Need some suspension/chassis guidance

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wheelman21

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So I've decided against a a manual swap in my 73 Dart sport, and since my motor and trans are setup for drag, I've decided to head in a "pro-street lite" direction as I'm calling it. Mini-tubs, the widest tires I can stuff back there, relocating the springs etc. I'm possibly going to add a supercharger or blower down the road and possibly a 4 link rear. I don't want to do full tubs as I don't think I need anything that big back there and I'l like to keep my back seats. Anyway, this leads me to a whole new bunch of questions. If I do the mini tubs and move the springs in under the frame, do I need to narrow the rear to maximize the width of tires. I'm hoping to run at least 325s. Any advice or info you guys can add to help would be great. Thanks.
 
The rear could stay the same width, but might look odd due to the wheel and tires being offset towards the center. My opinion would be mini tub it, buy the wheels and tires that will fit with the offset you like. Put them in position, and measure from the back side of the wheel to back side of wheel at the mounting flange. Have the rear cut so it's that measurement axle flange to axle flange. Have the spring pads moved to the width of the springs that you moved. Allow for room between the tire and the fender and spring.
 
So I've decided against a a manual swap in my 73 Dart sport, and since my motor and trans are setup for drag, I've decided to head in a "pro-street lite" direction as I'm calling it. Mini-tubs, the widest tires I can stuff back there, relocating the springs etc. I'm possibly going to add a supercharger or blower down the road and possibly a 4 link rear. I don't want to do full tubs as I don't think I need anything that big back there and I'l like to keep my back seats. Anyway, this leads me to a whole new bunch of questions. If I do the mini tubs and move the springs in under the frame, do I need to narrow the rear to maximize the width of tires. I'm hoping to run at least 325s. Any advice or info you guys can add to help would be great. Thanks.

You may also consider Caltracs mono leafs vs the 4 link. If you go for link, I'd look for a triangulated 4 link since you will be mostly drag racing it.
 
Knowing what you have right now for a rear axle would be helpful for determining which would be the most beneficial way for you to go. For example, if you have a 7 1/4, nobody is going to tell you to waste money narrowing that. Assuming you have an 8 3/4, which one, A-body SBP or BBP, B-body? How much are you willing to spend? What tools do you have access to? Can you weld? Are you planning to do all the work yourself? Have you ever done a 4-link before? Those are just a few questions I came up with off the top of my head.
 
My opinion would be mini tub it, buy the wheels and tires that will fit with the offset you like. Put them in position, and measure from the back side of the wheel to back side of wheel at the mounting flange. Have the rear cut so it's that measurement axle flange to axle flange. Have the spring pads moved to the width of the springs that you moved. Allow for room between the tire and the fender and spring.

This is what I did. Except the 68 Barracuda stock tubs are big enough to accept the 325/50-15 DRs, and I only needed to move the springs over with the offset kit. My 15 x 10s have a 4.5inch backspace. This is common amongst 15s and makes changing wheels later, an off-the-shelf deal.
My car is lowered some, with nearly flat leafs, and the 325s did rub with moderate cornering. They only rub in one same place on each side. I have beat that area heavily but there is "something" behind the panel that refuses to to be moved.I think it's the shock mounting bar, but don't recall(was 12 years ago).So I moved the wheels over with 1/8 inch spacers, and trimmed the outer fender lips. Now is good to go;mostly..... At stock ride height, I don't think it would be an issue.
Be advised that the rear end may not currently be centered in the car, so order your rear a bit narrower than you measure, and do not have the perches pre-installed. Then you can mock it up, center it, set the pinion angle, tack in the perches, blow it all apart, and final-weld it. I had allowed 1/4 inch for spacers, and used only 1/8; so had I ordered exact-fit I would have been 1/8 too wide. But here's the thing, if the rear ends up too wide, you are sorta screwed, needing new wheels. If it's a hair narrow, you can just space the wheels out.
Of course all of this is moot, with mini-tubs.

