Mopar 8 3/4 VS 8 1/4
 

Can I expect a gain in ET buy switching from one to other if using the same gear ratio? How about overall weight?

Re: Mopar 8 3/4 VS 8 1/4
 

8 1/4 will be easier to break.

Re: Mopar 8 3/4 VS 8 1/4
 

I broke an 8 1/4 with a warmed over slant six and a 4 speed but it was not a posi unit. With a locker and aftermarket gears it might live behind an automatic but in my opinion it's not worth the weight savings,

JimR

Re: Mopar 8 3/4 VS 8 1/4
 

Not worth the trouble! You *will* break the 8 1/4 ! Jim

Re: Mopar 8 3/4 VS 8 1/4
 

I read a long time ago that Bob Lambeck ran an 8 1/4 in a Duster 360 stocker but I don't know how long it lasted...

Re: Mopar 8 3/4 VS 8 1/4
 

Does anyone or did anyone make a spool for a 8.25? I don't think so, but I could be wrong. If you do go the 8.25 route, you will have to get the right suregrip unit to fit your application. I have a NOS one in the garage since I bought two for my warlock just in case I needed it.

Axles are another concern here too. Not sure how strong the factory original units were/are after 25 and more years.


Eric

Re: Mopar 8 3/4 VS 8 1/4
 

Eric, does your Dakota have an 8 3/4 in it?

Re: Mopar 8 3/4 VS 8 1/4
 

I know some that made a spool themselves back in the days and got it to last a long time in a 360 duster stocker...but it finally gave in and had to leave room for a 8.75..the gear selection isn't very good...a 4.56 looks like "top of the line"!

Re: Mopar 8 3/4 VS 8 1/4
 

I ran a 8 1/4 for years in a 72 Duster 340. Broke one tooth once on ring gear. Car ran mid 11's in "stocker trim". Full interior all steel. I think it is less hassle with 8 3/4 being able to use a spool and not have to replace the Posi in the 8 1/4 every few years or so. I did change to an 8 3/4 but made a gear change so I can't say if one is faster.

Monty

Re: Mopar 8 3/4 VS 8 1/4
 

:)I think Jim Durham ran a 8.25 in his F/SA til a couple of years 'l ago...If you equalized the weight I used to be .01 faster with 8.25 but hardly worth to trouble. I will give you a housing for free if you get my way again. PS I lost your number again.:):)




s

Re: Mopar 8 3/4 VS 8 1/4
 

I assume Philip is asking about it for his slant six/ automatic combo.

Not knowing a thing about Mopar rears, I'm still going to offer my opinion:
Do it.

Re: Mopar 8 3/4 VS 8 1/4
 

There was a bracket racer that raced at State Capital Dragway in Baton Rouge who used an 8 1/4" in his Dart Sport. He ran high 10's with a 360 with it. I say if you can find the ratio you need, run it. It can't be any weaker than say an old 8.2" GM...

Re: Mopar 8 3/4 VS 8 1/4
 

Loge's use to run one in their Volare stocker.

Re: Mopar 8 3/4 VS 8 1/4
 

I've run an 8.25 for years and never had an issue with it 12 sec.vehicle....over 1000 passes with the original suregrip and 4.56 gears (they are getting replaced now)..... Moser made me a set of alloy axles when I first built it and recently I picked up a locker for it for the rebuild....I guess the the main issues would be axle retention and the fact that you can run a little shorter driveshaft with the 8 3/4 allowing more rpm before driveshaft issues....

Re: Mopar 8 3/4 VS 8 1/4
 

I have been using the 8 1/4 all season with out any issues and I'm sure it is plenty strong enough for what I use it for, I'm wondering if the 8 3/4 is more efficient or not. I don't really have any concerns about the ease of gear changes, Is it worth the hassle of changing the hole assembly ET wise?. Hey John, have you swapped out the rear in the mirada yet? Any one have a phone number for Loge? Sound's like he would have experiance to give me the right answer.......

