8 3/4" rear end modifications

[Marc]

I was wondering what (if anything) I still need.
I have a tubbed 71 Demon street car with a mild 500+ hp motor which runs a ford 9" with 4.56 / 5.13 center sections. They are war cases with 31 spline four spider posi's, everything new in each and NO cracks in the hats. Ladder bar/coil over car. This thing spits diffs out. The pinion angle is 1 1/2 degrees down. everything looks normal. I've grown to hate 9" rears.
My coupe I've decided to try the 8 3/4" route. The rear is 40" wide overall, with a deep gusset. It's got a 4 link with additional bracketry. I've installed load bolts for the ring gears caps thru the gusset/housing. I've also put in an inspection cover to take the guesswork out of what, if anything, ever goes wrong. I've got 489 and 742 case pumpkins. I'm planning on running the 742.
Am I whacked? What do you think of an 8 3/4" over a 9"? A local racer (Mas) who recently passed said that a stock configuration 8 3/4" was good for 650 to 700 horse. He ran a 1300 horse 33 Willys race car that went low 8's and said he had no worries with the 8 3/4" with the bolts supporting the ring gear caps.
What do you think? This guy was no dummy. He was one hell of a machinist/racer. Am I going the right way?

[Christopher]

I'll put it this way...A bunch of the Top Fuelers and Funny Cars from the 70's and a bunch of the current nostalgia fuelers all still use the 8 3/4.The 8 3/4 has some bearing sizes the same as the 9" Ford,in fact they are listed in the Timken bearing catalog with the same part number.I'm partial,so I say use the 8 3/4.But my partiality is also based on that I know it's cheaper to use a 8 3/4 than a 9" Ford.

[DUSTER340]

I have a friend who runs a 8 3/4 in his 64 A S/A PLYMOUTH and loves it. I know you will be pleased with it also. MOPAR or I walk!@#$%^&*

[Marc]

Duster340 - I'm the same way. The Coupe even had a cut down 69 Charger gas tank and a 1970 Charger dash last time around. This time i want to do it right, and , money being no object. As much as possible, anyway. I chose the 8 3/4" for it's mechanical abilities. My Demon runs a ford 9" and I don't like it. Thanks though.

[DART/MAN]

Marc,
I run a 4.56 geared 8 3/4 in my race car, it is 40 & 1/2" wide flange to flange, it has a Moser spool and axles in it, with 14x32 good years, I twisted the axle housing once, I redid it and installed a back brace and haven`t had any more trouble. I run a 500 inch 440.

[Marc]

DART/MAN - What time is your car running? What weight is your car? What spline is your axles? Thanks. Marc

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Tubbed 40 Plymouth Coupe
Tubbed 71 Demon
1989 Shelby Lancer
1978 BB ClubCab
1973 Scamper 440 MHome

[DART/MAN]

Marc,
the car weighs 3500# with driver, runs 10.28 at 129mph and usually 60 foots in the 1.43- 1.44 range. I run 30 spline axles and spool.

DART/MAN
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69 M-Code 440 Dart GTS
69 499 inch Dart
66 440 Imperial
65 440 Imperial
48 Dodge Power Wagon
41 Dodge 2-ton Dump
52 Buick Special
87 Shivy Rollback

[Beeracuda]

Our car has a braced (1/4 plate), 8 3/4 with 4.86 pro gears and 35 spline axles/spool. We have had no problems except R & P's when we were running the street gear. The pro gears look great after about 175 passes.

Our car weighs about 2850, we run 14x32W's. It 60 foot's in the 1.39 to 1.41 range. We've run a best of 10.23 but normally run 10.40's in the summer with our density altitudes in the 5800' to 6600' range.

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[Marc]

Thanks. Just what I hoped to hear. And by the way - nice cars, DART/MAN.

[DART/MAN]

Thanks!!!

