Brake fluid change

[56G80S]

May be of interest to those with the modern AJS. I recently gave my Yamaha XJ600S it's 16k service.

I always knew brake fluid was hygroscopic and did as the manual; said (sort of, I didn't take the calipers apart and replace the seals).

After riding the Matchless for so long, I thought the Yamaha's brakes were good. Now, after flushing everything through with clean DoT4 I realise they weren't as good as they could've been.

The difference was really noticeable and thanks to the help of my eldest son it was very straightforward to do. The old fluid was quite discoloured but there were none of the tell tale black specks to suggest seal problems. All for a few quid of fluid.

I didn't replace the hoses as careful inspection showed them sound. The machine was always garaged when not in use, and still is, so no sunlight damage. I will replace them over next winter and put some nice new ones on.

Johnny B

[thornebt]

When I had older cars I found a couple of times that a change of brake fluid caused the system to develop a leak. I don't know if that was co-incidence but it didn't seem like it to me. There's probably a scientific explanation for this! Cheers. Bruce.

[1608]

Where were the leaks? I think that when changing fluid in an older system you will be causing the pistons in the slave/master cylinders to travel back and forth within the cylinders causing the seals to breakdown. On a couple of occasions some years ago I remember trying to bleed new clutch slave cylinders ( cars ) only to have the master cylinder seals pack up at the same time.

[56G80S]

By heck, hope you're wrong.

Certainly all OK on a a ride out of about 80 miles the other day.

I'll keep a careful eye on the matter.

JohnnyB

[1608]

My theory only really applies to reasonably high mileage vehicles.