Bleeding ZF5 clutch

[Littlebeefy]

Hi guys,

I am having a hell of a time bleeding the clutch master/slave that I just installed. It is CENTRIC 13665513. It is a pre-bled system, but I had to replace the line so it needed to be bled again. We used a power bleeder but it clearly has air in it because I'm getting very little action in the slave. This unit has a bleed screw with a separate little hole in the back of the unit, so you can't attach a hose to see bubbles (it just spills out of the back of the unit through the pin hole when the screw is loose). So I can't use a speed bleeder screw or a vacuum bleeder.

When I look online, I see about a million tips on this, and some of them are contradictory. Some say to tip the master up, some say down, some say level. Some say that air usually gets trapped in the slave and others say it usually gets trapped in the master. Some say to only bench bleed and others say it is easier in the truck.

Between the integrated reservoir in the master and the separate bleed hole in the slave I'm having some difficulty. Anybody done the full bleed on one of these and if so any set of instructions that you found worked best? Like I said, I have a power bleeder if there is a way to make that work best.

Thanks,

Chad

[Gary Lewis]

Can you drive the truck? In Big Blue's case I had to drive it and bounce it around to get the air out.

At first I couldn't get the clutch to disengage so I started in 2nd gear and drove a bit, which got enough pedal to shift gears. Then it got better and better as I drove and shifted.

[Littlebeefy]

Can you drive the truck? In Big Blue's case I had to drive it and bounce it around to get the air out.

At first I couldn't get the clutch to disengage so I started in 2nd gear and drove a bit, which got enough pedal to shift gears. Then it got better and better as I drove and shifted.

Thanks, Gary. In theory, yes, I could drive the truck. We finally got it "completed" last night and I test drove it about 2 feet forward and two feet backward. Sort of sounds similar to what you described except I can shift with a noticeable "thud". With the pedal fully depressed I was getting minimal contact between the disk and the flywheel (enough that I had to keep the brakes pressed in to keep the truck from moving with the clutch pressed in). If I let the clutch pedal out even a minute amount, I get bite instantly.

If the correct way to bleed it involves driving, I could probably do that around the block a few times. Is that what I should do at this point? Then bleed them again or what?

[Gary Lewis]

Thanks, Gary. In theory, yes, I could drive the truck. We finally got it "completed" last night and I test drove it about 2 feet forward and two feet backward. Sort of sounds similar to what you described except I can shift with a noticeable "thud". With the pedal fully depressed I was getting minimal contact between the disk and the flywheel (enough that I had to keep the brakes pressed in to keep the truck from moving with the clutch pressed in). If I let the clutch pedal out even a minute amount, I get bite instantly.

If the correct way to bleed it involves driving, I could probably do that around the block a few times. Is that what I should do at this point? Then bleed them again or what?

Yes, I recommend driving it around the block, and pumping the clutch pedal. Pretty soon I think you'll be able to shift.

I didn't bother to bleed after that. Once it was shifting I was happy.

[Rembrant]

I have done a couple M5OD hydraulic clutches with the concentric slave cylinders. I have a vacuum bleeder that uses compressed air, so it provides a constant vacuum and it's hands free, so I just hook it up and leave it pulling. I then pour fluid in the master, and keep pouring it in never letting it run dry. I stop every now and then and pump the clutch pedal 20-25 times, and then go back to pouring more fluid in. That seems to have worked for me both times starting with dry systems. I poured a half a liter or more though the system over a 15 minute period with the vacuum on and me randomly pumping the pedal. After that, I never touched it again.

[reamer]

I have done a couple M5OD hydraulic clutches with the concentric slave cylinders. I have a vacuum bleeder that uses compressed air, so it provides a constant vacuum and it's hands free, so I just hook it up and leave it pulling. I then pour fluid in the master, and keep pouring it in never letting it run dry. I stop every now and then and pump the clutch pedal 20-25 times, and then go back to pouring more fluid in. That seems to have worked for me both times starting with dry systems. I poured a half a liter or more though the system over a 15 minute period with the vacuum on and me randomly pumping the pedal. After that, I never touched it again.

If the slave is on the side of the tranny:

Easiest way to do this is to

Bench bleed the MC.

then

Remove the line and slave from the truck and assemble (master, the line, the slave)

get a 6' or higher step ladder

attach the master to the top of the ladder pitching downward (so the line at the lowest point)

With MC cover off, open the bleeder on the slave, Keeping the MC full at all times.

pump the MC a few times to get most of the air out of the slave. Close bleeder.

Now, this is the best part, Take a 5/8" wrench and tap the line, starting by the Slave and go up the line.

