Topic: GL1000 front end rebuilt for a CB750 K6

[Clembig]

Hello guys,

Pretty stocked to be a new comer in the SOHC community, thanks in advance for having me !

I have a little challenge i would need advise on.
I recently bought a CB750 K6 that i am working on. This guy is equipped with a GL1000 double calipers front end.
Let me explain my problem, this fork is straight as wood, driving this bike is like doing mountaineering bicycle with a race road bike.
I am planning on removing them from the bike, opening them, purging them, inspecting the spy seals (that look like new from the outside, most likely rebuilt but not till the functioning state) and rebuilding them so they spring.
I took a look at the springs in there already and they are way shorter than the initial lenght of the GL1000 ones, the previous owner (or his mechanic) added stainless spacers about an inch long to compensate, so it raises the bike, but do not improve the compression at all.

I know that the GL1000 was way heavier than the CB750 K6 and i am not a big guy either (160-165 lbs) so here is my dilemma, should i put progressive springs of a CB750 with the right spacers and having the tubes sticking up a bit more from my T clamp (not looking for a custom pair of tubes or springs, not the budget, i would like a stock solution) in that GL1000 front end, or should i go with the GL1000 progressive springs ?
The outer diameter of the CB750 progressive are 25 mm when the ones for the GL1000 are 28 mm, The length can be compensated with spacers, but what about the diameter ? does it needs to ?

thanks in advance for your answers guys

[calj737]

Spacers create “preload” against the damping potential of the springs. Might be easiest to service them (fluid and air purge) and reduce the length of the spacers or remove them entirely) and ride to determine their suitability before changing anything else.

What you have may work well once adjusted and tuned for you. This is the best budget value.

[Clembig]

Hi calj737,

I understand your point, but i checked the springs in my tubes, they were definitely the right size and the right model i think, but they are already 0.6'' shorter that the gl1000 stock ones. So they must have been good at some point, but not anymore. The overall compression range of it is so affected that i am willing to change them.

i am just in between the CB750 ones and the GL1000 ones and not sure about which ones i should go with regarding the weight and dimension factors

[Alan F.]

Spacers create “preload” against the damping potential of the springs. Might be easiest to service them (fluid and air purge) and reduce the length of the spacers or remove them entirely) and ride to determine their suitability before changing anything else.

What you have may work well once adjusted and tuned for you. This is the best budget value.

This is sound advice, choose one set of springs or the other and go for it. Please report back with your experience including the length of the springs you used, the length of any preload spacers you used, and what oil you chose including which brand. Good luck, sounds like you've got this.

[calj737]

I would choose to use GL springs because the tubes you have are best suited for them. Changing the weight of the fork oil has a massive effect on damping. Start with a 5 weight fork oil. If that’s too soft, move to 7.5 weight. But use legitimate fork oil, not motor oil as some do. It makes a noticeable difference in the performance of the suspension.

[newday777]

If you don't have the budget to get new springs, stay with the GL springs and make spacers to bring the length even with the top of the tube threads. Make the 2 springs and spacers to end up the same total measurement of each other, spring and spacer total length, so each side have equal total length giving you a balanced ride.
If you can afford to get new springs, get Racetech straight wound springs rated for your weight, for the GL tubes(far better ride than progressive springs, the harshness you explained!).

[Clembig]

@calj737, thanks so much for the tips, will move forward with this, it was the direction I was looking for !

@newday777, going through the internet and feedbacks from couple of mechanics friends, I had understood that the progressive technology was the best on the market, is racetech way better ? I hear different stories but racetech is more expensive for sure

I can afford new ones, the existing ones were not progressive,and completely wear down (-1,5 cm compared tk stock)

Thanks for your feedbacks guys, Really appreciated