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Discussion Starter · #1 ·
So I'm looking for cheap mods for my suspension and have decided that once I set the sag this weekend if I still think the suspension is to soft for my weight of 240 I'm going to change the front fork oil.

what I need to know is if I have the general idea of it down.

Pull the forks, loosening the top caps first. Once the forks are free take off the top caps and any loose parts, turn the forks over and drain all the oil. add the stock spec amount of oil plus a few mls (how much?) work the forks up and down to get all the air out. Replace any loose parts as they came out. Put top caps on then refit the forks on the bike. Torque the caps down, refit the front end and go ride.

Sound about right?

Also I was thinking of using a 20w oil, for my weight with out adding any valves would this be over kill?

Also who sells rear springs and how much do they usually go for?
thanks
tom
 

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You'll need to pump the forks a few times (10) to pump all the old oil out of the cartridges and then pump again on refill to get the new oil into them. After that, you can set the level.

I haven't done mine yet but I like the dipstick method for setting the oil level. Forks fully compressed with springs in place, measure the oil level from the top of the tube. Now you can add, or subtract with a turkey baster, oil to suit. I won't know dimensions or their effect till I start to play with mine.

BTW, heavier oil isn't going to help if you don't have enough spring. As I recall from a previous post, you are um, substantial, get some fork springs of the right rate.

Traxxion Dynamics or Race Tech will happily sell you springs for front and rear. Changing the rear spring can require some special equipment, depends on the shock.
 

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I put 15wt oil in with 15mls more and I find it too firm. I am going to drain 15mls out next week. FWIW I am 90kg with a 50 kg pillion

IMO 20wt would be too much
 

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I tried this in another thread but got no response. Rather than drain the oil and add new, heavier oil plus some extra above the stock spec, is there any reason he shouldn't leave the stock oil in the forks and just add a few mls of even heavier oil? Is it worth an experiment? Anyone done this?
 

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G'day Tom, I just changed my fork oil on the weekend. It's pretty easy but I would be really careful about loosening the top caps, there's a fair bit of spring pressure under there and you need to keep the whole shebang weighted down while you are undoing it or things could go flying. You could also rip out the bottom thread on the top cap as its only soft aluminium. It's not hard just take it easy - use a ratchet and the correct socket for best results.

Also putting the cap back on is critical because it is very easy to strip the thread. (No I didn't stuff mine up).

Yes you need to do the pump thing to get all the old oil (and metal) out. (I think I need new bushes :D) And you need to pump it once you fill the tubes to get it to settle. The Haynes manual says I need 145mm from the top but I have put in 130mm both times I have done this with 15w oil. All on a 2000 Sprint. Results have been pretty reasonable but I would like to uprate the springs.

I'm about 80kg and although the 15w oil makes things a little harsh I'm too lazy change it, have had almost no scary moments and like what it has done to remedy some of the diving issue. I tried a new Sprint and didn't like the setup - too spongy on the shop setting they had.

I reckon 20w oil would about snap your wrists on a big bump. The spring thing is probably best with 15w oil. There are all sort of mods you could but you would probably find the simple things are fine unless you are a legend track day rider.

Also its pretty critical how you put the front end back together again - everything needs to be free to move as it should and well torqued - I would recommend a Haynes or a Clymer manual to be safe and sure, especially with the suspenders.
 

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Tom,

I've got a post somewhere on the site that describes the procedure in detail.

Do not use 20wgt oil. The oil is the damping effect, which damps the speed at which the fork slider moves, especially at small deflections. The spring is what keeps the bike 'suspended', and also decelerates the slider on compression, as it tries to get it back to where it was (the 'static' sag). 20w oil will give you a very 'harsh' front end.

Basically, you need a stiffer (or, 'higher rate') spring. Several outfits sell them. The choice of 'progressive rate' and 'straight rate' spring is up to you. RaceTech used to have a calculator on their site that would recommend spring rates for your bike with you on it. IIRC, they have not updated the Sprint in quite a while, but the bike has not changed a lot in the suspension and frame design.

Two things to add in the oil change procedure.

First, when you remove and install the cap, I found it very helpful to have one person hold the cap and press it down, while a second person lifts and spins the tube. It is a lot easier to control the cap that way. I hold the slider by clamping the upper brake caliper mount in a vise. Just be very careful that you have some room over the tube. You don't want to pinch yourself between the cap and a shelf or something.

