Is it wise to push a 7 1/4?

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DartVadar

DartVadar

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I have been putting on a few miles on my dart lately and there are friday night track days near me, and I'm planning on going this friday. I want to take my dart out to just see what it will run with the new 360. Only problem is it still has the 7 1/4 rear end in it...I'm still putting together the new 8 3/4.

I have about 400HP with the new motor, but street tires so less traction. I have given it a few blasts on the street but never from a stop, I've always stepped on it going about 10mph, nothing has broken...yet.

I guess I'm mainly asking how weak are the 7 1/4 really? Think it'll survive if I ease onto the gas off the line?
 
Yes it is very wise to push a 7.25 rear...right into a scrap pile. Unless want a tow bill, wait till you finish your 8.75 rear. But if you have to do it, do a burnout in front of your house. This way when it blows up, you're a lot closer to home and won't have to tow it but you'll still be waiting for the 8.75 to be finish. That said you might find yourself finishing the 8.75 a lot sooner than you thought.
 
Push it all you want. If wanna walk.
 
Bear in mind that when the rear end blows, it generally takes the trans with it. Also do you have a rev limiter if it breaks and the engine freewheels?
 
Well I guess I'll just continue to do easy street driving with it and get the rear done soon. I didn't think about the potential of wrecking other parts either, I don't have a rev limiter, so I wont push my luck too much.
 
It's not gonna snap like a dry twig unless you seriously hit the tires hard..not likely with street tires. The spiders are the weak link, and anything you can do to equalize traction is going to work in your favor. I would overinflate the driver side tire...45-50 psi, underinflate the pass. side...to about 25psi. Pile anything you've got in the trunk behind the pass. tire. You could also cross weight the chassis a bit by cranking up the driver side torsion bar....figure raise that corner of the car about 1.5 inches. All of these things done correctly will net the same basic effect of having a SG in the car and greatly increase the chances of the 7.25 living.
BTW, if my car weight was less than 3200 pounds wet, I had a 350-400 horse engine, a stock converter and was running normal street tires and nothing deeper than a 3.23, I would be working to make the 7.25 as bullet proof as possible and sticking with it. 50 pounds lighter and substantially less torque to spin than the 8.75.
 
Ive pushed it a few times...LOL but Ive been making sure not to break traction. Now to make it stronger could I weld the differential? Dont have much more time to drive the car and I know its hard on tires but would that even be worth it?
 
my dart back in the day had 3.23 rears / 4 speed / heavy clutch / BFG street tires.
small rear.

i didnt break the rear but broke the yoke at the front of it lol. snap.

i think you posted that yours is a 2.76
 
DartVadar said:
Ive pushed it a few times...LOL but Ive been making sure not to break traction. Now to make it stronger could I weld the differential? Dont have much more time to drive the car and I know its hard on tires but would that even be worth it?
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If you weld the spiders...and do it right!...you've eliminated most of the problems associated with that rear. The next weak link is going to be the cap bolt bosses on the pass. side of the ring gear. You could drill them deeper...I'd say 3/4 of an inch, and replace the bolts with longer studs. You could also brace the center of the cap with a nut and bolt through the back cover. Do all that, and I would not hesitate to use that rear in any mid weight, auto trans 12 second car.
 
whitepunkonnitro said:
If you weld the spiders...and do it right!...you've eliminated most of the problems associated with that rear. The next weak link is going to be the cap bolt bosses on the pass. side of the ring gear. You could drill them deeper...I'd say 3/4 of an inch, and replace the bolts with longer studs. You could also brace the center of the cap with a nut and bolt through the back cover. Do all that, and I would not hesitate to use that rear in any mid weight, auto trans 12 second car.
Click to expand...

Hmm I might just do that then. My uncle is a welder and works on cars alot so he would know how to properly weld the spiders up. The rear also has 2.76 gears in it, so its pretty bad off the line, helps keep it in tact I guess. That and possibly strengthening the bolt cap bosses I should be good to increase its reliability.
 
