2002 F150 FX4, 275/70/17 tires

I cranked the torsion bars at about 30k miles, not all the way level just an inch or so. At 60k miles replaced shocks with Rancho RSX. 2 years later, heard a thunking in suspension, shop said front shocks blown (nothing visibly broke externally). Replaced with Rancho 5000's, as I hadn't saved my receipt for lifetime warrany. 1 year later, same thunking, right front. Replaced again. 6 months later, same thunking, this time replaced with Monroe SensaTrac. 2 MONTHS later, right front blown again. This is just from driving to and from work, no offroading.

Anyone experience anything like this with shocks blowing out internally? Think it might have anything to do with torsion bars cranked?

thanks

 

did you get longer shocks or stock length? if your not stock height and using stock length shocks thats your problem

 

Agreed. Your travel changed about an inch so your shocks are too short. You need to order longer shocks...Rancho's are orderable but not sure about the Monroes.

 

Yep, stock length, that's what I also am thinking is the problem. However, many owners have cranked their bars and as far as I know keep the stock shock with no issues.

I may replace them 1 more time, lower the bars, and see what happens.

 

RIght. Your suspension travel is limited by the bumpstops. You shouldn't need longer shocks with just cranked torsion bars.

 

You guys are incorrect (except for wandell)...sorry. Cranking torsion bars is irrelevant and not the cause of your problem. Cranking torsion bars full to the stops still mandates a stock length replacement shock. Cranking the torsion bars does not constitute a lift, nor does it alter the distance between the mounting locations (like a lift kit does). It also does not alters the amount of suspension travel from stock requiring a longer than stock shock. Cranking the torsion bars simply alters where the truck sits in its normal, stock suspension travel. You have something else going on.

 

Actually if im not mistaken what i said was correct. its about angles and geometry. yes the actual distance between the control arms is the same the shock distance changes because its at a different angle.

think of it like this. on the 2wd with coil springs. i put a 1.5" spacer on the spring which didnt change the distance the control arms were mounted but changed the angles of the suspension and with that i broke a shock because it was at its almost full extension at normal ride. the same applies to the 4x4 just with cranking the tbars rather than adding a spacer, the angle changed and the distance the shock travels does also. this angle change is very apparent in the ball joints which you can agree wear out faster at extreme angles from cranking. (same applies to the stock length shocks)

 

Wow, this makes no sense to me...not that you are wrong, its that I cannot envision what you are saying.

Cranking the torsion bars is like putting stiffer coils on an IFS front end...it does lift the front as the the spring rate/preload is increased. The shock's lower mounting point is therefore lowered...in other words the distance between the lower and upper mounting points is increased, thereby reducing shock travel on extension.

And to Wandell's point about bumpstops, yes, the bumpstops will stop compressed travel, but not extended travel. If the shock is too short, the shaft will pull out against the shock body. If that doesnt break the shock or mounts, a subsequent violent compression could bend or break the shaft and or body of the shock. I reread the original post and OP says his shocks are blowing out internally and not actually "breaking" so I guess this is irrelevant, but I was unaware of any bumpstop to prevent extended travel on the F150.

Not trying to start any arguments here, but I was pretty sure I knew how torsion lifts worked until I saw this post. If I am wrong, I'd like to understand this better.

 

OK, look at it like this...(these numbers are made up to make a point and make the math easy)

Lets say the truck has 10" of suspension travel from full compression to full extension (limited by the bump stops). When you lift the truck off the ground by the frame, the suspension would hang at full extension. And then lets say when you sit the truck down on the ground, the suspension compressed and used up 5" of it's travel. This is its normal resting point in the travel. You now have 5" of compression and 5" of extension from this point.

When you crank the torsion bars, all you've done is prevented the truck from settling into its normal range of travel. Under the weight of the truck, the truck now settles 3" into its travel instead of the 5", raising the front 2". (You have not "lifted" the truck in the sense of adding a lift kit, you've simply altered the range in the normal travel)

However, you have not altered the geometry, range, length, or anything from the stock amount of travel built into the suspension.

The (stock) shock by all accounts should be long enough to handle the full range of suspension travel, period! Look at it like this...when you guys talk about increasing the distance between shock mounting points, the only time this distance matters is when a lift is installed AND only done at full suspension extension. With a torsion bar crank, the distance between these two points at full suspension extension is 100% stock, completely unaltered by the fact you cranked the bars. Thus, a stock length shock is still maintained.

A shock should absolutely and damn well better be able to handle any service or position within this stock range of travel. The shock (unlike a ball joint) does not care where it comes to rest at or where it spends most of its time. It is the same through out its range of travel as well.

Did that help clear the muddy water any?

 

I don't have a 4x4, but I think I understand what Galaxy is trying to say. Let me see if I can help explain it.

I think what he means is that the preload you put on the torsion bars is just that PRELOAD. So it puts pressure on the suspension to raise the normal resting point of the truck.

Now, while this raises the normal resting point due to pressure, it doesn't change the relative angles between the control arms. It would be the equivalent of just taking a jack to the bottom of the truck and raising it. So essentially your not going to need a longer shock because it doesn't change the travel, just adds upwards pressure from torsion.

At least I think that's how it works. Like I said I don't have a 4x4 so I'm just visualizing the suspension in my head lol.

Either way if you want to test whether the suspension under full extension is putting pressure on the shocks couldn't you just do the following:

Raise the truck on jack stands so the front suspension is fully extended. Then unbolt the shock to see if it travels any lower.

If it does then the shock is holding it up, if not then its perfectly fine.

At least that all makes sense to me lol.

- Erik

 

You are absolutely correct...you could very well do this. And, if you discovered the shock was too short as a result of this, it is not because you cranked the torsion bars...it would do this regardless. There are literally thousands of success stories with guys cranking up the torsion bars on these trucks, none of which has been the root cause for shock failure.

 

I agree with Galaxy.

 

Actually that does clear it up. You're right, the part I am missing is that the "lift" created by the increased preload is still within the stock shock travel.

Back in the mid 80's, we were lowering trucks via the torsion bars and putting shorter shocks. The stock shocks were bottoming out...but we were shaving/removing bump stops too. Having never lifted via the TBs, I got it in my head that new shocks were always needed.

Your explanation definitely paints a clearer picture!

Ok, sorry for the hijack. Back to your regular programming...