I am replacing my brake booster and master cylinder on my 69 GS400? Any tips or tricks to help me complete this project. Do I have to bleed the brakes? I have never done this so any help would be much appriciated
You must bench bleed the m/c till there are no bubbles, the replacement m/c usually has instructions and fittings to do this. Anytime you open up the system you should bleed the brakes starting with the furthest wheel away from the m/c, that would be rr, lr,rf and finally lf. After a number of years it's a good idea to bleed the brakes even if you're not replacing anything. Fresh brake fluid will help slow down rust and corrosion in the system. Gene:TU:
What I usually do is bench bleed it first. This step is the most important, any trapped air will just end up somewhere else and cause trouble. Then I open all 4 bleeders down at the wheels and let them gravity bleed for a while, making sure to keep the fluid level up in the reservoir......if it goes empty, you have to start all over. ou: Then after that, I get a helper to pump the pedal 5 times and hold, bleeding each wheel individually until the stream is clear and has no air.......beginning with the right rear and ending with the left front. :TU:
Its not too bad of a job, I replaced the booster and master cylinder on mine last year. The hardest part was getting to the bolts on the passenger side of the booster since I was too lazy to remove my wiper motor. I could not believe the amout of sludge in the bottom of my original master cylinder... Bench bleed the master cylinder per the instructions... When I bled the brakes (at the wheels) I ran a long clear piece of plastic tube from the bleeder into a clear jar with brake fluid, pumped the peddal until the bubbles stopped and then moved on to the next wheel. I almost put myself through the windshield the first time I applied the brakes since they worked so much better.... :beer
There was no directions that came with the master cylinder? Can anyone explain the steps on bleeding the master cylinder?
Plug the fluid outlets. Secure in a vise, fill reserviors with fluid, push plunger in with a phillips screwdriver until bubbles stop. Then install. Then bleed brakes as stated above :grin: My buddy and I did it while the master was in the car. He put his fingers over the outlets while I SLOWLY applied pressure to the brakes- That worked too.
The complete proceedure is in the Chassis Service Manual. If you don't have this book yet, it's time to get one, you'll need it. Also, you might want to start soaking the wheel cyl. bleaders with some penetrating oil, one of the bleaders breaking off can ruin your day. Depending on when the last time the brakes were done, I'd plan on replacing them as well. Flush the system, replace the master and wheel cyl., bleed them per the manual and never worry about it again. Good Luck, Rich
If you decide to bench bleed the m/c in the car instead of a vise be very careful with the amount of pedal pressure you apply, do a couple of slow short pushes with someone watching the bubbles. Also since you haven't done this before, be advised that brake fluid makes a great paint stripper Gene
I had heard that if going to bleed might as well use DOT 4 fluid even if you are not flushing the whole system, my understanding is it is compatible with DOT 3. Is this true??
