Clutch free play changes when bike warmed up

G4LIA2001

G4LIA2001

Joined
Jun 16, 2021
Messages
11
Age
67
Location
Newcastle upon Tyne
Bike
2011 ST1300 44k mil
Hello all

I'm a new owner of a ST1300 2011 and just getting to grips with a few issues as I bought the bike private.
Sorting out sticking calipers / pistons at the moment but after a 30 minute drive, I lost a lot of clutch free play.
In effect, the clutch started to engage about 1" from the pulled in position, whereas normally is towards the end of the lever returning to the "normal" fully released postion.

Anyone else come accross this problem? - Master cylinder is full btw

Joe (Newcastle upon Tyne)
 
The clutch master cylinder reservoir should not be brim full. Only up to the line inside the reservoir. I assume that this is what you meant ?

Post retracted - The OP confirmed that it was not a loss of free play, but a reduction in the amount of movement at the slave cylinder. I've left tha nswer here otherwise the later posts don't won't make sense.

G4LIA2001 said:
Sorting out sticking calipers / pistons at the moment but after a 30 minute drive, I lost a lot of clutch free play.
Click to expand...

If the fluid level is ok then let me just check that I understand: The clutch disengages soon after you start to pull the lever in when the bike is hot. But you have to pull the lever in much further when it is cold before the clutch disengages the drive from the engine?​
By disengage, I mean that the engine is no longer driving the wheels - which is what normally happens when you pull in the clutch lever.​
​
If I have that correct (I am not sure that I have) then I think there are two things here.​
​
1. The brass bush in the clutch lever has a hole in its side. The plunger for the master cylinder should fit inside that hole. I think that the plunger is pressing on the side of the brass bush rather than in the hole. In other words it is already pushing on the the master cylinder. When the fluid gets hot, it expands and exaggerates the effect that this has.​
Before you take the bush out, draw a mark across the top of the bush and continue it onto the lever. Then you will know for certain if that was the problem. If it was, clean off the mark, and draw another one to indicate where the hole is. It makes it easier to align properly.​
2. I think you have air in the clutch line. If there is no air and that plunger isn't in the hole in the brass bush, then when the engine heats up, there is enough expansion to disengage the clutch by itself.​
​
I reckon the previous owner may have discovered this, thought there was too much pressure in the fluid, and let some fluid out / air in to compensate !​
 
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You got this john?
I'm juggling several at the moment, and don't want to spread myself too thin at the moment.
Thanks for responding so quick.
@OP your in good hands, john will get you sorted right away.
Igofar
 
jfheath said:
If the fluid level is ok then let me just check that I understand: The clutch disengages soon after you start to pull the lever in when the bike is hot. But you have to pull the lever in much further when it is cold before the clutch disengages the drive from the engine?
Click to expand...
He's saying the opposite: the clutch engages sooner (closer to the grip) when hot.

He should be saying that there's more free-play when the engine warms up.
 
I was confused by his description because of the contradiction.

He said less free play - which seems to be clear. I have heard people use the phrase 'engage the clutch' when they mean that they have pressed the pedal (in a car) - so I thought that was possibly the confusion.

Hopefully @G4LIA2001 will come back with a clearer description.
 
I have the same issue on my 1100, only when it gets well above normal temperature, and goes away soon after cooling down.

It was suggested that water in my slave cylinder turns to steam and becomes compressible. I'm not fully convinced, though.
 
Larry Fine said:
I have the same issue on my 1100, only when it gets well above normal temperature, and goes away soon after cooling down.

It was suggested that water in my slave cylinder turns to steam and becomes compressible. I'm not fully convinced, though.
Click to expand...
I agree with you - not being convinced. If you really have water in the brake fluid that is turning to steam, you will know it soon enough with a completely inoperable, corroded clutch. When was the last time you flushed the brake fluid in the clutch?
 
SMSW said:
When was the last time you flushed the brake fluid in the clutch?
Click to expand...
Um, well, not since I bought it. :rolleyes: It's almost three years, but less than 6,000 miles.

I do have a fresh can of DOT-4 fluid, but haven't done it yet.
 
jfheath said:
The brass bush in the clutch lever has a hole in its side. The plunger for the master cylinder should fit inside that hole. I think that the plunger is pressing on the side of the brass bush rather than in the hole. In other words it is already pushing on the the master cylinder. When the fluid gets hot, it expands and exaggerates the effect that this has.
Click to expand...
Hi Joe:

Welcome to our forum community, and welcome to ST 1300 ownership.

I think that John has nailed it with his explanation above - I'll bet you a cup of coffee that the problem is a mis-aligned bush. Have a look at this post, it shows pictures of the bush: click here. FYI that bush is a 'wear part' - the little hole in it enlarges over time, and the bush eventually needs to be replaced.

Michael
 
You should definitely flush your clutch and brake fluid asap. These bikes need this done every other year it seems. There is also a specific sequence to do so for the brake fluid. Then you can investigate the clutch lever bushing , etc.
Your brake issues might be your SMC which is located on the front left caliper. Lots and lots of issues with those causing the rear caliper to stay on. Check the articles pages for lots of good how to's.
 
jfheath said:
The clutch master cylinder reservoir should not be brim full. Only up to the line inside the reservoir. I assume that this is what you meant ?


