ST1100 OEM shock questions.

shrekster

Joined
Mar 24, 2011
Messages
8
Location
Glasgow, Scotland.
Bike
1991 ST1100
I've stripped my oem shock down removing the spring, top adjuster and damping rod. I've made a drain point, drained the oil and flushed the shock out. My plan is to rebuild the shock with fresh oil and possibly a slightly heavier spring.
Can anyone tell me what the standard spring rating is? And what the standard oil weight is?
If i can find this out i can do an oil change every year as it's fairly simple to dismantle the shock.
regards,
Jim.
 
The *standard* weight is 7.5, (I use 10wt as a replacement) the spring that I would use to replace the stock spring is 1.2kg.

Good luck!
Mark
 
I think Mark's comments of 7.5 oil and 1.2kg refer to the front forks, which are often changed.

Shrekster said "shock" so I assume he is talking about the rear. AFAIK there is no official published spec, but I believe the stock rear spring is variable rate, about 375 to 390lb. I have a 425lb straight rate on my Penske shock and find that adequate even 2-up, still higher rate than stock. Some others have gone for 500 to 550lb rear spring. I started with 500lb and found it too stiff. Your mileage may vary.

In all my years on ST forums, I've never heard of anyone rebuilding the rear shock internally, so not sure if anyone would know the fluid weight. You may have to experiment.
 
Hi, thanks for he replies, yes i should have made clear it's the rear shock absorber i'm working on. I have found some info on what oil may be in the shock but as you say i'll have to experiment.

regards,

Shrekster.
 
Nope, there is only oil in the shock, it's very basic and easy to replace the oil if i can find out what grade it is.
regards,
Shrekster.
 
Woah! this is starting to get a little complicated, thanks for the links but the second one is a little beyond my abilities. I think i have found a suitable oil as a replacement, i'll report back when i've tested it out.

thanks again,

Jim.
 
The easy way to measure the viscosity would be to take a drop of the old oil drop it on a tile or plexiglass propped up at 45 degrees and measure the time it takes to dribble down the plate an inch or 2. The just sample some other oils you have laying around. I imagine close enough is good enough.
I'm a....uhhh visual learner too:D
 
Thanks for all of the great info...looks like a rebuild in the future for me. Might save about 400 bucks.
 
STranger said:
I'm a....uhhh visual learner too:D
Click to expand...
I really should have paid more attention at school :eek::

Ok, i've done a few crude experiments with a few different oils to see how the viscosities compare. As i say it is a little basic but i set up a syringe and poured in 20ml of the oem oil and timed how long it took to drain with a stopwatch. I repeated this 5 times then noted the average time taken, amazingly all 5 times were within 0.4 seconds of each other.

So with a base figure to work with i did the same test with two other oils i have lying spare in my garage. One was pouring out a fair bit faster so that was ruled out, too thin. The other, Shell Advance 5w fork oil gave figures within a second of the oem times. I reckon this would be fine as a direct replacement for the oem oil. Obviously this 'test' can't take into account what happens when the shock warms up in use, this is what i'll use as a start and if it's too thin i'll try blending some different weight oils to get something that works.

I've included a couple of pics of the shock partly stripped down, the main body is not accessable without cutting it open.
 

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I would guess since the fork oil is 10wt and the 5wt was a second off...10 wt might be the answer. The link I put up earlier the guy put in aft which generally runs between 10-15 wt depending on company. He commented on it being quite a bit firmer that before which would make sense........but if the heavy weight causes return issues the shock will pack going over bumpy stuff in a row.
 
Hey Guys,
This is an old thread but I'm in the middle of trying to upgrade/refill my shock.
So far I have it disassembled like in Shrekster's photos.
First question is what is the black bit laying in the front on pic 2. Looks like a rubber bumper that would go on the shaft but mine doesn't have one. Maybe that is why mine will just about break you neck when it bottoms out........
Second, I didn't drill a drain hole. I put a hose on the end of the shaft and worked it back and forth till all of the oil was pumped out the hollow shaft. Got about 75cc of old fluid. Now working on getting the oil back in little at a time while working out the air. Seems to be working, got about the same amount of fluid back in. Do you recall using about 75cc of fluid?
Third, and the tricky one is the rebound damper pin. It's placement seems to be critical and would depend on where the jam nut is placed on the saft to lock on the top mount. Then the rebound adj. screw providing fine tuning. Any body got a good starting point for that? And no I didn't mark or measure before I did the disassembly.
If I run the jam nut towrd the top of the shaft, the rebound pin actually will bottom out in the shock before the main piston. Which I think would bend it if the shock was to bottom at some point.
Forth point is that I measured about .400" difference in the point where the spring would bottom out (total distance of 11 coil diameters) and the shock would botton out (distance between top and bottom shock perches with shock fully bottomed). So I was thinking of adding a spacer for the spring to allow more preload. Anybody tried that one yet?
Or I could just by a new shock........
Enough of my rambeling. Any advice woulb be appreciated.
Bent Mt Dave
 
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