Re: Mopar 8 3/4 VS 8 1/4
 

Sold the Mirada to North Carl. family.. beleive they are still running the 8.25 with no problem. I would research gear availablity ... have not seen any gears past 4.50 since 1980. Mopar in its race seminars did not encourage us to run then in high HP stockers even in 1970's.:)

Re: Mopar 8 3/4 VS 8 1/4
 

Phil I may be wrong but are you building a hemi car ? Tires and converters have changed from the old days and an 8.75 will not live, just ask Larry Hill, his Cuda with a 440-6 broke at every important run when he needed it most. If your not convinced start out with a 741 case and try Jim Bailey at Finished 330 858 1842 his treatment of rear part is the best bar none. I still think you will need a dana, look under John Shaul's Maxie.

Re: Mopar 8 3/4 VS 8 1/4
 

Sure does. The challengers 70 and 72 have dana 60's. All three 4.88 gears. Rounding out the collection is the 78 lil red stock 9.25 with a detroit locker and 4.56 gears.

You can never have too many racecars, or baseball bats. You never know when you might break one!

Re: Mopar 8 3/4 VS 8 1/4
 

Don't you mean "742" case? 741 has the smallest pinion @ 1 3/8" and smallest variety of ratios.
Then there are aftermarket steel caps, aftermarket 489 nodular cases and the Mopar Aluminum 742 cases.

It might be the same Mirada GTX John mentioned, but I know of one that does run the 8 1/4".
Personally I'm happy with my 8 3/4". Car weighs 3,530+ but have only had broken teeth 2-3 times in 10+ years and the ease of swapping gears is too good to pass up. Current gears have been holding up for the last few years, but I have a set at Jim Bailey's right now.

Re: Mopar 8 3/4 VS 8 1/4
 

Think about this. 8.75 Any ratio you need, multiple spool manufacturers, axles to any spline, any width (we make our own housings) We run the 742 housing in both my large land barge and the GT/FA. Real easy choice to me. And get Bailey to treat them. Now at about 3600 lbs with 700+ hp, 600+ torque, the 8 3/4 will probably give up. Hope this helps.

Re: Mopar 8 3/4 VS 8 1/4
 

What is the "Bailey treatment"?

Re: Mopar 8 3/4 VS 8 1/4
 

What Bob said.

Having your ring & pinion "FINISHED" will not only make it live longer, but I've found that it's worth a couple hundredths, too!

REM Isotropic Superfinishing plus Cryogenic treatment. There's some info on his site, finishedracing.com

Re: Mopar 8 3/4 VS 8 1/4
 

Richmond is making a 4.86 in a Pro Gear for the 8 3/4 , or were you talking about the 8 1/4 ? Part numbrt 79-0133-L

Cheers

Chris

Re: Mopar 8 3/4 VS 8 1/4
 

yea Richmond has a part number but they stopped making them, told us we need an order of $10k to get a set, oh well Jim Baileys stuff has held up better then anything i have ever bought from Richmond. Also the 8.75 rear is great if its set up correctly i've been 10.7's @ 3200+ lbs and no prob with the rear just the richmond street gears.

Re: Mopar 8 3/4 VS 8 1/4
 

Bob, No I am not going to use the 8 1/4 behind the hemi. This question is for the slant six wagon. I have a garage full of spare parts for any rear axle I use I'm just wondering if I will gain any ET by putting a 8 3/4 under the wagon, The strengh is not in question.


So is a 8 3/4 faster than a 8 1/4? anybody have a real answer?

Re: Mopar 8 3/4 VS 8 1/4
 

With the limited choices of ratios for the 8.25 if the optimum gearing for your combo turns out to be between those ratios and it is available for the 8 3/4 then the latter would be the rear assembly to use....I think that any small benefit (if there is one) in performance with the same ratios in each would be overcome by the flexibilty of the 8 3/4.....

D L Rambo