If the fluid level is ok then let me just check that I understand: The clutch disengages soon after you start to pull the lever in when the bike is hot. But you have to pull the lever in much further when it is cold before the clutch disengages the drive from the engine?
By disengage, I mean that the engine is no longer driving the wheels - which is what normally happens when you pull in the clutch lever.

If I have that correct (I am not sure that I have) then I think there are two things here.

1. The brass bush in the clutch lever has a hole in its side. The plunger for the master cylinder should fit inside that hole. I think that the plunger is pressing on the side of the brass bush rather than in the hole. In other words it is already pushing on the the master cylinder. When the fluid gets hot, it expands and exaggerates the effect that this has.
Before you take the bush out, draw a mark across the top of the bush and continue it onto the lever. Then you will know for certain if that was the problem. If it was, clean off the mark, and draw another one to indicate where the hole is. It makes it easier to align properly.
2. I think you have air in the clutch line. If there is no air and that plunger isn't in the hole in the brass bush, then when the engine heats up, there is enough expansion to disengage the clutch by itself.

I reckon the previous owner may have discovered this, thought there was too much pressure in the fluid, and let some fluid out / air in to compensate !
Click to expand...
Hi John - thanks for the prompt reply.

When cold the clutch work normally - no problems.

When hot - say after 10 mins riding, the clutch fails to disengage (uncoupling the gearbox from the engine) until the clutch lever is about 15mm from the bar.

I've read a few posts here and there and the one thats seems more relevant to me refers to the rubber pressure pipe expanding when under load when hot.
I should say, when the bike cools down the clutch works perfectly normally.

I hope that better explains the issue.

Cheers

Joe
 
Larry Fine said:
He's saying the opposite: the clutch engages sooner (closer to the grip) when hot.

He should be saying that there's more free-play when the engine warms up.
Click to expand...
Or he could have said the clutch engages closer to the grip when hot. Saying there's more free-play sound more like a bushing problem which shouldn't be heat sensitive.

Or the clutch disengages closer to the grip when hot. Not infrequently I'll have to read a description of a clutch problem 2 or 3 times to see what the OP is trying to say. If and when I have similar trouble I think I'll just refer to the relative location of the friction point. Oy.
 
I retract my earlier reply then - it isn't relevant to your situation.

If you 'lost a lot of free play' as you had stated then my answer is spot on. And that situation where the plunger isn't in the hole definitely has a serious effect after about 7 minutes of riding. It disengages the clutch due to the heat expansion of the clutch fluid.

How do I know this ?

Here is my brand new St1300A9 - 3 Feb 2014 - having covered 7 miles on its very first ride before losing all drive and leaving me stranded. I had it brought home by the recovery service. Found out what the fault was, and then made the dealer pick it up and check it over as it had been delivered to me in a dangerous state.

temp.jpg
 
The hoses are much more able to flex when they get warm. That will always happen.
Also the fluid will expand. So will any air bubbles. When the lever is relaxed, any expansion will push excess fluid through the compensation port. Any air bubbles trapped further down will not. The bubbles will be larger but they will still compress to almost nothing - meaning that you have a bigger ratio of air to fluid in the lines. So more movement at the lever before any movement at the slave is felt.

Make sure that you have got all of the air out of your hydraulic lines.

Tap the joints, make sure that the bars are turned to full right lock. Some advocate cracking open the banjo bolt at the master cylinder when the lever is compressed to allow any air at the union to escape. Personally, I have never found the need. Pump the lever a few times to build up pressure, hold the lever in and open the bleed valve (use a non return bleed tube). Close the blled valve before releasing the lever. Repeat ad nauseum. Keep an eye on the reservoir fluid level.

When you think you have had enough, put it on its centre stand, put it in gear, tie the lever back to the handle. Check that you can move the rear wheel. Leave it overnight.
When you come back to it, before you do anything else, see if you can move the rear wheel. If you can't or it is much harder than it was before, then you have a leak in the hydraulics somewhere. Fluid is getting past the seal at wither the master cylinder or the slave cylinder - if there aren't any obvious signs of fluid escaping from the system.

When it does this, does it get any better if the clutch lever is pumped a few times ?

@Upt' North - can you help / shed any light on this ? I don't know if NE3 is anywhere near to you ? (edit - Ive just checked the RAN list. It's a good 40 miles away)
 
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The only reason I can think that it is affected by temperature is that there's moisture in the fluid. It doesn't need to turn to steam (which implies boiling temperatures) but the warmer the fluid the larger portion of any moisture present will move into the vapor phase from the liquid phase introducing bubbles and compressibility to the system. You don't need boiling temperatures to evaporate water. Before doing anything else flush and bleed the system thoroughly with fresh DOT 4 fluid from a new unopened container.
 
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wjbertrand said:
The only reason I can think that it is affected my temperature is that there's moisture in the fluid. It doesn't need to turn to steam (which implies boiling temperatures) but the warmer the fluid the larger portion of any moisture present will move into the vapor phase from the liquid phase introducing bubbles and compressibility to the system. You don't need boiling temperatures to evaporate water. Before doing anything else flush and bleed the system thoroughly with fresh DOT 4 fluid from a new unopened container.
Click to expand...
Will do Jeff - just bought the fluid today - Thanks
 
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