1975 Fork Oil Replacement

[brueschj]

Hi All,

I'm replacing the oil in my 1975 GT-750. I usually do this in conjunction with a fork dismantle but decided to try and keep the front end together this time since nothing else has to be done up there. Anyway I have no experience doing just an oil replacement.

The owner's manual shows the top fitting to be a cap with a hex head to accommodate a wrench. The manual says to drain the forks from the bottom screw (messy!) and then refit the screw and top it up with 5.3 Oz from the top. However, my bike actually has a rubber plug that lifts out to reveal a circlip that retains a steel plug in the top of the upper tube, which is easy enough to remove but then I wonder if the spring, etc. will emerge when I do so. Also the handlebar might be in the way of the plug coming completely out. Has anyone actually replaced fork oil this way on the 1975 model? Will I have my hands full of spring-loaded parts when I remove the circlip? And then do I just pour the oil in and refit the plug and clip?

Thinking I'll use 10W30 oil like the book says, or ATF. Any reason to spend a lot of money on special fork oil? (I have a bottle of 20W PJ1 fork oil that I was given years ago, but that may be too thick for general use).

Thanks!

[PaulD738]

It's an easy enough job to do made easier with the circlip type of fork tops. First job to do is remove the drain plug (I do one at a time to save having oil everywhere) and pump the forks until the forks are empty. Repeat for tother side, leave the drain plugs out for another 15 mins with the bike on the main stand just to make sure it's all out. Replace drain plugs and then with the bike still on the main stand get a suitable sized weight and put it on the rear of the seat to take the weight off the front end (wife, girlfriend, boyfriend etc is useful for this) then remove circlips being careful just in case there is still a little preload on the springs. Top up with fresh oil to required level, I use a big vets syringe for this and then Bobs a minion her jobs done.

[brueschj]

Thanks Paul - should be able to forego the weight since I presently have the front wheel off for a new tire. Hope I can get the plugs out without removing the handlebar. You didn't say so but I presume the plugs under the circlip have to come completely out in order to pour the oil in.

[PaulD738]

Yes, there will be an "O" ring around the plug. You may have to put a bit of weight on the leg to get it to come out but not enough to make it go into orbit a rag wrapped around the top of the fork will stop any mishaps. If the oil in the leg is very dirty/contaminated you can flush the leg out with parrafin before you fill with fresh oil. Just pour some in the leg, reaplace the top and bounce up and down a couple of dozen times then drain it all out, et voila clean internals
The syringe method of filling is very good by the way, accurate and no mess either. Once you have bought one you will find dozens of uses and you will wonder how you managed without one.