In about 1979 I purchased a 74 DartSport 360-4spd. It came with N50-15 Pro-Tracs; remember those? The tubs were stock. The wheels were Keystone 15 x 10s.The rear was raised some. I don't remember how big Ns were, but I think they mightabin pretty close to 325s, but closer to 60 series. I do recall that the treads were inside the fenders, although the sidewalls were closer to flush with the outside body line.The cops made me put mudflaps on the backside. Those tires didn't rub on anything. But with the back up, you couldn't push it hard around corners anyway.
Point of story is this; Ima thinking DartSport tubs are same as or similar to, the 68Barracudas
 
Thanks for the good info guys. I'm just getting rolling with this but I want to try and get it done sooner than later before other projects get in the way. I run a european performance garage and right now is our slow season except for a few long term projects. I really want to get the tire up into the wheel well and get the car low. Will I be able to do that with mini-tubs and the right leaf setup or do I have to go to a 4 link? I don't want it on the ground, but I definitely want to tuck those big rear tires up in there.
 
Knowing what you have right now for a rear axle would be helpful for determining which would be the most beneficial way for you to go. For example, if you have a 7 1/4, nobody is going to tell you to waste money narrowing that. Assuming you have an 8 3/4, which one, A-body SBP or BBP, B-body? How much are you willing to spend? What tools do you have access to? Can you weld? Are you planning to do all the work yourself? Have you ever done a 4-link before? Those are just a few questions I came up with off the top of my head.

Yes it's a 8 3/4. I believe it's a B body rear. I'm trying to keep this a low budget as possible of course as this is mostly a street car I want to have some fun with. But I know I will have to spend some money. Yes I can weld and do fab work very regularly. I have a good MIG and a TIG. The only thing I don't have is a plasma cutter or a bead roller. I have a torch etc. I haven't done a 4 link but i'm no stranger to fab work. I've done my fair share. I plan to do as much myself as possible. I will probably have a guy I know narrow the rear as he is more qualified than I am at that. I'm not afraid to send stuff out if need be. I.E. I have a paint guy for my shop as I'm not experienced enough to do the paint work I need sometimes at my shop.
 
You can get the rear as low as you want with the leafspring setup. 4 link is cool, but probally not needed in your case. Sometimes keeping it simple is the best plan. Wouldn't be complicated doing a simple spring relocation, and if you need it lower, lowering blocks are readily avalible.
 
You can get the rear as low as you want with the leafspring setup. 4 link is cool, but probally not needed in your case. Sometimes keeping it simple is the best plan. Wouldn't be complicated doing a simple spring relocation, and if you need it lower, lowering blocks are readily avalible.

That's what I was thinking. This is largely a boulevard brawler. I'm not going bracket racing. But right now the 245s won't put the power down. They spin like crazy. Great for smokey burnouts. Not so much for coming off the line. I think it all comes down to if I need to narrow the rear end and if I need to mini-tub or no tub or full tub.
 
Thanks for the good info guys. I'm just getting rolling with this but I want to try and get it done sooner than later before other projects get in the way. I run a european performance garage and right now is our slow season except for a few long term projects. I really want to get the tire up into the wheel well and get the car low. Will I be able to do that with mini-tubs and the right leaf setup or do I have to go to a 4 link? I don't want it on the ground, but I definitely want to tuck those big rear tires up in there.

yep, you for sure can, you really should look into the Monoleaf Cal trac setup, affordable and pretty simple and they have rave reviews.
 
you can put plenty of tire under there with just a minitub. Heck I think a 275/60/15 drag radial fits with NO minitub in those
 
There are some REAL fast leaf spring cars. I don't understand why everybody wants to jump on 4 link. Remember, whatever the spring setup, that as you get wider with tires, and less room for suspension, you are going to need "more and more" for an anti-sway bar for body roll control.

