Sagging front iso

Front ISP is sagging by about 2mm. Dave Taylor head steady and mk 3 rubbers/adjusters that are about 18months old/5000mile. Pretty sure I bought em from rgm but will have to confirm.
Is this the service life of these or am I doing something wrong?

Ugh, can't do anything wrong with the rubber cushions supporting, unless of course you grind em 1/2 narrowed like I do and love it. Iso's are well known to sag-set in the rear and some like me stick in extra doughnuts there, but front not expected to deform as much or fast. The rod links don't affect-cause this type isolastic issue at all. Oil tends to soften them while dry rot tends to stiffen them. There are a variety of compositions and stiffness's sold so maybe you got some weaker ones chemically or elastically. 2mm ain't much to bother the range of isolation motion and not uncommon after a time. They do take a sag set so many like me will just flip em over when ever inside the iso's. Kind of a compromise of soft to get lowest isolation and hard not to sag so much mountings bind and vibe. Personally I'd rather have saggy soft than hard/stiff sense, especially with some linkage helpers. Rider Patton has sutffs rear with 6 big cushions and still complained they sagged in a season or so to alter his rear rump link alignment, though no report it caused vibration.

If its hitting the larger ' bump stop ' / Limit Stop ones , youd get a stronger thumping vibe . So you could then rotate the Iso ones upside down ,
And It'd be 2 mm UP . :mrgreen:

The spring support of 850's might of been to help stifle the insidious sag of the cushions somewhat. I have big doubts that the smaller OD cushion ever come into play except road loads thru swing arm, like creek play or flying over pot holes or roots levers down on front mount while warmed up softer.

Ever seen one idleing at 500 rpm steve ? , Im figureing its bounceing of them there . And got a mean chunter at 2000 on smooth seal pulling up on the rear brake
which would load the front down , presumeably .

Alledgedly there were differant grades of Rubber , stock early & late , and Prod Racer . I dont think many realise what a essential element of the motorcycle they are . After all , the Iso Chassis MAKES it ' the Commando ' . Nothing else has got it .

Was common to boil rubber suspension bushes to HARDEN them , also they used to do some trick to harden the dirt track race tyres , which could lead to embrittlement & ' Chunking ' , - throwing bits of tread as the hardening couldnt always be got even .

Obviously harder ones would stiffen it , & could transmit more vibes . But the might not . Matching of frequencies and rubbers supposed to be self damping -
Such As B.M.C. Mini etc rubber cone suspension . The culpret could be ones made to fit to easilly , so theyre NOT in Compression ( radially ) Static .
Should be a bit of an act to get them in , unless you hold youre tounge right . If they slip in easily there going to be No Pre Tension .

AKIN to triming rear cush drive isolators at the rear sprocket . Here a chamfer at the outer , or better , have them half out when tounges engage
and theyll tow themselves in .IF you hold youre tounge right . :wink:

I've seen em down to 400 rpm and my 750's to and measured the front up/dn motion with and w/o blip ups, so sticking to my story I don't think engine crank sling is enough to touch the inner cushions unless road load added. I love the rubber isolastion even more than going fast and furious so I grind mine to almost peaks on the rim to get earlier isolation and deeper sense of nothing getting through. One can't tell much about isolastic behavior until good tires with good inflation and fr/rr air balancing. Since I've been back here last 3 yr we had a few other reports front iso's rather dramatically sagged too soon. So far as I can tell mine ain't sagged enough to detect anything but visual effects. But you know this un-tamed isolastic business is for the slow birds around breezie bends and there's another way around i ain't found any limits to so far and nil sense of any bike under me causing it, so another surreal Commando experience to me.

When I removed my gators to install my Hemmings adjusters, I was really surprised to see how much my front iso sagged, about 1/4", and this is with new (2 years) donuts. I installed the MK3 spring when I installed my home made Taglieri style head steady and I tightened up that spring nearly as far as it would go. Way past the recommended. But it did remove the low rpm vibrations, can't say it did anything for on the road, but it did bring up the sag to less than 1/8", it seemed to center the rear iso too. Now I've got the frame mounted center stand too, so that doesn't help.

I did invert my donuts when I installed the adjuster, and it didn't make a whit for the sagging.

