A Body Tire Clearance

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Gold Rush

Gold Rush

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Hey all, first time poster here.
I recently acquired a 1974 Plymouth Valiant with a 400 swapped into it. I was wondering what people are doing for rear end widths for maximum tire clearance with the offset shackles from Dr. Diff. I'm going to have to build a custom width rear for this thing to begin with since the car has an 8.25" under it currently.
 
Since you are going to customize width, only limits are your ability or wallet capacity. So, it depends on what size tire you want to run, what offset rims you want to go with them, and if those will all fit within the OEM wells or require tubbing.
 
A street- friendly 400 should live quite well with an 8.25 rear end- why subject yourself to all the issues involved with changing it out?
With the Dr. Diff kit installed, just figure out the backspacing you'll need on your wheels and slap 'em on.
If you need gears or a Sure-Grip for your rear, Jeep Cherokees, early Dakotas, and even some half ton trucks and vans commonly had decent gears and Sure-Grips in them, and can be sourced pretty cheaply from the boneyard.
Just be aware that the axle spline count changed in the mid/late nineties at some point, so you need to stay with the early versions.
 
Absolute biggest you can go with a Valiant body and a 1/2” offset will be 275’s, and even that will probably require some quarter lip trimming/rolling. Backspacing will depend on on the width of the rear axle, if you do plan on customizing the width then just pick the wheels you want and set the width on the backspacing you can get.

Although I agree with Professor Fate, an 8.25” isn’t a bad choice with a 400 unless you’re talking about a big power build or lots of racing.
 
Not a valiant but my 70 Dart had wheel well lips rolled etc. it only fits a certain rim and back space and other than that with my 8.75 I can relocate the leafs in board I think but I havent i have stock 14 inch ralleys on it right now and aluminum slots as spare wheels.
 
Professor Fate said:
If you need gears or a Sure-Grip for your rear, Jeep Cherokees, early Dakotas, and even some half ton trucks and vans commonly had decent gears and Sure-Grips in them, and can be sourced pretty cheaply from the boneyard.
Just be aware that the axle spline count changed in the mid/late nineties at some point, so you need to stay with the early versions.
Click to expand...
1996 was the change over, so you need to be on the look out for early 1995 build dates.

just an FYI, jeeps got upgraded frequently so keep a hairy eyeball peeled and make sure the parts are copacetic and not some aftermarket bobo stuff that don't work with what you've got.

bonus, you can also upgrade to jeep grand cherokee/dakota rear discs with that 8.25 too!
 
I've got a sure-grip equipped 8.25 in my 71 Satellite Sebring with a 318. I plan to race this Valiant, though. I don't exactly want to break down in my local Mexico because the car broke an axle.
 
'74 Valiant - so it's a Scamp, right ? Which means it has Dart wheel wells & openings.
They don't accept much with an 8x15 wheel, if that's the size you're planning.
Springs and wheelhouse and wheel opening restrict wheel/tire size to 15x7 & 235/60s on the Darts I had & a Buddy's '70 Dart.
15x8s I've used were 4.5" BS, the 15x7s were 4.25" BS (factory-sized BS).
Moving springs the small amount that the relocation brackets allow will help a bit, but not a lot - even on a Duster.
Ft of wheel opening restricts tire OD, but there's about another inch available if you cut them.
The right side on all of my '68-'74 A-bodies has been tighter than the left by about 1/4".
If it's actually a Duster, they have more room, and a 275/60 on 15x8 with 4.5 BS usually fits, but are pretty tight @ stock ride height.
 
topside said:
'74 Valiant - so it's a Scamp, right ? Which means it has Dart wheel wells & openings.
They don't accept much with an 8x15 wheel, if that's the size you're planning.
Springs and wheelhouse and wheel opening restrict wheel/tire size to 15x7 & 235/60s on the Darts I had & a Buddy's '70 Dart.
15x8s I've used were 4.5" BS, the 15x7s were 4.25" BS (factory-sized BS).
Moving springs the small amount that the relocation brackets allow will help a bit, but not a lot - even on a Duster.
Ft of wheel opening restricts tire OD, but there's about another inch available if you cut them.
The right side on all of my '68-'74 A-bodies has been tighter than the left by about 1/4".
If it's actually a Duster, they have more room, and a 275/60 on 15x8 with 4.5 BS usually fits, but are pretty tight @ stock ride height.
Click to expand...

