what can i use switching from a 8.25 to 8.75?

-
67cuda360

67cuda360

Well-Known Member
Joined
Nov 11, 2009
Messages
462
Reaction score
24
Location
St.John's NL, Canada
Hi, i'm looking into switching my 8.25 to a 8.75 rear end. I have a lead on a complete a-body 8.75 without the 3rd member, i found another 489 3rd member that i could buy for cheap to rebuild. My question is, what can i re-use from the 8.25 rear?

I read in another forum (i think pettybludart commented) that the complete drumbrake setup can be used.

What about the axles? I currently have the large bolt pattern axles in the 8.25. I assume the 8.75 is small bolt pattern. Can the large boltpattern axles be used in the 8.75 or do i need to buy new ones?

Will any modifications need to be made to the axle shaft to fit large boltpattern axles? What about the driveshaft, will this need to be shortened?

So many questions ha ha?
 
67cuda360 said:
My question is, what can i re-use from the 8.25 rear?

I read in another forum (i think pettybludart commented) that the complete drumbrake setup can be used.
Click to expand...
Yes, the entire thing can be swaped over.

What about the axles? I currently have the large bolt pattern axles in the 8.25. I assume the 8.75 is small bolt pattern. Can the large boltpattern axles be used in the 8.75 or do i need to buy new ones?
Click to expand...

No, not the axles IIRC Don't assume the 8-3/4 uses a small bolt pattern. It can use ethier. New ones would be a reasonable thing to pay for, not terribly expensive and it wold be a excellent upgrade for seious power enhancement.

Will any modifications need to be made to the axle shaft to fit large boltpattern axles? What about the driveshaft, will this need to be shortened?
Click to expand...
The axle ahfts between the 1/4 and 3/4 will not work, again, IIRC. You can purchase new axles with the bolt patten you spec.

OH, you will need to shorten your driveshaft a bit.
 
I just heard from the seller, the axel is small bolt pattern. So switching over to a large bolt pattern is as easy as only buying new axles and a bearing set? No modifications to the actual axle? I thought i heard somewhere the axles needed to be drilled to except large bolt pattern axles.
 
You just told me that a member did that.
 
the 8.75 you are getting has small bolt pattern? if so, you can get them axles drilled for bbp
 
rumblefish360 said:
You just told me that a member did that.
Click to expand...

Sorry for the confusion.
I think 340 plot just answered my question lol. I meant to ask if the axle shaft from the rear end (currently small bolt pattern) needed to be drilled out to fit the large bolt pattern axles that i would have to buy to upgrade so that i can use my large bolt pattern rims and drumbrakes from my 8.25.

Does anyone know if this is expensive to have done?

are there any other things that i should consider?

So is the below all that needs to be done?
- buy the a-body rear axel (small bolt pattern)
- transfer drumbrakes from the 8.25 to the 8.75
- buy large bolt pattern axels for the 8.75
- install new bearings on axels
- drill out the 8.75 axle shaft to fit the large bolt pattern axels
- shorten the driveshaft
- buy a working 3rd member
- install and lay rubber.... :)

am i missing anything?
 
I'm sorry, but this;
drill out the 8.75 axle shaft to fit the large bolt pattern axels
Click to expand...

Makes absoultely no sense at all to me.
 
You either drill the small bolt pattern 8.75 axles or purchase axles with the large pattern to fit your housing and all your big bolt pattern stuff will bolt up
 
You can take the SBP axels(4 inch) to a local machine shop to be drilled for LBP(4 1/2 inch)re-install and your good to go.

Your confusing members with your comment...re-drilling axels to fit axels?

Your re-using the same axels,so Yes they will still fit the axel HOUSING of the 8 3/4.Good Luck.
 
You can not swap the brakes from an 8.25 to an 8.75 unless you get custom axles with the large bolt pattern AND the proper offset for the wider 8.25 axle's brakes. 8.75's offset is set up for 1.75" wide brakes the 8.25 is set up for 2.5" wide brakes.

The spline count is differnent between 8.25 and 8.75 not to mention the axle bearing differences so the axles can't be swapped between the rear ends.

Not sure about the difference in the axle center line to yoke center line between the two rear ends to know if the axle length will need to be modified but it's quite likely the 8.25 will have a 7260 u-joint and the 8.75 will have a 7290 u-joint so you will at the very least need to use a conversion u-joint.

Also, why go through the expense of making that swap at all? Unless you are making or plan to make in excess of 450 HP and run slicks the 8.25 is more than adequate.
 
pettybludart said:
You can take the SBP axels(4 inch) to a local machine shop to be drilled for LBP(4 1/2 inch)re-install and your good to go.

