69L71

After review of the failure that occurred to my Perfect Park 7000 lift on March 15, I believe I have determined the cause. Or should I say causes. The collapse was caused by a dual failure of the actuation system and the locking mechanism in the post. The actuation system failure was diagnosed by the manufacturer, Gemini Auto Lifts, and appears to be right on.

Actuation System:

The actuation system on virtually all residential 4-post lifts is comprised of a hydraulic ram that acts on a series of cables that attach to the top of the posts. The cables run through pulleys, both under the runways and on the crossbars. As I said in my earlier post, I had assumed that I had let one of the cables get slack and that the cable had fallen off the pulley. This was a logical assumption at the time. After consulting Gemini, however, they had a different opinion.

This picture shows one of the pulley-packs under the runway.



A stud is installed up into the runway, and the pulleys are installed with brass bushings and a brass spacer. Then the stud is capped off underneath the runway with a nut, which is secured by either locktite or weld (hard to tell which). Gemini suggested that damage/wear to the bushings could cause galling on the stud/axle. They surmised that friction between the pulley and the axle/stud caused the stud to back out of the runway, allowing the pulley to separate. One of my pictures taken the day after the collapse suggests validity to that theory.



Removing the stud and inspecting it, showed the galling and damage Gemini expected:



Owners and operators of all residential 4-post lifts need to understand that this pulley-pack design is not unique to Perfect Park Lifts. They all have an identical or very similar configuration. After talking with a friend who recently replaced the bushings in his Stinger lift, I advise that all of you inspect your axle studs/bolts and bushings.

Understanding this failure, what prevented the post from locking?

Locking System:

The lock blocks in the posts, combined with spring-loaded lock mechanism are supposed to assure positive engagement of the locks should a malfunction of the actuation system occur. In general it is a well conceived design that should provide plenty of safety. Again, this concept is not unique to the Perfect Park. Perfect Park is unique because of the enclosed slider track, pulleys, cable, and locking mechanism, provided by creating a 3-sided box column. Most others are exposed. The locking mechanism with the column removed is shown below, as is the locking mechanism of a competitor’s lift (thanks paso) so you can see how the locks engage.:





With the column installed it looks like this:



As you can imagine, as the lift elevates in its track the lock tangs scrape against the lock blocks and snap into place via spring pressure. When operating the lift, one can hear the locks engage at each stop. If they don’t all snap at the same time it suggests that the cables need adjustment. Obviously, it is reasonable to assume that the lift will show signs of wear on the blocks after several uses. This is certainly not a bad thing, and in fact should be seen as a source of confidence. I had my lift for about a year and when I inspected the inside of my columns I saw the telltale wear on the blocks – on the 2 rear columns that engaged. The Right front column (the one that collapsed) showed very little wear on the blocks.



Sorry the pics aren't better. The LR column was outside (hense the rust from the previous night's rain) so I had plenty of ambient light to photograph. The RF Column is stuck in the garage so I had to resort to flash.

The other front column could not be inspected because it’s on its side with the lift laying on it. The lack of wear suggests to me that the column that failed had probably not been strongly engaging all along. Obviously, when the lift is lowered onto the lock blocks the tang of the lock would be pulled into the locked condition if there was positive engagement (adequate overlap between the tang and the block). If there was NOT adequate overlap the tang would remain unengaged, and thus, unlocked. This seems to have been what happened in the case of my collapse.

It is unclear to me why the one column showed significantly less wear. I suppose it could be a tolerance buildup, defective spring, or binding in the linkage.

What to do if you own a 4-post lift?

If EITHER the hydraulic/cable system OR the column locks had operated as designed my lift would not have collapsed. Both needed to occur to get the outcome I experienced. That said, I would:

- Inspect your axle studs/bolts and bushings for wear/damage
- Ask your manufacturer and ask if there are inspection or lubrication requirements on the bushings.
- Ask your manufacturer and ask if there are any product improvements that could increase the safety of your lift.
- Inspect your locking mechanism to see that the locks are ALWAYS positively engaging.
- Periodically check your axle studs/bolts (and any other related hardware) for tightness.

This summary is not an indictment of Perfect Park or any other 4-post lift. As I’ve stated before, a lift is a tool, and should be treated with care and respect. My incident, hopefully, will lead to product improvements by the industry and greater awareness by the operator.



[Modified by 69L71, 8:47 PM 4/3/2002]

Cooter Tech

I have been following your posts very carefully, as I have just purchased a four post lift. Obviously I am concerned about what has happened to your lift, can also affect my lift. I am glad that you are keeping us informed as to what was the cause and what can be done to prevent another accident. Thanks for keeping us informed. Roger L. Gibbons

sb69coupe

Chris, this kind of analysis and post-mortem is very valuable. As a recent purchaser of a Superior lift, I REALLY appreciate your feedback on the cause(s) of your lift failure. Thanks again! On one hand, I'm a little reassured that the cables didn't come off the pulley during operation. On the other hand, I'm not too thrilled about how the pulley bolt/stud failed. As you mentioned, if the locks were properly engaging when the lift was being raised, they could have provided a safety failover. The thing that concerns me is that if the pulley failure occurs when the lift is being lowered, the locks are not engaged to provied that secondary safety margin. Then all bets are off. That's a worst-case scenario.

