Possible front fork issues

[lonerider41life]

Hello.
I started riding my recently bought motorcycle. One of the possible problems I noticed was the rigidity of the front fork. The fork stroke seems a bit small to me, about 80mm, it bends and comes back hard. When driving on the road, if there are small unevenness, the handlebars vibrate as if the suspension were rigid-fixed. I don't know the history of the suspension service. When braking, there is a slight forward bending and return. I'm thinking of disassembling and cleaning it. I'm curious if I can put ATF oil in the shock absorbers. On other Honda models (VT500E and VF750S) that I had previously, I used ATF oil (Dexron2), with very satisfactory results. You have experience with such an oil in the fork? I am 1.78m tall and 84kg in weight. Thank you.

 

[CYYJ]

Hello, and welcome to the forum community.

There are a lot of really detailed and informative posts about ST 1100 suspension service here in our forum, in a sub-forum called ST 1100 Suspension. There might also be a few exceptionally good discussions about ST 1100 suspension in the sub-forum called ST 1100 Articles, which is the library where the most useful and very best posts get stored for future reference.

Have a browse through there (make a coffee first!) and see what you find.

As for using transmission fluid - the specified fluid, which is Honda fork fluid, is not that expensive, I think it would probably be safer to use a fluid specifically intended for motorcycle forks.

I was riding my ST 1100 in Northern Romania a couple of years ago, near Cluj Napoca - wonderful country you live in, great people, great food, great riding.

Michael

PS: Be aware that there is an anti-dive mechanism on (some? all?) ST 1100 model front forks - that mechanism is a bit complex to service, and may need some replacement parts, so do quite a bit of reading about it before you start disassembly.

 

[red one]

Hello.
I started riding my recently bought motorcycle. One of the possible problems I noticed was the rigidity of the front fork. The fork stroke seems a bit small to me, about 80mm, it bends and comes back hard. When driving on the road, if there are small unevenness, the handlebars vibrate as if the suspension were rigid-fixed. I don't know the history of the suspension service. When braking, there is a slight forward bending and return. I'm thinking of disassembling and cleaning it. I'm curious if I can put ATF oil in the shock absorbers. On other Honda models (VT500E and VF750S) that I had previously, I used ATF oil (Dexron2), with very satisfactory results. You have experience with such an oil in the fork? I am 1.78m tall and 84kg in weight. Thank you.

I remember mine did that probably at the 35K mile mark. Had it drained and the fork oil was black so it was probably shot. I put in the 10 weight Honda fork oil and it seemed better. I wonder though on a high mileage bike how much sag have developed in the springs? If oil change don't do it you may need to go further. I think someone else mentioned the anti dive check that out too.

 

[Larry Fine]

I wonder though on a high mileage bike how much sag have developed in the springs? If oil change don't do it you may need to go further.

God point. when I rebuilt the fork on my '96 Nighthawk 750, I checked the spring lengths. They matched and were about 1/4" longer than spec, so I put them back in. I added about 1/4" more oil than spec'ed for sightly stiffer compression.

 

[lonerider41life]

PS: Be aware that there is an anti-dive mechanism on (some? all?) ST 1100 model front forks - that mechanism is a bit complex to service, and may need some replacement parts, so do quite a bit of reading about it before you start disassembly.

I forgot to say, it is a CBS-ABS-TCS model and yes, it have anti-dive mechanism. Today I removed both fork "legs". The one on the left side is soft, it compresses easily and decompresses quickly. The one on the right side, which also has an anti-dive system, is strong as a wooden stick, it compresses very hard, a little and it decompresses hard.
I hope to be able to disassemble them tomorrow or just drain them, clean and change the oil.

 

[CYYJ]

Have a look at this post: ST1300 Front Fork Overhaul: An Illustrated Bibliography. Although it describes how to do the work on a 1300, not an 1100, there might be some good information in there for you about how to take things apart and how to put them back together again.

Michael

 

[ChriSTian_64]

I think one possible cause, for a stiff front suspension, is if it was maintained before, and too much oil was put back in, and... the weight of the oil is important also.

If it was never maintained before... I heard that the small internal orifices can get clogged with dark thicker oil.

In any case, it could just help to flush the oil, inspect the inside cleaness, and put new oil, with the correct weight and quantity.

Me, I have the opposite problem. I feel that it is too soft. So, it is also on my list of things to do. Probably in a month, when it will get almost too hot to ride

 

[TerryS]

The description of the behaviour of the right leg sounds like it has overly thick oil in it, and possibly too much. I agree that you should disassemble the leg and clean it fully, as in removing the spring and any spacer, and unbolting the damper rod from the bottom, but not necessarily separating the upper and lower leg; you will easily be able to feel if there is any unusual binding in the seals and bushes with the inner parts removed. If the bushes are binding or loose then these should also be replaced.

I would then start with the recommended weight (10W) and depth of oil (140mm right, 136mm left, measured from the top, fully compressed springs out) from the manual. The two legs are mechanically quite different, with cartridge damper on the left and an old-style damper rod to the right with the TRAC system. If the TRAC system has an adjuster I would suggest setting that to the minimum.

Take your time when refitting the forks to make sure they are in their best relaxed position for least binding. Leave the axle clamps loose and give the forks a good bounce to allow the left leg to find the best position on the axle before you tighten things up.

 

[lonerider41life]

Thank you, all, for the suggestions.
In this morning I dismantled both suspensions and drained the oil from them. I have no ideea if someone or sometime do a fork service. It look like never been worked there. The oil was dark gray on both "legs". The one on the right was darker than the one on the left and seemed to have deposits. I put ATF twice in both for rinsing / cleaning, I shook them and compressed / decompressed several times and left them to drain out for several hours. I did not disassemble the interior parts and will do this in winter (a complete overhaul). Unfortunately, I was unable to disassemble and verify the TRAC or anti-dive system. It seems that someone tried to remove it before and broke allen screw head from two of them, so it remained unverified. I don't know if there is a way to adjust it, it's a round piece at the bottom, but I didn't see any way to move it. After reassembling the suspensions, now they work differently than they were before the disassembly, they don't cling, they don't block, they can compress them relatively hard and they come back the same. I put Motul 10W fork oil in both suspensions (it is very common fork oil that I can find here). I cannot do a test for ride behavior and road holding today, but I will do it tomorrow after change the motor and filter oil.