[ame="https://www.youtube.com/watch?v=cO3jFdKMd_s"]Worlds FASTEST Stock Suspension Mopar!! - YouTube[/ame]
 
Yes it's a 8 3/4. I believe it's a B body rear. I'm trying to keep this a low budget as possible of course as this is mostly a street car I want to have some fun with. But I know I will have to spend some money. Yes I can weld and do fab work very regularly. I have a good MIG and a TIG. The only thing I don't have is a plasma cutter or a bead roller. I have a torch etc. I haven't done a 4 link but i'm no stranger to fab work. I've done my fair share. I plan to do as much myself as possible. I will probably have a guy I know narrow the rear as he is more qualified than I am at that. I'm not afraid to send stuff out if need be. I.E. I have a paint guy for my shop as I'm not experienced enough to do the paint work I need sometimes at my shop.

OK, low budget. In that case, here are my recommendations:

Stick with leaf spring style rear suspension. Possibly look at SS Springs or some of the monoleaf springs that others will recommend. I believe SS Springs will suit your purpose and you can still easily find them at a reasonable price. They do raise the rear of the car though so probably the monoleafs will be the direction you want for tucking the tires up in the fenders.

Since you can weld and fabricate, a mini-tub should be easy for you; spring relocation shouldn't be too difficult for you either.

Since you already have a B-body 8 3/4, I wouldn't waste money having it narrowed. Depending on the year, mid 60s to 1970 B-body housings fit well under Demons, Dart Sports, and Dusters. Besides, if you happen to break an axle shaft at the track, you won't have to spend big bucks looking for a custom axle to fit a custom width housing. You'll be able to find used wheels with the right backspacing at numerous swap meets or on-line.

325s may be pushing it with the tire tucked all the way up in the well; I honestly don't know as I've never ran them. I'm sure you have noticed that the rear axle sits closer to the fender lip on the front than the rear. Due to this, I recommend moving the rear axle back some to accommodate the larger tire, assuming 325s are narrow enough to be tucked up in there after you relocate the springs and mini-tub. You may have to trim the lip of the fender for clearance on the outside of the tire. I did't really care about the body on my 75 Dart Sport, so I just beat the inner lip flat against the inside of the fender with a rubber mallet. Never had a tire rub issue after that.

There's no need for a plasma cutter, except for expediency. I used cut-off wheels in a die grinder and a hack saw for my mini-tub.

I'm in the same boat as you with paint. I have most of the tools for doing body work, DA, long board, and jitter bug sanders, paint guns, etc..., but I leave it to the pros. With the price of paint nowadays, I'm not ready to waste a bunch of money learning how to.

Whichever way you decide to go, good luck with your project.
 
You guys are awesome! I've got a great direction to go. I think I will start by moving the leafs in and moving the perches. After that I think I'll get the wheels and tires I want to run and try and tuck them up in. If they don't go, I'll go to a mini-tub. I'll roll the fender lip up in no sweat. We roll rear lips all the time on everything from full size cars to VWs.
 
If I may ask, can you guys tell me what the best wheel width would be for the size tire? 15x10?
 
Generally; The rim width should be plus or minus 1 inch of 70% of the section width, or equal to the tread width. So .70 x 325/25.4 = 9 inch;the manufacturer thus thinks you could mount that 325 on a rim of 8 to 10 inches.But,since the tread on a 325 is closer to 10, and since it would be really difficult to find a 15 x 9; then 15 x 10 it should be, cuz 8 inches would not work very well for most applications, and certainly not for you.
Since the section width of a 325 converts to; 325/25.4 = 12.8inches when mounted on the 70% rim(9inch), this section width will grow a tad when mounted on the 10 incher, perhaps a qtr inch per side, making your 12.8 section equal to about 13.3inches, or an actual 338mm section.
Clear as mud, right?

