Pre-load adjustment - is it just me? - BMW Luxury Touring Community
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post #1 of 22 Old Apr 5th, 2014, 8:16 am Thread Starter
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Pre-load adjustment - is it just me?

I still have the original rear shock on my 2002LT. Over the years, I've noticed that my bike would sit lower and lower over the coarse of a few weeks because the oil was supposedly "leaking" its way out of the pre-load adjuster. I would put the bike on the center stand, back off the adjustment the entire way, remove the reservoir and discover that it was still full. When I re-installed it and set the height to the middle of the adjustment range, the bike would always be a noticeable inch higher when I straddled the seat.

Now when I can feel that I'm sitting too low, I simply get off the bike, back the adjustment all the way out and then I can feel a great amount of resistance as I set it back into the center range again. When I remount the bike, the height is definitely higher and the ride is much smoother over the bumps. I'm wondering if anyone else has noticed this on their bike? It seems like the pre-load gets stuck somehow and just needs to be reset on occasion. I haven't bothered to add more oil to the pre-load reservoir in the last two seasons since I discovered this peculiarity.

Secondly, I have read about all the final drive failures and I have not experienced one yet. I have logged 55k miles on my bike, but when I notice the road bumps hammering on my seat, I have always fixed the situation. I'm not an expert on suspensions by any means, but could this be a possible cause for rear drive failures?

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post #2 of 22 Old Apr 5th, 2014, 9:53 am
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Re: Pre-load adjustment - is it just me?

when you remove the preload do you push the ram back before you check/fill it?
you said there was resistance when you back off the preloader that does not seem correct.preloader may be failing

i think it is time for either a spring(hyperpro) or a shock change.i did the spring change and it worked very well for a lot less money than a new shock
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post #3 of 22 Old Apr 5th, 2014, 10:40 am Thread Starter
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Re: Pre-load adjustment - is it just me?

Yeah, sorry. My description may be bad. When I back off the pre-load it is very easy to loosen. Then I let it sit for about 10 seconds fully backed off. Then I tighten it back down to the mid-way position and it is firm turning the entire way as it lifts the bike again.

I'm thinking that the internal piston of the pre-load reservoir may slowly leak the oil around it and this may allow the fluid to totally fill the reservoir again and make the bike appear to be "bottomed out" on the shock.

Whenever I remove the reservoir to check the oil level the internal piston/plunger is seated all the way back away from the opening and the reservoir is full. This is what is making me think I have a slow leak around the internal piston of the reservoir. I don't think the problem is in the shock itself, but I can certainly tell when the frame is down on the shock as the bumps are much more abrupt, until I reset the pre-load.

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post #4 of 22 Old Apr 5th, 2014, 8:36 pm
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Thumbs up Re: Pre-load adjustment - is it just me?

After you back off the adjuster, you have to remove it turn it over, remove the hose on the bottom of the adjuster, push a rod in the hose hole to depress the plunger. then add oil and reassemble.
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post #5 of 22 Old Apr 5th, 2014, 9:39 pm Thread Starter
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Re: Pre-load adjustment - is it just me?

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Originally Posted by sperra View Post
After you back off the adjuster, you have to remove it turn it over, remove the hose on the bottom of the adjuster, push a rod in the hose hole to depress the plunger. then add oil and reassemble.
I understand that to be the procedure if the pre-load needed oil, but the times in the past when I tried this it was full of oil. I think my pre-load adjuster has a slow internal leak and I was curious if anyone thinks this kind of thing would be the cause of final drive failures. In other words, would the final drive have a high likelihood of early failure if the frame were always sitting on the rear shock with no pre-load applied.

Also, I was wondering if anyone else has noticed this or if they had a pre-load reservoir fail in the same manner. I never lose any oil, but my suspension slowly lowers down onto the rear shock over the course of a couple days of riding and then I need to reset it by fully backing out the pre-load and then tightening it down again. This raises the bike frame up off the shock again.

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post #6 of 22 Old Apr 6th, 2014, 8:07 am
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Re: Pre-load adjustment - is it just me?

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Originally Posted by cealbrecht View Post
I understand that to be the procedure if the pre-load needed oil, but the times in the past when I tried this it was full of oil. I think my pre-load adjuster has a slow internal leak and I was curious if anyone thinks this kind of thing would be the cause of final drive failures. In other words, would the final drive have a high likelihood of early failure if the frame were always sitting on the rear shock with no pre-load applied.

Also, I was wondering if anyone else has noticed this or if they had a pre-load reservoir fail in the same manner. I never lose any oil, but my suspension slowly lowers down onto the rear shock over the course of a couple days of riding and then I need to reset it by fully backing out the pre-load and then tightening it down again. This raises the bike frame up off the shock again.
I have not noticed this with mine, but it seems plausible that the seal in the adjuster piston could lye oil leak around it.

