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Fork springs and damping #794610 01/02/20 4:47 am
Joined: Oct 2008
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DavidP Online Content OP
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I now have the 73-4 Triumph disc front end on the Trident. This used to be on my A65.
A couple of years ago I installed Progressive springs and replaced the O rings in the dampers with something from Madigan. I've always used F-type ATF in the forks, 190cc on the BSA, 230cc on the Trident.
Problem now is that I seem to be getting the fork to top out over bumps. I haven't noticed any dive, but I haven't had to brake really hard yet.
In any case, I notice that Progressive list no springs for the T150 on their site. Ikon lists them, but specifies 37mm x 27mm spacers in this application. The Progressive springs came with a section of PVC, but no instructions or suggestions for lengths to which to cut it.
Is this a spring issue, a damping issue, or both?
Should I add some spacers and go with maybe 15w fork oil?
Are the Ikons better than Progressive, they're about the same price.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
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Re: Fork springs and damping [Re: DavidP] #794617 01/02/20 10:41 am
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kommando Offline
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If you are topping out then it could be as simple as your static ride height is wrong rather than the spring rate is wrong. Set your static ride height with a normal load including rider to be 1/6th of the total travel, if its less than that now then that explains the issue.

You always start with static ride height, also called static sag, use spacers to set the height as changing the length of the spring changes the spring rate.

If its still topping out with the correct ride height then you move onto damping and springs but find out more about the rest of its action ie dive on braking and effect of hitting bumps before deciding what to do and only make one change at a time..

Re: Fork springs and damping [Re: DavidP] #794619 01/02/20 1:57 pm
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bodine031 Online Content
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DP I have a T-160 frt/end on my 69 T-150. Race Tech spring kit FRSP- S2643 & Belray 15wt oil. Rear shocks are from my 03 Bonny. Magura hand brake, Dot 5 fluid, SS line & EBC HH pads, stock rotor just drilled. combo on it over 10 yrs. I did not record the length of PVC . Race -Tech web site has lots of info and a tech line. This bike is a mutt but does handle and stop real good. Still running 19" wheels both ends. Ever get the carbs working??

Re: Fork springs and damping [Re: DavidP] #794782 01/04/20 6:43 pm
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DavidP Online Content OP
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I checked the sag as well as I could just measuring the distance between the bottom clamp and the top of the boot.
Static sag = 19mm
Total sag, laden = 25.4mm
I can't find a spec for total travel on these forks. The difference between wheel in the air to fully compressed just bouncing the forks with the front brake on is about 52mm.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: Fork springs and damping [Re: DavidP] #794783 01/04/20 6:51 pm
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kommando Offline
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It should be in the 5" range going on pre OIF forks.

Re: Fork springs and damping [Re: DavidP] #794821 01/05/20 4:58 am
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DavidP Online Content OP
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Thanks,
New seals, gaiters, and 15w oil on the way. We'll see what difference that makes.
Probably check those damper seals while I have the tubes off.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: Fork springs and damping [Re: DavidP] #795424 01/12/20 5:13 am
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DavidP Online Content OP
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While rebuilding the forks which will go on the A65 I took the opportunity to compare springs.
The springs which came out of the Trident's original forks are about 3/4" longer than those which were in the A65.
I'll just put those back in the Trident forks and put the Progressives back on the BSA.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: Fork springs and damping [Re: DavidP] #796863 01/29/20 1:32 am
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DavidP Online Content OP
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I rode my regular 12-mile loop today. Original springs, 230cc Bel Ray 15w fork oil and one notch more preload at the rear. Handles much better with minimal dive during braking.
Crudely measured front sag = 32mm.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"

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