Hydraulic Clutch Problems

[Ken R]

I admit that I don't know what is going on in the hydraulic clutch master except that a piston squeezes fluid into the line to the slave cylinder and releases the pressure when the clutch lever is let back out.  But something else must be happening:

2019 FLHTK with AIM master cylinder

HAPPENS ONLY AT HIGH ELEVATIONS!

Squeeze the clutch to the grip, no friction zone.  Clutch is limp.  I pumped vigorously for 50 - 100 pumps and regained enough clutch friction zone so I could start the engine and put it into first gear.
Long days of riding and had to stop twice during three long days because the clutch lever became hard out to the unsqueezed stop and clutch was slipping.  In order to continue on, I had to slightly loosen the banjo bolt to relieve the fluid pressure in the clutch line and regain some freeplay.  Over the miles on three days of the trip, I had to do this twice each day.  Else, the more and more clutch slippage would occur and fear of destroying the throw-out bearing. 

Actually, the "squeeze the clutch to the grip" problem happened last year, also at elevation and cold mornings while on a camping trip in RMNP.  Didn't experience the clutch line pressure build-up last year.  Once pumped up, the clutch behaved for the rest of each day. 

Back in Dallas last year, no problem.  But I replaced the fluid anyway when I got home to my workshop; thinking that I probably solved the problem.  Sure enough, not a whimper from the clutch the entire year; even on our coldest days in January/February where it was around zero degrees each night.  (I left the motor outside on several days just to see if the cold temperatures were causing the problem and to make sure that replacing the fluid fixed it.

But this year on a Yellowstone camping trip back at elevations above 5,000 ft to 8,500 ft in New Mexico, Colorado, Utah, and Wyoming last week; the problem (way excessive freeplay to the grip and no friction zone) happened every morning, just like last year.   The build-up of hydraulic pressure in the line to the slave problem was a new issue added this year.  It seems that the line pressure should drop to zero after the clutch lever is released; but even for 2 hours of riding without any clutch usage at all, the freeplay would gradually disappear and the lever would get to be hard against the stop. 

I'm thinking to just buy a new clutch master.  But there's no way to test this remedy without going back to high elevation; which is not planned until next year. 

Hoping that a mechanic with direct experience can help me with this. 

Ken

[Hossamania]

I can't help with your specific problem of elevation, but a friend put the AIM cylinder on a few years ago, which was the fix for the stock failings, and it failed after a year, he has switched to a Recluse and likes it even better.

[Ken R]

I can't help with your specific problem of elevation, but a friend put the AIM cylinder on a few years ago, which was the fix for the stock failings, and it failed after a year, he has switched to a Recluse and likes it even better.

Well, that's not encouraging.  I wonder what the failure of the AIM was. 
I've installed 4 AIM's and one Mueller for people (including my AIM).  Some of them travel with me and experienced no issues like mine has. 

I don't want to waste money on a new master cylinder if it's not the source of the problem I'm experiencing. 
The slave is pretty dumb; it simply moves a piston when hydraulic pressure overcomes the clutch spring.   The Master, though, probably has some sort of valving in it.  But I don't know for sure what or how. 

Ken

[HogMike]

Sounds to me like the problem would be in your master cylinder.

I don't believe you should have a problem with heat or cold issues.

I don't have the AIM slave (Muller) but I think all the after market ones are very similar in their operation.

I've ridden my 2019 bike from below sea level to over 12000 feet, 115 degrees to about 40 degrees with zero issues

Maybe try another master cylinder or rebuild kit?

[rigidthumper]

Unless the relief port is clogged, or a seal torn, there's not much to go bad in a master cylinder. Maybe tiny bits of air trapped in the system? I've seen small bubbles caught in the upper 1/2 of the banjo bolts, and air is more affected by altitude than Dot4.

[road-dawgs1]

I went with Muller due to all the problems AIM had with their first gen unit. Which generation do you happen to have?

[Bigs]

The early AIM's had plastic encapsulated O-rings which had a tendency to leak. I had one and I thought that maybe I had a air bubble that worked it's way in the system so I bled the caliper with me Mighty Vac and all was ok for a while then things went south. Called AIM and they sent me a O-ring kit that had regular O-rings and so far so good. This was on a '17 RK.
   Bigs

[Shadowbennie]

I admit that I don't know what is going on in the hydraulic clutch master except that a piston squeezes fluid into the line to the slave cylinder and releases the pressure when the clutch lever is let back out.  But something else must be happening:

2019 FLHTK with AIM master cylinder

HAPPENS ONLY AT HIGH ELEVATIONS!

