My Son Said Use the 8.25 Not the 8.75

Which Rear End to use

  • 8.25 with 3.21 Sure Grip and Grand Cherokee Disc Brakes

    Votes: 6 31.6%

  • 8.75 with 3.23 Sure Grip and Mustang-based Disc Brakes

    Votes: 9 47.4%

  • Someone is bound to say sell him the 8.75/8.25 and find a 7.25

    Votes: 4 21.1%
  • Total voters
    19
  • Poll closed .
-
65 Dartman

65 Dartman

1 of None 65 Dart Sedan Delivery
FABO Gold Member
Joined
Sep 24, 2006
Messages
13,752
Reaction score
4,599
Location
Strasburg, VA
My youngest son (he's going on 40) will eventually inherit my 65 Dart wagon. He stopped by today to work on his Aerostar's rear brakes (can't do it at his apartment). He spotted the A Body 8.25 that I might build and said that's the rear end that should go in the wagon and not the 8.75 sitting on my homemade rear end stand! I asked why and he said in his opinion the Grand Cherokee rear discs are easier to work on compared to the Ford disc brakes on the 8.75! He's basing his opinion on working on the Aerostar's caliper piston that must be rotated back into the caliper. Plus he said the E Brake within the rotor on the Cherokee is easier to work on!!

So with gearing being the same (3.21 vs 3.23), both being LBP, both being a SG (cone style), and both semi rebuilt with new bearings, is he right or doesn't know what he's talking about?

FWIW with the Mustang-based disc brakes on the 8.75, 14 inch Magnum 500's clear the rotors and with the Grand Cherokee discs, 15 inch wheels are mandatory
 
Last edited:
Depends if you want BBP or stay with SPB

i am going with a 7 1/4 in my slant six wagon only because in am staying SBP.

An 8 3/4 is better suited in a different type car imo.

An 8 1/4 is an excellent choice but there, we run into the BBP vs. SBP question.

I would say go with the 7 1/4 only because they are better than what people give credit for, sure they have limits but are you going to ape it, or normal drive??

Only you know what you are going to do with your car :)
 
Rainy Day Auto said:
Depends if you want BBP or stay with SPB
Click to expand...

The wagon will be LBP all the way around and the plan from the beginning was to be 4 wheel disc - maybe overkill with a slant, but what the hey! A LBP 7 1/4 could work I guess but there goes the rear discs!
 
65 Dartman said:
I thought the Dana 60 was the king; 8.75 the Crown Prince!!
Click to expand...
Almost Dana is king and 9 1/4 is Prince like it or not. The 9 1/4 is stronger, cheaper and easier to find parts for. I will say that the 8 3/4 is a easier to bolt in but by the time you get you a posi and converted to Big bolt pattern you have a thousand bucks in it. I guess it make a difference how much power you are put to the tires. You can even get a rear wheel speed sensor for any lock brakes if you like. A 8.8 would work fine to but that mite be blasphemy to some.
 
Last edited:
65 Dartman said:
My youngest son (he's going on 40) will eventually inherit my 65 Dart wagon. He stopped by today to work on his Aerostar's rear brakes (can't do it at his apartment). He spotted the A Body 8.25 that I might build and said that's the rear end that should go in the wagon and not the 8.75 sitting on my homemade rear end stand! I asked why and he said in his opinion the Grand Cherokee rear discs are easier to work on compared to the Ford disc brakes on the 8.75! He's basing his opinion on working on the Aerostar's caliper piston that must be rotated back into the caliper. Plus he said the E Brake within the rotor on the Cherokee is easier to work on!!

So with gearing being the same (3.21 vs 3.23), both being LBP, both being a SG (cone style), and both semi rebuilt with new bearings, is he right or doesn't know what he's talking about?

FWIW with the Mustang-based disc brakes on the 8.75, 14 inch Magnum 500's clear the rotors and with the Grand Cherokee discs, 15 inch wheels are mandatory
Click to expand...
easier to work on - that's the argument/reason? So - I'm lazy, so I would gladly sacrifice strength for "easy" repair - ? :BangHead: It's disc brakes, how much easier can one possibly be over the next? (and who cares!?) ~ of the two choices - the only answer 8.75.
 
