GT380J Fork Spring Size?

[JFISHSOLEVIBE]

Sorry if this post is redundant guys! Did my best to search the forum before posting. I'm looking to replace my tired fork springs with a modern equivalent. It's a 1972... Any ideas? The fronts gotten really mushy and I think it's time to replace them as the bikes about to hit 17k!

Also gonna pick up a modern set of year shocks to replace the old originals as well. If I recall these were 11" stock. Would I be safe to go up to 12"? Wouldn't mind raising the rear up a tad.

Thanks as always!

[pearljam724]

Raising the front and the rear both are extremely good things to consider. You can do both aftermarket rear piggybacks and dropping the front forks through the triple trees anywhere from 1/4 to a half of an inch. On the fork springs, you need to be aware of your specific weight. Depending on your specific weight, how and where you ride most should dictate what you want to do with shocks and forks. The fork springs on all of these bikes are pretty soft for anyone over 150 -180 pds. The heavier you are, the stiffer spring you will need. If you like to ride in a lot of twisty turns at higher speeds. Heavier springs. Raising both ends of the bike will be more suitable to twisty rides. As a result of it sitting higher, it will turn in with less resistance in motion. But, the sag of your front and back suspension must be proper to those new components and you specific weight, riding preferences, road conditions, etc. The correct thing to do is install aftermarket springs designed and sold for your weight. But, you can nearly accomplish the same principle by putting a heavier wt motor oil in your forks. I have 20 wt in mine and love how it handles now. Not to say that motor oil wt is suitable for your needs or anyone else. That produces pretty stiff forks. But, that's what accommodates me, how and where I ride.

[JFISHSOLEVIBE]

Thanks man! I'm with ya. I know my desired spring rate etc...

Specifically what I'm seeking out is the diameter and length recommendations for springs in that fork. I've measured the spring diameter but I have no idea what the length should be considering I'm not sure on how much these old ones have squished.

Anyone have the data on the GT380J fork spring diameter and length?

Thanks Pearl!

[pearljam724]

Thanks man! I'm with ya. I know my desired spring rate etc...

Specifically what I'm seeking out is the diameter and length recommendations for springs in that fork. I've measured the spring diameter but I have no idea what the length should be considering I'm not sure on how much these old ones have squished.

Anyone have the data on the GT380J fork spring diameter and length?

Thanks Pearl!

You're welcome. But, unless you intend to put in the same soft springs. The new springs, will be longer or shorter depending on your weight when you buy them. Progressive springs for example will all be different lengths and diameter. According to the weight they are designed for. Why would you want to know the oem length and diameter, if they are going to be just as soft as the ones you have now ? Because they will be.

[JFISHSOLEVIBE]

Sorry if I am being confusing here... And correct me if I am wrong, but the stanchion tubes will only contain a spring that is so large (or small). For instance let's say the fork tube diameter is 3cm, you could not and would not attempt to use a spring larger or smaller than that. Larger would not fit and smaller would bounce around inside the tube.

As I am aware, spring rate is not determined by the length of a spring, so length in this case is not arbitrary either, as you would not want to use a much longer, or much shorter spring if the stanchions are for example, 30cm in length.

I am looking for the baseline measurements of the original springs in order to shop for my desired spring rate in the proper sized spring. Thanks for your responses, and sorry if I was confusing. Ideally I would like to obtain the same size springs for my fork as came in the bike, in the proper spring rate for my weight. They are soft and springy because they are worn out.

[pearljam724]

Your best bet is to contact a progressive spring distributor. They should absolutely know what the oem spring length is. Yes, springs can become weak over time when put to a lot of use. But, my opinion is that is totally over rated on a motorcycle of any age. A lot of people will mention that springs are 30 to 40 years old on a motorcycle that hasn't seen a lot of constant abuse compared to a car for example. I guarantee, if you install a new spring of the same rate in the same bike. There will be next to no difference in the spring rate. Regardless, of age. Just don't want to see you disappointed in money spent comparing how soft the old springs were. Compared to the new springs of the same rate. That's all. Rear shocks are different, because of enclosed seals. Absolutely, those should be replaced due to their age. I have original fork springs in 2 of the 4 bikes I own. All of those bikes are a minimum of 27 years old. How soft the springs are, has nothing to do with their age. They were soft when they were installed. Modern bike springs are also too soft for a lot of people. Unless you are lucky and fall into the category of the person's weight they were designed for. And your riding characteristics are the same.

[JFISHSOLEVIBE]

Thanks for the reply. Im with you on the softness preference thing, however, just as clutch springs wear out overtime, so do suspension springs. I've been running 15w oil in there for almost 2 years, as I do prefer a stiffer dampening. However that said, a heavier oil is not the fix. The rebound I experience in my front end is soft and springy. Having personally ridden this bike for 10,000 of its miles, I have noticed a difference in handling over the past 2000 or so. Having changed the fork oil regularly, and noting that the seals do not seap or leak, tired springs is all I can figure. Now, again I could be completely off my mark here but I do expect that with a proper spring rate on new Racetechs for instance that I would greatly improve the performance of this front end. Next to emulators I don't suspect there is much more I can do. I ended up just using my own measurements on the springs, so I will let you know what I hear from Racetech on Monday.

Thanks again!

[pearljam724]

If that's the case, than I completely understand. Good luck and be sure to give us some feedback on your purchase. How much do you weigh, if you don't mind telling ?

[JFISHSOLEVIBE]

Yep! I'll definitely report back on the results. Think it'll be a nice change (I hope)!

I'm about 180 with my boots and jacket on.