You'll see the air bubbles rise up to the MC.

Keep tapping till the line is solid, now take the assembly off the ladder and bench bleed the MC again, it will be very hard to push now.

Re-install the whole assembly on the truck.

Works too if the slave is installed around the shaft, Bleed the slave, then bench-ladder the line and MC

 

[85lebaront2]

If the slave is on the side of the tranny:

Easiest way to do this is to

Bench bleed the MC.

then

Remove the line and slave from the truck and assemble (master, the line, the slave)

get a 6' or higher step ladder

attach the master to the top of the ladder pitching downward (so the line at the lowest point)

With MC cover off, open the bleeder on the slave, Keeping the MC full at all times.

pump the MC a few times to get most of the air out of the slave. Close bleeder.

Now, this is the best part, Take a 5/8" wrench and tap the line, starting by the Slave and go up the line.

You'll see the air bubbles rise up to the MC.

Keep tapping till the line is solid, now take the assembly off the ladder and bench bleed the MC again, it will be very hard to push now.

Re-install the whole assembly on the truck.

Works too if the slave is installed around the shaft, Bleed the slave, then bench-ladder the line and MC

Here is a trick from a Mercedes-Benz service manual. On their cars in the late 60s they started using an inside the car clutch master cyl that sits on an angle and is virtually impossible to bleed normally.

Their method is to take a hose that will fit over the bleeder screws and run it from the left front caliper bleeder to the clutch slave bleeder. Loosen the clutch slave bleeder about 1 - 1 1/2 turns, using a helper or pressure bleeder, bleed the left front caliper through the clutch system. This pushes the air to the top and out. The one recommendation I have on this, if there is a top/bottom on the slave, use the bottom for the bleeder so air has to come out through the master.

[Littlebeefy]

Here is a trick from a Mercedes-Benz service manual. On their cars in the late 60s they started using an inside the car clutch master cyl that sits on an angle and is virtually impossible to bleed normally.

Their method is to take a hose that will fit over the bleeder screws and run it from the left front caliper bleeder to the clutch slave bleeder. Loosen the clutch slave bleeder about 1 - 1 1/2 turns, using a helper or pressure bleeder, bleed the left front caliper through the clutch system. This pushes the air to the top and out. The one recommendation I have on this, if there is a top/bottom on the slave, use the bottom for the bleeder so air has to come out through the master.

It does seem like genius to use pressure from the the brake master to reverse bleed the clutch. Those Germans!

But... if you happen to have a pressure bleeder instead of a friend to help, why wouldn't you just hook that up to clutch slave directly instead of pressurizing through the master?

[RenoHuskerDu]

Here is a trick from a Mercedes-Benz service manual. On their cars in the late 60s they started using an inside the car clutch master cyl that sits on an angle and is virtually impossible to bleed normally.

Their method is to take a hose that will fit over the bleeder screws and run it from the left front caliper bleeder to the clutch slave bleeder. Loosen the clutch slave bleeder about 1 - 1 1/2 turns, using a helper or pressure bleeder, bleed the left front caliper through the clutch system. This pushes the air to the top and out. The one recommendation I have on this, if there is a top/bottom on the slave, use the bottom for the bleeder so air has to come out through the master.

Genius tip! One of my sons is a full time wrench, and even he didn't know this trick. Just make sure your brake system has nice clean new fluid in it first.

[85lebaront2]

It does seem like genius to use pressure from the the brake master to reverse bleed the clutch. Those Germans!

But... if you happen to have a pressure bleeder instead of a friend to help, why wouldn't you just hook that up to clutch slave directly instead of pressurizing through the master?

You probably could do that, never had one to try it with, risk might be keeping the supply hose from coming off the bleeder on the slave cylinder. I have owned 3 vehicles with hydraulic clutches and driven many others. I taught my supervisor in the lab that trick, he had a Fiat X1 9 where the master is up front and the slave behind. Having driven full mechanical clutch cars (1964 Falcon, 1966 Shelby), cable clutch cars (1964 and 1965 Corvairs, 1981 Omni, 1987 Horizon) and hydraulic clutch vehicles (1958 F100, 1959 MGA, 1961 Mercedes-Benz 220Sb, 1963 Jaguar E-type and lots of the last of the MGBs as I dealer prepped them) I prefer the hydraulic clutches for ease of operation and smoothness.

Both the Falcon and Shelby broke the Z-bars by splitting them at the ends where the lever was welded to the tube, the cable clutches had a habit of giving little or no warning before the cable broke and the hydraulic could also fail without much warning, particularly where the plastic line ran close to the exhaust.