Newbie here. I drive an S2000 but today I get to replace Mom's brake master cylinder on her '90 Accord. I read the DIY on changing the master cylinder (great write up, by the way) and I have a couple of questions. (I couldn't find the answer when I did a search)

The '90 Accord has 42k miles on it and I doubt the brake fluid has ever been changed. I understand how water gets in and swells the seals in the master cylinder (and I think that's why it went bad). If I change the fluid in the entire system, will that affect the seals at the calipers and cause them to shrink and eventually leak? Or is it better to just leave the old fluid in the lines and let it be. I understand that if I bench bleed the master, I may not need to bleed the entire system.

BTW, I was gonna upload an avatar, but I guess I don't have those rights yet.

Thanks in advance,
Jimbo

 

I'd bleed the system to get fresh fluid throughout. It's not so much swelling of the seals, but as brake fluid absorbs moisture it gets corrosive.

Be careful opening up the bleed valves at each wheel. They're easy to break. Soak in PB Blaster or Kroil overnight. Hold the wrench to apply pure torque with no bending. Cross your fingers & toes & have plenty of beer on hand in case they break anyway.

Bench bleeding doesn't really avoid the need to bleed the brakes. It just avoids the problem of having to bleed again & again to work the last stubborn bubble out from the master cylinder.

42k miles? There's people around here who put almost that many on each year.

I'm gonna move this to General Tech since it probably won't result in a big new procedure write-up.

 

Thanks. Yeah, after I posted, I realized I probably stuck it in the wrong section.

Yup, 42k. As they say, "Only driven by a little old lady to church on Sundays."

I appreciate your input. This looks like a 3 beer job unless I have to adjust the pedal freeplay.

 

I hope you have a helper. Really just another set of hands. That MC is combersone to get in there and bolt back up by yourself.
I bench bled it and still had to bleed the brakes on my 95 V6.
But it did not take much brake bleeding at all.
You'll also need the helper for the brake bleeding job unless you have a power bleeder or whatever those are called.
I didn't have problems with my bleed screws thankfully.
I made sure to use a closed end wrench on them though.

It really depends how fast you drink the beer. As hot as it is where I am, an Oil change is about a 2 beer job. If I did it again this time of year, changing the MC would probably be about a 6 beer job for me haha.

 

Forgot to mention that...

Check the piston rod length sticking out from the master cylinder, old vs. new. They should be EXACTLY the same. This seems to be an issue for some cheaper aftermarket brand MCs.

If they don't match, Honda has a strange "tool" that's really a measurement fixture to transfer that length over to the vacuum booster, so you can make a corresponding adjustment in the pedal pushrod.

Details should be in the pdf manuals linked in a sticky thread in the DIY secton. Seems to be the same tool used over a 20-year span of Honda cars.