Leaf spring U bolts torque spec

-
W

WhickedDart

Member
Joined
May 21, 2013
Messages
10
Reaction score
0
Location
Philadelphia
The service manual specs out 45 ft lbs for the leaf spring U bolts. This sounds low concidering they are 1/2-20 threads. Everyone I have talked to says they need to be alot tighter 70-100 ft lbs. Does anyone know what is correct? Also do you torque them while the weight of the car is down on the ground or up on jacks?
 
I believe that I tightened mine to the 45 ft.pd. spec. That U bolt is probably not a grade 5 or grade 8 bolt.
It would be correct to do the final tighten with the weight on the suspension.
C
 
The factory torque spec is relevant to the original U bolts and nuts. Their special nuts weren't going to loosen. Initial torque of 45 lbs is fine if you know they will stay. Lock-Tite, jamb nuts, something for insurance is my suggestion.
 
clhyer said:
I believe that I tightened mine to the 45 ft.pd. spec. That U bolt is probably not a grade 5 or grade 8 bolt.
It would be correct to do the final tighten with the weight on the suspension.
C
Click to expand...

I'd bet they are grade 5. But a 1/2 SAE bolt for grade 2 even shows 55 ft lbs. A grade 5 shows 85 ft lbs but that is dry. Lubricated grade 5 is only 65

Still another torque chart shows grade 2 dry / lubed at 55 / 40, and grade 5 at 90 / 65 ft lbs
 
Ok thanks. But there must be a reason for the 45lb spec. The service manual also says in bold letters "do not over tighten u bolt nuts"
 
The reason they are only 45 is to allow the springs to slip in the spring plates as the suspension compresses and rebounds. Many argue the point saying that the center pin does not allow the leaves to slip. You have to think in terms of how the spring is made. There is a front segment and a rear segment. The entire spring does not flex together. The front segment flexes differently from the rear. Not only because they are different lengths, but also because they are twisting opposite directions of each other. Prove it to yourself. Hold two yardsticks together on one end very tightly with one hand. You cannot bend the yardsticks without the ends in your hand slipping. The center pin makes no difference whatsoever. If the spring plates are over torqued, the springs cannot work correctly. Period.
 
RustyRatRod said:
The reason they are only 45 is to allow the springs to slip in the spring plates as the suspension compresses and rebounds.
Click to expand...

I doubt that. I suspect 45 ft-lbs was determined by the factory to be sufficient in preventing a loosening of u-bolt nuts and/or decoupling of the spring, spring plates, and perch. A higher torque could/would crush the axle tube.

But maybe RustyRatRod has a reference. I'm interested.
 
Would you consider the Mopar Suspension Manual a proper reference? It's all right in there under the leaf spring rear suspension section. Read it. It talks all about the different rates between the front and rear segments, talks about how important it is not to over torque the U bolts. What?!?! Different rates for front and rear segments on the same spring? Guess what? That can only mean one thing. That the front and rear segments move independently of each other, just like I described. It even references the "booming" sound it can cause when they are over torqued. With the SS springs, it's more than just the sound. It can make for a harsh ride as well. It's all in the book.

Look guys, this stuff has been around since the beginning of leaf spring suspensions. What? On horse drawn buckboards? Before that? Question me all you wish. But this information is certainly nothing new and it's correct. I haven't dicked around the better part of my life as an alignment/suspension mechanic to learn nothing.

Now, what do you want next? A page number? Ok. Mopar Suspension Manual 9th edition. Start on page 307 at LEAF SPRING REAR SUSPENSION and go to page 316 all the way to the bottom. That way, you'll see it all , instead of one or two points. In fact, finish the whole section. I recommend it.

When I am adamant about something, it's because I am damn right about it. I don't really give a fig what you "doubt", "don't believe" or "think is wrong". It's not up to me to lead you by the hand and educate you. You wanna keep arguing? Go ahead. On this, you'll just be wrong.
 
I need to loosen mine up,Rob. Never knew. That would explain, the lack of transfer, after the D.C 7/8" relocation boxes . Thanks.
 
I wonder how many of us rattled them up with a 1/2" impact until they wouldn't go any more. I know I did. Thanks for the info. tmm
 
RustyRatRod said:
Now, what do you want next? A page number? Ok. Mopar Suspension Manual 9th edition. Start on page 307 at LEAF SPRING REAR SUSPENSION and go to page 316 all the way to the bottom. That way, you'll see it all , instead of one or two points. In fact, finish the whole section. I recommend it.
Click to expand...

Yep, it's in there.
 
And their special "scored" nuts guaranteed they would stay put. Simple way to get this from hardware store fasteners is doubled jammed nuts.
 
I've done my share of them with an impact, too. I bought my first Mopar engine and suspension manuals about 1985. Ever since then, I've torqued them.
 
Bad Sport said:
Yep, it's in there.
Click to expand...

Yup. I don't know how many times I've said it, either. I've lost count. Ed was one of the first to argue the point. I figured since he builds super stock cars for a livin, the Mopar Suspension manual would be something he would know front to back, since most of that stuff came from the super stock program.