Squeeze the clutch to the grip, no friction zone.  Clutch is limp.  I pumped vigorously for 50 - 100 pumps and regained enough clutch friction zone so I could start the engine and put it into first gear.
Long days of riding and had to stop twice during three long days because the clutch lever became hard out to the unsqueezed stop and clutch was slipping.  In order to continue on, I had to slightly loosen the banjo bolt to relieve the fluid pressure in the clutch line and regain some freeplay.  Over the miles on three days of the trip, I had to do this twice each day.  Else, the more and more clutch slippage would occur and fear of destroying the throw-out bearing. 

Actually, the "squeeze the clutch to the grip" problem happened last year, also at elevation and cold mornings while on a camping trip in RMNP.  Didn't experience the clutch line pressure build-up last year.  Once pumped up, the clutch behaved for the rest of each day. 

Back in Dallas last year, no problem.  But I replaced the fluid anyway when I got home to my workshop; thinking that I probably solved the problem.  Sure enough, not a whimper from the clutch the entire year; even on our coldest days in January/February where it was around zero degrees each night.  (I left the motor outside on several days just to see if the cold temperatures were causing the problem and to make sure that replacing the fluid fixed it.

But this year on a Yellowstone camping trip back at elevations above 5,000 ft to 8,500 ft in New Mexico, Colorado, Utah, and Wyoming last week; the problem (way excessive freeplay to the grip and no friction zone) happened every morning, just like last year.   The build-up of hydraulic pressure in the line to the slave problem was a new issue added this year.  It seems that the line pressure should drop to zero after the clutch lever is released; but even for 2 hours of riding without any clutch usage at all, the freeplay would gradually disappear and the lever would get to be hard against the stop. 

I'm thinking to just buy a new clutch master.  But there's no way to test this remedy without going back to high elevation; which is not planned until next year. 

Hoping that a mechanic with direct experience can help me with this. 

Ken

it's a pretty inexpensive and pretty quick fix to rebuild your clutch master, I think the piston & related orings & seals are like $50 on dennis kirk, and it's not difficult. Might be worth starting there to eliminate the possibility of a leak past the piston. The clutch master on my 2015 RGS started acting up last year where it would have more freeplay than usual after shifts and would take a few seconds to recover and build the correct pressure - the MC rebuild fixed that.

This is the DK p/n I purchased - Clutch Master Cylinder Rebuild Kit - 37200096-B

[kd]

Higher elevation equals a lower boiling point.     

[calif phil]

I have had a few AIM units, go bad.   I am doing the Rekluse units now with great results. SO FAR!

[hattitude]

Higher elevation euals a lower boiling point.     

You thinking maybe water in the fluid....??

It was fine for a year after his fluid flush, then acted up at altitude... again...

Maybe he got some really old or compromised brake fluid for his flush. Perhaps something (climate, riding conditions, etc) is causing a quicker than average build up of moisture in the brake fluid...

I read a thread on one of the forums I frequent, where a guy checked his brake fluid after 1 year with a tester and it was already back up to 3%....

[kd]

Higher elevation euals a lower boiling point.     

You thinking maybe water in the fluid....??

It was fine for a year after his fluid flush, then acted up at altitude... again...

Maybe he got some really old or compromised brake fluid for his flush. Perhaps something (climate, riding conditions, etc) is causing a quicker than average build up of moisture in the brake fluid...

I read a thread on one of the forums I frequent, where a guy checked his brake fluid after 1 year with a tester and it was already back up to 3%....

I thinking more about the possibility of boiling the fluid at the transmission with the combined gear heat including the close proximity of the exhaust.

[Ken R]

I ride in 100+ degree temperature in Texas.  I also do a lot of skills cone practice.  If it was overheating, that should certainly have made the symptoms appear.  But it doesn't.
The symptoms only appear at elevations over 5,000 to 6,000.   Coincidentally, it's cold in the mornings at those elevations where we've spent the night. 

Symptom #1:  Limip clutch lever on cold mornings at elevations
Symptom #2:  On long rides when traveling across country on highways requiring no clutch, the lever gradually works its way to the unsqueezed stop over time and eventually begins to disengage the clutch.

These symptoms seem opposed to each other. 
A new master cylinder would remove any doubt of the source, I suppose.  It's about a $150 expense. 
Problem is, the two symptoms NEVER occur when at lower elevations (like 500 ft ASL at home). 

I won't know if the issue has been solved without going back up.

Ken

Higher elevation euals a lower boiling point.     

You thinking maybe water in the fluid....??

It was fine for a year after his fluid flush, then acted up at altitude... again...

Maybe he got some really old or compromised brake fluid for his flush. Perhaps something (climate, riding conditions, etc) is causing a quicker than average build up of moisture in the brake fluid...

I read a thread on one of the forums I frequent, where a guy checked his brake fluid after 1 year with a tester and it was already back up to 3%....

I thinking more about the possibility of boiling the fluid at the transmission with the combined gear heat including the close proximity of the exhaust.