DartVadar said:
Hmm I might just do that then. My uncle is a welder and works on cars alot so he would know how to properly weld the spiders up. The rear also has 2.76 gears in it, so its pretty bad off the line, helps keep it in tact I guess. That and possibly strengthening the bolt cap bosses I should be good to increase its reliability.
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I've got a set of good, used 3.23's I can send you for $60 plus the ride. I can send along the carrier as well, and you can weld one up while you use the other.
 
whitepunkonnitro said:
I've got a set of good, used 3.23's I can send you for $60 plus the ride. I can send along the carrier as well, and you can weld one up while you use the other.
Click to expand...

I cant imagine getting it to me up in canada would be too easy...but I dont think its worth doing too much work to the 7 1/4 as I have a 8 3/4 with 3.55 gears that will be going in over the winter.
 
when i built my moderate 318 in my 67 dart it ran 14.60's with 2.76 peg leg 7 1/4. that was with 215/75/14 tires. i went thru three rears before i got an 8 3/4 under it. if you go to the track. DONT LAUNCH THE CAR. just roll into the throttle. its the shock that kills them. it will still be a blast and you should get an idea of what its got by the mph. light goes green and just gradually press the gas peddle down. should be flat to the floor before the 1/2 shift.

my car went from 14.60 with 2.76 gear to a 13.80 with the 3.55's and detroit locker.
 
younggun2.0 said:
when i built my moderate 318 in my 67 dart it ran 14.60's with 2.76 peg leg 7 1/4. that was with 215/75/14 tires. i went thru three rears before i got an 8 3/4 under it. if you go to the track. DONT LAUNCH THE CAR. just roll into the throttle. its the shock that kills them. it will still be a blast and you should get an idea of what its got by the mph. light goes green and just gradually press the gas peddle down. should be flat to the floor before the 1/2 shift.

my car went from 14.60 with 2.76 gear to a 13.80 with the 3.55's and detroit locker.
Click to expand...

I always eased on the gas so its never gotten too much of a shock, I guess I could try that, because I'm super curious about how fast it is, it feels really fast, I just wonder if it actually is.

But thats a huge difference from just a gear change! I know the 2.76 gears are holding me back big time, not a good match with my cam.
 
DartVadar said:
I always eased on the gas so its never gotten too much of a shock, I guess I could try that, because I'm super curious about how fast it is, it feels really fast, I just wonder if it actually is.

But thats a huge difference from just a gear change! I know the 2.76 gears are holding me back big time, not a good match with my cam.
Click to expand...

well it helps having two tires propel you instead of 1. it also helps being able to get traction. you can have a 1000hp car run 14s if it never hooks.
 
The higher the numerical ratio the less stress on the ring and pinion. 2.76 is much more likely to break during a holeshot than a 3.91.
 
Did that in my old dart very very bad! took the tranny with it,stock 318 with headers and 4 barrel
 
whitepunkonnitro said:
It's not gonna snap like a dry twig unless you seriously hit the tires hard..not likely with street tires. The spiders are the weak link, and anything you can do to equalize traction is going to work in your favor. I would overinflate the driver side tire...45-50 psi, underinflate the pass. side...to about 25psi. Pile anything you've got in the trunk behind the pass. tire. You could also cross weight the chassis a bit by cranking up the driver side torsion bar....figure raise that corner of the car about 1.5 inches. All of these things done correctly will net the same basic effect of having a SG in the car and greatly increase the chances of the 7.25 living.
BTW, if my car weight was less than 3200 pounds wet, I had a 350-400 horse engine, a stock converter and was running normal street tires and nothing deeper than a 3.23, I would be working to make the 7.25 as bullet proof as possible and sticking with it. 50 pounds lighter and substantially less torque to spin than the 8.75.
Click to expand...

All excellent point from someone whose been there. ^^^^^^^
 
The 7.25 is a boat anchor...don't romp on it until you have upgraded!

Anyone running a welded differential on the street should be arrested.
 
DartVadar said:
Ive pushed it a few times...LOL but Ive been making sure not to break traction. Now to make it stronger could I weld the differential? Dont have much more time to drive the car and I know its hard on tires but would that even be worth it?
Click to expand...

I would just bide my time this year and wait until you have the upgrade. That's just me. If you have a 727 especially, and the rear breaks, you will want to pull the trans and inspect it, IMO.

The 7 1/4 rear in my car was one of the first things that got upgraded when I bought it, now I can beat the piss out of it and have less worry.
 
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