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PostPosted: Wed Jul 16, 2014 10:41 am 
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To the on ramp

Joined: Tue Apr 30, 2013 9:28 am
Posts: 251
Location: Lebanon
Country: Lebanon
Bikes owned: gsx 750R, GPZ 750, GT380
Hi All
Is there anything i can do to firm them up? I recently put SAE40 regular oil in them which i intended to use to stop them leaking. In fact it worked but has this made them 'weaker;? Or is it all about the spring being knackered?
thanks for your advice
MJ


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PostPosted: Sat Jul 01, 2017 12:40 pm 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 771
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
I can't believe no-one has answered this one. At risk of being a tad slow to reply, I will give it a bash.
You mention the forks are leaking. So that is one problem that needs to be fixed.
Check the bushes are not worn in the fork leg, check the stanchions are not pitted on the seal area. Then replace the seals.
That will fix one problem, but...while you have it apart it might be worth sticking a set of progressive fork springs in. That should cover the other possible cause of saggy springs.
And the other option as you have already gathered is use a different thickness of fork oil. Make sure you have the correct amount in each leg.
If the front end is a little too soft for a heavy rider, it might be worth installing a set of adjustable caps with preload adjustment. I have got a set of these for my GT380 from ebay in Japan. Didn't cost a lot, but that was a year or two ago.
Oh and make sure your front tyre is pumped up to the correct pressure.

There now, I think that is most common problems covered.


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PostPosted: Sat Jul 01, 2017 5:25 pm 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3196
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Check the sag. Its how much the springs are compressed with you sitting on the bike.

Start with a convenient reference like the length of the fork boot, or distance between the dust seal & triple tree.
Measure the length with no load on the fork (on center stand if you have one).
Measure the length with you sitting on the bike & just balancing it with a foot.
Pump the forks a bit for both measurement to overcome fork friction & get a good reading.
The sag is the difference between the two measurements.

Total fork travel is 4.5” (I think). Ideal sag is 1/3 of the travel or 1.5”. Around 1 ~ 1.5" is good.
How much sag did you get?

Suzuki typically used fork springs that were stiffer than optimal and didn’t use much preload.
Then the springs collapsed a bit after 40 years, and you can end up with way too much sag.
If you have too much sag, you may be able to use a plastic or steel spacer to get the correct amount.

Cycle World had a good article about your forks:
http://www.ozebook.com/compendium/suzi/mags/EasyForkFixesYouCanDoAtHome.pdf

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Mon Jul 03, 2017 9:41 am 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 771
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
jabcb wrote:

Thats a great article. I wonder how changing to progressive springs would alter things. Will definitely try the rebound damping mod of brazing the hole up on my own bike


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PostPosted: Tue Jul 11, 2017 3:28 pm 
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AMA Superbike
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Joined: Tue Oct 14, 2008 6:47 pm
Posts: 1722
Location: Blythewood, SC, USA
The rebound mod works. I have it in my GT750. I also did the "increase the travel" mod.



Lane

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If you stroke it more than twice; you're playing with it.

Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........


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PostPosted: Thu Jul 20, 2017 12:28 pm 
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Road race school

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 771
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
I don't think I can do the "increase the travel mod" as you have to pop the forks up in the yokes and I think that will foul the ace bars. I have pre-load adjusters which are taller than the usual fork caps


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