[ultrafxr]

I think you most likely have some small amount of air in the system.  Years ago on my '99 Ultra I would have the very same problem with the rear brake every time I got to higher altitudes.  I'd have the system flushed and it might be ok for a while but it would come back.  H-D was using Dot 5 back then and it was only years later that I learned the pitfalls of Dot 5.  It is very easy to entrap air bubbles in the fluid just by handling the container.  And at altitude the lower air pressure lets the small bubble enlarge and cause a problem.

[chaos901]

Going on trips out west, I had issues with my hyd. clutch at altitude.  Pretty much went out.  Was solved when I started to change the fluid on a regular basis.  Now I change it every year before I go out there.   

[Ken R]

I've since learned of two personal friends whose clutches went out at elevation (Devil's Highway 191 in SW Arizona).  They called for road assistance and the motors were towed to Phoenix dealership for repairs.  It disrupted the trip for a dozen or more riders. 

The feedback was that all they needed was hydraulic fluid replacement and then were good to go for the rest of the trip (at even higher elevations).

The Harley hydraulic clutch systems seems overly sensitive.  Maybe that's why the company abandoned hydraulic and went back to cable. 

[calif phil]

I have had a few customers call on the road with boiled clutch fluid.   I was wondering if anyone has tried D0t 5.1 brake fluid.

[Ken R]

I have had a few customers call on the road with boiled clutch fluid.   I was wondering if anyone has tried D0t 5.1 brake fluid.

I hadn't considered the fluid boiling.  It would need to get awfully hot.
I wonder if boiled hydraulic fluid causes the vapor bubbles to go up and build pressure in the reservoir that pushes fluid into the line.  When I lost the friction zone on the highway (two or three times a day for the long mileage days), I didn't think about cracking open the reservoir.  Wish I had.  Instead, I loosened the banjo bolt to relieve the pressure in the line. 

I do use MOTUL 600-degree in my rear brake.  If not, when competing in cones, it's easy to boil the fluid in the slave cylinder and totally lose the rear brake.  Almost all skills competitor have switch to MOTUL for that reason.

[YPD485]

I went though 3 AIM units and they all failed. The last 2 were warranty covered. That's fine, but having to R&R them were a PITA. I then bought a Mueller and it works great for over 2 years now. To me, AIM is garbage.

[Ken R]

I went though 3 AIM units and they all failed. The last 2 were warranty covered. That's fine, but having to R&R them were a PITA. I then bought a Mueller and it works great for over 2 years now. To me, AIM is garbage.

That's discouraging. 

Can you describe the failures? 

I understand that they had an issue with the first ones where the piston seals weren't up to the job but rectified that.  Mine is about 2 years old now and was after they made changes; at least to the angle of the hydraulic line connection.   

[Ken R]

Well, I bought a hydraulic fluid moisture tester on Amazon.  It came late last night.  Too late to go out in the dark and check the motorcycle's system.

BUT, I have several opened bottles of hydraulic fluid on the shelf in the workshop, so I did run down and check those.  (All DOT4 MOTUL 600).  Checked them all, a half dozen or so bottles. 
All but one checked with <1  percent with one checking >4 percent.   Don't know why the one tested higher; it was the most full and they're all kept in air conditioned space.   I'll probably toss them all. 

TODAY, I checked the fluid in the motorcycle.  The level was just as I'd left it when I changed the fluid last winter.  But interestingly, the moisture level was >4%!  The tester lit up like a Christmas Tree! 
Out of curiosity, I then checked my brake fluid.  It was also >4%.   Both unacceptable.  No idea how much over 4%.     How in the world does moisture get into the sealed hydraulic systems? 

Just to be sure, I went back and checked a couple of the open bottles of fluid that I have on the shelf.  Both <1%. 
So I can believe the checker. 

Guess I'll pull the exhaust loose again.   GRRRR!  It'll be the 3rd time in 2 years.  

[rigidthumper]

It isn't completely sealed.  The caps have vents, which allow access to atmosphere, and over time, humidity from the air gets in the reservoir. That's why it should be changed at a minimum every 2 years, more often in high humidity environments.

[chaos901]

The DOT fluid that is used in the ABS brakes and hyd. clutches does not have much of a shelf life once the bottle is opened.  Not much good to change using a bottle that has been sitting on the shelf after being partially used weeks ago.  That likely just puts in fluid that has already drawn some moisture.  IMO 

[ultrafxr]

I have had a few customers call on the road with boiled clutch fluid.   I was wondering if anyone has tried D0t 5.1 brake fluid.

I hadn't considered the fluid boiling.  It would need to get awfully hot.
I wonder if boiled hydraulic fluid causes the vapor bubbles to go up and build pressure in the reservoir that pushes fluid into the line.  When I lost the friction zone on the highway (two or three times a day for the long mileage days), I didn't think about cracking open the reservoir.  Wish I had.  Instead, I loosened the banjo bolt to relieve the pressure in the line. 

