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View Full Version : How Can I tell if I need a new rear shock?



SweetT
01-23-2004, 09:49 PM
Hello all,
I have a 91 K75 w/ 125k mi that I bought last year from the widow of the owner. The bike was well maintained, but there is no record of the rear shock being replaced. I am going to take a week long camping trip in the near future with my lady, and I am beginning to wonder if the rear shock needs to be replaced. It looks like its in good shape from the outside, and I dont know enough about suspension components to determine if the shock is worn or not. As far as I know this could be the original shock or it could've been replaced the week before the guy died. How can I tell?

Thanks,
Tarren Shaw

LORAZEPAM
01-23-2004, 11:51 PM
In my experience, when a shock wears out, you will experience a lot of real wheel movement (up and down), and wallowing when in turns, especially 2 up or at higher speeds. If the bike feels well planted, and not squirrely at all, I imagine the shocks are good. If you cant hold a good line in a sweeper, or if sharper curves are hard to take at speed, I imagine it is shot. There are others who may be able to elaborate, but I sure can tel when mine have gone bad.

basketcase
01-24-2004, 12:05 AM
Plus, the "worn shock" image that comes to my mind can be expressed as, "hinged in the middle." You can for sure feel it when it's shot.

If it needs replacement, you can probably find up a stock shock for a modest amount, but my experience with the Works product prompts me to say, "At least consider an aftermarket custom shock." And particularly if you are going to do a lot of two up touring.

Harv Read
02-13-2004, 09:35 PM
Another way to tell if your shock is gone: The bike will "bottom" hard on modest bumps, like not-so-bad railroad tracks. If it passes this test (assuming the preload is adjusted "up") it is not shot. It may not be satisfactory for some of the go-fast guys who regularly drag hard parts in the twisties, but it's still good enough for us mortals. I just replaced the rear shock on my K12LT at 135k and it was not "shot". Really.

deilenberger
02-14-2004, 03:46 AM
Originally posted by Tarren Shaw
Hello all,
I have a 91 K75 w/ 125k mi that I bought last year from the widow of the owner. The bike was well maintained, but there is no record of the rear shock being replaced. I am going to take a week long camping trip in the near future with my lady, and I am beginning to wonder if the rear shock needs to be replaced. It looks like its in good shape from the outside, and I dont know enough about suspension components to determine if the shock is worn or not. As far as I know this could be the original shock or it could've been replaced the week before the guy died. How can I tell?

Thanks,
Tarren Shaw

You can't really tell easily. Handling isn't what it's supposed to be - but without a standard to judge this against - the handling is what you're used to.

As others have said - more movement in the suspension than you'd expect is a clue - as is the unstable feeling in sweeping high-speed corners (this can be really disconcerting..)

Since the bike has a lot of miles on it - and most people don't replace the stock shock with another stock shock (the stock one costs as much new as a much better aftermarket shock) if it was me - I'd assume (bad thing to do usually) that is is the original. And if it's the original with this many miles on it - it's about 80,000 miles overdue for a replacement.

You can use this as an opportunity for an upgrade - since IMHO - the stock K shock of this era came from the factory as over-sprung and under-damped.

Suggested replacements in order of increasing price/quality:

1. Progressive
2. Works Performance
3. Ohliins and Wilbers (tossup for performance, Wilbers gets the nod for a better value - more features for the $$$, quality on both is excellent)

Best,

DARKCLOUD
02-14-2004, 04:45 AM
First, contact the local BMW dealers and give them the VIN off your bike. They can access whatever has been entered into the computer regarding your bike by the selling/servicing dealerships.

If there is no sign of oil leakage by the piston ram, the ram is clean and not scarred, your shock is probably in good shape,however; given your bike is a '91 it may have leaked out and wiped off so you don't know.

You could remove the shock, and try and operate it by hand to see if it has resistance. It should be harder to compress than extend. If you have a dampening control, close it, ride the bike, curves, stops, rough road. Then open it completely and return on the same course you took, if there is no difference then you need a new shock.

The other method would be to ride a K75 with a good shock.

