1997 M750 Clutch problem

jerry · 12-09-2021, 05:05 PM

Sometimes randomly the clutch lever goes soft as if slave or master has lost pressure but then it becomes firm again ,, seems to happen in traffic ,,,its the early model with in case slave ,, no dragging or slipping ,,, ?????

fluid is fresh and clean no air in system and bled ok again ???

slob · 12-09-2021, 05:48 PM

how fresh? sounds like water vapour

jerry · 12-09-2021, 06:55 PM

I changed it all for fresh today the old stuff was dark ,and 1 year old ,now clear and clean , but I dont trust it

slob · 12-09-2021, 08:56 PM

i mean did it come from a sealed bottle?
dot3/4/5.1 glycol based brake fluid is highly hygroscopic (ie it readily absorbs moisture from the atmosphere) once a bottle has been opened this process starts. replacing the lid makes little difference. dot4 boils around 230c+, dot3 a bit less, dot5.1 a bit more. any absorbed water boils out at ~100c causing vapour lock (gas compresses, fluid doesn’t), once cooled again everything seems ‘normal’.
every time you open a bottle of fluid, write the date on it in sharpie and take it to your council tip for safe didposal after a couple of months.

I’ve experienced vapour lock on a rear brake and it was ****ing scary, i initially thought the pads had dropped out of the caliper.

ps. dont confuse dot5.1 with dot5 (dot5 is silicon not glycol based, it doesn’t absorb moisture, will not mix with glycol fluids, isn’t compatible with seals etc. not designed for it. afaik is only used in harleys as far as bikes are concerned)

sorry if i’m teaching grandma to suck eggs here.

jerry · 13-09-2021, 07:06 AM

I have a frsh bottle to hand DOT 4 so will re flush it ,, only takes 15 mins ,,, we Put DOT 4 in Petes HD its stops on a sixpence .. very sharp brakes

slob · 13-09-2021, 08:10 AM

If the HD says DOT5 on the master cylinder caps you will likely end up with problems with the seals. Glycol and silicon based fluids are incompatible. Glycol fluids generally provide better braking performance.

Mr Gazza · 13-09-2021, 08:14 AM

Quote:

Originally Posted by jerry

Sometimes randomly goes soft but then it becomes firm again
,, seems to happen in traffic ,,,

This is quite normal at your age sir. If it gets worse try these little blue pills.

I was sitting in traffic the other day, and er, I got run over!..

jerry · 13-09-2021, 08:26 AM

Quote:

Originally Posted by slob

If the HD says DOT5 on the master cylinder caps you will likely end up with problems with the seals. Glycol and silicon based fluids are incompatible. Glycol fluids generally provide better braking performance.

He builds all from new parts and not using HD brake bits CCA 4pots on front HD brembo 4 pot on rears stops really quick carb is Lectron ,, with Morris rare earth Magneto and WW 2hp starter motor ,,pulls like a train stops like a Ducati

my personel hydraulics are still working fine only problem is Timm is in Thailand and Im in YUK 18 months now seperated she is glowing red hot ,, i keep telling her to use the pappayas or bannanas she grows ,,,I have my bikes to ride ,, instead of her !!!!!! when I get back to her its gonna be explosive boom boom !!!!

12-09-2021, 05:05 PM	#1
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,816	1997 M750 Clutch problem Sometimes randomly the clutch lever goes soft as if slave or master has lost pressure but then it becomes firm again ,, seems to happen in traffic ,,,its the early model with in case slave ,, no dragging or slipping ,,, ????? fluid is fresh and clean no air in system and bled ok again ??? __________________ MONSTERMAN Last edited by jerry; 12-09-2021 at 05:09 PM..

12-09-2021, 06:55 PM	#3
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,816	I changed it all for fresh today the old stuff was dark ,and 1 year old ,now clear and clean , but I dont trust it __________________ MONSTERMAN

12-09-2021, 08:56 PM	#4
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,710	i mean did it come from a sealed bottle? dot3/4/5.1 glycol based brake fluid is highly hygroscopic (ie it readily absorbs moisture from the atmosphere) once a bottle has been opened this process starts. replacing the lid makes little difference. dot4 boils around 230c+, dot3 a bit less, dot5.1 a bit more. any absorbed water boils out at ~100c causing vapour lock (gas compresses, fluid doesn’t), once cooled again everything seems ‘normal’. every time you open a bottle of fluid, write the date on it in sharpie and take it to your council tip for safe didposal after a couple of months. I’ve experienced vapour lock on a rear brake and it was ***ing scary, i initially thought the pads had dropped out of the caliper. ps. dont confuse dot5.1 with dot5 (dot5 is silicon not glycol based, it doesn’t absorb moisture, will not mix with glycol fluids, isn’t compatible with seals etc. not designed for it. afaik is only used in harleys as far as bikes are concerned) sorry if i’m teaching grandma to suck eggs here. Last edited by slob; 12-09-2021 at 08:59 PM..*

13-09-2021, 07:06 AM	#5
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,816	I have a frsh bottle to hand DOT 4 so will re flush it ,, only takes 15 mins ,,, we Put DOT 4 in Petes HD its stops on a sixpence .. very sharp brakes __________________ MONSTERMAN

12-09-2021, 05:48 PM	#2
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,710	how fresh? sounds like water vapour

13-09-2021, 08:10 AM	#6
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,710	If the HD says DOT5 on the master cylinder caps you will likely end up with problems with the seals. Glycol and silicon based fluids are incompatible. Glycol fluids generally provide better braking performance.