I can't imagine this affecting FD life though. Worst case is it might shorten the u-joint lives if the angle of the driveshaft was greater with the suspension adjuster collapsed. But the FD itself shouldn't care much unless your spring is also broken such that you have no suspension other than the tire itself. This could transfer more shock to the FD if the bike's weight is fully on the FD with no suspension at all to help absorb shock loads.

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post #7 of 22 Old Apr 6th, 2014, 8:18 am
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Re: Pre-load adjustment - is it just me?

Is it possible that the rubber lines are stretching out over time since they're under pressure? When you release the pressure the lines return to form. When the preload is again turned higher, it takes a while for the lines to expand again. Just a thought since I recall this being mentioned years ago.

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post #8 of 22 Old Apr 6th, 2014, 5:15 pm
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Re: Pre-load adjustment - is it just me?

I guess I don't understand it when you say "the frame is on the shock". Since the frame is bolted to the one end of the shock and the swing arm is on the other. The shock total travel is 1.77 inches regardless of preload and that equates to 5.1 inches at the wheel. The purpose of preload is to place you statically sitting on the bike half-way through that travel. That way you have 2.6 inches above and below to move the suspension to respond to road loads. That is why it is important to understand and set pre-load correctly. It keeps you in the sweet spot.

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post #9 of 22 Old Apr 8th, 2014, 5:56 am Thread Starter
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Re: Pre-load adjustment - is it just me?

Thanks for the replies. I guess my pre-load is slowly lowering me onto the shock so that I have no travel. Sometimes I can really sense the road bumps under my butt. I don't know what's happening, but my pre-load adjuster doesn't need anymore oil. I'm guessing the internal bladder has a slow leak. I may purchase one from E-bay this spring and see if that cures the issue.

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post #10 of 22 Old Apr 8th, 2014, 6:09 am
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Re: Pre-load adjustment - is it just me?

John, I'm totally stupid on these things, how do I know what the right adjustment must be?
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post #11 of 22 Old Apr 8th, 2014, 5:34 pm
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Re: Pre-load adjustment - is it just me?

Quote:
Originally Posted by cealbrecht View Post
Thanks for the replies. I guess my pre-load is slowly lowering me onto the shock so that I have no travel. Sometimes I can really sense the road bumps under my butt. I don't know what's happening, but my pre-load adjuster doesn't need anymore oil. I'm guessing the internal bladder has a slow leak. I may purchase one from E-bay this spring and see if that cures the issue.
It may also have lost its internal gas pressure as well so it may be time for a new shock.

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post #12 of 22 Old Apr 8th, 2014, 5:39 pm
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Re: Pre-load adjustment - is it just me?

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John, I'm totally stupid on these things, how do I know what the right adjustment must be?
With the assistance of a helper you can measure it. First put the bike on the center stand, this will allow the wheel to be at its lowest point in the 5.1 inch travel. Make a scale that is 5 inches long and tape it to the underside of the pannier so that the zero point lines up with a mark or point on the rear drive near the center of the wheel. Then sit on the bike off the center stand and have your helper tell you where that spot or mark has moved to on your 5 inch scale. To have it set correct you want that movement to be 2.5 inches from where it started.

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post #13 of 22 Old Apr 8th, 2014, 8:26 pm Thread Starter
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Re: Pre-load adjustment - is it just me?

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With the assistance of a helper you can measure it. First put the bike on the center stand, this will allow the wheel to be at its lowest point in the 5.1 inch travel. Make a scale that is 5 inches long and tape it to the underside of the pannier so that the zero point lines up with a mark or point on the rear drive near the center of the wheel. Then sit on the bike off the center stand and have your helper tell you where that spot or mark has moved to on your 5 inch scale. To have it set correct you want that movement to be 2.5 inches from where it started.
Haha.....I treat the entire adjustment like I do my sleep number bed. Set it to the middle and then put the seat down and get on. If I stand flat footed and the seat is pressing against my butt, then I know that it is not bottomed out. Then I sit on it and take note of my knee flex with almost all weight on the bike. Then I bounce a little to get a feel for how much the bike is able to move vertically. Basically, if I compress the suspension by 1-2 inches with my weight, then there is should be enough play in the suspension to compress another 1-2 inches downward to absorb the bumps when traveling.

And yes, it may be time for a new shock. Now that the snow is disappearing, I will have many more opportunities to monitor my rear suspension and determine the cause of the slow "deflation".

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post #14 of 22 Old Apr 9th, 2014, 9:41 pm
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Re: Pre-load adjustment - is it just me?

I just wait until I bottom out on mall speed bumps... Then


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post #15 of 22 Old Apr 9th, 2014, 9:42 pm
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Re: Pre-load adjustment - is it just me?

