15/16 MC upgrade. Push rod too long??

[Horatio]

Picked up a remanufatured 1973 master vac. Also found myself a nice 79-81 15/16 MC (two separate resevoirs and says 15/16 and Nabco). I adjusted the push rod length adjusting nut so it was bottomed out. Reaction disk is in place. Seems that the push rod is still too long for the MC to sit flush against the MV housing (it sits out by about 3/8").

 

Am I correct that the push rod needs to sit flush against MC piston?

 

Any suggestions? Should I just grind down the adjusting nut so it will fit?

 

I thought the issue with this upgrade was the push rod needing to be lengthened?

 

Here's a pic of what I have:

 

[Horatio]

Ok, so the only thing i'm coming across on-line is adjusting the pushrod length while the complete system is intact and full of fluid.

 

Adjust by:

 

- opening the cap

- have someone depress the brakes

- observe the fluid in the resevoir for movement

 

You are looking for a "slight" movement of the fluid.

 

If no movement - Shorten the pushrod

 

If "excess" movement - Lengthen the pushrod

 

Now, can anyone explain what "slight" and "excessive" movement is?

 

Also, Does anyone have any idea what the initial setting should be to maximize my chances of not having to adjust things once I have it installed? (i.e. 1/8" from the psiton, 1/4" from teh piston"????)

 

Sooo, the push rod should not sit flush to the MC piston then??

[Horatio]

Can this be done during a bench bleed?

[Horatio]

Found this also. Seems to explain things a bit more. Suppose I could cut up my old MC to make a shim from the old mounting plate.

 

MASTER CYLINDER PUSH ROD ADJUSTMENT:

 

NOTE: Correct push rod length is essential to reliable braking. If the rod is too long, it causes the compensating ports in the master cylinder to be closed off, eventually resulting in brake drag. If the push rod is too short there will be excessive brake pedal travel and possibly there will be a groaning noise from the brake booster. Use the following procedure to check the push rod adjustment. CAUTION: Wear protective goggles when performing the following procedure! Brake fluid may erupt from the master cylinder with sufficient force to cause personal injury.

1. Remove the master cylinder reservoir cap or cover.

2. While an assistant slightly depresses the brake pedal, watch for fluid to erupt in the reservoir when the pedal is depressed 3/8" to 1/2". This indicates correct push rod length. On dual system master cylinder, fluid may spurt only from the front reservoir.

3. If the pedal travels more that 1/2" before master cylinder fluid erupts, the push rod is too short. If nothing happens no matter how far the pedal is depressed, the push rod is probably too long. 4. To adjust the push rod length, first remove the master cylinder from the power booster. Using a pair of pliers, turn the push rod adjusting nut in to shorten and out to lengthen the push rod.

5. If the push rod is non-adjustable, use shims between the master cylinder and power booster to shorten it. If too short, remove existing shims or remove the push rod from the booster and replace it with one of the proper length.

6. Install the master cylinder onto the power booster and recheck push rod length. 7. Connect the vacuum hose(s) to the power booster.

8. Reconnect the ground cable to the battery.

9. Make sure the braking system works correctly before moving the vehicle. If the pedal is soft or has excessive travel, it may be necessary to bleed the entire braking system.

[260DET]

Is the pushrod back as far as it will go in the booster? Needs just a touch of clearance to the MC piston, a few thou from memory, also from memory I think you can look down into the MC to see if the piston moves when the MC is bolted to the booster.

 

Its a while since mine was done, don't forget a spot of rubber grease on the back of the piston.

[Horatio]

Thanks Richard. A few thou, huh? How 'bout really, really close but not quite touching!!!!

 

Now, I know several have done this upgrade. Am I being ignored because there is an assumption I have not searched, or is everyone else as clueless about this as me??

[IdahoZ]

I too am in the middle of a 280ZX (15/16") MC upgrade on my 72 240Z. I too have questions about the push rod adjustment specs that I could not find a definitive answer on. I was trying to figure out what the GAP measurement would be between the end of the push rod and the MC piston.

 

I looked at both the Technical Service Manual (TSM) I have for my 1972 240Z and the one for a 280Z and the adjustment measurements are different? I find this puzzling, since the MC part number for both the 240Z and the 280Z are the same. Why would the gap between the end of the push rod and the MC piston be different?

 

The 240Z manual says to adjust the push rod so that the DEPTH from the flange surface to the push rod end is 3.5 to 4.0 mm.

The 280Z manual says to adjust the push rod so it is sticking out ABOVE the flange 9.75 to 10mm.

 

When I looked at my 240Z booster and MC after removing them from the car, the push rod was adjusted so the end of the push rod was ABOVE the flange surface about 10mm, which is within spec if you follow the 280Z service manual. This gave me push rod to piston gap of about 0.5mm. If I follow the service manual for the 240Z, the gap should be 13mm to 14mm which I could not achieve with the push rod I have as it is way too long?

 

The depth from the flange mounting surface to the piston on my new 280ZX MC is 9.8mm vs the 240Z MC which is 10.5mm. If I knew what the GAP measurement (measurement C on the attached sketch) should be, I can simply adjust the push rod length to work with the 280ZX MC.

