Brake Fluid
Thread Starter
Drifting
Joined: Oct 2003
Posts: 1,405
Likes: 4
From: Lorena Texas
Brake Fluid
I am working on a GS replica that has C4 suspension and brakes (no ABS). We are having trouble getting a good pedal. Have bled the master cylinder and complete system many times. Car has an electric vac pump for assist. The only thing different is that is has DOT 5 (silocone) fluid in it. Any suggestions?
Thanks
Thanks
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi I usethe Castrol SRF. Its the top grade of the Castrol portefolio. It manage extreme heat and is not so picking up humidity as easy as other liquids. I am very satisfied with it.
You appreciate it when using the brakes hard over a period. No spongy pedal
You appreciate it when using the brakes hard over a period. No spongy pedal
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
I don't think you are supposed to be using Dot 5. Kinda like dumping tranny fluid in the engine. So, you'd probably wanna flush that out quick many times to make sure all that Dot 5 is out of there. As I believe it eats up stuff.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Flush that DOT 5 fluid out! Get a couple quarts of a cheap DOT3 fluid to completely flush out all of the silicone fluid. DOT5 is not recommended for ABS systems as the fluid will cause cavitation in the pump and create air pockets. Even without the ABS system in the car, it's not really intended for the later brake systems and the rubber seals.
Did you remove the extra lines going to where the ABS pump was located? Have you tried pressure bleeding the system? Sometimes a simple gravity bleed can pull air pockets out. It's also possible that a hard line may have a slight leak at a junction or a flare at the end of a line is cracked. If you added new hard lines, are they all double flares at the ends? Is it possible that there could be some thread damage at unions?
There are some excellent DOT4 fluids that will work much better. MOTUL 600 and Castrol SRF have some of the highest wet boiling points and they are great for road racing.
Did you remove the extra lines going to where the ABS pump was located? Have you tried pressure bleeding the system? Sometimes a simple gravity bleed can pull air pockets out. It's also possible that a hard line may have a slight leak at a junction or a flare at the end of a line is cracked. If you added new hard lines, are they all double flares at the ends? Is it possible that there could be some thread damage at unions?
There are some excellent DOT4 fluids that will work much better. MOTUL 600 and Castrol SRF have some of the highest wet boiling points and they are great for road racing.
Thread Starter
Drifting
Joined: Oct 2003
Posts: 1,405
Likes: 4
From: Lorena Texas
Flush that DOT 5 fluid out! Get a couple quarts of a cheap DOT3 fluid to completely flush out all of the silicone fluid. DOT5 is not recommended for ABS systems as the fluid will cause cavitation in the pump and create air pockets. Even without the ABS system in the car, it's not really intended for the later brake systems and the rubber seals.
I'm not a fan of the stuff either but the owner must have it.
Did you remove the extra lines going to where the ABS pump was located? Have you tried pressure bleeding the system? Sometimes a simple gravity bleed can pull air pockets out. It's also possible that a hard line may have a slight leak at a junction or a flare at the end of a line is cracked. If you added new hard lines, are they all double flares at the ends? Is it possible that there could be some thread damage at unions?
This is a tube chassis GS replica and all the lines are new using C4 calipers and master cylinder. Front and rear are totaly independant from the master cylinder out.No ABS. I'm will check all the connections.
There are some excellent DOT4 fluids that will work much better. MOTUL 600 and Castrol SRF have some of the highest wet boiling points and they are great for road racing.
I'm not a fan of the stuff either but the owner must have it.
Did you remove the extra lines going to where the ABS pump was located? Have you tried pressure bleeding the system? Sometimes a simple gravity bleed can pull air pockets out. It's also possible that a hard line may have a slight leak at a junction or a flare at the end of a line is cracked. If you added new hard lines, are they all double flares at the ends? Is it possible that there could be some thread damage at unions?
This is a tube chassis GS replica and all the lines are new using C4 calipers and master cylinder. Front and rear are totaly independant from the master cylinder out.No ABS. I'm will check all the connections.
There are some excellent DOT4 fluids that will work much better. MOTUL 600 and Castrol SRF have some of the highest wet boiling points and they are great for road racing.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
I assume you have bench bled the master cylinder before installing on the car?? Any air in the MC could be the cause of a soft pedal.
There is a DOT 5.1 fluid that is not silicone based; I wonder if that may be what the owner wants to use??
Safety Car
Joined: Jan 2004
Posts: 3,759
Likes: 8
With no ABS on the car, the silicone fluid won't necessarily "damage" anything. It's just a fluid that I would not use with C4 brake parts. The older C1 to C3 brakes can use a DOT 5 silicone fluid but that may be due to the type of rubber seal in those components.
I assume you have bench bled the master cylinder before installing on the car?? Any air in the MC could be the cause of a soft pedal.
There is a DOT 5.1 fluid that is not silicone based; I wonder if that may be what the owner wants to use??
I assume you have bench bled the master cylinder before installing on the car?? Any air in the MC could be the cause of a soft pedal.
There is a DOT 5.1 fluid that is not silicone based; I wonder if that may be what the owner wants to use??
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