everything About Mopar Rearends
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Abraham Lincoln
Feature Winner
Who needs skills All i need is Logic
Posts: 141
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Post by Abraham Lincoln on Feb 10, 2012 0:53:54 GMT -5
8-3/4 info 8-3/4 is a bolt in axle design. Dropout center section (front load) with 10 bolts is the 8-3/4. If you see a bolt-on cover in the rear it is not an 8-3/4. 1964 & older "big nut" axles use a keyway to joint the axle shaft to the drive hub. These can be a real pain to deal with and are suspect for durability. The 1965 & newer one piece shafts are preferred by most derbiers big nut  one piece  all 8-3/4 center sections are interchangeable with all tubes and all shafts open differential:  cone type Sure Grip  clutch type Sure Grip  when welding the open diffs, weld the spider gears together and use old bolts as filler. DO NOT weld the center pin or you will find it very difficult to set the axle end play/ thrust I buy used gears from drag racers at swap meets. I'm not a fan of spools.... just welded rears. Brake parts can usually be interchanged from other axles, when I am setting up a new 8-3/4 I usually transfer all of the brake parts from a 70's model C clip axle (8-1/4 or 9-1/4) There were many different widths of 8-3/4 axles depending on model and year. The axle shaft length has to be correct for the tube length 3 wheel bolt patterns: 5 on 5.5" is 1966 & older Imperial; 5 on 5.0" is 67-73 Imperial, everything else is 5 on 4.5" 3 most common center section castings are 741, 742, and 489. Gearsets are particular to the casting 8-3/4 was in wide use up until 1969, after that they were slowly phased out and rarely seen past 1974 aint ever seen much on posi... my 78 newport, thought it had a 8 1/4, its got a 9 1/4, but on the back cover someone painted posi with a white marker, is factory posi good or bad for derby use? just aint seen much on it agree with dm440c as far as spools to a certain extent. If not setup right with green bearings forget it, it will not work. You sacrifice things to gain others with full spool. However axels stock can be broken, mopar more than 9 inch ford. in my experience it seems to have a lot to do with setup and driving style. Our crew has never had much trouble from broken 8-3/4 axle shafts but 9 inch differentials and gearsets seem to be made from peanut butter. As for the "posi" question you'll have to ask it in the GM section, that's where they discuss "Positraction" limited slip differentials. Here in the Mopar world we deal with "Sure Grip" limited slip differentials  But seriously, the pictures I showed above look basically the same in a 7-1/4, 8-1/4 or a 9-1/4. Pop the cover off and look at the diff to see if it is open or limited slip. ill be sure to do that this weekend.... thanks Will the yoke off of a 8 1/4 reared fit on a 8 3/4? Will the yoke off of a 8 1/4 reared fit on a 8 3/4? I'm having a bit of a brain fart on that one, I know a 9-1/4 yoke will fit on an 8-3/4 but I think the 8-1/4 is smaller than those other two. Not 100% on that but I think I have it right. Posi is a four letter word around here its a GM thing yes it is, dont ask about posi in here LOL, i found that out I was careful not to call the sure grip the other name. I see that dm440c prefers a welded open diff. I was wondering if there is a weak link in the clutch sure grip which would lead him to that preference? when i weld my gears i allow them to cool naturally for an hr or so then i fill them up with old motor oil so the steel can absorb the oil. i wont ever run a spool, sure grip, or posi because they have more parts to break. the spools just look dainty to me. i can afford open gears and they're plentiful. just my opinion my 78 newport has a factory 9 1/4 sure grip in it... my 78 newport has a factory 9 1/4 sure grip in it... Still not that great of rear I've snapped of a few and will never run one again.as for a full spool love it never broke an axle reliable. And if you do some shopping you can put a 8 3/4 set for around 500.00 don't have green berrings in mine used factor wrapped center spacer with some tape to fit it tight in center of spool and works fine When replacing bent axles, do those of you that run C body 8 3/4 rear ends buy used or go aftermarket for the replacements? Any issues with aftermarket axles aside from cost? I managed to bend both axles in my last derby and am looking for replacements. Thanks. If you have ever priced out the cost of a center section with a sure grip in it already, or just the sure grip unit itself, you would have your answer. Any sure grip unit I have found has been above the cost of a spool, or in some cases, more than the cost of better gears and a spool. He may have another reason but my guess is cost and simplicity. Thanks all great info and all things I did not know. If you have ever priced out the cost of a center section with a sure grip in it already, or just the sure grip unit itself, you would have your answer. Any sure grip unit I have found has been above the cost of a spool, or in some cases, more than the cost of better gears and a spool. He may have another reason but my guess is cost and simplicity. right on target, and that's my reason for most of the things I do. Bang for the buck is my deal. To directly answer the question, I see no specific durability issues with a clutch type Sure Grip. I've seen them burn up in the derby from serious abuse but they can be rebuilt. They just cost so darn much and welded diffs are so reliable (for me at least) that it becomes an easy decision to make. Cone type is much harder to recover when wore out, but I like the way they work on street cars. i used to have bent axels when i ran no rear brakes and it felt like more power without the drums on but no problems with drums on but moser makes a fine set of burley axels Anyone know where I can get housing lengths and what car itcame out of. I might be dealing with a bent housing and my axles are in great shape. My housing measures 58 3/4 outside to outside on the axle mounting flanges. I have to beat the axles to get them in. can someone tell me what kind of cars were 8 3/4 rearends and 489 case? can someone tell me what kind of cars were 8 3/4 rearends and 489 case? So far I've found them under 69 Polara and Nyer, 71 Nyer and 71 to 73 imps. The ones under the imps are 5 on 5 bolt pattern. The others are 5 on 4.5. can someone tell me what kind of cars were 8 3/4 rearends and 489 case? first year for 489 was 1969 the 489 was used for heavier duty applications than the 741 case, so typically found in big heavy cars, paired with the bigger engines, high performance such as Road Runner, etc. which 8 3/4 would fit best in a 80's ford? I'm getting one from a 68 imp. Would that fit? They will go under just have to get some 9 inch ears from AFAB or cutter is his screen name and make a bracket that bolts to factory leaf spring perches.  wow, thanks, was just coming on to ask that same question Get you 2 jacks and a jack stand a 12 pack and it will come together. ;D  is narrowing an 8 3/4 something that can be done at home? or is that somethin a machine shop should do is narrowing an 8 3/4 something that can be done at home? or is that somethin a machine shop should do you could narrow a housing at home if you are a competent fabricator. It would require a certain amount of skill to get the lengths right and make sure the flanges are true pretty sure i seen it somewhere but was there any year distinction in course and fine splined 8 3/4... i havent got the rear yet but i wanna go ahead and order my yoke so i can run my slider All of the stock 8 3/4 I have had have been fine spline. From 66 - 73 newports and newyorkers. The only ones with course splines that I have had are the ones I've installed my self well its out of a 69 dodge monaco wagon if that helps at all the axle shafts are all the same, if you mean the splines on the pinion stem for the yoke then it can be tricky. The vast majority of the aftermarket gearsets are all coarse spline, but not all. The factory gearsets can be either coarse or fine and the only way to be sure is to look. Generally the 60's ones were coarse spline and the 70's ones were fine spline but no guarantees. In other words you have to look to be sure, it's not safe to assume anything yes there is thanks alot, dont know much about chrysler rearends and i just bought one while back thanks for the info. ;D |
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But seriously, the pictures I showed above look basically the same in a 7-1/4, 8-1/4 or a 9-1/4. Pop the cover off and look at the diff to see if it is open or limited slip.