[krace72]

If your are going to run a 8 3/4 I would suggest buying billet aluminum caps to hold in the spool or carrier, you can buy them from Strange eng. The reason I know this is because I split the stock caps in half which of course destroyed everything, the aluminum will flex enough at the launch to absorb the shock. Definetly with that kind of h.p. a set of pro gears, just as long as you dont do much street driving.I would also make sure you have good aftermarket axles.I wanted the strongest rear end for the money and went to a DANA.Itwould have cost me about $500 or more to build up the 8.75 or a Ford 9" cant put one of those under a MOPAR CAR!The only draw back is the 35lbs weight difference.Plus were talking about a heavy car with a tranny brake!indy cylinder 440 and 33.16.15 hoosier slicks.For the money DANA is the strongest!!!! The reason I say that is any old 70s dodge truck has one which are still easier to get than 8.75, even 75 to 79 chevy 4X4 trucks have them.Still manufactured by Chrysler.

[Christopher]

Same reasons why we have Dana 60's in our cars.

[Marc]

Krace72 - Precisely the reason I put load bolts for the ring gear caps on my housing. I may run the aluminum caps as well as the load bolts, for extra insurance.
Also, the car is a high mile per year STREET car, so no spool for me. I had one in my Demon, and ended pulling it out in favor of a 31 spline 4 spider posi unit. My axles in my Coupe are Dutchman Pro Street units.
I like the Dana also, but I like the ease of gear swaps(as well as the LACK of expense) associated with the drop out rear. I've owned lots of street racing cars, and never had a problem with an 8 3/4".
And even though I run a Ford 9" in my Demon - I bought the car with it (as a rolling race car shell),and don't really like the design of the pumpkin or the price tag of the parts. The pinion hits too low on the ring gear for my liking, and the cases walk around so much it's a wonder the FORD guys like them. I went through half a dozen cases before I found one I consider stable.
Just my .02 cents worth.

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Tubbed 40 Plymouth Coupe
Tubbed 71 Demon
1989 Shelby Lancer
1978 BB ClubCab
1973 Scamper 440 MHome

[wedge542]

i was glad to see something about the 8.75,i didnt know anything about the bolts thru the ring gear caps,im havin trouble wth the pinion bearing,wth 5deg pinion angle i need for traction i eat up set of gears around 60 passes,pro street,backbraced,4link,2850lb daytona,was at 800hp,now building a 1200hp and last time had 1.24 60ft,now around 1.14,has moved car about 10feet and sheared the pinion gears to a smooth handle,pluse didnt have my high rpm limiter in and went 8500 before i could blink,tach playback showed,what do any of you think about useing 8.75 in this combo?

[Marc]

Wedge542 - I was told by the late Mas of Diamond Engines/Bill Phillips that without the load bolts for the ring gear caps the rear would be vulnerable to damage with high HP and/or heavy car launchs. He had a 1933 Willys with a 1300? HP engine, and said he had no trouble after installing the load bolts. This info was given to me by a mutual friend, and I adopted this into my rear. My brace was done in such a way as the middle is parallel to the axles, so th bolts can be secured by a second jamnut. Send me your e-mail address and I'll send photos and you can give me your opinion.
I might be wrong, but shouldn't your pinion angle be 2 degrees nose down? Are you using bushed ends?(Pro Street style) Marc

[wedge542]

marc,the 4link ends are c.moly,ive tried all from 2-5deg and stopped at best setting,i know theres alot useing these rears so i know i can but need to get ideas how and what mods to do,i think the pinion goes away cause of houseing twist or flex and that much angle on pin bearing cant be good but may have to back of angle and adjust launch rpm lower.email is wedge542@aol.com...thanks

[Beeracuda]

Marc,

Could you send me the pics, too?

montyb@ramaircraft.com

Thanks!

[Marc]

Here they come!! Tell me what you think.
Marc
wedge542 & montyb - Did you get them yet???

[This message has been edited by Marc (edited March 01, 2000).]

[Rob74]

Marc id be interested in seing those pics if you could send them to onequickfish6850@aol.com id really appreacate it thanks, Rob

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74 pro street cuda 446cu 600 hp 95 Ram sport 6 in lift 35/14.50 super swamper thornbirds

[jay]

I haft to agree with the Dana60 rearend. It has a better sellection than the 8 3/4. 8 3/4 are getting harder to find. It has a bigger pinion shaft than a 9 inche, but finding spare 742 carriers will be a search. Dana 60 are still in production today making it easier to find parts. As for strength I believe it to be stronger than the 8 3/4 or the 9 inche. Well good luck in whatever you do. Thanks Jay