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 Posted: Apr 24, 2017 03:38PM
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US
Yup!  I've been using the synthetic DOT 4 for years. 

 Posted: Apr 24, 2017 03:33PM
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So if my brake DOT 3 is low I can add DOT 4?

 Posted: Apr 24, 2017 03:28PM
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US
DOT 4 synthetic fluid is compatible with DOT 3 and does not seem to harm paint.  I use it in a slew of classic survivors,  66 S, 67 Moke,  Rotary Pickup, K5 Blazer w/4-wheel disk, Lotus Elan, Pontiac GTO, even a soap-box derby car I built with a Cooper S master cylinder and Brembo brakes off a Ducati!  Never had a problem, in both brake and clutch systems.... It's not expensive, and you can add it to DOT 3 already in the system!

 Posted: Apr 22, 2017 11:00PM
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This is good explanation of the brake fluid rating system ://www.rdabrakes.com.au/page/TB04.aspx.  

Dot 5 is good in vehicles that sit around a lot.  However, as the label says, it readily absorbs air at the microscopic level which means it can be VERY difficult to get a solid pedal.   Also because any water that does get in stays in a blob which, if overheated, turns to steam = instant no brakes.....  

IMHO (having never used the stuff but know people who have) DOT5 is fine if you own a multi$$$ show car; mainly because it doesn't damage paint.

Otherwise DOT4 is a lot less hassle in normal use.

Yes, you can use different fluid in the brake and clutch systems but I can't see and sensible reason to do so....  

Both clutch and brake use rubber in the hoses and cylinder seals....

Cheers, Ian

 Posted: Apr 22, 2017 05:18PM
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can I keep the DOT 3 in the brake system and use the 5 for the clutch since if I change the brake also have to all the wheel cylinders.. not sure if the brake parts have rubber or just the clutch slave cyl hose

 Posted: Apr 22, 2017 05:03PM
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yes..  it is pricy and you need to flush out all the DOT 3 also..

 Posted: Apr 22, 2017 04:30PM
 Edited:  Apr 22, 2017 04:32PM
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wow.. thank you. will try to get DOT 5
can that be gotten at stores?

would that be for the brake system also

 Posted: Apr 22, 2017 03:01PM
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NO.. do NOT use DOT 3 as it will eat the rubber hoses.. use at least DOT 4 . and really you need DOT 5..  

 Posted: Apr 22, 2017 10:14AM
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we pulled end of slave cyl off.. no leak

then we saw the hose from the slave cyl. leaking. that seems to be the culprit. as well as the cause of the clutch master dirty.

as far as the DOT. meant. 3, is DOT 3 ok?

thank you all for your help.. will try the hose and get fresh system

 Posted: Apr 22, 2017 08:05AM
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US
Both aftermarket master cylinders are low on fluid. 

Start by peeling back the rubber end on the slave cylinder to see if there is fluid leaking. Check the clutch brake pedal up near where it connects to the master cylinder. Look for a fluid leak there, too.

As bc says, DOT 4 if you are using "regular" brake fluid. That's not the cause of your problem, though.

 Posted: Apr 22, 2017 07:17AM
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jim.. check the slave cly..  might be clutch is finally going bad.. ??  what is DOT 30?/ I always use DOT 4.. later bc

 Posted: Apr 22, 2017 04:43AM
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trying to trouble shoot shifting problem.

could not shift.. bled lines.. was able to shift for about 20 minutes of ride, then got hard to shift.. could not get into 1st some after some stops.. pedal felt funny

1. how high should clutch master cylinder be filled

2. is DOT 30 correct for this?

what else can be easily ruled out or looked at before bigger issue may be at hand?