Synthetic brake fluid question

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rsbcruiser

rsbcruiser

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I have been runnning Valvoline synthetic dot 3-4 brake fluid in my brake and clutch sytems for 6 years now. No complaints concerning the brake system, brake components have held quite well now for years. The clutch hydraulics on the other hand are a different bird. I have replaced both the master and slave twice now in the last six years. Beginning to think it is the syntho brake fluid. The clutch system accumulates an excess of black particles in the fluid much more so than the brake system. Question is, has anyone experienced a similiar problem? Should I switch back to the old stuff? What the heck is going on here? Along those lines.
 
I don' know why but my hyd clutch discolors the fluid quickly as compaired to the brakes. I just flush it more often. I have always used DOT3 so cannot comment on the syth deal. The way I look at it is the thing was designed way before sythetics were avaialable so why not just use what's calleld out?

Spending more money on something has hardly ever made me feel better. This whole dino vs synth debate is discussed often, but to the best of my knowledge, has never been won.
 
Warning, major thread self hijack in process

Oh ya! funny set of cicumstances has led to a self diagnosis of the root cause. First off, bought a rebuilt clutch slave cylinder from Thrifty, dumb de dumb, tossed the reciept before confirming that the part was yes indeed the WRONG part, dumb ditti dumb. What to do? Maybe I can use the new one to rebuild the old one, hmmmmmm out come the calipers, sure enough, only 0.001" difference in piston diameters.
clutchslave1.webp
 
Where I went wrong in the past

I pour brake fluid on top of the piston. Lubricate the boot mating surfaces with lithium grease. Doing my part to promote boot mating in the wild. Install the boot and the pushrod. Hmmmmmmmm, maybe I should have greased the bore instead of using brake fluid.
clutchslave5.webp
 
I went and bought one of those ss lines (no give). with that in mind I cinch up the slave to the hose using an adjustable wrench and a regular ol wrench. Install and then cinch tight the hose. This way, no twist and I don't have to seperate the other end. Took it for a test drive. Seems to be holding for now. One thing I noticed was there seems to be less clutch chatter now. Has anyone ever heard of this? Maybe the slave piston was hanging up.
clutchslave6.webp
 
island 45s' post? just timing I guess, funny because I was reading his post while figuring out what had happened to mine. Thinking I should have coated the slave ID with lithium (rubber safe grease) to prevent rust. Bet you guys have similiar problems to what we experience here in the NW, raining all the time.
 
Wrong again, sorry. You are refering to your own post. I went and looked at my can of white lithium grease. Nothing on there about being rubber safe. I will double check this. maybe the lithium is not the way to go with rubber, I heard that it is.
 
Thumbs down on the synthetic: I've used it and switched back to dot3. quality dot 3 and 4 is getting harder to find at the parts shop. My biggest problem with the syn. was a lack of good pedal. sounds like bs but I can tell the difference. Maybe I'm getting less air out with the syn. or it just doesn't seem to work for me. I flush out my lines every other year so moisture doesn't build up. I used to run a silcon dot5 brake fluid and thought it was absolute s*** for good pedal. It's easier to maintain as it doesn't pull in moisture like 3 and 4 but I've not been happy with it either. Looks like you fix it is coming along nicely. Good luck
 
F-junker said:
Thumbs down on the synthetic: I've used it and switched back to dot3. quality dot 3 and 4 is getting harder to find at the parts shop. My biggest problem with the syn. was a lack of good pedal. sounds like bs but I can tell the difference. Maybe I'm getting less air out with the syn. or it just doesn't seem to work for me. I flush out my lines every other year so moisture doesn't build up. I used to run a silcon dot5 brake fluid and thought it was absolute **** for good pedal. It's easier to maintain as it doesn't pull in moisture like 3 and 4 but I've not been happy with it either. Looks like you fix it is coming along nicely. Good luck
Click to expand...

No need to explain the good pedal, me likes feeling and hearing how it works because, after all, especially with these old rigs, thats what is all about. high boiling temp and lower moisture retention are what this V syntho (non-silicone based) dot 3-4 is all about. But like you, reality is where its' at. Now that I might have figured out why I have been having so many problems with my clutch hydros I plan on staying with it. like usual, I blamed the equipment, like usual, it probably was my wrenching.
 
Lots of rain all year round but the worst thing is the wet winters with rock salt on the roads.

On the synth fluid, never used it but the bike people often complain it's hard to bleed, something about micro bubbles forming, supposedly the can take weeks for the micro bubbles to form bubbles big enough to bleed.

Micro anything + Land Cruiser = Error
 
If you think about it, the clutch master cylinder probably gets a lot more use than the brake master cylinder. Especially if you do a lot of city driving. This would account for the blacker fluid in the clutch reservoir; the piston cups wear faster therefore contaminating the fluid quicker.

Just an aside, the 1971 FSM does not mention the use of rubber grease for the piston cups at all. It says to just dip them in brake fluid before assembling. I think the lithium grease will really turn your fluid black and may be detrimental to your piston cups.
 
Yes, I've had problems running the synthetic brake fluid. I had my clutch master, slave & brake master cylinders bored out & sleeved w/ bronze from Apple Hydraulics. When I finally got my 40 trail ready, I noticed fluid coming down the firewall from both master cylinders :doh: Called up Apple & thought they may have inserted sleeves w/ loose tolerances around the pistons. They asked what fluid I was using & said my rubber components were not designed to use synthetics & were causing the rubber to deform. I disassembled the units & found that to be true. The slave seems fine, but I'll need to check that too :bang:
 
Ok, malcb, Coolerman, LChamma, it is silcone based grease for contact with rubber, petro based dot 4 for the hydros. Guess I have a weakness for new stuff, but I'll tell you one thing, Gorilla tape! duct tape has been dethroned!
 
I've switched back to dot 3 dino, ran with it a couple days. <<<<< F-junker >>>>>, I have to concur with you about the feel. My stock 74 drums have honestly never felt better than they do now. The only way I can descibe it is they ARE harder, less spongy. Rust caused the the last failure in my clutch slave cylinder. I was thinking that maybe the synthetic non-silicone brake fluid softens the rubber, causing it too seal to the cylinder too well, preventing leak by and therefore, the part of the cylinder exposed to the elements does not get lubricated. just a thought.
 
rsbcruiser said:
the part of the cylinder exposed to the elements does not get lubricated. just a thought.
Click to expand...


Hmmmmmm, not sure of that one, the fluid is hydroscopic and attracts water DOT 3 & 4 are glycol based, don't know if they include a corrosion inhibitor. Could be the case though, interesting that the old stuff feels better - perhaps it's because of the larger volumes used in the drum brake systems?
 
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