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Don't forget about your clutch fluid #5354904 02/19/20 09:40 PM
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Number_35 Offline OP
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Hello all. I'm pretty OCD about maintenance. For years and years I've been bleeding my brakes every couple of years. Our '09 Mazda 5 has a manual transmission, complete with hydraulically-actuated clutch. The clutch and the brake system share the same fluid reservoir.

I bled the clutch when we got the car back in 2013, but had not since. I figured that having fresh fluid in the reservoir would be sufficient to keep the clutch system happy. Not so!

Heading out of town a few days ago, the tranny was hard to shift, and the clutch pedal felt extremely soft. I turned back, later than I should have, and bled the clutch in the driveway at a balmy -15 C. On the way home, I had to lift up the clutch pedal with the toe of my L shoe, just to shift into N. Repeat to get into the next gear. No fun at all! I had some old DOT-4 on hand. Instant cure!

Anyway, I think I know the answer to the debate as to whether or not brake fluid circulates. I'll say definitely not.

As soon as the weather improves a bit (-36 C this morning as we left our vacation spot in western Manitoba), I'll do a complete flush on all four brake calipers and the clutch! I'll be using DOT-3 as recommended in the owner's manual. DOT-3 vs. DOT-4 can be a whole other thread.

Cheers.

Last edited by Number_35; 02/19/20 09:49 PM.
Re: Don't forget about your clutch fluid [Re: Number_35] #5354919 02/19/20 09:56 PM
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Chris142 Offline
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There is no way for brake fluid or clutch fluid to circulate. Wherever the fluid is it stays.


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Re: Don't forget about your clutch fluid [Re: Chris142] #5354934 02/19/20 10:10 PM
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LotI Offline
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The fluid essentially goes back and forth with little mixing.

Based on your climate you should consider a DOT4LV. Superior low temperature flow endorsed by several Euro OEM’s.


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Retired:
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Re: Don't forget about your clutch fluid [Re: LotI] #5354960 02/19/20 10:47 PM
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Number_35 Offline OP
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I wondered about DOT-4. I've been reading a lot about brake fluid over the past few days, and am trying to sort through some of the information out there. As they say, it's a bit like trying to drink out of a firehose. Here are some of the things that seem to have been said consistently:

- As the DOT number increases, so does the boiling point. Therefore, all other things being equal, a higher DOT number is better.

- Brake fluid is rated DOT-3, -4, -5, and -5.1

- DOT-3, -4, and -5.1 are glycol-based, and are hygroscopic. That is, they absorb water. As they do so, their boiling point decreases.

- DOT-5 is silicone-based, and does not absorb water.

- The glycol-based and silicone-based fluids are not compatible, and must not be mixed.

- The glycol-based fluids have both a "dry" and a "wet" boiling point. The dry boiling point applies to new fluid, and the wet boiling point applies to fluid containing a certain % of moisture. As the moisture content increases, the boiling point drops. It can drop so low that heat from the brakes can cause the contaminated fluid to boil, rendering the brakes ineffective.

- DOT-4 is more hygroscopic than DOT-3.

- DOT-4's wet performance drops off much more quickly than DOT-3's. That is, at some level of water contamination, DOT-4's boiling point will be lower than DOT-3's.

- DOT-4 and DOT-5.1 contain certain elements that can degrade the rubber seals in brake (and clutch) systems designed for DOT-3 fluid.

- If a system were rated for both DOT-3 and DOT-4, I would not hesitate to use DOT-4 if I were to be diligent in bleeding the system annually or so.

Please jump in and correct any of the above that's incorrect! Given that our vehicle specifies DOT-3 fluid, I would worry about using DOT-4, although the LV formula sounds like a good fit for our winters.

Re: Don't forget about your clutch fluid [Re: Number_35] #5354983 02/19/20 11:33 PM
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CR94 Offline
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Hydraulic clutch actuation was a technological great leap backwards, in my opinion. In over 1.4 million miles combined, I, my brother, and our parents never had a single problem with clutch cables or linkage.


2011 Toyota Prius now at 110K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: Don't forget about your clutch fluid [Re: CR94] #5355013 02/20/20 12:36 AM
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oldhp Offline
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Originally Posted by CR94
Hydraulic clutch actuation was a technological great leap backwards, in my opinion. In over 1.4 million miles combined, I, my brother, and our parents never had a single problem with clutch cables or linkage.


I agree. Never had a problem either, and the throw out bearing didn't spend it's life spinning all the time for no reason.


"None of us are getting out here alive.....drink that beer.....eat that pizza......drive that Hot Rod"
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"I don't run...........I just wait"
Re: Don't forget about your clutch fluid [Re: Number_35] #5355019 02/20/20 12:54 AM
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69GTX Offline
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I'm not so sure that clutch fluid doesn't circulate somewhat. I've done feed and bleeds with syringes on my T56 clutch reservoir with excellent results after several cycles. The first time I did it the fluid was 12 years old and very dark. 3 cycles of changing the reservoir fluid and about 30 clutch pedal pumps each time and that fluid was clean. It stayed clean too. Now I do a refresher of one cycle every year. If there were no circulation it should have cleaned up in the first emptying of the reservoir....which it didn't. It got progressively better on each syringe drain/fill cycle.