Dave
69S

Dkt26 said:

Front ISP is sagging by about 2mm. Dave Taylor head steady and mk 3 rubbers/adjusters that are about 18months old/5000mile. Pretty sure I bought em from rgm but will have to confirm.
Is this the service life of these or am I doing something wrong?

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It is simply settling on the secondary bumpers inside.

That's the DT headsteady for ya. No vertical support.

I'm pretty sure you can get the DT with the spring.

Dave
69S

Hi Fellas,
Thanks for the input. I have the DT with the spring. it did dramatically improve handleing over the stock item. i had the beast set up like it was a train on rails prior to my "local expert" rebuiulding the engine. ever since then i have struggled to get it set up properly due to the reassemble approach the expert used.
i have picked up a set of turcite busshes for the front end to compliment the landsdowne kit as i am also having issues with front end so even though the isolatic is an isolated issue from the front forks suddenly turning to shit, i think i will totally go through the setup of the iso's and headsteady from scratch and see if i can make some gains.

its strange, since this rebuild ( which i will never let anyone do again) my "Marea" has struggled to handle as she once did.

Oh what to do with a problem like Marea!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

Bad handling sucks big time especially after ya know what it can be like.
I don't understand what-how mis-assembly could upset the handling and make Lansdowne forks disappointing. If not crashed it should go right back as prior but maybe for too open iso gaps, which I can't imagine you've over looked with cushions on your mind with this subject. First thing that come to my mind is the tires may of taken a set after sit up time or their front to back air balance is off. Try 32 rear 30 front for a base line if not already. I've had good forks go bad just sitting up so spring and stanchions rusted to restrict smooth motion till cleaned up.
I've run some pretty bad out of line rear wheels and skewed sideways head steady mount w/o any handling bother other than innate isolastics powering around lumpy windy bends.

hobot said:

Bad handling sucks big time especially after ya know what it can be like.
I don't understand what-how mis-assembly could upset the handling and make Lansdowne forks disappointing. If not crashed it should go right back as prior but maybe for too open iso gaps, which I can't imagine you've over looked with cushions on your mind with this subject. First thing that come to my mind is the tires may of taken a set after sit up time or their front to back air balance is off. Try 32 rear 30 front for a base line if not already. I've had good forks go bad just sitting up so spring and stanchions rusted to restrict smooth motion till cleaned up.
I've run some pretty bad out of line rear wheels and skewed sideways head steady mount w/o any handling bother other than innate isolastics powering around lumpy windy bends.

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Cheers Steve,
i too am absolutely miffed as to what has happened with regard the set up. i have even gone through and checked all my parts to ensure that the have not been "swapped" for others. The fact remains though that i gave em a bike that handled exceptionally well; i would often surprise fellas on new bikes in the mountains with the speed i would pull into undulating corners at, to a bike that wont track well, and to be honest feels like a honda Z50 monkey bike would out handle it.
i have lost cofidence with the "rebuilder". the final drive sprocket was fitted finger tight. Finger tight with the locking screww fitted beleive it or not!!!!!!!!!!!!!!!!
i discovered that little gem after about 700 miles during replacing some bushes in the gearbox that had been flogged out. Bit un-nerving knowing that i have been pushing the engine during break in beyond 70mph.
DKT

Might pay to back off the pinch bolts & check / reset the steering head , if the wrenches Bionic fingers were awol on assembly .

Are ' the Shakes ' about normal ? as was . Are there any vibes transmitted indicateing tight / missaligned mountings . ?

Thats as serious as a heart attack DKT. I don't think the finger tight counter sprocket is much an issue as ain't much in any side loads but still an alert to what else might be too loose. Don't really sound like forks at this point unless they don't swing free, which i'd think ya'd noticed. Same parts is good finding. Check headsteady and iso gap clearance - though bet ya did too. I was rather shocked how much more secure stable Trixie Combat was on lumpy turns after using up the hard cast off break in tires then putting on merely decade old nicer tires and now with luxury of new tires she's not sports bike teasing but fun enough for me on an untamed Commando. Loose spokes? Shock mount missing? I've had too slack primary chain flapping to tug on too slack drive train parts for annoying to scary somethmes straight some times leaning. That was pure chance tugging on chain to notice the same rhythm scaring me. So I suggest ya send me the old tires for cheap as next logical step.

Cheers. I didn't think of spokes. I'll have a looksie at the suggestions as I re-fit everything and report back.
Cheers guys
Dkt