750 rear shock mounts, top bottom not accurate.

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750 rear shock mounts, top bottom not accurate.

Postby Freddy » 01 Mar 2019, 09:01

Refereed to this in another thread, but thought it worth sticking in one of its own.

Basically I've been struggling ever since I bought the Zephyr 750 to get a decent sporty but not harsh ride out of the rear. Started with rebuilding the OEM shocks, twice actually, no cigar. Next bought top of the line Wilbers. Still couldn't get them right over a number of years, rebuilding several times, with any number of valve changes and modifications. Decided to bin the Wilbers and try Nitron R3's.

Still couldn't get them how I wanted. You either had to accept a harsh ride, or mushy soft, nothing in between. Well last night after what 6 years of trying and a few thousand dollars latter I finally found the problem. Total of 60 cents to fix ......

The bottom swing-arm shock mounts are a different width to the top mounts posts welded to the frame. The top mounts are narrower than the bottom, 3-4 mm different on each side. The rubber eyelets in the top and bottom shock mounts allow this relatively small inaccuracy to be taken up when fitting the shocks without difficulty. BUT as the shocks are not dead parallel, tapering in at the top, excessive friction (stiction) is present. When the top retaining bolts were lossened off and the shock bumped out to sit dead parallel the amount of sticking in the suspension reduced by half.

Again the alignment was checked by removing each shock, one at a time, bolting it up in just the swingarm bracket with the top free of its mount. Then in it natural position swung forward to rest against the top mount post. Each side the shock sat 3-4 mm clear of the 'bottom' of the mounting post, confirming that's the amount they are out. As it was the exact same measurement both sides, this mean it wasn't due to twist or wear in the swingarm. The swingarm is flush with the concentric chain adjusters. The bottom shock mount brackets on the swingarm are simply wider than the top mounts on the frame.

Spaced the top shocks out 3mm each side using a thick gal washers with a 14mm hole that I found in the hardware shop (cost 30 cents each), MASSIVE difference. 6mm out of parallel over the full length of the shocks might not sound much, but it is. They now work like you expect top line shocks to work, instead of being 'strangled' by friction. Adjusting them in now easy and intuitive.

I can't imaging my Zephyr is unique in having this manufacturing inaccuracy in the rear suspension. If as I suspect they are all like this, this simple alignment exercise should improve the performance of all rear shocks.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby David Richard » 01 Mar 2019, 21:03

hi freddy I have read this with great interest i still have the oe shocks on mine ,so probably past there best but when i get the bike out i will try this this ,cheers david
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Re: 750 rear shock mounts, top bottom not accurate.

Postby gazzz » 01 Mar 2019, 21:59

Interesting information, thank you Freddy. I bought my Zephyr 750 with Ohlins shocks already installed and they works perfect.

However, I used original Zephyr 750 and 550 shocks in my cafe-racer projects and found them quite good once rebuilt and with gas reservoirs refilled to original 8bar of pressure.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby Freddy » 01 Mar 2019, 23:04

gazzz wrote:Interesting information, thank you Freddy. I bought my Zephyr 750 with Ohlins shocks already installed and they works perfect.

However, I used original Zephyr 750 and 550 shocks in my cafe-racer projects and found them quite good once rebuilt and with gas reservoirs refilled to original 8bar of pressure.


Question: Would they work even better if stiction (static friction) can be reduced? The answer for any suspension, any bike, front or back, is yes. Any reduction in stiction, even the most tiny amount, improves performance significantly.

The only uncertainty is if you have stiction that can be reduced. And the way to know that is measure it. I now have 4mm in the rear, think its about 6mm in the front (fork seal are sticky, even the SKF low friction ones). Prior to aligning the shocks properly I had 9 mm of stiction in the rear suspension when measuring free sag (just weight of bike alone). After spending the effort to get the rear shocks as parallel as I could this was instantly reduced to 4 mm.

Five millimeters of stiction is very significant. When I first fitted the front fork brace to my 750 (anyone interested in improving handling should do this, its about the cheapest best improvement to handling going)) it introduced about extra 5mm of stiction to the front end. The increased harshness in ride over corrugations was immediately noticeable. It was easily corrected. It was due to one of the fork leg clamp faces not sitting absolutely inline with the corresponding face on the opposite leg clamp. When you tightened up the interlinking plate, this perhaps 0.05 mm deviation created an every so slight kink in the fork alignment. You could feel it immediately in the ride. If someone does fit one, just make sure the interlinking plate sits dead flat on the full clamp faces before doing up the screws. That's the critical alignment you want, not just how the clamps look on each individual leg.

