Need to Replace Master Cylinder, and brake lines...

J.HK · 03-20-2002, 07:56 AM

I'm planning on replacing the master cylinder in my 72 911T. It is leaking brake fluid on to the pedal cluster area. I'm also planning on putting all new brake lines on as well.

What order would you replace these things in? If I flush all of my brake fluid, will I have a very hard time bleeding everything well? I was thinking of bleeding with the traditional pedal method with an assistant.

Any info on which order will produce the best results with the easiest bleeding experience would be very helpful.

J

dhaines · 03-20-2002, 08:14 AM

My take would be to open the furthest bleeder and pump the fluid out of the system first. This will minimize the mess from fluid leaking everywhere. From there, it does not really matter, start replacing cyl and brake lines. The point is that you will need a good bleed afterwards. I just used the pressurized system the Pelican sells (Motive??) after doing the same job you describe, including caliper rebuild. I'll tell you it was worth the investment for the power bleeder. Follow the tech notes on their home page for bleeding brakes. FYI, there are a bunch of helpful posts in the archives.....

Jim Sims · 09:01 AM

Get a Motive pressure bleeder; its easily worth the investment and you'll use it every two years at a minimum. I'd flush out your old system with an inexpensive compatible DOT-4 brake fluid (Castrol, etc.) before you take it apart to install the new MC and brake lines. Do this to avoid putting any water or debris into your new components.
See:
http://members.rennlist.com/911pcars/brakefluid.htm

Be sure and get new MC gromments (you'll need 2- Pelican Part No. A-355-929-00); these seal the feed lines from the reservoir. These gromments likely will not come with the new MC. I'd also consider getting four new wheel cylinder bleeder valve dust seals (caps), the originals are likely gone or are brittle. I'd also have a spare wheel cylinder bleeder valve on hand. You'll need a reasonable quality metric flare nut wrench (or tube wrench) set to change out the brake lines; the polished set at Sears is a good buy or look here on Pelican. And don't forget the can of Ate super racing blue brake fluid.

Given the vintage of your car you could very well encounter a "frozen" brake line nut/fitting. If you end up rounding a nut or otherwise damaging a "hard" brake line you can likely obtain replacements at Pelican. Cheers, Jim

marcesq · marcesq's Garage

Remember, if you choose the pedal method, do not bottom out the pedal with the new master cyl. installed as the seals can be damaged.

My 1 cent.

KTL · 09:37 AM

I'll second Jim Sims comment on the frozen fittings. I soaked the fittings long in advance (weeks) with PB B'laster and still had stuck fittings. Ended up twisting many of the hard lines. If you're not too keen on replacing the hard lines (not at all difficult and they're not expensive, except one I think), i'd recommend scraping around the end of the fitting where the tubing enters the nut. Use light pressure with an awl or small phillips screwdriver. This should help break free some of the crud buildup, corrosion and so forth. Will help the penetrating lube get into the fitting a little more.

Make sure your flare nut set includes all sizes. I think the sizes are a little different like 11mm, 14mm, and 17mm? Can't remember exactly, but I did have to buy another wrench- the 11 I think.

Quote:

Remember, if you choose the pedal method, do not bottom out the pedal with the new master cyl. installed as the seals can be damaged.

I thought this was only a controversial problem with the MC when it's old, not new? I remember Warren getting a bit fired up about this subject.

The Motive bleeder is a great piece for the price. You can combine pressure and manual bleeding when using the Motive. A few pumps of the pedal can help dislodge stubborn bubbles while you're pressure bleeding. Motive also helps avoid running the MC reservoir dry 'cause you can fill it up with a bunch of fluid and you don't have to bother checking the reservoir as frequently (or at all really).

I'd replace the lines, then the MC. The old MC still maintains pressure and you can use it to keep the lines from dripping while replacing the flex lines. Push and hold down the pedal with a piece of wood and the lines won't run but a little fluid at first when opened. New MC will keep lines from running too, but replacing the MC will introduce some air into the system which might make more fluid run. No big deal really. Whatever's easiest for you I think.

Jdub · 03-20-2002, 10:49 AM

JHK:

You might consider rebuilding your pedal rack while you are at it. If the brake fluid has been down there, you will have 1) swollen pedal assembly bushings and 2) rust developing under the pedal rack (you would be surprised).

John

PS: Marc, I understand the old plunger/new seal problem that can rip things up, but with a new MC would this be a concern?

J.HK · 03-20-2002, 09:00 PM

Why would you damage the Master cylinder bottoming out the pedal?

Wouldn't it get damaged during hard breaking then as well???

???

KTL · 03-21-2002, 04:55 AM

On an old master cylinder that's never been manually bled, the bore can sometimes develop some corrosion or the like in the area of the bore that never gets touched by the inner seals. You don't bottom-out the pedal of your car in normal use or even hard braking, so that's why that area of the bore is not swiped by the seals. Supposedly if you manually bleed this MC, the seals can get damaged from the corrosion . You then end up with a soft pedal when you're done.

This would not be a problem with a new MC. Manual brake bleeding has been done for a long time!!!

J.HK · 03-21-2002, 08:09 AM

For stuck brake lines what is the best stuff to spray on them in hope of breaking them free without damaging the hard lines??

Is there anything that works well??

And if I flush all of the brake fluid from the system and work with essentially a dry system installing the lines and MC will it be very difficult to bleed??

Jim Sims · 03-21-2002, 08:31 AM

Two products used are "Kroil" and "P. B. Blaster" in aerosol cans. Spray on the night before and let the fittings "soak". One additional technique is to try and turn the stuck fitting slightly in the tightening direction and then back off. This sometimes helps break corrosion products free. If a fitting rounds then it's time for a small pair of vice grips on the fitting as you're going to want to replace that section of hard line anyway. You can flush the old system with new "cheap" fluid until its dry (all the new fluid pumped out too), then disconnect the old MC and hoses and work with the system open. There is no need to bench bleed the new MC. You'll find getting the feeder lines from the brake fluid reservoir into the new bushings in the top of the MC a bit of a chore due to the cramped working space and their resistance to going in. I lubed the bushings with a bit of brake fluid. Remember brake fluid damages paint! Cheers, Jim

KTL · 03-21-2002, 08:40 AM

Quote:

Originally posted by J.HK
For stuck brake lines what is the best stuff to spray on them in hope of breaking them free without damaging the hard lines??

Is there anything that works well??

I just started using the PB B'laster and it's good stuff as Jim said. Most say Liquid Wrench is futile. I agree. Stuff shouldn't squeak when you've lubed it in an attempt to loosen it. Liquid Wrench squeaks sometimes.

I remember somebody posting about this same topic (maybe last summer) and he said his dad recommended tobasco sauce. He tried it and it worked I guess. Never tried it myself.