doctor diff 8.75 case review
#3170339
08/25/23 11:44 AM
08/25/23 11:44 AM
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Joined: Jan 2003
Posts: 1,412 Johnstown
69dart
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,412
Johnstown
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So we grenaded the 8.75 in our belvedere and replaced it with the aftermarket case from doctor diff. If you are interested in more details check out the video on YouTube - 8.75 VideoYou really can't beat doctor diff. Great stuff.
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Re: doctor diff 8.75 case review
[Re: 69dart]
#3170350
08/25/23 12:26 PM
08/25/23 12:26 PM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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I would have stolen an old school trick used on Connecting rods, and polished out those casting striations on the upgraded 489 caps. With the OP's initial failure of ring broken teeth, it would matter little in the final outcome once a broken tooth gets wedged between the R&P however since something has to give/break. Breaking on a by run?
Last edited by jcc; 08/25/23 01:02 PM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: doctor diff 8.75 case review
[Re: 69dart]
#3170362
08/25/23 12:50 PM
08/25/23 12:50 PM
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Joined: Jan 2003
Posts: 75,017 U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,017
U.S.S.A.
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Spool , crush sleeve, cast caps and stock axles , that thing was definitely on borrowed time.
running up my post count some more .
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Re: doctor diff 8.75 case review
[Re: J_BODY]
#3174265
09/10/23 07:20 PM
09/10/23 07:20 PM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Closed what out cheap, R&P? which failure of caused the carnage pictured?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: doctor diff 8.75 case review
[Re: J_BODY]
#3174283
09/10/23 08:37 PM
09/10/23 08:37 PM
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Joined: Jan 2003
Posts: 10,564 Freeport IL USA
poorboy
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,564
Freeport IL USA
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Monte preached to us long ago about the 8.75 . I remember when Mopar closed these out for CHEAP! Looks to me like the case cracked and probably flexed, which caused the issue with the ring & pinion that finished off the case. If you look at the broken edge, there are several places where the break appears to be not as fresh (more dull in brightness) as other places. Those places that are not as bright have been cracked or broken longer then the bright places.
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Re: doctor diff 8.75 case review
[Re: poorboy]
#3174303
09/10/23 10:45 PM
09/10/23 10:45 PM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Not the way I see it, if case cracked first under very high load conditions, I suspect the R&P would break contact extremely fast with a few broken teeth as that occurred. If the R&P became locked solid with a broken tooth leading to more broken teeth and quickly escalating. I can visualize force building enough to destroy the pictured or any case. I don't fault the case here based on what I see any more than I would blame an Alum KB block destroyed/windowed by a cheap over revved failed con rod.
edit, under very loads causing any initial crack in the case, that would be the end of any case flexing and failure would be immediate.
Last edited by jcc; 09/11/23 06:40 AM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: doctor diff 8.75 case review
[Re: jcc]
#3174316
09/11/23 12:18 AM
09/11/23 12:18 AM
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Joined: May 2003
Posts: 13,189 aZLiViN
J_BODY
I Live Here
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I Live Here
Joined: May 2003
Posts: 13,189
aZLiViN
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Closed what out cheap, R&P? Mopar performance in the mid 90’s discontinued the aluminum center section and liquidated them. Think we got them at work for something like $200 at cost. I never used them and sold them off.
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Re: doctor diff 8.75 case review
[Re: poorboy]
#3174317
09/11/23 12:25 AM
09/11/23 12:25 AM
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Joined: May 2003
Posts: 13,189 aZLiViN
J_BODY
I Live Here
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I Live Here
Joined: May 2003
Posts: 13,189
aZLiViN
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Monte preached to us long ago about the 8.75 . I remember when Mopar closed these out for CHEAP! Looks to me like the case cracked and probably flexed, which caused the issue with the ring & pinion that finished off the case. If you look at the broken edge, there are several places where the break appears to be not as fresh (more dull in brightness) as other places. Those places that are not as bright have been cracked or broken longer then the bright places. Pinion relationship to the ring gear and no pinion support….. lifting of the left cap has been a thing with the 8.75 forever. I think with the aluminum center it was the cap through design saying “I got this”, and physics saying “hold my beer”.