Measure stiction, both front and back. Its dead easy. Rather than write a long explanation of how to measure stiction, look up the 'Race Tech' method of setting sag. It involves taking two measurements (by a slightly different approach). The average between these two measurement is what is used as the sag number, and the difference between them is the amount of stiction present in the suspension. In a perfect world of no friction the two numbers would be identical. All suspensions will have some stiction, but the less the better.

P.S. I though the OEM shocks were total junk, even when rebuilt, and spending money on getting them rebuilt would be better spent in putting it towards buying a set of top line shocks e.g Wilbers, Nitron, etc. Also after having shocks with independent high/low compression damping adjustment I would never consider buying a shock/s without this feature again.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby gazzz » 01 Mar 2019, 23:48

Question: Would they work even better if stiction (static friction) can be reduced?


Sure, I'll check positioning right as soon as weather became slightly more rideable, it's still cold here in Ukraine.

P.S. I though the OEM shocks were total junk, even when rebuilt, and spending money on getting them rebuilt would be better spent in putting it towards buying a set of top line shocks e.g Wilbers, Nitron, etc. Also after having shocks with independent high/low compression damping adjustment I would never consider buying a shock/s without this feature again.


Couldn't agree with statement about stock shocks are junk, but sure, shocks with 1000$ price will work better.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby Freddy » 01 Mar 2019, 23:59

In this type of discussion, always think the often used quote from Paul Thede, owner of Rae Tech in the USA, is pretty relevant .....

"The best you've ridden is the best you know!"

Applies to all of us.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby Freddy » 02 Mar 2019, 00:12

gazzz wrote:Couldn't agree with statement about stock shocks are junk, but sure, shocks with 1000$ price will work better.


Just the fact the OEM rear shocks use linear springs is alone enough to qualify them as not worth spending money on. I've experimented with several sets of different weight linear springs on $2000 shocks, and they do not work. No single rate can give the desired ride 'quality', yet at the same time the 'support' in hard cornering. You either have to take one or the other.

There is a very good reason virtually all retro twin shock race bikes there days use dual-rate springs. Even more important on a road bike due to road conditions being worse that a track. Cost of new dual-rate springs $150?, to rebuild the OEM shocks $250? total $400. And what have you got a shock with 4 positions for rebound damping and the same for compression. A poor setting (excessively harsh/wallow) on a good shock with 24 clicks can be as little as 1 click either side of the optimum.

Better of putting that money toward a pair of decent shocks.
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Re: 750 rear shock mounts, top bottom not accurate.

Postby gazzz » 02 Mar 2019, 10:06

Yep, the standing alone

"The best you've ridden is the best you know!"


is working all right. But in combination with calling things junk I could easily imagine the guy who might say that whole Zephyr is junk don't worth any suspension upgrade. However, we here case we like this bikes.

Freddy, I absolutely agree that performance shocks with springs picked to correspond bike and rider weight will be much better.

But Zephyr shocks (and other kayaba shocks of similar build), even counting their limited adjustments still are fully adjustable and hell yes, retro looking. They works well, at least in my opinion and on Ukrainian roads, that is so to say are far from perfect. This year snow came off and looks like it took good part of paving from the roads with it.

P.S. Rebuilt is not that pricey if you do the work on your own. Could you, please, indicate a source of dual rate springs that fit Zephyr shocks?
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Re: 750 rear shock mounts, top bottom not accurate.

Postby Freddy » 02 Mar 2019, 10:26

gazzz wrote: I could easily imagine the guy who might say that whole Zephyr is junk don't worth any suspension upgrade.

Could you, please, indicate a source of dual rate springs that fit Zephyr shocks?


And the guy who says a whole Zephyr is junk, is entitled to his opinion, but basically doesn't know what he's talking about. A couple days ago I chased a new Kawasaki Z900RS Cafe through one of our local 'public race tracks'. Now while neither of us were going 100% as there has been a heavy police blitz on the area, neither was he mucking around. He certainly piked up the pace when a couple very expensive Italian cars joined in the 'procession'. It was a good gauge of an improved Zephyr against a brand new bike of similar style. Bottom line: he had nothing on the Zephry, nothing. Neither in acceleration or corner speed.

Back on topic, its a pity I didn't take a couple pictures BEFORE making the fix. Here's a picture of the lower shock mount after the fix (a 3 mm spacer on the top mount). Note how the shock 'banjo' now fits dead parallel on the 'knuckle'. Prior to the 3 mm spacer being added to the top it tapered across noticeably at the top. It wasn't noticeable on the Wilbers or OEM shock due to the nature of the low shock mount style they use.

Image

Image

Regarding dual rate springs to fit an OEM Zephyr shock, I'd probably give Nitron or one of their dealers a call. Their springs seem reasonably priced. Wilbers are VERY expensive, that I know. Race Tech also worth a try.
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