Your confusing members with your comment...re-drilling axels to fit axels?

Your re-using the same axels,so Yes they will still fit the axel HOUSING of the 8 3/4.Good Luck.
Click to expand...

Sorry guys :) I apologize for the confusion but i'm a novice when it comes to axles. So please bear with me.

The drilling bit was the part i wasn't clear about. I didn't know what part needed to be drilled. Here is an image to help me explain what i thought ha ha.

I thought the axle diameter, (C, on the image) of a large bolt pattern axle was larger than that of a small bolt patter axle, so i thought the axle shaft (A, on the image) needed to be drilled out to fit the larger axles.

But that obviously isn't the case :)

So pettybludart, you mention "You can take the SBP axels(4 inch) to a local machine shop to be drilled for LBP(4 1/2 inch)". So is it part (B, in the image) the machine shop would re-drill?

Thanks for hanging in there guys, i'm learning

P.S. image is not a Chrysler axle, pulled it off the web just for quick reference :)
 

Attachments

  • axle.jpg
    77.5 KB · Views: 235
I have a machinist that charges me 50.00 to drill 4 in to 4 1/2.If I have the axles out.He drilles the hole larger and installs a larger base stud.I have one that has lived behind a 341 hemi for 4 years now with no problems,and I have sold six without a problem.So buy new if you want but im sure they will cost over 50.00
 
Good point DGC333, i am trying to wrap my head around what the best approach is to put a sure grip unit in my car. I'm currently running a large bolt pattern 8.25 with highway gears (open diff) and i would really like to bump it up a notch, nothing wild but something like a sure grip with 3.55 gears.

If i buy the new ring and pinion gears and a sure grip unit + the installation kit from summit racing, have them shipped to Canada and installed by a trained professional, i'm sure i'd be looking at around 1500 CAD before i'm done. I'm just trying to see if i could put an 8 3/4 together for around the same amount of cash.

I won't be putting more than 350 maybe 400 hp in the future so if everyone here thinks it will be too much trouble for the gain then i'll stick with the 8.25. Maybe i'll get lucky and find a nice complete sure-grip rear that i can just bolt in ha ha. (think positive they say)
 
67cuda360 said:
Sorry guys :) So pettybludart, you mention "You can take the SBP axels(4 inch) to a local machine shop to be drilled for LBP(4 1/2 inch)". So is it part (B, in the image) the machine shop would re-drill?
Click to expand...

Yes area B. You can have the axles re-drilled for the 4.5" bolt circle but you will need to use the narrow 1.75" drums which will need to be redrilled too. Most folks get new axles with the correct offset for the wider 2.5" drums which then allows you to use readily available brake parts.
 
Get in touch with Dr. Diff

(406) 883-4772


Cass can explain your options and provide you will the necessary parts.

Especially if you want to do it right and do it once....
 
i dont want to offend any one but i think redrilling axles is the worst possible way to go about this. you leave very little meat on the axle. if you make any power and get traction you will have problems. is it worth losing a tire and taking out your quarter panel?
 
jamesdart said:
i dont want to offend any one but i think redrilling axles is the worst possible way to go about this. you leave very little meat on the axle. if you make any power and get traction you will have problems. is it worth losing a tire and taking out your quarter panel?
Click to expand...


X2.

New axles aint that much. Save your nickels.
 
good, option 1: re drill your axles from 4" to 4 1/2" bolt circle

better, option 2: get a set of 4 1/2" bolt circle axles from a C-body 8 3/4 rear and have them shortened and resplined to fit an A-body 8 3/4 housing

best, option 3:buy new aftermarket axles
 
Thanks for all the response guys.
Sure gave me a lot to think about.

I think i'll stick with my 8.25 and upgrade the carrier and ring gear on it. Pettybludart "Scott" offered me a great deal on a 3.23 gear set and i found a sure-grip carrier online so i think that'll be my winter project :). I'm sure it'll wake up the car quit a bit while keeping the rpm down on the highway.

Again thanks for all the replies.
Wilco.
 
I think keeping and upgrading your 8 1/4 is your best bet. I would still talk to Dr. Diff about Sure grip carriers and gears.
 
jamesdart said:
i dont want to offend any one but i think redrilling axles is the worst possible way to go about this. you leave very little meat on the axle. if you make any power and get traction you will have problems. is it worth losing a tire and taking out your quarter panel?
Click to expand...

Not being smart but how many redrilled axles have you seen fail?
 
You must log in or register to reply here.
-

Back
Top