ScampMike said:
easier to work on - that's the argument/reason? So - I'm lazy, so I would gladly sacrifice strength for "easy" repair - ? :BangHead: It's disc brakes, how much easier can one possibly be over the next? (and who cares!?) ~ of the two choices - the only answer 8.75.
Click to expand...

I vote 8.25 with discs.
Lots of aftermarket parts and plenty strong for a slant or even a mild drag racing smallblock later if the mood struck.
You could probably pay for the entire 8.25 swap with that 8.75
 
stroked340 said:
Your taking advice from someone driving an Aerostar:rofl::rofl::rofl:
Click to expand...

All he's ever been around growing up was our Darts, Chargers and Challengers, and he's had a couple of Dakotas and Rams, but with 2 teenagers on the weekends, the Aerostar was free and large enough to haul everyone around. I guess he does what he had to do lol!
 
Last edited:
What about the 9 3/4 Dana 60.
 
In a slant six wagon with highway gears, I think you're gonna want to keep unsprung weight to a bare minimum.
 
Since it's not a high horsepower build and bbp is your goal the 8.25 is plenty. If I had the 2 rears to choose from for a V8 I'd go 8.75.
As far as the brakes. The parking brake in caliper brakes are easy enough to service. You just need the tool to wind them back in. Drum in hat like the Cherokee brakes can actually be more work because they need adjusting where the others don't. Also more parts involved and can be more expensive.
 
If it's staying a slanty,and it's staying off the track,then my vote goes to the 7.25 drum brake . If you really want a bbp, you can get a later Dart one. I think those will accept the Dakota SG. On a lot of A-bodies you could disable the rear brakes entirely and most guys wouldn't even miss them.
 
AJ/FormS said:
If it's staying a slanty,and it's staying off the track,then my vote goes to the 7.25 drum brake . If you really want a bbp, you can get a later Dart one. I think those will accept the Dakota SG. On a lot of A-bodies you could disable the rear brakes entirely and most guys wouldn't even miss them.
Click to expand...
It's staying a slant. With the mods (a hefty increase in CR, a stout cam, headers, Offy or Dutra Hyperpak - I have both - coupled with FI and a 4 speed) and the plan had always been 4 wheel LBP discs, a 7.25 BBP is not even in consideration!

I ought to add the 8.75 is fully assembled with the Base 94-04 Mustang discs, 3.23 Sure Grip, and new hard and soft lines. Interesting with this setup is 14 in Magnum 500s clear the calipers; otherwise 15 in rims will be necessary like with the disc brake 8.25. The 8.25 is a bare housing with all the parts waiting to be installed- 3.21 Sure Grip and all the Grand Cherokee disc brake stuff.
 
When I was about 1/3 of the age I am now, someone came up with "Different strokes for different folks"
 
If you are going to keep it a slant, stick with the 7.25. Build a cruiser.

If you are going to hop the wagon up with a small block, then yah. 8.75, disc, etc etc.

.02
 
>If a regular 2.66 low4 speed, 3.23s are gonna be a big disappointment with any performance cam. The starter gear is just 8.59.A teener doesn't like that one tiny bit. A 340 has to be slipped out, and even a 360 complains about it.
Your slanty will probably want a starter gear in the 10s. That would be a minimum 3.73s.(10/2.66=3.76) The 1-2 rpm drop with this one is 28%. So reving to 4000, the Rs will drop to 2872. With 3.73s this will be about 30.5mph. In Second gear now TM will be 3.73x1.91=7.12 ;Great!
>If a 3.09low non-od then the 3.23s are the very minimum. But don't be surprised by the 38% drop in rpm on the 1-2 shift.(10/3.09=3.24) Reving to 4000 the Rs will drop to 2472/30.3 mph with 3.23s. In second now, TM will be 1.91x3.23=6.17; we are losing steam big time; a 13.4% power loss, compared to 7.12.
>If a 3.09od, you are in big trouble, the 1-2 rpm drop is 46%;killer to a 360 with a cam, never mind a slanty! Reving to 4000, the Rs will drop to 2162,..ow;still at 30.3 mph with 3.23s. Got torque? Well in second now, TM will be 1.67 x 3.23=5.39;nearly a 25% power loss compared to 7.12, so NO! there will be no acceleration to be measured with a stopwatch.For performance in second,with this tranny, you will need TM at least 7:1, so this would be 4.10s minimum. But 4.10x3.09low=12.67= race car starts.