I called Superior to discuss this failure with them and explore the pulley/bushing/bolt failure. They told me to talk with another employee more familiar with the design and specs, so I'll call back tomorrow. I'll post what I find. In general I plan to ask the following things:

1 - what grade hardware is used for the pulley mounting bolt/stud?
2 - how is the pulley bolt/stud secured to prevent it from backing out?
3 - what lubrication is recommended for the pulleys and bushings?
4 - how can adequate inspections be performed on the pulleys and bushings with the under-ramp covers in place
5 - is there anything to look for to make sure that the locks are within calibration on each post during raising or lowering the lift.

Shannon

paso

Nice report. I think you should submit a bill for writing up such a factual report. I'll be checking my hoist. :)

QuickVet

i still cant believe that happened :smash:

PRNDL

My head is spinnin... :confused: it's my limited attention span again.
Think I will start digging a pit in my garage..... much simpler. MJ

SBR

I was thinking the same thing.

69L71

Shannon:

Those are exactly the kind of questions I hope everyone asks their lift manufacturers.

Be advised of one thing though: Superior and Perfect Park lifts are manufactured in the same facility by Gemini Auto Lifts in Ft Worth. The designs are nearly identical except for the enclosed column on the PP. As I mentioned, Gemini is aware of the problem with the axle/stud. They supposedly have a fix in work. You might try looking them up online and discussing it with them directly. Ask for Bud or Sam.

Frank75

Chris,

Excellent analysis; thanks for keeping us informed.

Shannon,

Am looking forward to your post on what you learn with Superior. I haven't been able to start the installation of my own lift yet as I had to go out of town on a family medical emergency. I will start looking carefully at components tomorrow though and will post any concerns on anything that jumps out at me.

thanks again,
Frank

0Mike69@ECS

Great Post Chris...

Now.... what's up with the cars??? What happened with the insurance?

69L71

Mike:

I'll have the estimates in hand by the end of the week and will submit them to Gemini for payment. Tony is writing them up now after inspecting both cars Monday. The 96 wasn't damaged too bad, but the crack in the clamshell is right across a seam in the wheel lip. It will get a new hood, which is fine by me. I want it fixed right. The 69 needs a surround panel and fender, new bumper, a couple of grill pieces, a headlight bucket, and obviously paint. There doesn't seem to be any frame damage, still the repair will be fairly pricey. Tony's shop is the best and they charge accordingly.

I'm still not sure what I'll be doing with the car yet. I know I could fix it myself for not too much money, because I'd use my own labor rates ($0/hr). I'll wait 'till I see what the settlement $$ looks like. I'll probably sell the car to someone looking for a nice body-off convertible that needs some patching-up. Meanwhile I'll be pulling the body back off the L71 a week from Sunday and forging ahead with that project, with the aim (pipe dream?) to make Carlisle. Wanna help?

0Mike69@ECS

I might be able to do that... Actually that might work out really well. Donna and I were tentatively planning on going to Skyline that weekend and leaving Saturday evening... Maybe I'll have to make a stop in your neck of the woods. We could grab a room - or even stay at the boat that night.... I'll buzz you in the next couple of days after she finishes telling me I'm :crazy: !!!

liftman

Chris,The new pictures you showed are identical to the two Superior lift failures in Eugene,OR..Superior claimed it was the customers fault,and Gemini told the leasing company it was my fault,It is nice to see that the truth is coming out.The end result is they knew these failures were occuring years ago and chose not to do anything about it.I have been informed that Gemini is also marketing under the name of American lifts and will be at the Good guys shows."Caveat Emptor"Let the buyer beware.
Liftman

69L71

paso:

I'd love to submit a bill for the post-mortem, but my guess is neither Lifts Unlimited or Gemini is all that thrilled that I did it. In fact, I'm fairly convinced that I would have been in the same boat as the other users liftman talks about were blamed for their failures if it weren't for the forum. The fact of the matter is, its the corvetteforum that is making all this come together. By posting here it sprinkled daylight on the industry (17,000 hits on a subject is a lot of light). Now both companies want to take care of me and you guys get the benefit of my experience by learning what to do to make/keep your lift safe.

Now all I need to do is get the settlement check and get on with things...

sb69coupe

Chris, as promised, here is the feedback I got from both the folks at Gemini and Superior.

First, Gemini told me that the stud did back its way out of the captive nut. The fellow I talked with indicated that he thought that it did so due to the cable being off the pulley and turning the stud. He indicated that they plan to begin tack-welding the head of this bolt/stud to the underside of the track to prevent it from turning once it is installed. He said that there is no requirement to regularly lubricate the pulley shaft or bushings, but it likely would not hurt to do so.

I spoke with Superior at great length this morning as well. They indicated a number of things that I can do as an owner to make sure that things stay safe and operate properly.

