'83 vf750f clutch issue when hot

Hiya. I have had this problem and posted on it before but thought another shot might shed some light...

When my bike heats up the clutch starts slipping and I end up stuck for about an hour somewhere until the bike cools down. The bike worked fine for a summer without this problem and then all of a sudden it started acting up. It had problems and would begin slipping after about 15 min when it was at its worst and then after I bled the clutch well with a pump it worked perfectly for about a week then started slipping again after about 15 min.

I flushed and filled the radiator, changed the oil, put in a new thermo sensor and fan switch, flushed the master and slave cylinders and cleared all the lines, put in a perfect clutch from a spare engine I have (14,000 miles on it) and bled the clutch with a bleeding pump. Nothing worked and it would slip after 15 min until I bled the clutch with the pump. After I bled it the bike ran like a champ for about a week then started slipping again. It runs perfectly until it heats up a little then it wont move at all. I can roll it without a problem while in gear with the lever out when it starts to slip.

Because the only thing that seems to have helped is bleeding the clutch with the pump, it makes me think that maybe I should rebuild the master and slave cylinder? Is it perhaps slowly sucking in air and causing the problem when it heats? I figure that maybe there is some air somewhere and the bubbles come together when it gets hot and that causes the slipping? I have no idea. Ideas?

 

are your torque specs right when re assembling?

 

yup, everything was put back together correctly and with the correct torque. I also had replaced the slave cylinder with the slave from the spare engine though I cannot gurantee that it didnt have some sort of problem. If the slave is removed and the lever applied the cylinder moves just fine and seems to not leak. I cannot hold the cylinder in with my hand either showing it has good pressure. Everything works like a dream until it heats up. I'm on vacation now but I will bleed the clutch system again when I return and see if that affords me another week. Oh, and I'm not losing any clutch fluid. Thanks for the reply :0)

 

mmm, dare I say this ones easy.
First, you did some excellent troubleshooting. Good job there.
Lets think about what happens when an engine heats up... forget the water, cause lets face it, its a totally separate system. not enough water, it overheats, whole nother issue right?

longer running engine = hotter temps = things expand. molecules of oil expand, metal expands, seals expand, pipes expand... etc etc.

Either your fluid is wrong, and it is not rated for your bikes heat. (double check it), I think mines a DOT4 only... very insistant about that. Using the wrong fluid could cause your fluid to boil. Since the master cylinder is a reservoir type, it has air in it, and the air can get into the fluid.
OR, your seals are warn, and or damaged. Expanding seals, especially at the secondary cylinder, because you have ID ad OD seals, can open up and allow air in.

Both cases can significantly reduce the pressure on your clutch rod, which could limit the clutch rod travel, and thus not allow your clutch plate to push past the springs, and engage your clutch.

I would replace all your seals, (relatively cheap), and while your at it, flush out the system and replace the fulid, (also relatively cheap).

If this doesnt work, then you need to look at your springs in the clutch basket to see if one of them is broken or expanding at a poor rate.

 

Have you changed oil

Hey

Just a tought have you put any cheap oil on the bike.I started to use oil from ELF special made for clutches and my clutch is much better.It is a long shot.And your DOT 4 fluid from the master to the slave doesn´t heat up but it right with Ghost that use right fluid and the I mean DO NOT USE DOT5 it has silcone in it then you are fucked then you need to change every seal.But check for air in the hose.So can it just be a bad clutch.

 

Yeah, it looks like doing a rebuild is the next step. The fluid is dot 4 and nice and clean. I switched to a synthetic blend oil to see if it would help cool the bike down because it is running a bit lean and thus hotter (need to rejet soon) and noticed no changes and I tried many different kinds. I have heard good and bad about the various types of oils but noticed no real differences in engine performace (heat or otherwise) or clutch function. The coolant system work was an effort to help keep the bike cooler as it was running hot even when it was functioning just fine (almost always maxed out on the temp gauge). I'll have my dear friend ebay help me out with finding a new set of seals within the next day or so. Thanks for the help and I'll provide an update on how it all works out. :0)

 

It's very simple problem with an even easier solution. You have a plugged return port in your master cylinder. Takes about 10 minutes to fix.

Linky: Clutch/PluggedReturnPort - SabMagFAQ

 

Hi Guys,

I'm just restoring a 1983 VF750FD (1,980 genuine miles) and after completing the cosmetic resoration with 100% genuine Honda Parts, turned to the mechanicals.

Literally every rubber seal, rubber mount and gasket was replaced because 28 years is way too long to rely on these parts remaining serviceable.

With the clutch friction plates just sitting there soaking in oil that surely must have seen time when it became very acidic, I decided to replace all the friction plates, steel plates and springs just to be on the safe side.

The condition of the friction plates after this period of time, even with the low miles
was a sorry sight with the cork material bubbled and just unserviceable.

A EBC Kevlar full kit was ordered in to solve the problem.

Maybe you clutch friction plates are in a poor state as well ??

Another point ... Honda Australia, Honda USA and EBC all recommended I stay with a 100% mineral oil and not use a synthetic based oil, again because of the clutch design.

Maybe this may give you further food for thought ?

Warren
Melbourne, Australia

 

I resolved this issue shortly after posting 2 years ago. I should have posted a follow up to confirm the fix. The issue was just as Mason had suspect; a clogged return. A needle and 5 min of my time and I haven't had an issue since. Best of luck.