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Should I Replace Clutch Master Cylinder?


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I have been in the process of doing a lot of brake work and was working on replacing the brake booster and master cylinder today.  Once the old units were out of the car I was able to get a good look at the clutch master and I'm concerned.  First off, the reservoir is bone dry, then it looks a little rough around the master cylinder and lastly it looks like it may have been leaking on the inside of the car.  It is really hard to tell since the brake master cylinder seems to have been leaking based upon the condition of the under side of the booster and the inside of the firewall.  Pix of everything below.  What do you guys think?

 

 

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Inexpensive to replace, Easy to get to with the booster out and your already under the dash side by side with the pedals. With it being dry the slave cylinder could be leaking as well. Pull back the dust cover and take a look.

Edited by Yarb
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I have just read that when replacing the clutch master it is recommended to also replace the clutch slave.  I see two different clutch slaves available.  I am guessing you match up the slave to the year tranny you have rather than the chassis right?

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1 hour ago, texasz said:

 I am guessing you match up the slave to the year tranny you have rather than the chassis right?

I think it matches your clutch fork.  The adjustable ones have a hole in the fork, and an adjustable rod in the slave.

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I'm guessing that your brake booster is shot?  Once brake fluid gets in there, it messes up the diaphragm.  I just had to replace mine due to a leaky master cylinder. 

I had done the clutch master and slave years ago.  I seem to remember needing to transfer over the original push rod on the clutch master to the new one, because the new master had a shorter rod.  The shorter rod wasn't long enough even with the pedal connection spun all the way to the end.  It just didn't have enough throw to completely disengage the clutch.  

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Here's where I landed on the brake stuff...I got the Wilwood 1" master and an 8.5" booster with a conversion mounting kit to prevent modifying the firewall.  Here's a link to the booster for anyone interested:  https://jdm-car-parts.com/products/datsun-240z-8-5-inch-brake-booster-upgrade-kit-for-1969-1972?variant=2376693317641

 

I'm keeping all the original parts in case I want to revert back to stock at some point so thank you for the tip on who can rebuild the booster.

 

Here's a picture of the brake items ready to be installed after I address the clutch master cylinder.

 

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Just now, texasz said:

I am also putting Speed Bleeders everywhere!  On the front calipers, rear wheel cylinders, brake master cylinder, and so on.

I was very disappointed in the speed bleeder approach.  Just couldn't get all the air out.  Had to resort to someone helping me do it the old fashioned way.  

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10 minutes ago, Vorticity said:

I was very disappointed in the speed bleeder approach.  Just couldn't get all the air out.  Had to resort to someone helping me do it the old fashioned way.  

I've heard good things from many people over the years about them...I hope my experience is better than yours was.  We shall have to wait and see.

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10 minutes ago, siteunseen said:

you get a 10% discount from MSA with your user number fyi. Looks like yours is 2593.

No!  I wish I had know (remembered) about that before placing orders...I've ordered a few things from them over the past few months (this item, header, fuel pump for example).  😞

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22 minutes ago, texasz said:

No!  I wish I had know (remembered) about that before placing orders...I've ordered a few things from them over the past few months (this item, header, fuel pump for example).  😞

Add it to your profile on their site, they usuallly automatically add it to the order, I’ve gone to their store in OC and they add the discount there too don’t even have to ask.

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20 hours ago, Vorticity said:

I had done the clutch master and slave years ago.  I seem to remember needing to transfer over the original push rod on the clutch master to the new one, because the new master had a shorter rod.  The shorter rod wasn't long enough even with the pedal connection spun all the way to the end.  It just didn't have enough throw to completely disengage the clutch.  

Make sure to measure the rod distance of the old one before throwing it away or switching the rod.  That way you won't have to do the trial and error approach.  Match the distance and you should be golden.

Also, while you're under the dash at the pedal you might want to change the clevis pin.  They get grooved and reduce throw plus they start to click.  Very annoying.

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2 minutes ago, Zed Head said:

Make sure to measure the rod distance of the old one before throwing it away or switching the rod.  That way you won't have to do the trial and error approach.  Match the distance and you should be golden.

Also, while you're under the dash at the pedal you might want to change the clevis pin.  They get grooved and reduce throw plus they start to click.  Very annoying.

I certainly took great care in the rod measurement/adjustment.  I used this:  https://www.amazon.com/gp/product/B079QGXY55/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

 

On the booster it came with a new pin for attaching to the brake pedal.

 

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Did you pick up a slave cylinder for your clutch system? I can only see the master cylinder in the Z store link.

You can use both types of slave cylinder and they will work perfectly. You have the early model clutch fork with the hole through it, so you will need to re-use you push rod in the later type slave cylinder.

If you do use the later version slave cylinder, do not use the external spring.

 

The slave cylinders function a little differently.

Early type with manually adjustale push rod and return spring:

The spring pulls the pushrod back until the slave cylinder piston bottoms in the slave cylinder.

Setting frre travel is done by adjusting the push rod until there is no free travel and then turning the nut 1.5 turns back. The throw out bearing is free from the pressure plate.

Later type with fixed length push rod:

The slave cylinder has a small internal spring that applies a small amount of force on the push rod. The spring has a free length of about 25mm. Normally you can apply pressure on the clutch fork with your hand and the push rod will compress about 10 to 20mm depending on clutch plate wear. When you release your hand it will return to its rest position and take out all free play in the clutch fork. The throw out bearing is always in contact with the pressure plate.

 

If you use the later version, adjust it by bottoming the push rod and adjust the nut until the distance between rest position and bottoming is about 10 to 15mm. You will never need to adjust it again, the clutch disc will be long worn out before the 10mm free travel is gone.

 

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Another thing to look out for with the clutch master cylinder is the poor quality assemly work. The parts are good quality, but the pre-assembly cleaning is not. You often find metal shavings left over from machining the cylinders. This can destroy the rubber cups and cause early failure.

It is recommended to dismantle the master and slave cylinder and clean them thoroughly before use. Do not use gasoline or aggresive degreasers, but use a simple brake cleaner spray can.

Assemble with grease suitable for EPDM rubber. A lot of people don't realise the brake and clutch systems use EPDM rubber where the fuel and radiator systems use NBR or FKM fluoropolymer (viton). EPDM does not go well with gasoline.

 

While you are at it, it would be a good idea to change the clutch hose. It generally doen't endure the forces and movement the brake hoses go through, but it can age over the years.

Edited by EuroDat
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@EuroDat, I have not picked up the slave yet as I will be replacing the engine/transmission after the brake work is complete and I'll work on the clutch slave at that time.  I will likely use the later slave, I'll be running a later model 5-speed (either from a 280Z or 280ZX, I have not decided which one yet).

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20 hours ago, texasz said:

I certainly took great care in the rod measurement/adjustment.  I used this:  https://www.amazon.com/gp/product/B079QGXY55/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

On the booster it came with a new pin for attaching to the brake pedal.

That's a cool tool.  I had clicking on my clutch pedal, and I've read about others having it also.  Every clutch release, click, click, click.  You can see the groove by eye, so you'll know if it's going.

image.png

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