First, make very sure that each cable is adjusted properly. They suggested raising the lift until the locks are between stops, then measuring the distance from the column top cap to the bottom of the lock block at each post. Adjust the cables until there is no more than 1/8" of difference all the way around. Make sure that all locks are coming off their stops at the same time when raising the lift, and adjust accordingly to achieve this. This will help prevent a single lock hanging up between stops, and causing slack in the cable if the lift gets out of level.

Second, when lowering the lift, always make sure that all 4 locks are fully disengaged. An easy way to do this is by looking under the lift at the crossbar at the far end. You should be able to see the angled "tips" of the locks pointing at the floor. They will be visible beneath the crossbar when the locks are fully disengaged. To calibrate the lock release, use a helper at the other end of the lift to look at the movement of the locks as the release lever is turned. There is some flex and torsion in the long lock rod under the ramp, and you can calibrate this using the coupling and locknuts to get all the locks disengaging in sync with each other front to rear. Then adjust the lock rods to make sure side to side is also is in sync.

Check the tightness of the studs that hold the pulleys. Visually check to make sure they are not backing out. I am considering either tack welding mine down once I make sure they are tight, or putting a dab of paint on each head so I have a visual reference to make sure that they haven't moved.

In general, these lifts are pieces of heavy machinery. They require caution when using them, calibration when installing and setting them up, and regular inspection and adjustments to make sure they are operating safely.

I've learned a great deal from these threads. I don't question the safety of the designs, and I have a greater understanding of how they work. I also feel much more confident that I know how to operate and maintain my lift to get many years of trouble free service.

Shannon

sb69coupe

liftman, I'm reluctant to open this can of worms, but I think we could possibly learn some more by digging deeper. So, first let me make a request. I'd like to avoid anyone badmouthing any specific lift product, name calling, etc. Let's keep it civil and discuss the facts and merits as outlined below.

Can you tell me of another design in the industry that would not be succeptable to this kind of failure? I do think that the pulley stud inserted from below the ramp is a sub-optimal design. The proposed change to weld the head of the stud will help remedy the problem of the stud backing out. What other designs are being used that may not be prone to this kind of failure?

Are there any other lifts that use a different design for attaching the pulleys? Do any other designs provide a different way to keep the cables on the pulleys in a more captive manner?

If you don't want to name the specific manufacturer, that's cool. Just a description of how the design is different would be helpful.

Shannon

69L71

Good points on setting up the cables. That is part of the initial set up procedure on the Perfect Park. I think you'll see that there will be some cable stretch and mis-alignment over time. The adjustment should be almost periodic.

Looking to assure that the locks are disengaged is a great idea, but not possible with the Perfect Park. The lock mechanism is enclosed in the column and is not visible unless you stand right over it. Luckily you suggestion should work for almost every other lift out there.

As for the damage being caused by the cable coming off the pulley, that just isn't so. In fact, note the picture below.



The pulley is galled to the cable even now. I can't separate them. The spacer bushing failed causing the incident. Look at the picture of it; there is no cable-induced damage to the outside of the bushing. Gemini knows the failure mode and it has nothing to do with cable disengagement. Superior is just trying to deflect some of the responsibility.

Be careful about tack welding the stud to the underside of the runway. I thought about that, and it does seem like a decent solution, EXCEPT that it will make it very difficult to inspect, repair, and lubricate the bushings. The lift is built by installing the stud and pulley-pack, and then the lower plate it welded in place. If you weld the stud you can never get it out. I also doubt there is sufficient clearance to get in there and weld. Replacing the stud with a boly and using lockwashers/safety wire might be a better solution. Also, it pays to periodically check the torque.

DaveL82

As with any stud or bolt that is used under load and should not back out, most use a castle nut and cotter pin to make sure that the nut cannot back off. Maybe I'm not seeing the big picture, but that seem would to be a must for such applications.

Frank75

Shannon,

Did you have any discussion with Superior about bushing materials? I can see either a washer or the edge of a bushing when I look at mine. Looks like it's steel so I'm hoping it's a washer. Chris said in an earlier post that the bushings werer brass: hope he meant bronze.

I'd appreciate any comments.

thanks

C5GARY

OK, you guys just keep my mind racing.. as fast as you guys start new threads!
WHAT ABOUT LUBRICATION?? I'm just a EE but whenever metal slides on metal under load... don't you NEED LUBRICATION???
The pictures of your "bolt" shows alot of wear... that didn't happen on the day of the "collapse". I am pretty sure Superior told me I didn't need to lube my lift.. now I see on their web site instructions that they recommend silicon spray to lube the pully's once a month... WTF?? SILICON spray?? That's what I use to stop the squeeks from rubber weatherstripping against painted metal!! What do you ME's think? Shouldn't these pully axles be lubed by something much more substantial than silicon spray? What about oil.. or say GREASE!
OK, what your pictures show is substantial damage to the threads at the end of the axle. If the threads fail, you are going down. HOW did you get that damage? The possiblities I can think of are:
1. Overtorquing during assembly (at the factory) relative to the "softness" of the material.
2. There was enough "friction" between the pully and axle to "overtorque" the threads.
3. The axle was just plain ripped out of the captive nut.
4. Crossthreading at the factory.
Gary