Dot 5 brake fluid and master cylinder issues

[gtx6970]

Anyone had master cylinder issues when using DOT5 brake fuild ( system is completely brand new btw ) so there is no chance of mix issues with non dot 5 fluid

My challenger was dot 5 and the charger in now is dot 5 , and  have NO problems.

yet , the cuda in the shop now, I can't get the new master cylinder to bench bleed to save my butt, the piston hangs up in the bore and doesn't return to full release
the master cylinder on the car feels like it's not releasing quick enough ( thus the change ) Yet it bench bled normally and also bled the system on the car just fine

every single item on the car is brand new, from the master cylinder to the wheel cylinders and calipers.

And this is the 2nd master cylinder from this vender with the exact same issue

[A383Wing]

I'm gonna guess that they are using rubber piston seals that are not compatible with Dot 5 fluid

[Big Sugar]

 

I've also read that Dot.5 can also give you a spongy brake pedal feel.


Ron

[John_Kunkel]

All fluids that get a DOT rating must be compatible with other DOT fluids and the system components.

Did the piston hang up when the MC was dry? New is no guarantee of "good".

[gtx6970]

Well, as it sits everything works.

My problem is coming in when I attempt to bench bleed the new master cylinder - it hangs up in the bore and doesn't return to full release , thus not allowing fluid to re-enter into the piston bore. And this is the second unit I've received from this vender with a very similar problem .
1st unit would bleed the primary side( larger side ) and but I could not get any fluid from the secondary ( smaller ) side that services the rear brakes. This newest one I get no fluid from 'either' port during an attempt to  bench bleed it.
My customer is getting these new master cylinders from a vender at Carlisle and this vender is also usually at the Nats . As per the packaging they are coming  in says Centric if it matters

The cardone reman unit on the car now is 'by casting number' for an A-body. It fits the car perfectly and bench bled just fine but it seems to be slow releasing after applying the brake pedal to stop the car. As it sits the car will stop fine and the pedal is perfect, but it hesitates maybe 1 or 2 seconds before the car will roll easily once the brakes are released. it will roll but takes and ever so light effort for a seond or so once the pedal is released. Whether this is related to the fluid issue is unknown, but like I mentioned it bench  bled fine .

I've used DOT 5 fluid in everything I've done in the past 5 years and this is the 1st time I've ever had ANY issues of ANY kind

1969 Charger in the shop along side this car is also all brand new,,, and it works perfectly with the exact same fluid out of the exact same bottle. It bled fine both on the bench and on the car and stops perfectly with no issues and no spongy pedal 

every single piece on both  cars are new- from the wheel cylinders to the master cylinder and everything in between

[gtx6970]

Did the piston hang up when the MC was dry? New is no guarantee of "good".

John,
To be honest I did not think to try it dry before hand. so I can't answer that one

[resq302]

I have heard that some companies that rebuild brake parts do not guarantee their rebuilds when you use DOT 5.  There is something with DOT 5 and not being compatible with all rubbers which causes them to swell.  Kinda like what you are experiencing Bill.  That is the primary reason why I stuck with Dot 3 / 4. 

[A383Wing]

I have heard that some companies that rebuild brake parts do not guarantee their rebuilds when you use DOT 5.  There is something with DOT 5 and not being compatible with all rubbers which causes them to swell.  Kinda like what you are experiencing Bill.  That is the primary reason why I stuck with Dot 3 / 4. 

agreed...that's what I have heard as well

[John_Kunkel]

I'd say that if some companies have a problem with rubber compatibility they're not using DOT-approved rubber components.

[resq302]

If that is the case then people should avoid Apple Hydraulics for another reason other than the issues I had with them!  The clearly state in a piece of paper that they send you that you can not use DOT 5.

[Charger-Bodie]

Ive used gallons of dot 5 over the years and the only complaint Ive ever had is that its a little harder to get all of the air out. Once bled it works perfect and Ive never had any of the issues with swelling either.

[bill440rt]

I've had DOT5 in my '70 for years, no problems. Completely stock yet rebuilt brake system.

However, when I purchased the Wilwood setup they told me it was DOT3 or 4 ONLY (they recommended the DOT4 over the DOT3). SSBCrap told me the same thing.

I'm about to take the plunge on a Master Power kit for my '68, they also state DOT3 or 4 ONLY, and that using DOT5 will void their warranty.

[Back N Black]

Can DOT 5 Brake Fluid Be Used Instead of DOT 3 or 4?

Always refer to vehicle owner's manual for what the manufacturer recommends or warns against. As a rule, vehicles equipped with antilock brakes (ABS) should not use DOT 5 brake fluid.

DOT 5 brake fluid is silicone based. DOT 3 (standard) and DOT 4 (heavy-duty) are glycol-based. It can be distinguished from conventional brake fluids by its purple color (which comes from a dye).

Silicone does not absorb moisture. DOT 5 brake fluid does not become contaminated with moisture over time as conventional DOT 3 and 4 brake fluids do. Silicone is also chemically inert, nontoxic and won't damage paint like conventional brake fluid. It also has a higher boiling point.

Because of this, it is often marketed as a premium "lifetime" brake fluid. It is often used to preserve brake systems in antique vehicles and those that sit for long periods of time between use.

DOT 5 silicone brake fluid is also very expensive (costing four to five times as much as ordinary brake fluid), and it won't mix with glyco- based brake fluid (creating concern over sludging if all old fluid isn't removed when a system is refilled with silicone).

Silicone also has slightly different physical properties and compressibility, making it unsuitable for ABS systems calibrated to work with DOT 3 or 4 brake fluid.

[resq302]

I've had DOT5 in my '70 for years, no problems. Completely stock yet rebuilt brake system.

However, when I purchased the Wilwood setup they told me it was DOT3 or 4 ONLY (they recommended the DOT4 over the DOT3). SSBCrap told me the same thing.

I'm about to take the plunge on a Master Power kit for my '68, they also state DOT3 or 4 ONLY, and that using DOT5 will void their warranty.

Bill, 

I guess it all comes down to who uses what grade of rubber when they build/rebuild the components.  Do you remember who rebuilt the stuff on your 70?  Or if they said you could use DOT 5?

[bill440rt]

I've had DOT5 in my '70 for years, no problems. Completely stock yet rebuilt brake system.

However, when I purchased the Wilwood setup they told me it was DOT3 or 4 ONLY (they recommended the DOT4 over the DOT3). SSBCrap told me the same thing.

I'm about to take the plunge on a Master Power kit for my '68, they also state DOT3 or 4 ONLY, and that using DOT5 will void their warranty.

Bill, 

I guess it all comes down to who uses what grade of rubber when they build/rebuild the components.  Do you remember who rebuilt the stuff on your 70?  Or if they said you could use DOT 5?

I'd have to go thru my old paperwork, I honestly don't remember 100% but something tells me Master Power rebuilt everything. Calipers were stainless sleeved, wheel cylinders, etc. At this point, it's well out of warranty! 

I have DOT5 in the '68 as well, stock brake system again but all lines & hoses were replaced. Same with the wheel cylinders.

The DOT4 I'm using is a SYNTHETIC fluid. It will still damage paint, though. I plan on switching to DOT4 in the '68 after the brake conversion.