A bad driveshaft can give bad handling in curves. JON

deilenberger
02-14-2004, 05:07 AM
Originally posted by Dark Cloud

First, contact the local BMW dealers and give them the VIN off your bike. They can access whatever has been entered into the computer regarding your bike by the selling/servicing dealerships.

Not to be argumentative - but the dealer can only access records for repair on bikes they worked on - the BMW national computer doesn't record this type of work if it isn't warranty.

It might be worth asking the parts managers in the local dealerships if they can find a record of selling a shock to the former owner.


If there is no sign of oil leakage by the piston ram, the ram is clean and not scarred, your shock is probably in good shape,however; given your bike is a '91 it may have leaked out and wiped off so you don't know.

If only it was that simple.. shocks can fail by fluid breakdown inside the shock. No sign of leakage - but the fluid has changed viscosity and no longer performs the damping it was designed to. They can fail by internal wear to the fluid passages, and they can fail by internal seal failure. Any of these will give the appearance externally that nothing is wrong - but it is.


You could remove the shock, and try and operate it by hand to see if it has resistance. It should be harder to compress than extend. If you have a dampening control, close it, ride the bike, curves, stops, rough road. Then open it completely and return on the same course you took, if there is no difference then you need a new shock.

True - if you could easily remove the spring. It's not a simple job on the stock K bike shock of that era. And there is no control on these shocks except perload - 3 positions


The other method would be to ride a K75 with a good shock.
Very true if you can find one comparibly equipped.


A bad driveshaft can give bad handling in curves. JON

Please elaborate on this.. I can't think of any way an early K bike driveshaft would effect the handling of the bike - in curves or straight ahead.

I think the real point here is - it's an unknown shock, the original poster doesn't have a lot of confidence in it, and in any case - the stock shock that came on that era K bike - even brand new, isn't really a very good one.

I'm NOT a canyon carver - but I can feel instability in high-speed sweepers - and that's exactly how even a good stock shock on the early K's made them feel. They were oversprung and underdamped. A change to a modern aftermarket shock is a really enlightening experience in how well one of these bikes can handle. It's one of the better investments you can make in an early K bike.. especially one this old with that many miles on it.

Best,

SweetT
02-14-2004, 05:08 PM
Thanks for all your input everyone! the bike feels okay when I ride it; I rode my dads old 71 honda 350 last weekend which still has all the original shocks on it and I was able to tell immediately that it needs new rear shocks. Fortunately my K75 is not near that bad. I"ll probably go ahead and replace the shock in the next few months since I'll be riding two up to spokane this summer (about 4500mi round trip) and I'd like the security of knowing that I'll have good suspension components during the trip.

Thanks,
Tarren shaw

knary
02-14-2004, 07:51 PM
Originally posted by Tarren Shaw
Thanks for all your input everyone! the bike feels okay when I ride it; I rode my dads old 71 honda 350 last weekend which still has all the original shocks on it and I was able to tell immediately that it needs new rear shocks. Fortunately my K75 is not near that bad. I"ll probably go ahead and replace the shock in the next few months since I'll be riding two up to spokane this summer (about 4500mi round trip) and I'd like the security of knowing that I'll have good suspension components during the trip.

Thanks,
Tarren shaw

I'll add my 2 cents. Listen to what Eilenberger wrote. If you can remotely afford it, invest in a new aftermarket shock. It will transform the feel of the bike for the better.

hankb
03-06-2004, 07:06 AM
Originally posted by deilenberger
Since the bike has a lot of miles on it - and most people don't replace the stock shock with another stock shock (the stock one costs as much new as a much better aftermarket shock) if it was me - I'd assume (bad thing to do usually) that is is the original. And if it's the original with this many miles on it - it's about 80,000 miles overdue for a replacement.


Would the same hold for a '95 K75RT with 50K miles? Would I be 10K miles overdue for a new rear shock? I have no particular reason to believe it is bad other than age and miles. I've only ever ridden this bike and only for the last 13K miles, so I wouldn't know what it is supposed to feel like.

thanks,
hank

deilenberger
03-06-2004, 03:28 PM
Originally posted by HankB
Would the same hold for a '95 K75RT with 50K miles? Would I be 10K miles overdue for a new rear shock? I have no particular reason to believe it is bad other than age and miles. I've only ever ridden this bike and only for the last 13K miles, so I wouldn't know what it is supposed to feel like.

thanks,
hank

Hi Hank!

