And, like SPYRYDER, I love and happy with my two 2009 RS SM5 Spyders, one has 16,000 miles and the other has 12,000 miles. My best friend is on his second Spyder 1st-2008 RS SM5 11,000 miles and his current one is a 2011 RT SM5 with 21,000 miles. I try and do as much service to all three, the RS's are a dream to work on, that RT is a bear to work on, and is constantly in and out of the dealers with bull**** problems
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ALL OWNERS OF ALL SPYDER MODELS NEED TO CHECK THE CAPS ON YOUR BRAKE RESERVOIR
- Thread starter MISTERZ06
- Start date
And, like SPYRYDER, I love and happy with my two 2009 RS SM5 Spyders, one has 16,000 miles and the other has 12,000 miles. My best friend is on his second Spyder 1st-2008 RS SM5 11,000 miles and his current one is a 2011 RT SM5 with 21,000 miles. I try and do as much service to all three, the RS's are a dream to work on, that RT is a bear to work on, and is constantly in and out of the dealers with bull**** problems
I'm pretty happy with mine too. I've got around 11,000 miles on it now. It's had the DPS recall and the ECM was changed when one cylinder quit firing. I haven't done anything else other than oil changes and a new battery last year. :thumbup:
So what do you think? am I wrong with my old-school theories that use to work? Or am I all wet from Brake Fluid. Just looking now for theories.
Thanks Tom n Carol, SI,NY
PMK
Active member
FWIW, I have not inspected our 2014 RTs yet.
It is typical on brake and hydraulic clutch systems to run a sealed system. As mentioned, this prevents contamination from moisture, which is absorbed by brake fluid and lowers the boiling point of the fluid.
The rubber diaphragm should have no venting to ambient air. The metal or plastic rigid cap will have vents above the sealed diaphragm that allows the bellows portion of the diaphragm to expand as the brakes wear and fluid is displaced into the caliper.
Hydraulic clutches are the same.
So, I decide, let's go have a look, 2014 RTs, new in Jan. Removed both caps, pulled both rubber diaphragms from each cap. Each cap has a vent slot. Each rubber diaphragm has a V slit and a short straight slit. So since this defies anything typically seen before, I decide to read the owners manual. The V slit is supposed to be there, my best guess is that it will vent fluid if the brakes overheat, or maybe if the fluid is overheated by the known heat concerns from the engine and exhaust. If the fluid has nowhere to vent, the brakes will be applied and create other issues.
Outside of that, it makes no sense, is not done to any other vehicle I have ever worked on, and honestly can only recommend be aware and bleed the brakes more often in higher humidity or wet areas.
Copied from the owners manual.
All the best with it.
PK
1. Add fluid to MAX level.
NOTICE Brake fluid can damage
painted surfaces or plastic parts.
Wipe up any spills.
2. Reinstall filler cap as follows:
2.1 Check that V slit is in good condition.
2.2 Ensure diaphragm are properly
positioned.
rbg2008-003-002_a
TYPICAL
1. V slit
vmr2008-033-062_a
TYPICAL
1. Correct position
2. Wrong position
3. Close the seat and ensure it is fully
It is typical on brake and hydraulic clutch systems to run a sealed system. As mentioned, this prevents contamination from moisture, which is absorbed by brake fluid and lowers the boiling point of the fluid.
The rubber diaphragm should have no venting to ambient air. The metal or plastic rigid cap will have vents above the sealed diaphragm that allows the bellows portion of the diaphragm to expand as the brakes wear and fluid is displaced into the caliper.
Hydraulic clutches are the same.
So, I decide, let's go have a look, 2014 RTs, new in Jan. Removed both caps, pulled both rubber diaphragms from each cap. Each cap has a vent slot. Each rubber diaphragm has a V slit and a short straight slit. So since this defies anything typically seen before, I decide to read the owners manual. The V slit is supposed to be there, my best guess is that it will vent fluid if the brakes overheat, or maybe if the fluid is overheated by the known heat concerns from the engine and exhaust. If the fluid has nowhere to vent, the brakes will be applied and create other issues.
Outside of that, it makes no sense, is not done to any other vehicle I have ever worked on, and honestly can only recommend be aware and bleed the brakes more often in higher humidity or wet areas.
Copied from the owners manual.
All the best with it.
PK
1. Add fluid to MAX level.
NOTICE Brake fluid can damage
painted surfaces or plastic parts.
Wipe up any spills.
2. Reinstall filler cap as follows:
2.1 Check that V slit is in good condition.
2.2 Ensure diaphragm are properly
positioned.
rbg2008-003-002_a
TYPICAL
1. V slit
vmr2008-033-062_a
TYPICAL
1. Correct position
2. Wrong position
3. Close the seat and ensure it is fully
I think we're both right, it just depends which decades we're talking about! It looks like the pre 60's cars were really simple like on that '55 cap. I don't think there was a diaphragm under that and the vent hole could get plugged pretty easily.
Then they started with those big accordian diaphragms and I don't believe they were vented since they could displace a lot of air or fluid if the level dropped, especially with disc brakes when the pads wore.