So my conclusion is go with the 2.66low box and at least 3.73s. The 2.66box has the tightest splits, to keep the slanty "on the pipe". 3.73s are the minimum to get you off the line,while 3.91s will help immensely to keep the car moving in third gear, just when wind resistance is starting to eat up power.

And 3.91s of course would be just right, when you get to third. With 3.91s 4000 will get you 40.5 mph in second. The rpm drop will be to 2911rpm, and with the right combo, this will continue to pull to 56mph @4000rpm, and 4286@60. The rpm@ 60 in 4th will be about 3100, with those 3.91s and 25.5 inch tires.
 
Last edited:
@AJ/FormS I really enjoy your comments on the starter gear/rear end gearing and have learned a lot! Thank you!

The trans is a non-OD 65 ball and trunnions style with the 3.09 low and it seemed to work well in the 65 Signet with a stock 6 that I pulled it from. I suspect that car had 3.23's but never checked it before letting it go.

I have to use what I have on hand - a 3.21/3.23 Sure Grip and 3.55 Sure Grip. With the amount of highway driving I anticipate- from northern VA to Carlisle (125 miles or so) and to the Nationals (400 miles or so), the 3.23's will be more highway friendly than the 3.55's.

The right T5 would probably better suited for a transmission coupled with higher numerical gears I suspect.
 
65 Dartman said:
@AJ/FormS I really enjoy your comments on the starter gear/rear end gearing and have learned a lot! Thank you!

The trans is a non-OD 65 ball and trunnions style with the 3.09 low and it seemed to work well in the 65 Signet with a stock 6 that I pulled it from. I suspect that car had 3.23's but never checked it before letting it go.

I have to use what I have on hand - a 3.21/3.23 Sure Grip and 3.55 Sure Grip. With the amount of highway driving I anticipate- from northern VA to Carlisle (125 miles or so) and to the Nationals (400 miles or so), the 3.23's will be more highway friendly than the 3.55's.

The right T5 would probably better suited for a transmission coupled with higher numerical gears I suspect.
Click to expand...
If you are limited to 3.23s You better go real easy on the cam. And if you go easy on the cam, then you will have to pay particular attention to the DCR. And above all, the Q will be somewhat critical; stay away from .050 to .080, or you may not find octane enough to actually drive the old girl.
If you are just looking to blast off the line, then the 3.09 x 3.23s- 9.98 should be fine.

The problem comes when hitting second. Typically, when just driving normally,a streeter shifts into second at around 2800, cuz the engine is singing a sweet song there. For you tho the Rpm drop will be to 1730, and a big-cam engine will fall flat on it's face there.The cure of course is to rev it to a higher rpm right? well yes and no. You will have to rev it to something like 3600, to drop in at 2225, and again the big-cam engine is still kindof sleeping at that rpm. But if you are just cruising, then, now you are at 27mph(3600). Wait what? Yeah 3.23s will get you 27 mph at 3600 in First, with 25.5 tires. Do you really want to scream it up there every time? Of course not. 2800 was much better at 21mph. But if you put it into second at 21 mph@1730 rpm, you are kindof lugging it if you step on it too hard, and if you didn't pay attention to the Dcr and Q,during the planning stage, you could be into detonation plenty quick.
So the real problem is in the split from 3.09 to 1.91 second. It's too big for a slanty with 3.23s, and a big cam.
So if you are limited to a 3.23 rear and the 3.09 low box, then the cure is to have torque at 1730 rpm/21mph. And that means the big cam is G-O-N-E!
But that also means, you will have to very carefully manipulate the Dcr and Q, or you will have to take measures to suppress detonation: Ie race-gas, octane-boost, or water-injection.

I think it's just waaay easier to use the 2.66 box and 3.91s.
Okaaaay maybe the 3.55s, and 1.91second will get you by, with a cam maybe one or two sizes bigger than stock, but man easy on the Dcr. I'm thinking about second gear again; 3.55 x 1.91=6.78. If you are easy on it and get the tune just right, it could work.....I suppose. Well if you kept the small carb on it probably no worries,lol
 
Last edited:
You must log in or register to reply here.
-

Back
Top