MNS brake fluid change

[ATracksler]

I have to replace one of my brake lines on my 1980 MNS.

I know I have to Derain all the brake fluid from the line to replace the first section that I have to replace. Do I need to get all the fluid out of both sides completely before I take the line off?

Or do I get enough fluid out and replace the line and then flush and get the air out?

Is there a method with dual front disks? Or do I just use one side? I have the Clymer manual and it isn't specific about completely draining the lines to replace the first section.

Thanks in advance, ad

[HalfCentury]

Brake fluid should be changed regularly per the factory manual schedule.

Some people will use a syringe other means to push the fluid backwards from the bleeder nipple through the line into the master cylinder. This eliminates most or all of the air bubbles before bleeding. This requires that you do not have a fancy bleeder nipple installed.

[TADracer]

If you still have the original lines remember they are now 36 years old rubber. You might consider changing them all to something newer. In any case with brakes its clean, clean, clean. You can use the master cylinder to remove all the fluid or if you have a hand-held vacuum pump you can suck it all out. When bleeding the system after the hose replacement you might need to bleed the master cylinder first and then connect your top line and bleed the system. Bleed from both calipers until you get clean fluid. Keep brake fluid off of your paint!

I use a vacuum pump and change the fluid each year during my Spring tune-up. Only takes about twenty minutes to change out all the fluid front and back.

[DiverRay]

Per Yamaha manual, brake fluid should be replaced every two years, when you replace the seals or when you work on the brakes.

[ATracksler]

When Im draining the fluid, do I have to drain it out of both sides? or will it all come out of one side?

[DiverRay]

You will need to drain out of both calipers on your bike. The '80 works BOTH front calipers, and the '81 just works 1, with the rear brake working the left front, IIRC.

[ATracksler]

Do I do them one at a a time or both at the same time?

[DiverRay]

I did both at once when I changed the brake lines on my '80LG. I put a pan under one side, pulled the bottom of the line from the caliper, pullded the bolt from the master and let that line drain. I then went to the other side and put the pan under it and pulled the bottom of the line to let it drain. Replaced all three lines up front, and I did flush some new, clean brake fluid through them to clean out the splitter on the front forks. I then bolted the lines on the calipers, the splitter, and then the top line bottom to top. After that, I filled the MC with fluid and started to bleed with the vacuum bleeder.

[cajun31]

Brakes

Atrack.... you will be better served to go through the entire brake system front and back. If you still have the original brake hoses you should replace those as has been previously stated. They are rubber and with the age on them they do break down. I would spend the time rebuilding all the calipers as well as both master cylinders. Kits for all are available and worth the investment. It will give you the opportunity to inspect and repair all components as necessary. You might also want to think about replacing the caliper pistons with Stainless Steel replacements. I am a firm believer in making sure the braking system is clean and works properly. Leaving them to chance is a recipe for disaster. Too many bad things can happen. Doing as I recommend wil solve you problem of fresh brake fluid too.