There are several members running 255's on 15x7's with 70+ Darts and the springs in the stock locations. My own '71 Dart has enough room to do that. The backspace on the wheels has to be perfect, but it's possible on some cars. 245's should fit pretty much all Darts if the wheels have the proper backspace.

The 1/2" offset is usually good to go up to the next wider tire available on both Dart and Duster bodies because of how the tire sizing goes. On a Dart the 1/2" offset can get you to a 275 tire, again, there are several '70+ Darts on this board doing exactly that. On a Duster the 1/2" offset can get you to a 295 in there. Depending on ride height some quarter lip trimming will probably be necessary, especially on the Dart body. But I was running 295's on my Duster after the 1/2" spring offset and a bit of quarter lip trimming, and my car sits lower than factory. With super stock springs I wouldn't have needed to cut anything.

Your backspaces are all based on an A-body 8 3/4 with BBP axles, any other axle width would require different backspacing, including the factory BBP 7.25 and 8.25" rear ends which are substantially narrower than the A-body 8 3/4.
 
I can only confirm what I've dealt with, but OK. FWIW, my '74 Duster had its factory 8.25, all the rest except 1 Slant -6 '73 Dart had 8.75s.
In every case, the springs (whether with small relocation kit or stock), the wheelhouse size, and the opening were limiting factors, especially with the Dart body.
Maybe I just "got lucky" with the several A-bodies I've owned...
 
Just make the tires fit.
IMG_20240129_171916609_HDR.jpg
IMG_20240203_200152218_HDR.jpg
 
Gold Rush said:
Full on in boarding kit? I have been seriously contemplating some fender flares. I'll make me tires fit no matter what. I'm going to do it 70s style and stick them out the fender, though.
Click to expand...
I sectioned and narrowed the factory frame rails. Big tires sticking out Looks real good with super stock wheel openings. It looks much better when the car is on the ground.
IMG_20240406_135524169.jpg
 
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MOPARMAGA said:
I sectioned and narrowed the factory frame rails. Big tires sticking out Looks real good with super stock wheel openings. It looks much better when the car is on the ground.View attachment 1716344790
Click to expand...
I'm definitely looking into recreating those wheel openings. I dig that look. A nice set of Mickey Thompson slicks to fill that wheel opening will look slick.
 
Gold Rush said:
I'm definitely looking into recreating those wheel openings. I dig that look. A nice set of Mickey Thompson slicks to fill that wheel opening will look slick.
Click to expand...
If you zoom in you can see this tire fills it pretty well, it's quite a bit of work to do the wheel well openings like that but this tire is a 29.5 - 11.5 w 15.
Real dimensions are 30.6 - 13.5 - 15 with almost 16 inches at section width.
The differential is in stock location.

IMG_20240408_163110515_HDR.jpg
 
MOPARMAGA said:
If you zoom in you can see this tire fills it pretty well, it's quite a bit of work to do the wheel well openings like that but this tire is a 29.5 - 11.5 w 15.
Real dimensions are 30.6 - 13.5 - 15 with almost 16 inches at section width.
The differential is in stock location.
Tt's quite the cage.
Click to expand...

MOPARMAGA said:
If you zoom in you can see this tire fills it pretty well, it's quite a bit of work to do the wheel well openings like that but this tire is a 29.5 - 11.5 w 15.
Real dimensions are 30.6 - 13.5 - 15 with almost 16 inches at section width.
The differential is in stock location.