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Re: doctor diff 8.75 case review
[Re: J_BODY]
#3174328
09/11/23 06:46 AM
09/11/23 06:46 AM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Monte preached to us long ago about the 8.75 . I remember when Mopar closed these out for CHEAP! Looks to me like the case cracked and probably flexed, which caused the issue with the ring & pinion that finished off the case. If you look at the broken edge, there are several places where the break appears to be not as fresh (more dull in brightness) as other places. Those places that are not as bright have been cracked or broken longer then the bright places. Pinion relationship to the ring gear and no pinion support….. lifting of the left cap has been a thing with the 8.75 forever. I think with the aluminum center it was the cap through design saying, “I got this”, and physics saying, “hold my beer”. The thru bolt upgrade in this case evidently solved that cap lifting issue shortcoming mentioned and moved the failure to next weakest point when overloaded or suffering a jammed R&P tooth failure IMO. Regarding these Alum cases, Summit was selling them for approx $650 in 2004, and $1087 in 2008. In past few years I have seen them on ebay new for $2800.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: doctor diff 8.75 case review
[Re: Stanton]
#3175112
09/14/23 08:29 AM
09/14/23 08:29 AM
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Joined: Jan 2003
Posts: 21,645 San Jose,CA
migsBIG
YouTube is my go-to news source
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YouTube is my go-to news source
Joined: Jan 2003
Posts: 21,645
San Jose,CA
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Photos are of three different cases ... who makes what ??? The aluminum one looks like the discontinued Mopar performance (center) Gold Iridate (Bottom) is something I've never seen on a diff, like it was a display model or something for pics? (top) diff looks super beefy and looks like it's pretty sturdy, which is different from what the OP has in his video. Would love to know which case that top one was from.
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Re: doctor diff 8.75 case review
[Re: migsBIG]
#3175117
09/14/23 08:48 AM
09/14/23 08:48 AM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Mark Williams, long out of production, a 742 Style
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: doctor diff 8.75 case review
[Re: jcc]
#3175242
09/14/23 08:28 PM
09/14/23 08:28 PM
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Joined: Jan 2003
Posts: 21,645 San Jose,CA
migsBIG
YouTube is my go-to news source
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YouTube is my go-to news source
Joined: Jan 2003
Posts: 21,645
San Jose,CA
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Mark Williams, long out of production, a 742 Style Thank you. Now I just have to hope one shows up or figure out if Doc’s is just as strong. If the new diff is good to 600hp/lbs of torque, I would buy a couple over buying a new Dana 60 rearend.
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Re: doctor diff 8.75 case review
[Re: migsBIG]
#3175340
09/15/23 11:20 AM
09/15/23 11:20 AM
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Joined: Dec 2013
Posts: 4,680 Wichita
GY3
master
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master
Joined: Dec 2013
Posts: 4,680
Wichita
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Mark Williams, long out of production, a 742 Style Thank you. Now I just have to hope one shows up or figure out if Doc’s is just as strong. If the new diff is good to 600hp/lbs of torque, I would buy a couple over buying a new Dana 60 rearend. Why?! Get a full floater Dana 60 for cheap out of a pickup, cut the ends off your 8 3/4 (or use aftermarket), use your existing backing plates/brakes and get axles from Dr. Diff. Cheaper and stronger. I have just under $1k in my Dana after dealing with trying to get an 8 3/4 to live behind a 600 hp stroker. We're over 850 HP now with a heavy car and so far no issues with the Dana.
'63 Dodge 330 11.19 @ 121 mph Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs. 10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.
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Re: doctor diff 8.75 case review
[Re: GY3]
#3176549
09/19/23 11:57 PM
09/19/23 11:57 PM
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Joined: Jan 2003
Posts: 11,712 Portage,michigan
B3422W5
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 11,712
Portage,michigan
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Mark Williams, long out of production, a 742 Style Thank you. Now I just have to hope one shows up or figure out if Doc’s is just as strong. If the new diff is good to 600hp/lbs of torque, I would buy a couple over buying a new Dana 60 rearend. Why?! Get a full floater Dana 60 for cheap out of a pickup, cut the ends off your 8 3/4 (or use aftermarket), use your existing backing plates/brakes and get axles from Dr. Diff. Cheaper and stronger. I have just under $1k in my Dana after dealing with trying to get an 8 3/4 to live behind a 600 hp stroker. We're over 850 HP now with a heavy car and so far no issues with the Dana. I am running 10.40’s at almost 3400 pounds. I bought a nodular case 8.75 from Moser, after a 50 year old case failed..Billet adjusters, all grade 8 hardware, very nice piece. But I footbrake. Wouldn’t use a brake. This is a 4 inch stroke deal that makes plenty of torque
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight 418 BPE factory replacement headed stroker, 565 lift solid cam Best so far, 10.40 @127 1/4 1.41 best 60 foot 6.60 at 103.90 1/8
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Re: doctor diff 8.75 case review
[Re: B3422W5]
#3177014
09/21/23 06:48 PM
09/21/23 06:48 PM
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Joined: Dec 2004
Posts: 10,554 Rittman Ohio
fourgearsavoy
I Live Here
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I Live Here
Joined: Dec 2004
Posts: 10,554
Rittman Ohio
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I built an 8 3/4 with one of those Yukon cases for a 10 second foot brake Duster and it held up very well. Casting was a little rough but it was thick where it needed to be. If I had a regular bracket car it would have an aftermarket 9" under it. Using NO factory Ford parts. Gus
64 Plymouth Savoy 493 Indy EZ's by Nick at Compu-Flow 5-Speed Richmond faceplate Liberty box Dana 60
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