DIY - 720 Truck Clutch Master Cylinder Installation

[Lugnutz]

It's been a while since I posted a DIY, but I had to replace my clutch MC this past weekend. It died (sorta) after 212K miles. The inner piston got stuck inside the MC.

Anyway, the swap looked easy, but it gave me a little trouble. The new MC was cheap - $19 at Autozone. :biggrin:

Bleeding the air outa the lines had me frustrated, but I finally got it right. Anyway, here are some pics to help guide you through some of the process.

Remember:

1. The new MC MUST have the same bore and stroke as your old unit.

2. Your clutch line fittings are probably corroded so I suggest using a vice grip to break them loose on the first try and then using a line wrench to tighten them back up when putting things back together.

3. Brake fluid will eat paint, so don't get it on your nice paint. Wipe spills off right away.

4. Now would be a good time to bleed all the old DOT3 outa the clutch lines and replace it with fresh.

5. I am not a mechanic, so right or wrong, what you read here is just how I did it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Lugnutz]

 

 

 

 

 

 

 

[banzai510(hainz)]

great writeup.

[Eagle_Adam]

awesome detail, thanx man!

[thestrangebro]

you have no idea how helpfull this is. kickass write up

[oldskoolvws]

Very detailed. Thanks. When bleeding with a helper, you should always have the helper stop on the down stroke (pedal to floor) and hold prior to opening the bleeder valve. After you close the bleeder, only then they should release.  This addresses two issues. Provides constant pressure while you bleed air and does not allow air to re-enter the system.

 

I used to do my bleeding like this, with my own home brew garden sprayer, I still have it. The problem with this style is the MC caps. So many variations, very annoying trying make it work for everything.

 

I recently went to one of these. Way better. Pressure from below, forcing bubbles up. Fits everything and forces bubbles up; its natural path through liquids.

http://www.youtube.com/watch?feature=player_embedded&v=Y195Pti7aFo">http://www.youtube.com/watch?feature=player_embedded&v=Y195Pti7aFo" type="application/x-shockwave-flash" width="425" height="350">

 

Sorry, embedded video is not playing well right now.

[Lugnutz]

The pressure bleed idea is good and not difficult.  Suction (or vacuum) bleeding is also well liked.  For me, I need someone at the reservoir making sure it doesn't run dry.

The method I described uses pressure but not CONTINUOUS pressure.  Pumping the pedal builds up pressure in the system because of the valve design in the MC piston AND the clutch damper.  As the helper pumps the pedal a few times (with the slave bleeder closed) you can see the slave piston extend to its maximum length.

 

With the slave piston at its max, there is pressure coming from 2 directions.  The clutch is trying to force fluid back into the slave AND there is pressure in the metal tubing coming from the MC.  When you crack open the slave bleeder, the clutch and the MC are simultaneously pushing fluid out of the slave bleeder.  Crack it open, then quickly close it. Repeat.

 

I'm not a mechanic, so the main feature of my DIY was to show that a clutch MC is rather simple to replace.  Bleeding options are numerous.  I just bought a Craftsman Vacuum Bleed kit (same as Mityvac silverline).  It was affordable and doesn't take up as much room as the graden sprayer.

 

I'm glad people seem to like this thread. B)

[oldskoolvws]

It's a great write up. Just throwing out options and ideas.

 

To overcome the restrictions of the seals in the MC when pressure bleeding, slightly engage the foot pedal to slide the seals between the ports. You'll know. A downside to the way I bleed is that the MC reservoir can actually become over filled. Just need to keep an eye out for that.

 

If anyone is in NORCAL, you can HAVE my garden sprayer setup I made less the MC cap (for VW anyway).