As a general answer- yes - you're due for a new shock. The difference will be noticeable. IMHO - the stock shock when brand new is oversprung and underdamped.. a good aftermarket shock setup for your riding and weight will greatly increase your enjoyment of the K75RT - especially when loaded up with a pillion passenger or touring gear.

Best,

hankb
03-13-2004, 03:29 AM
Originally posted by deilenberger
Hi Hank!

As a general answer- yes - you're due for a new shock. ...

I went with a new-to-me used shock that I bought from the president of the IBMWR. He sold it as a Progressive and it came in a Progressive box, but the shock was labeled Works Performance and matched one I found on their web site.

I put it on today and put a few miles on the bike. I *think* it feels better, but I didn't hit anything really bumpy so it is hard to tell. One thing for sure, I had a slight steering wobble at 45 mph when I let go of the bars and that is gone. It still does it a little bit at 55 mph, but that is reduced in intensity from what it used to be. (Of course, it is possible that the steering damper is stiffer at 30 deg F and that reduced the shake...) I could have bought his slightly used factory shock for half that but based on your comments decided it would not be worth it.

thanks,
hank

deilenberger
03-13-2004, 04:27 AM
Originally posted by HankB
I went with a new-to-me used shock that I bought from the president of the IBMWR. He sold it as a Progressive and it came in a Progressive box, but the shock was labeled Works Performance and matched one I found on their web site.

I put it on today and put a few miles on the bike. I *think* it feels better, but I didn't hit anything really bumpy so it is hard to tell. One thing for sure, I had a slight steering wobble at 45 mph when I let go of the bars and that is gone. It still does it a little bit at 55 mph, but that is reduced in intensity from what it used to be. (Of course, it is possible that the steering damper is stiffer at 30 deg F and that reduced the shake...) I could have bought his slightly used factory shock for half that but based on your comments decided it would not be worth it.

thanks,
hank

Hank - interesting. Works can "freshen" the shock for you..
cost depends on what they do. You might want to stop
by a dirt-bike suspension shop - and just have them check
the nitrogen fill in it - they'll have the valve and gas to do
it. I think you made a good decision with the aftermarket shock.

As far as wobbles.. can be:

1. Front tire
2. Steering head bearings loose and/or worn
3. Bent rim (front or rear)
4. Steering damper out of place (it happens when a wrench is sloppy)

I had it on THE K75S - if I took my hands off the bars. I improved it (made it less) by putting a very slight amount of drag on the steering head bearing adjustment. That helped. This was recommended to me by Paul Glaves who has LOTS of K75 experience (about 300k on his now..) You only want a very tiny bit of drag - no so much that the bike tends to not come out of a turn by itself.

What finally fixed it was sending my rear rim to Tim Bond and having him take the wobble out of it. No wobble at ALL on the bike now at any speed I've had it to. It had a 1/8" side to side wobble in it - now it has none. Tim did a great job at a very reasonable price.

If you're running a Metzler-ME-88 on the front - they are known for inducing a wobble as they get worn, and a fresh one might just cure it.

The K75S is fairly sensitive to all of these things which is why BMW added the steering damper to it in early '87..

I think you'll find the Works shock doesn't give you that unnerving floating feeling in high-speed sweepers that the stock shock likes to give. That feeling really spooked me more than once.

Best,

hankb
03-14-2004, 10:09 PM
Originally posted by deilenberger
Hank - interesting. Works can "freshen" the shock for you..
cost depends on what they do. You might want to stop
by a dirt-bike suspension shop - and just have them check
the nitrogen fill in it - they'll have the valve and gas to do
it. I think you made a good decision with the aftermarket shock.
I'll have to look into that. As for the wobble:


1. Front tire
I've replaced the front twice and it makes no difference. (Currently running a ME 330)
2. Steering head bearings loose and/or worn
On my list of things to check.
3. Bent rim (front or rear)
I'll have to check those. the front rim had a slight bend at one point when I bought it, but I didn''t think to check for a wobble.
4. Steering damper out of place (it happens when a wrench is sloppy)
I'll have to check that when I check the bearings.