 

[h4nsm0l3m4n]

I installed my 15/16" MC a while back an went through the same headache. I couldnt find a consistent number for the length of the pushrod. I think eventually what I ended up doing is looking in the FSM for the 280zx the MC is out of and setting the length of the pushrod as close as I could to those specifications.

 

Unfortunately, if I remember right, this still wasnt perfect so I had to do some trial and error testing to get the right length. Hopefully that helps a little...

Edited March 8, 2010 by h4nsm0l3m4n

[h4nsm0l3m4n]

double post... sorry

Edited March 8, 2010 by h4nsm0l3m4n

[Nigel]

It seems that very few people are aware that '73 240Z's have the same braking system as the 280Z. So they read the service manuals and assume all 240Z's are the same, or worse, that all Z's are the same, which leads to all sorts of confusion. 1973 and later Z's have a longer brake booster pushrod nose (length from the tip of the pushrod to the hex) than earlier Zs, as is seen in the picture IdahoZ posted. It's a little hard to see the nose of the pushrod on the 240Z drawing, but it's significantly shorter than what you can see on the 280Z drawing, or the picture at the beginning of this thread, which is of the longer pushrod. The pushrod is longer because the MC on '73 and later Zs have a deeper bore where the pushrod makes contact with the MC piston. Earlier 240Z MC's have a much shallower bore, and consequently, a shorter pushrod nose. Therefore, a 280ZX master cylinder will bolt up to a '73 or later Z without requiring much if any adjustment to the push rod (my '73 didn't need any adjustment to the pushrod). If you put a later MC on an early 240Z booster with the short pushrod nose, you need to unthread the pushrod almost all the way to get the right length. That doesn't leave the pushrod with many threads holding it in, so a much safer solution is to to swap out the pushrod with the later long-nosed version (this is what I did for a friend with a '71 Z). Then, use the dimensions for the 280Z to set the proper length.

 

I looked at both the Technical Service Manual (TSM) I have for my 1972 240Z and the one for a 280Z and the adjustment measurements are different? I find this puzzling, since the MC part number for both the 240Z and the 280Z are the same. Why would the gap between the end of the push rod and the MC piston be different?

 

What year of 240Z MC did you look the part number up for? If it was a '73 240, then it will have the same PN as a 280. If it was from an earlier 240, where did you look up the part number? If it was from an aftermarket book, then they may have just lumped all the Z's together, assuming they are all the same.

 

Nigel

'73 240Z

[IdahoZ]

Thanks for the clarification Nigel. It is starting to make sense, I think? What's confusing is the diagrams in the FSM I have for the 1972 model shows a very short push rod on the master-vac/booster and a deep throated MC? One of the diagrams has to be wrong. It makes sense that the earlier models had a very shallow throated MC.

 

I just downloaded the brake section from a 73 FSM and the master-vac diagrams shows the push rod is longer, but the push rod adjustment instructions are the same as the 72 FSM, which can't be done with the longer push rod???

 

I also looked at the 81 280ZX FSM and the push rod length spec is 9.5mm to 10.5mm. My rebuilt 280ZX MC has a 9.8mm throat?

 

The MC part numbers I mentioned were from Victory British and Black Dragon. They show the 72-78 model years as using the same MC.

 

I guess I will just adjust it so I have about 0.5mm to 1.0mm gap and see how it works? I really want to adjust it once and be done. I think the main thing is to adjust the push rod length such that you have some sort of gap between the push rod and piston so that the MC piston can fully retract, but not too big of gap to give you a soft pedal.

Edited March 8, 2010 by IdahoZ

[Nigel]

Thanks for the clarification Nigel. It is starting to make sense, I think? What's confusing is the diagrams in the FSM I have for the 1972 model shows a very short push rod on the master-vac/booster and a deep throated MC? One of the diagrams has to be wrong. It makes sense that the earlier models had a very shallow throated MC.

 

I just downloaded the brake section from a 73 FSM and the master-vac diagrams shows the push rod is longer, but the push rod adjustment instructions are the same as the 72 FSM, which can't be done with the longer push rod???

 

I also looked at the 81 280ZX FSM and the push rod length spec is 9.5mm to 10.5mm. My rebuilt 280ZX MC has a 9.8mm throat?

 

The MC part numbers I mentioned were from Victory British and Black Dragon. They show the 72-78 model years as using the same MC.

 

I guess I will just adjust it so I have about 0.5mm to 1.0mm gap and see how it works? I really want to adjust it once and be done. I think the main thing is to adjust the push rod length such that you have some sort of gap between the push rod and piston so that the MC piston can fully retract, but not too big of gap to give you a soft pedal.

 

I've never compared the specifications given between the FSM's and there may be more differences and/or similarities between the years than I'm aware of. I recall that when I did my friend's '71 Z, I ended up measuring the depth of the MC and then adjusting the pushrod accordingly to leave a bit of a gap. It's worked find for about 6 years now.

 

Nigel

'73 240ZT