It amazes me how many learned people haven't cracked those books. Ever. Or how many insist on NOT buying a factory service manual for the car they have. Heck, I've read both the engine and suspension manuals many times cover to cover, yet, sometimes I just go get one to flip through again to keep me fresh on it.

They may be 40 plus year old technology, but the stuff WORKS. Engine recipes and all. Why argue back and forth on forums about how to run 10s, when you got complete instructions on how to do it already printed out, part numbers and all? Maybe I'm stupid like that. People have pounded on me for bringing them up before, saying they are obsolete, or dated. I say hogwash. I just love readin through those recipes. Maybe one day I will get to build another one.

I've seen and heard people say stuff like "oh, Mopar is just trying to sell all their stuff". Well duhhh. They're in business to make money. You can argue about the hundreds of ways to do something, but in the end, ain't you doin it? So, what difference does it make how you got there? In my mind's eye, Mopar had a genius plan. Make it easy for the racer to build race cars, and we'll sell stuff. Really, why have to call this cam maker and that, hang out on forums trying to glean info from people that might have it wrong and end up going nowhere?

Yeah, I know you don't NEED a Six Pack to run in the 12 second bracket. But if you use it like they say, the **** WILL run 12s. And it's kinda cool seein the chebbie boys wonder how you got six barrels to work so well, ain't it? Yeah, you can do it with one carb, but who wants to do that? Can you say boring? I always thought they threw that in there to sorta keep the Six Pack package alive and kickin for a long time. I'm glad they did it, but I've seen where people (especially on forums) said it was the stupidest thing ever. Really? A Six Pack stupid? I think they are six barrels of wide open awesomeness.

I always looked at those manuals and recipes like this. Say I build an 11 second car following the recipes in those books. I race it several seasons. Just have a good old time with it. I sell it. Maybe to somebody that doesn't even know Mopars. I recommend he go out and buy those manuals. He does. Even though he's all the way across the country, now he has an instruction manual on a car he's never seen before and a brand he's not even familiar with. It's sheer genius, I tell you. But you gotta buy the books and read them, not leave um at the store or on the shelf. Same with the factory service manual for your car.

NO other automobile manufacturer EVER supported racing with as much comprehensive information as Mopar, yet no other information was so widely ignored. The chebbie guys never had it that good.
 
I am curious...why did the mopar u-bolts come with the cross-hatch pattern on them? What was the purpose of it?
 
To aid in keeping the rear from rotating. When you apply torque to the drivetrain the rear wants to rotate upward.
 
RustyRatRod said:
Would you consider the Mopar Suspension Manual a proper reference? It's all right in there under the leaf spring rear suspension section. Read it. It talks all about the different rates between the front and rear segments, talks about how important it is not to over torque the U bolts. What?!?! Different rates for front and rear segments on the same spring? Guess what? That can only mean one thing. That the front and rear segments move independently of each other, just like I described. It even references the "booming" sound it can cause when they are over torqued. With the SS springs, it's more than just the sound. It can make for a harsh ride as well. It's all in the book.

Look guys, this stuff has been around since the beginning of leaf spring suspensions. What? On horse drawn buckboards? Before that? Question me all you wish. But this information is certainly nothing new and it's correct. I haven't dicked around the better part of my life as an alignment/suspension mechanic to learn nothing.

Now, what do you want next? A page number? Ok. Mopar Suspension Manual 9th edition. Start on page 307 at LEAF SPRING REAR SUSPENSION and go to page 316 all the way to the bottom. That way, you'll see it all , instead of one or two points. In fact, finish the whole section. I recommend it.

When I am adamant about something, it's because I am damn right about it. I don't really give a fig what you "doubt", "don't believe" or "think is wrong". It's not up to me to lead you by the hand and educate you. You wanna keep arguing? Go ahead. On this, you'll just be wrong.
Click to expand...

I have the 8th edition. I see caution wording in regard to shim installation saying "Overtightening can cause spring friction, which will produce a "booming noise inside the car." So there you have it. I'm not sure my doubt was worth the venomous response, but OK. Thanks.
 
Wasn't meant as "venomous" it was only truthful. I cannot help it if people who are supposedly into Mopars do not own and read perhaps the two most important books ever written about them. It's complete ignorance to me. Much like anyone who owns a Mopar, but does not have the factory service manual. It befuddles me. Then on top of that, those same people question ME about something that not only is confirmed in the Mopar manuals, but in a lot of others, plus confirmed with my own experience. Instead of a smug "I doubt that", it could have been "Hay Rob, how bout a reference?" But you had to put a dig in first and it's not the first time for you. Your "I doubt that" discounted all of my experience. Period. I should have told you to F off, but I explained myself instead and you call my response venomous. Lemmie tell you buddy, you ain't seen me get venomous. Yet. I gave you what you asked for. A reference. You don't like my delivery? Then think about your response next time.
 
You must log in or register to reply here.
-

Back
Top