I do use MOTUL 600-degree in my rear brake.  If not, when competing in cones, it's easy to boil the fluid in the slave cylinder and totally lose the rear brake.  Almost all skills competitor have switch to MOTUL for that reason.

Several things going on here.  1) You're in the mountains so the motor works harder going up grades.  This increases heat.  2) The fluid that boils is the water in the system and since the lines are very close to the exhaust pipes it get very hot down there.  3) At altitude the boiling point of water is lower than at sea level.  Combine all this an you're got steam in your line.  Happened last year to a friend as we were riding up Pike's Peak.  Limped to the parking lot at the top and when he cracked the bleed nipple a big shot of steam came roaring out.  We bled it there some and got back to town got a new bottle of Dot 4 and flushed it real good.  No more problems.

[nibroc]

ultra---

glad you were able to get off pikes peak ok.........

[les]

2020 Electra Glide Standard.  I just rode through Leadville, Colorado.  No problems with the clutch.

[Merch]

Recently the clutch on on my 2018 is dragging, not fully dis-engaging when clutch lever pulled fully in. Fluid has been flushed and changed, bleed a few times. Shifting between gears is normal. Require significant brake at a stop to hold the bike bad at a stop in first. Finding neutral is 50/50. Primary Oil (Amsoil V-Twin Primary) is clean, very little clutch wear on drain plug. Bike has the AIM slave installed as soon as the recall came out (approx 20 000 miles on unit since). Elevation and temp does not seem to make a difference. Bike can sit over night, no issues, next day problems. What are the symptoms of the AIM unit failing?

[david lee]

master cyclinder air leak ?

[HogMike]

Well, I bought a hydraulic fluid moisture tester on Amazon.  It came late last night.  Too late to go out in the dark and check the motorcycle's system.

BUT, I have several opened bottles of hydraulic fluid on the shelf in the workshop, so I did run down and check those.  (All DOT4 MOTUL 600).  Checked them all, a half dozen or so bottles. 
All but one checked with <1  percent with one checking >4 percent.   Don't know why the one tested higher; it was the most full and they're all kept in air conditioned space.   I'll probably toss them all. 

TODAY, I checked the fluid in the motorcycle.  The level was just as I'd left it when I changed the fluid last winter.  But interestingly, the moisture level was >4%!  The tester lit up like a Christmas Tree! 
Out of curiosity, I then checked my brake fluid.  It was also >4%.   Both unacceptable.  No idea how much over 4%.     How in the world does moisture get into the sealed hydraulic systems? 

Just to be sure, I went back and checked a couple of the open bottles of fluid that I have on the shelf.  Both <1%. 
So I can believe the checker. 

Guess I'll pull the exhaust loose again.   GRRRR!  It'll be the 3rd time in 2 years.  

Trim the bottom of your side cover, just enough to clear the exhaust.
Glue the rubber strip back on and in the future you can leave the exhaust alone.
 

I check my fluids about once a year and change as needed. The clutch seems to have a higher moisture content than the brakes.

Going on 4 years with the muller slave, stock HD master, 59k miles in all kinds of weather and altitudes on my 2019 with no issues.

 

[Merch]

Master cylinder appears good to be leak free. Going to try and source a new slave cylinder.
Another failed AIM slave cylinder replaced. Internal seal leak.

[r0de_runr]

Well, I bought a hydraulic fluid moisture tester on Amazon.  It came late last night.  Too late to go out in the dark and check the motorcycle's system.

BUT, I have several opened bottles of hydraulic fluid on the shelf in the workshop, so I did run down and check those.  (All DOT4 MOTUL 600).  Checked them all, a half dozen or so bottles. 
All but one checked with <1  percent with one checking >4 percent.   Don't know why the one tested higher; it was the most full and they're all kept in air conditioned space.   I'll probably toss them all. 

TODAY, I checked the fluid in the motorcycle.  The level was just as I'd left it when I changed the fluid last winter.  But interestingly, the moisture level was >4%!  The tester lit up like a Christmas Tree! 
Out of curiosity, I then checked my brake fluid.  It was also >4%.   Both unacceptable.  No idea how much over 4%.     How in the world does moisture get into the sealed hydraulic systems? 

Just to be sure, I went back and checked a couple of the open bottles of fluid that I have on the shelf.  Both <1%. 
So I can believe the checker. 

Guess I'll pull the exhaust loose again.   GRRRR!  It'll be the 3rd time in 2 years.  

Trim the bottom of your side cover, just enough to clear the exhaust.
Glue the rubber strip back on and in the future you can leave the exhaust alone.
 

I check my fluids about once a year and change as needed. The clutch seems to have a higher moisture content than the brakes.

Going on 4 years with the muller slave, stock HD master, 59k miles in all kinds of weather and altitudes on my 2019 with no issues.

 

why glue the rubber strip back on?