Clutch problem

A few weeks ago I took my 1988 VF750 Magna to a Honda dealer's repairshop. I know the foreman well and asked him to help me because clutch fluid was leaking from the clutch handle out of the reservoir, or rather out of the clutch pump housing, and I had to top up the fluid every 3 weeks or so. He told me that the clutch piston that goes in the clutch pump right there at the handle was worn and had to be replaced. I tried to buy a new one but no luck in my neighborhood. He then found a piston from a Honda CBR 250 and said it was the same size as the one that I needed and put it in place of the old one. Very good and not a drop leaking. However, there was another and serious problem that started after this. As the engine gets up to normal running temperature it seems that the clutch does not work and I have to pump the handle several times in order to get it to work. I want to add it's hot weather here - around 100 Fahrenheit - and the engine can get pretty hot. It seems that in a cold state, things work fine but in the hot weather somehow the clutch won't work normally. I want to add that I have had some fan problems and a mechanic here removed the water temperature sensor and installed a manual switch becuase the riders of older bikes want to control the fan manually, as they need it on most of the time and don't trust the sensor to cool it sufficiently. But in my case, because of electrical problems I will describe later, the fan does not work at all which is not good of course. I barely made it back home this morning as I had to select suitable gears in advance and pump the clutch maybe 20 times before it would disengage, this is outright dangerous I know. Finally the bike stalled and I had to push it the last few hundred yards.

Question: Can it be that the hot engine will cause some kind of slippage in the clutch so that I have to pump it this many times - or is the piston that the mechanic put in not right for this bike even if it works while the engine is relatively cool?

 

turn the push rod end for end and try it again

 

It's easy to make bonehead mistakes when reassembling master cylinders. You might also check the little hole at the bottom of the reservoir, they're known to clog (brake fluid can get rock hard with time) and cause clutch slippage issues. Just a wild guess.

 

It could also be that your slave cylinder is also leaking....sometimes a new master cylinder will "finish them off". Leaking brake fluid is hard to see down there, since it leaks down the side of the block behind the output case trim piece.

If it's not that, check to be sure the clutch is bled properly. I like to reverse bleed them, it's difficult to get all the air out. You can also use a zip-tie to hold the lever in over night (the bubbles will slowly rise into the reservoir...the system can almost bleed itself). It might just be coincidence and happening at the same time as the engine is warming up.

Is the reservoir fluid level dropping at all? There are a lot of Hondas that use the same clutch slave. I think it's a Nissin design. Just match up the piston with the cylinder diameter. If the piston is slightly too large or one of the seals is twisted, it'll bind up.

I had a similar problem with my temp sensor and fan on a V65 Sabre. They're not that different. I found that the wiring, temp sensor and fan were all OK. Turns out that the fuse box had a cracked terminal on the fan circuit fuse. Once I rebuilt the fuse box out it all worked perfectly.

 

Probably easier/cheaper to get a new master cylinder off a later bike than try and repair your old one which has obviously got air in it.

 

It's rare to need a replacement clutch slave or mc piston unless it's a very hi-mileage bike or rusted. In most cases, properly cleaning the piston and bore and using a new seal will fix it cheap. Try bleeding the clutch master first at its banjo before bleeding at the bottom, and fully retract the slave piston with a C-clamp if it's off the bike. I don't trust shop mechanics much, and i'd ask him to return to me anything he replaced, like a probably-unnecessary new slave piston for example.

Leak could also be due to damaged sealing washers on the mc banjo or just under-tightened.

 

Thanks to all who have replied to my thread. As this is the first thread I have started I am glad of the responses. I can see that this forum has some interested members who like to participate actively in discussions. This makes me optimistic that the board will work for me. I hope to be able to contribute some opinions also as time goes by. I am just a "normal" biker, but I've had experiences of many sorts when it comes to repairs. As I am located in a very hot country, there are special problems with cooling for example. Again, thank you all for your valuable advice. What you wrote is useful and I am looking into it.