A Corvette racer has used his "Ranger Method" on clutch reservoir exchanges via syringe very effectively....increasing clutch fluid life and making their times more consistent as well as faster. Gotta be some sort of circulation. I've never seen anyone disprove his method or results. I would agree that brakes don't get far changing only the reservoir fluid.....much bigger volume of fluid to exchange via reservoir. The clutching system is usually only a few ounces.

Ranger Method

Ranger video

Last edited by 69GTX; 02/20/20 01:01 AM.

----------------

2001 Lincoln Cont 4.6L DOHC/ 50K mi / QS HM 5w30 / FUG XG2
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1969 Ply GTX/RRs
Re: Don't forget about your clutch fluid [Re: Number_35] #5355049 02/20/20 02:44 AM
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Olas Offline
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General maintenance is important. Try to get into the habit of bleeding your clutch&brakes annually.

Re: Don't forget about your clutch fluid [Re: Number_35] #5355142 02/20/20 07:38 AM
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atikovi Online Content
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Originally Posted by Number_35
The clutch and the brake system share the same fluid reservoir.


Not sure if that's a good design. What if one system has a leak? Than both systems are compromised. My Honda's have a separate clutch fluid reservoir.

[Linked Image from fototime.com]

Re: Don't forget about your clutch fluid [Re: CR94] #5355174 02/20/20 08:32 AM
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supton Offline
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Originally Posted by CR94
Hydraulic clutch actuation was a technological great leap backwards, in my opinion. In over 1.4 million miles combined, I, my brother, and our parents never had a single problem with clutch cables or linkage.

Been a long time, but I recall cable being smoother than mechanical. But hydraulic... very smooth. But cable does allow one to set the engagement point to where one wants it, so there's that. But cables can rust out so maybe it's all a wash.

I am reminded that I've never changed it in the Camry... one more thing to look into.


2011 Toyota Camry, base, 2.5L/6MT, 203k, hers
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Re: Don't forget about your clutch fluid [Re: CR94] #5355200 02/20/20 08:57 AM
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E150GT Offline
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Originally Posted by CR94
Hydraulic clutch actuation was a technological great leap backwards, in my opinion. In over 1.4 million miles combined, I, my brother, and our parents never had a single problem with clutch cables or linkage.

Never had a VW? That cable was stiff as a board, snapped and was a real pain to get back on

Last edited by E150GT; 02/20/20 08:58 AM.

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Re: Don't forget about your clutch fluid [Re: supton] #5355230 02/20/20 09:34 AM
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ARCOgraphite Offline
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Originally Posted by supton
Originally Posted by CR94
Hydraulic clutch actuation was a technological great leap backwards, in my opinion. In over 1.4 million miles combined, I, my brother, and our parents never had a single problem with clutch cables or linkage.

Been a long time, but I recall cable being smoother than mechanical. But hydraulic... very smooth. But cable does allow one to set the engagement point to where one wants it, so there's that. But cables can rust out so maybe it's all a wash.

I am reminded that I've never changed it in the Camry... one more thing to look into.


Having owned mainly MT cars, I have had more problems with hyd clutch systems.

I absolutely DESPISE the "self adjusting" systems that always adjust too close to the carpet and kill the trans and shift quality for a month until it wore in to a good spot.

The only issue I had with mechanical clutch actuating systems,
was on my 1969 428 Cobra Jet Fairlaine, when it broke the DS motor mount,
the engine would lift and the pivot bar ( that had a pivot ball on the block ) would fall apart and I would have to drive home with the clutch engaged.

Last edited by ARCOgraphite; 02/20/20 09:35 AM.

2019 VW Jetta S 6MT OCI#2 7378mi-MOTUL Specific VW508.00+VW Service Filter; '17 Subaru Crosstrek CVT OC#8 60864mi-Subaru Idemitsu 0W20 + SOA Filter
Re: Don't forget about your clutch fluid [Re: Number_35] #5355251 02/20/20 09:51 AM
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sloinker Offline
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No good reason to change the fluid in the slave or master cylinder for a clutch if it's on its own system, probably not even if it is on a shared system. The only possible reason I could think of is if the fluid had absorbed so much moisture it would rust the internals. The boiling point of the fluid is a non factor in a hydraulic clutch. I would be more concerned with its freezing point and moisture contamination/freezing point on a shared system. Otherwise I would change it only when a replacement clutch/cover is installed along with a new pilot and throw out bearing.


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Re: Don't forget about your clutch fluid [Re: Number_35] #5355253 02/20/20 09:56 AM
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ARCOgraphite Offline
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Water in the slave is easy given its location, Internal Corrosion will kill the slave.


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Re: Don't forget about your clutch fluid [Re: Number_35] #5355286 02/20/20 10:23 AM
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WyrTwister Offline
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50 years ago , when I was a Pup , I was told or I read that the brake fluid of that time absorbed moisture . Keep the cap well secured on any containers . Keep the cap secured on the master cylinder reservoir well secured .

Never had a MT vehicle with hydraulic clutch . All were mechanical .

Best I remember , all of my vehicles indicate DOT 3 brake fluid .


Wyr
God bless
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