thanks,
hank

knary
03-15-2004, 02:47 AM
Originally posted by HankB
I'll have to look into that. As for the wobble:


1. Front tire
I've replaced the front twice and it makes no difference. (Currently running a ME 330)
2. Steering head bearings loose and/or worn
On my list of things to check.
3. Bent rim (front or rear)
I'll have to check those. the front rim had a slight bend at one point when I bought it, but I didn''t think to check for a wobble.
4. Steering damper out of place (it happens when a wrench is sloppy)
I'll have to check that when I check the bearings.

thanks,
hank

I chased down a front end wobble for some time on my old K.

A few thoughts:
1. when were the forks last service?
2. steering head bearings: how many miles are on the bike? The idiot-proof way of servicing them - what I chose - is to take the stem to a shop and have them remove the old bearings and press on the new ones.
3. I had to install a *third* front tire to finally solve the problem. That was the last time I will ever use a Metzler bias ply tire. Give yours a spin and see if it really is round. FWIW, there are, IMHO, much better tires out there.

babbling. need another guinness.

hankb
03-16-2004, 04:10 AM
I'm not sure if your questions are rhetorical or otherwise, so I'll answer.

Originally posted by knary
1. when were the forks last service?
2. steering head bearings: how many miles are on the bike? The idiot-proof way of servicing them - what I chose - is to take the stem to a shop and have them remove the old bearings and press on the new ones.
3. I had to install a *third* front tire to finally solve the problem. That was the last time I will ever use a Metzler bias ply tire. Give yours a spin and see if it really is round. FWIW, there are, IMHO, much better tires out there.

1. I changed the oil last summer using the BMW fork oil. The seals do not appear to leak. Is there other service required?
2,3. need to check both. I did wear out a Michelin Tarmac so it has not been Metzler tires the whole time.

thanks,
hank

knary
03-16-2004, 04:19 AM
Originally posted by HankB
I'm not sure if your questions are rhetorical or otherwise, so I'll answer.


1. I changed the oil last summer using the BMW fork oil. The seals do not appear to leak. Is there other service required?
2,3. need to check both. I did wear out a Michelin Tarmac so it has not been Metzler tires the whole time.

thanks,
hank
#1. that's about all you really need to do.
If #2 & #3 don't take care of it, you're left with a few other choices.
4. swing-arm bearings
5. rear shock. While it is "new" to you, it may either need to be serviced, or need to be adjusted to better suit you. A sagging rear shock will give you a light front end and possibly amplify the other problems, thus giving you a head shake.

csbrownjr
04-08-2004, 12:31 PM
If one of them has gone, but no the other, the bike will wallow and weave in high speed corners as the load comes on and off them. This causes the front tire to twist from side to side.

If this is the case, have both sides serviced.

Charlie

knary
04-08-2004, 12:44 PM
Originally posted by csbrownjr
If one of them has gone, but no the other, the bike will wallow and weave in high speed corners as the load comes on and off them. This causes the front tire to twist from side to side.

If this is the case, have both sides serviced.

Charlie

If memory serves...a 1991 K-bike, no matter the flavor, has damping only in one fork leg as by then, they were all equipped with a variation of the S forks.

csbrownjr
04-08-2004, 01:06 PM
hmm. Then my dealer probalbly was pulling one of my legs when he replaced the seals on both sidess of my 95 k75a3. Oil had been weeping from the right side.

Charlie

knary
04-08-2004, 01:39 PM
Originally posted by csbrownjr
hmm. Then my dealer probalbly was pulling one of my legs when he replaced the seals on both sidess of my 95 k75a3. Oil had been weeping from the right side.

Charlie

There is oil in both legs. But one leg has an "open" damping system. The damping rod that does the work is only in one leg.

LORAZEPAM
04-08-2004, 02:34 PM
While the fork is apart, you may as well replace both seals. It reduces the labor time, and is a good idea, especially with an older bike. I would think highly of a mechanic who took the time to do both, and not rush and do just one.