I have found that a 325 on a 10 inch rim is fine for the dragstrip and fine for most driving situations, but in reality the tire pressure has to be pretty low so that the tread wears evenly, like 20 to 24 psi. Well that don't corner worth beans. My 295s are barely supported on a 10 incher; requiring 24 psi for long tread life. And it don't corner all that well at 24, but it's acceptable for an old fart like me who is slowing down.So,
it is my opinion that if I was to run my 325s full time, I would want a rim wider than 10 inches, so I could drive a little harder around the corners, without the rearend doing it's little squiggely dance.But my stock wheelwells would not accept that, as the section width would grow enough to put the sidewalls into the tub walls on a more or less continuous basis.
With minitubs, Ima thinking 12 inch rims would work for me.And the deep dish wheels would look great.
But for you,I also suppose that the rear end would need to for sure be narrowed with 12s and the springs would need to be moved into the rails for sure.Even with a custom offset wheel, which,even though I like the look of deep-dish wheels, I would still forgo,by using a large backspace wheel in an effort to put the cornering force towards the outside of the wheel, and maybe put less twisting stress on the studs. I'm no engineer but it makes sense in my little head.
And that takes you back to post #2..............
 
Generally; The rim width should be plus or minus 1 inch of 70% of the section width, or equal to the tread width. So .70 x 325/25.4 = 9 inch;the manufacturer thus thinks you could mount that 325 on a rim of 8 to 10 inches.But,since the tread on a 325 is closer to 10, and since it would be really difficult to find a 15 x 9; then 15 x 10 it should be, cuz 8 inches would not work very well for most applications, and certainly not for you.
Since the section width of a 325 converts to; 325/25.4 = 12.8inches when mounted on the 70% rim(9inch), this section width will grow a tad when mounted on the 10 incher, perhaps a qtr inch per side, making your 12.8 section equal to about 13.3inches, or an actual 338mm section.
Clear as mud, right?

I have found that a 325 on a 10 inch rim is fine for the dragstrip and fine for most driving situations, but in reality the tire pressure has to be pretty low so that the tread wears evenly, like 20 to 24 psi. Well that don't corner worth beans. My 295s are barely supported on a 10 incher; requiring 24 psi for long tread life. And it don't corner all that well at 24, but it's acceptable for an old fart like me who is slowing down.So,
it is my opinion that if I was to run my 325s full time, I would want a rim wider than 10 inches, so I could drive a little harder around the corners, without the rearend doing it's little squiggely dance.But my stock wheelwells would not accept that, as the section width would grow enough to put the sidewalls into the tub walls on a more or less continuous basis.
With minitubs, Ima thinking 12 inch rims would work for me.And the deep dish wheels would look great.
But for you,I also suppose that the rear end would need to for sure be narrowed with 12s and the springs would need to be moved into the rails for sure.Even with a custom offset wheel, which,even though I like the look of deep-dish wheels, I would still forgo,by using a large backspace wheel in an effort to put the cornering force towards the outside of the wheel, and maybe put less twisting stress on the studs. I'm no engineer but it makes sense in my little head.
And that takes you back to post #2..............

I have 325's on my dart with a mini tub, i don't think you could fit any bigger tire. I have about 3/4 on each side but that with the wheel lips trimmed down.


 
If you want to run that big of a tire and you want the car to sit down low, I'd suggest cutting the outer house off the wheel tub and running a panel to the quarter.
 
I have 325's on my dart with a mini tub, i don't think you could fit any bigger tire. I have about 3/4 on each side but that with the wheel lips trimmed down.



That's exactly the kind of look I'm going for! What size wheel are you running. I'm assuming you narrowed the rear? It looks like it in the photo. Did you run your tubs all the way to the quarter? And are those 15s?
 
That's exactly the kind of look I'm going for! What size wheel are you running. I'm assuming you narrowed the rear? It looks like it in the photo. Did you run your tubs all the way to the quarter? And are those 15s?

15x12 wheels with a 3 1/2" backspace, 325/50/15 et streets. The rear is narrowed, I don't remember the dimension though. This is how i did my mini tub then just seam sealed it to the quarter.



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good advise from above posts....

IMHO....best for the money

a.) mono-leaf with Caltracs moved onto the frame rails. SS springs are designed with a lot of arch and came out in the late 60's / early 70's before tubbing and it was necessary to get the rear in the air to clear the tires......not the look you said you were after.

b) run the tubbs all the way to the 1/4...only way to get the car low with the wider tires. I found utilizing a set of trailer fenders with their curved radius can eliminate some of the patching.
 
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