Flushing a hydraulic brake hose

[Arjimlad]

I am not experienced with hydraulic brakes but managed to bleed & top up my son's MTB Clarkes Exo brakes recently. No visible sign of a leak but they have been on the bike a long time.

These use DOT4/DOT5.1 fluid.

The rear brake was easy but the front one had considerable resistance to the syringe, even though I opened the bleed nipple more than a quarter turn. I think I may need to flush the pipe out to see if there is some crud in it before refilling it with brake fluid.

What fluid should I use to do the flushing?

Would a blast of GT85 or WD40 mess up the DOT4?

Thanks in advance.

 

[richardfm]

It's usual to use fresh brake fluid to flush the old out. Anything else is going to contaminate the new fluid.

 

[Electric_Andy]

I've never used them, but my colleague once said he had to use 2 syringes - one to force the new in, and one to suck the old out?

 

[Jody]

Check the piston isn't sticking in the lever. Or disconnect the hose at the lever end and try to push fluid up.

If it flows with ease you've found your issue.

Flush with DOT fluid and nothing else.

 

[Arjimlad]

Check the piston isn't sticking in the lever. Or disconnect the hose at the lever end and try to push fluid up.

If it flows with ease you've found your issue.

Flush with DOT fluid and nothing else.

Thanks. I will try this.

 

[figbat]

Would a blast of GT85 or WD40 mess up the DOT4?

Yes, don’t do this.