Second, when you pour out the oil; after you pump the slider a couple of times, pour in about a half cup of clean mineral spirits. Pump that around real good, and pour it out. Repeat. Then set the tube upside down and fully collapsed in a plastic cup, where it can't fall over. It will drain while you take on the other fork tube.

And you definitely need a stiffer shock. Look at the other threads for options. A shortcoming at one end of the bike will make the other end less effective. So, fixing your forks will not fix the bike. It may in fact slow down your steering, since the forks will be 'stiffer', thus keeping the front of the bike higher. That will increase the rake, and slow your steering.

Oh, one last tip. Cover all that pretty paint work with a couple of shop towels or a soft blanket. It'd be a shame to drop a wrench or fork cap and ding the bodywork.
 

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tom,

You really need to go through the suspension threads.
There are a couple of simple guidelines.

1. The springs support the all up weight of the bike.

2. Valving and fluid control the support and spring action so the supporting springs won't act like a pogo stick.

Putting in a heavier weight oil will not change the static sag.

If your current springs will not support the all up weight properly, meaning you are running out of pre-load adjustment trying to get the sag set for a realistic amount, the springs need to be changed before anything else can be done.

Adding a heavier weight oil will not help matters and in fact will degrade and put you in the wrong direction.

My advice is to forget the oil and get it sprung properly first then twiddle with the valving.
 

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Discussion Starter · #9 ·
ok, so save the $ on oil and get the springs. If I do a rear spring then do I need to do work to the shock as well?

I guess a set of racetech springs are the next purchase.

Thanks guys
Tom
 

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+1 for Dolson

No amount of oil can fix a fork that is undersprung.

Heavier oil will make your increase your compression but no one ever mentions that it will also make your rebound slower as well (which is not usually desireable especially if you are under sprung).
 

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I guess a set of racetech springs are the next purchase.

Thanks guys
Tom
You could try Sonic Springs for your fork springs, they are great value and Rich provides great customer service. They also have a spring rate calculator on their website.

You can source the rear spring from an Eibach reseller in your area.
 

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On that note... anyone know any good spring people in Australia?
 

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Discussion Starter · #14 ·
So can I buy any coil spring that is the same size but correct spring rate and install it on the rear?

Gonna order some springs in 2 paydays so that i'm all set for the season.
 

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Discussion Starter · #16 ·
So Im having trouble trying to locate specs on the rear spring and a vendor for one. Does anyone know of where to look? And the approximate cost? RaceTech has a great spring rate calculator that spec'd out the rates front and rear.

Also I think I'm going to go with the sonic fork springs as they are much cheaper than RaceTechs. Anyone have a review on these?
 

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So can I buy any coil spring that is the same size but correct spring rate and install it on the rear?

Gonna order some springs in 2 paydays so that i'm all set for the season.


The rub is that you need to have a shop do the swap. Some M/C shops can do it. The tool required is a special type of shock compressor.

I had the stock spring swapped out on my OEM Showa for a 1000lb/in spring. A buddy saw a bunch of them for sale on eBay. Apparently there was a pallet load of Ohlins seconds for sale.

The stiffer spring has made a world of difference!

I think I still have the shock spring measurements at the office. I'll post them here tomorrow.
 

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Discussion Starter · #19 ·
So I miss spoke a bit. I can't find a site that has a spring rate calculator for the rear spring. Any one know what a 225-240 rider would need? I say 225 cause I'm in a weight loss competition and when I do that I usually lose around 15lbs for good.

also has anyone ran the hyperpro springs? I can get a rear spring for $120 and I can't complain about that.
Thanks
Tom
 

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So I miss spoke a bit. I can't find a site that has a spring rate calculator for the rear spring. Any one know what a 225-240 rider would need? I say 225 cause I'm in a weight loss competition and when I do that I usually lose around 15lbs for good.

also has anyone ran the hyperpro springs? I can get a rear spring for $120 and I can't complain about that.
Thanks
Tom
I think the best way is to talk to people from all of the companies you are considering ordering from, via phone or email. They'll be responsive, and if they aren't then take your money elsewhere.

As for hyperpro - at one point I was considering them, and there are a few older threads mentioning them. Opinions vary widely of course. But with regard to cost I've found in my own research that most shock springs run about the that same price.
 
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