View attachment 1716344893
Click to expand...
That's quite the cage. Are you going for an 8.5 e.t. certification?
I'm not afraid to cut on this car. I'll probably be welding this up with oxy-acetylene in all honesty.
The car is already a hack job. I'd sure like to cut out the inner fender wells like you did to both shave weight and help with access to the plug wires. Plug #6 is hard to reach on an A body with a B engine in it. The "builder" of the car cut a hole to access the plug from the fender well.
 
Gold Rush said:
That's quite the cage. Are you going for an 8.5 e.t. certification?
I'm not afraid to cut on this car. I'll probably be welding this up with oxy-acetylene in all honesty.
The car is already a hack job. I'd sure like to cut out the inner fender wells like you did to both shave weight and help with access to the plug wires. Plug #6 is hard to reach on an A body with a B engine in it. The "builder" of the car cut a hole to access the plug from the fender well.
Click to expand...
Yes, It's certified 8.50 now . Knowing my luck I'll have to get it recertified before the damn car goes down the track lol.
If you cut the inner fenders, I would do something to strengthen the frame rails and tie that into the firewall, There pretty thin sheet metal .
 
topside said:
I can only confirm what I've dealt with, but OK. FWIW, my '74 Duster had its factory 8.25, all the rest except 1 Slant -6 '73 Dart had 8.75s.
In every case, the springs (whether with small relocation kit or stock), the wheelhouse size, and the opening were limiting factors, especially with the Dart body.
Maybe I just "got lucky" with the several A-bodies I've owned...
Click to expand...
I have a 1974 dodge dart sport with the 8.25 rear. I have always wondered if 15x8 and 4.5" backspace will fit. I have installed the offset mopar shackles and front spring mounts. Also moved perches. I plan for 15x8 rallys just not sure if they fit.
 
Gold Rush said:
That's quite the cage. Are you going for an 8.5 e.t. certification?
I'm not afraid to cut on this car. I'll probably be welding this up with oxy-acetylene in all honesty.
The car is already a hack job. I'd sure like to cut out the inner fender wells like you did to both shave weight and help with access to the plug wires. Plug #6 is hard to reach on an A body with a B engine in it. The "builder" of the car cut a hole to access the plug from the fender well.
Click to expand...
So you are going to braze up a unibody car?
If so, don’t touch the rails and get a lot of practice with your bonding skills.

A cheap mig is going to pay for itself if you go in as deep as you are talking about and you will have it for your next project.
 
QuickDart360 said:
I have a 1974 dodge dart sport with the 8.25 rear. I have always wondered if 15x8 and 4.5" backspace will fit. I have installed the offset mopar shackles and front spring mounts. Also moved perches. I plan for 15x8 rallys just not sure if they fit.
Click to expand...
you should be good, the limiting factor is generally to the outside ie the fender lip which you don't need to worry about as much with the wheel opening on the dart sport.
 
dowboy1970 said:
So you are going to braze up a unibody car?
If so, don’t touch the rails and get a lot of practice with your bonding skills.

A cheap mig is going to pay for itself if you go in as deep as you are talking about and you will have it for your next project.
Click to expand...
Yep, I 100% agree. A mig welder is necessary.
I use my Tig and mig constantly on this car.
 
QuickDart360 said:
I have a 1974 dodge dart sport with the 8.25 rear. I have always wondered if 15x8 and 4.5" backspace will fit. I have installed the offset mopar shackles and front spring mounts. Also moved perches. I plan for 15x8 rallys just not sure if they fit.
Click to expand...

With an 8.25" rear and the stock spring locations if you go for 275's a 15x8 with a 4" backspace usually works better, the 4.5" backspace is typically for an 8 3/4 with BBP axles and the 8.25 is narrower.

Now, with the springs offset a 1/2" the 4.5" backspace will be no problem for you.
 
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