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collar for front strut

11K views 19 replies 8 participants last post by  SkipW 
#1 ·
anybody know what size of collar is need to put on the front strut like the one in the mfc lift ?
 

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#5 · (Edited)
Amen @gravitywell !!!!

It is refreshing to see someone else who is also brave enough to admit that the emperor has no clothes.

The front struts mount in the steering knuckle via the built in clamp design. Look at the knuckle, it has a slot machined out from top to bottom. That is the pinch point of the knuckle clamp. The knuckle bolt is torqued at 83 ft-lb and provides the force for the knuckle to clamp onto the last 2-3.5 inches of the strut (depending on it is "lifted" or not). There is absolutely NO need for any other dead weight.

Happy trails,
unofficial Jeep Field Test Engineer
 
#6 ·
I disagree, dropping to 1.5 inches you will want something there in the front, you are reducing the surface area that the strut clamps to reducing the clamping force. If you are just dropping to 18 mm as per the original Aussie Lift then I think you are OK but you are not maxing what you can get from the stock setup.

I know of one person (not MFC) that dropped down to 1.5 inches without support and Yes he did have problems and had to have his CV replaced after the knuckle slid back up.
 
#7 ·
How do you think the collar has any factor in CV joint angles? Over-lifting is Over-lifting. Collar or no collar, we have a safe limit of what we can do.

You're welcome to drink the Kool Aid, however, a silly little collar isn't doing a single to protect your CV joints.

Sent from my ONEPLUS A3000 using Tapatalk
 
#10 ·
Actually, I did the math when the original Aussie lift was introduced, at 18 mm you are losing around 16% surface area which translates into a like reduction in clamping force, dropping that knuckle down 1.5 inches which is more than double increases the reduction in surface area and clamping force. At best it's double the reduction since I don't know if it's linear or not.

I talked to automotive engineers, they thought it was safe at 18 mm anymore than that and you are taking chances. Here's what you can do, drop your knuckle to 1.5 inches and abuse it like I have mine then come talk about the results. Anything else is empty speculation and you can have fun with that.
 
#9 ·
to answer your question, you need one with a 2" inside diameter to wrap around the strut body.

i used these types of clamps on my jeep because its added insurance, which is why the MFC kit has them.
 
#11 · (Edited)
You're confused on at least two points.

[1] the Aussie lift instructions recommend 19mm (3/4") of strut travel in the knuckle.
My travel is 1.25" (32mm). Your reported mfc travel is 1.5" (38mm). Note that 6mm is not a big delta in ground clearance, which is why any off-roader lifts their vehicle in the first place. I have 17K+ miles with my lift in place. Not sure where you get 18mm.

[2] You are confusing clamping force or load and clamping pressure. The clamping force is the torque load on the knuckle bolt, 83 ft-lb for a 12mm, grade 10.9 bolt. Note that Dave Thomas incorrectly sites using a 100 ft-lb torque. At any rate, the torque load is constant no matter if there is 2 inches of strut in the knuckle or 4 inches.

Pressure (P) is force (F) divided by area (S). The surface area of a cylinder is 2*(pi)*R*h. For argument sake, let's say the strut dia is 2". The height of the knuckle is 3.5" (on average, it's actually tapered on the bottom). Thus, the engaged S of an OE strut is 22 in^2. If the knuckle is lowered 1.25", then h becomes 2.25" and S=14.1 in^2. Similarly when the knuckle is lowered 1.5", h becomes 2" and S=12.6 in^2.

Back to the clamping pressure, P=F/S. Use any force number you want because it is constant. For argument sake, let's use a round number like 100 lbs. So
At OE, P=4.55 psi
At 1.25", P=7.09 psi
At 1.5", P=7.94 psi

Do you see a trend there? Increasing clamping pressure as surface area decreases. So what's the argument for using a dead weight clamp ring? Oh yeah, so you can charge more for a lift kit. How much was that again?

Note that there is a critical h value where the entire strut is above the torque bolt. The force is now no longer uniform. It is not necessary to go into those equations. There is another critical h value where the CV angles are too sharp for the OE design. Each of these cases is unfavorable.

Also note that 83 ft-lb of torque on the knuckle bolt does not equate to 100 lbs load. However, I don't need to drag that equation out to prove my point.

Anyway, your lift is not better, it's just different and more expensive. If 6mm means you have a better lift then I give up and you be the winner. Whatever lift you have just enjoy it and go Jeeping.

Happy trails,
unofficial Jeep Field Test Engineer

References:
[1] Dave Thomas, http://www.justaskdave.com.au/kl-cherokee-lift/
[2] Robert K. Emmons, Jr., http://www.jeepforum.com/forum/f428/there-s-hope-off-shelf-cherokee-kl-lift-3655881/
 
#14 ·
One thing I know, I don't know a single person that's done tougher trails than snowhawk2015. Not even me. And I've done some **** tough trails (for a Trailhawk). He's the only one in a Trailhawk I know of that's done Gold bar rim and Golden spike. Check out YouTube "Golden crack". He's been there done that.
 
#15 ·
Oh I don't doubt that he's a badass driver but when you are using bad math to prove a point and calling someone else confused as a result of that bad math and logic better be ready to reap what you sow, just a little spanking, that's all.

I always think it's better to be open to new approaches, a sample size of one shouldn't be used to make any claim with any degree of certainty. Anyone will agree with that.

Can you get away with not using additional support? Sure, I have myself but I also know that there are limits to what you can call safe. Jeep and any other OEM does t engineer components because they like throwing money away. They don't over engineer but I'm sure they build in safety tolerances, how far can you go before you start to exceed those margins of safety? I for one don't want to find out.
 
#19 · (Edited)
Henry, your argument for the use of the collars seems to be based on the fact that you believe that they help to provide additional safety support by bridging the gap between the knuckle and the strut, providing support in the case of a slippage-type failure of the modification. Assuming for the moment that a hypothetical scenario exists where slippage of the knuckle on the strut is likely (it's not), the issue with this theory is that in the event of catastrophic failure of the knuckle and a sudden and violent slip of the knuckle on the strut, the thin, flimsy plate that the collar is sitting directly underneath is in no way prepared to withstand that kind of stress. It is simply tack welded in place and is ONLY there to provide a place to hold the brake lines away from moving parts, it is not designed to be a strong, structural support piece in any way. In that scenario (and even an infinitesimalmy larger likelihood where there is gradual slippage over time instead of sudden catastrophic slippage) that plate will sheer off and you would find yourself in the exact same position you were had you bought the less expensive lift, only you'd have a few extra dollars in your pocket to help pay for the repairs. The collar is snake oil and is not resting between two structures that are anywhere near strong enough to withstand the weight of a 4400 lb vehicle coming down on top of them. 100% of the structure in this type of suspension design is clamping power, which is why such a substantial (and extremely specific) torque amount is required to hold this setup in its place. We promise you, that collar is providing you with absolutely zero protection. None. Nada. Ziltch. Zip. All absence of support. Did I mention none? Oh, I did already. However, if you somehow feel that it is providing you with some mystical protection (hey, maybe you had it blessed by a monk, to be fair, I didn't ask), then mozel tov, keep using it. If you already overpaid...er...purchased the MFC aloft and you're trying to save face, hey, I get that too. Just take a note from Jerrg Seinfeld and quit while you're ahead, even if you aren't.
 
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