Just wind that thing all the way down and up ... Sounds dumb but works for me


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post #16 of 22 Old Apr 10th, 2014, 6:39 am
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Re: Pre-load adjustment - is it just me?

Quote:
Originally Posted by cealbrecht View Post
Thanks for the replies. I guess my pre-load is slowly lowering me onto the shock so that I have no travel. Sometimes I can really sense the road bumps under my butt. I don't know what's happening, but my pre-load adjuster doesn't need anymore oil. I'm guessing the internal bladder has a slow leak. I may purchase one from E-bay this spring and see if that cures the issue.
I think you have a little misunderstanding of how the shock and adjuster work. The bike is ALWAYS sitting on the shock, preload adjuster has nothing to do with this. All the preload adjuster does is adjust the load on the SPRING, by compressing the spring a little as it is adjusted down. It has absolutely nothing to do with the action of the shock absorber, only the position it is in it's travel in any load condition.

The preload adjuster has a very short travel, just a small fraction of the shock's travel.

I see you have 55K miles on the bike, stock shocks are shot at this mileage. The nitrogen pressure is surely gone, and the shock piston seals likely badly worn. Without the nitrogen pressure, the shock will bottom out far easier.

If you were to put Ohlins or Wilburs shocks on, you would be absolutely shocked and amazed at the difference. It would feel like a totally different bike! The Ohlins and Wilburs shocks are re-buildable, so the high initial outlay is made up for a little every time they are rebuilt. I found that the Ohlins need at least a nitrogen recharge about every 30,000 miles to get the crisp handling back.

Shock absorbers on vehicles go bad so slowly over time that one does not realize that they are changing until they are really bad, which is what you are experiencing.

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post #17 of 22 Old Apr 10th, 2014, 8:14 am
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Re: Pre-load adjustment - is it just me?

Question for one of you mechanical genius's. My understanding of a pre-load system is that you need a spring with a progressive rate because pre-loading a standard constant rate spring does nothing as the rate is the same and does not get stiffer, is that correct?
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post #18 of 22 Old Apr 10th, 2014, 8:27 am
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Re: Pre-load adjustment - is it just me?

Your shocks were gone years ago, time for a new motorcycle.

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post #19 of 22 Old Apr 10th, 2014, 9:21 am
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Re: Pre-load adjustment - is it just me?

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Question for one of you mechanical genius's. My understanding of a pre-load system is that you need a spring with a progressive rate because pre-loading a standard constant rate spring does nothing as the rate is the same and does not get stiffer, is that correct?
Spring RATE is how much a spring changes force over distance, ex: 250 pounds per inch. Given that spring rate, 1/8 inch of length change would result in 31.25 pounds change in force, at 1/4" 62.5 pounds, 3/8" 93.75, etc.. Normal wound springs have a pretty consistent rate over the working distance. Progressive rate springs are different, in that the rate is not consistent, but increases as the spring is compressed. The same spring as above, but with a progressive rate, could as example increase rate by 20% every 1/8" so the forces would be 31.25, 68.75, 112.5 pounds.

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post #20 of 22 Old Apr 10th, 2014, 7:03 pm
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Re: Pre-load adjustment - is it just me?

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Question for one of you mechanical genius's. My understanding of a pre-load system is that you need a spring with a progressive rate because pre-loading a standard constant rate spring does nothing as the rate is the same and does not get stiffer, is that correct?
No, not correct. Preload doesn't make any spring stiffer, it just changes the static ride height as John explained earlier. A progressive spring will feel stiffer as you are binding the coils that are less stiff, but you haven't fundamentally changed the spring.

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post #21 of 22 Old Apr 10th, 2014, 7:52 pm Thread Starter
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Re: Pre-load adjustment - is it just me?

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Just wind that thing all the way down and up ... Sounds dumb but works for me


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This is basically what I am doing as well. I think there is a problem with the pre-load adjuster, because after I do this, the ride is definitely smoother and the bike sits higher again.

As for needing a new rear shock, is there a way to tell that the stock one is no longer any good? Like I said, the ride is definitely smoother after I reset the pre-load. I'll admit that I don't know much about suspensions and can't tell a paralever from a telelever.

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post #22 of 22 Old Apr 10th, 2014, 8:29 pm
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Re: Pre-load adjustment - is it just me?

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No, not correct. Preload doesn't make any spring stiffer, it just changes the static ride height as John explained earlier. A progressive spring will feel stiffer as you are binding the coils that are less stiff, but you haven't fundamentally changed the spring.
It does change the spring load at any point in the travel. By compressing the spring some, it affects the ride height because the spring is now pushing the bike up harder than when it is shorter. That is what raises the ride height.

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