Now I think the technology is using these smaller caps with the slits. They actually operate like little two way valves which are normally closed. But if there's a vacuum or pressure in the system due to expansion or contraction from temperature change for instance. That diaphragm will get sucked down or pushed up deforming it and opening the slit just enough to keep pressures equalized and letting in as little air and moisture as possible. I hope that makes sense.
Oh and I think those V shaped slits on the Spyder are a bit overkill too. They don't need to be that big.
Last edited:
Bob Denman
New member
Are we ready for the "Group Hug" yet? 
billybovine
Active member
Now that's settled.
This has been discussed in previous threads. The conclusions are always the same. The slit is suppose to be there. Most modern vehicles have a slit in the diaphragm and older vehicles did not.
One thing that has not been mentioned yet is. If the caps are put on backwards (vent to the front) they will leak. If the caps are put on correctly vent to the rear less likely to leak.
This has been discussed in previous threads. The conclusions are always the same. The slit is suppose to be there. Most modern vehicles have a slit in the diaphragm and older vehicles did not.
One thing that has not been mentioned yet is. If the caps are put on backwards (vent to the front) they will leak. If the caps are put on correctly vent to the rear less likely to leak.
PMK
Active member
I wanted to give this a check...the caps have a paint dot and I need to see if it aligns with something.
PK
There was a recall way back in '08. This was looked after a long time ago.
billybovine
Active member
The vent passage is under the rib. So vent or rib to the rear is the same thing.
PMK
Active member
Agree and no problem...as I mentioned, the caps on our machine also have painted dots. I need to see if those are visual alignment marks. I don't see them on yours.
As time permits I will check...the caps are properly installed on our machine.
PK
I believe the reasoning for the vent hole only in the cap and not in the rubber diaphragm is for two reasons
1 - To let the rubber diaphragm expand into the cap when atmospheric pressure changes, which I believe is the same as gravity.
2 - suction/vaccum When you depress/engage/push/step on your brake pedal, brake fluid is pushed (pressurized) thru the brakes lines, and forces the pistons inside the caliper to push the brake pads against the rotor - VIOLA - STOP
When this # 2 action occurs, a vaccum pulls the brake fluid out of the brake reservoir and into the brake master cyclinder and into the brakes lines.
When you release the brake pedal, that brake fluid under pressure flows back into the brake fluid reservoir because the vaccum/suction has ceased and atmospheric pressure/gravity takes over.
If you have this slit/vent hole in your diaphragm, the vaccum action will pull outside air (which contains mositure) into the brake system, when brakes are applied
I say NO SLIT - NO AIR
Was at a large, large Motorcycle dealer yesterday and I looked at BMW, DUCATI, TRIUMP, SUZUKI, POLARIS, VICTORY, HARLEY DAVIDSON, dirt bikes, ATVs, them 4-wheel large 2-4 people things , in the woods/rough terrain vehicles, and none, to the best of my memory (phone takes lousy pics) had vents in the brake reservoir caps.
This is why when you remove the old style automobile single/double covers, the rubber diaphragm is collapsed.
Vaccum>Gravity>Atmospheric No-Slits
BMWpilot
New member
Both my previous R1150RT and K1200RS brake systems were vented. Part of the yearly maintenance on the bikes was to drain, fill and bleed both the clutch and brake/ABS system to due to moisture accumulation in the fluid.
The brake fluid returns when you let off the brakes, because the vaccum has stopped, and yes, the level of brake fluid in the reservoir decreases due to wear in the brake pads, and that is why the brake code comes on your screen, telling you the fluid is at a low level.
To remove that orange brake code on your screen, you turn the Spyder ignition switch on, do not start, and then you depress on the brake pedal for (not sure, its in the service manuual) 10-20 seconds, turn ignition off, wait a bit, and that orange brake code should be removed, providing that the brake fluid in the reservoir is at the propre level. And if no dissappear, repeat. In the reservoir is a low brake fluid sensor.
3 Wheel Addict
New member
Actually he's right and wrong but what has not been figured into this mess of vents or no vents is the actual fluid itself. I'm pretty sure that the DOT 4 and 5 fluid is moisture resistant and can pull off having the vented cap. The small size of the caps and lack of bellows is why the system needs the vents and by using better fluid they can pull it off. He's right in his thinking but wrong in his application, leave the vented caps on your spyder. I do a lot of boat trailer brakes and those systems are vented to and have really small caps with no bellows. We get longer fluid life with DOT 5 silicone brake fluid.
Gray Ghost
New member
DOT 4 and DOT 5.1 are polyglycol based just like DOT 3 and are hygroscopic (absorbs water). DOT 5 as you mentioned is silicone based so it does not absorb water. Both systems do get water in them from condensation though, in a DOT 4 system it mixes into the brake fluid but with DOT 5 you end up with having pockets of water collecting in the system. Couple the water pockets with longer time between fluid changes and you have a recipe for corrosion. Harley was using DOT 5 for awhile but they have gone back to DOT 4.
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