Jump to content
HybridZ

1972 240z 7/8ths master cylinder pushrod cavity deeper than 1980 280zx 15/16ths


Recommended Posts

So I have very thoroughly researched this before posting here and I hope I don't catch any heat for this.  I understand for the 15/16 master cylinder conversion onto my 1972 240z you are normally going to lengthen the pushrod that actuates the master so that it can reach and do its job.  Well I bought this cylinder from Oriellys and it had no markings whatsoever on it.  No Nabco or 15/16 forged on. I saw on the listing for it that it had a .9375 ratio 15/16=.9375.  It did have the brake ports in the same position as the original and bolted on great.  I am having issues building brake pressure and this may be a possible reason.  The back part of the 15/16 master cylinder where the pushrod pushes is actually much more shallow than the same part of the 7/8.  This would mean I have to shorten my pushrod instead of lengthening it like EVERY single person that I have come across and read about.  Is this normal and I have just been confused the whole time or is this abnormal for a 15/16 master and I should try another one?  This may be the reason I can't build any pressure in the lines because this cylinder is wrong.  Any input would be appreciated!!

 

 

 

Link to post
Share on other sites

Perhaps a cavity search is in order.

 

Did confirm that you have the correct master cylinder?  If not, anything we tell you may be wrong.

 

See pictures. 

 

Did you bench bleed the master cylinder? The brake section has many how to threads on bench bleeding. If there is air in the MC you will never have a hard pedal.

post-178-0-49210400-1438613863_thumb.jpg

post-178-0-31195400-1438614005_thumb.jpg

Edited by Miles
Link to post
Share on other sites

I have seen the pictures you posted here in an older thread and basically think of a third master cylinder, the one on the left for the zx was 1.02 inches, then the one for the 240z was .8 inches, now imagine mine being .5 inches.  I did the on car bleed where you crack the bleeders and let the fluid go back into the master quite a few times and saw zero air bubbles after the first bleed. Same goes for all brakes around the car, I am getting a syringe for that method and also another master from a different supplier to make sure what I have is what I need.  I just have never heard of anyone getting one and it ends up being much shallower instead of deeper like your picture shows.. would a poorly adjusted pushrod make for a soft pedal as well?  I adjusted the pushrod so I could just barely install the master without feeling any resistance of the pushrod. 

Link to post
Share on other sites

You must have the wrong master cylinder.

 

Push rod too short =  the pedal  may be soft, but it will feel like it  has a long weak throw and then come on harder.

 

Push rod to long = brakes will feel hard and if the push rod is too long, the return ports in the MC will be covered such that fluid can not return to the tanks. Trapped fluid in the lines will eventually lock the brakes in which you will notice the brakes dragging more and more until they lock. The pressure is relieved by opening the bleeders on the MC, but you will have to shorten the rod a little at a time and retest until the rod is the correct length. You do not have to remove the hard lines to the MC to make the adjustments.

 

As I recall, the starting point for my 280ZX MC push rod adjustment was about 13mm  and for my Wilwood one inch MC it was about 14mm - 15mm. 

Edited by Miles
Link to post
Share on other sites

 I am having issues building brake pressure and this may be a possible reason. 

People have trouble bleeding brakes all the time.  You might be over-analyzing (no jokes, please).  Can you pump the pressure up?  That could be air.  How much play is there between the pedal and the MC piston moving (have someone watch the fluid in to and out of the reservoir).  The volume of fluid moving in/out of the reservoir is a good sign of air in the system also.  The volume is compressing the bubbles.

 

Finally, most people do this MC conversion as part of other brake work.  So, what other brake work did you do?  Toyota calipers, maybe?  Rear discs?  They have their own issues.

Link to post
Share on other sites

I did do a brake upgrade, my rear drums were trashed so I put on 1985 maxima rear calipers with new rotors and a custom bracket I made, lines up good and all the pad is being used, I also did the toyota 4x4 fronts.  I am using new rubber lines on all the calipers as well.  Hoping this will make it a fun little track rat with the l24 and n47 head and a few other bolt ons.  I can have the pressure I want with the car off but with it on the pedal goes to the floor.  I am researching which brake booster I want to go with, right now for whatever reason it has the 6 inch booster even though the car is a 72.  I have not removed it but it looks like it is original (or at least no other holes drilled in the firewall looking from under the dash)  The pushrod actuating the master cylinder I believe is adjusted too far out right now because the pedal moves down a little and then feels like it bottoms out (unless thats just how firm its supposed to feel but I think its bottoming out) Brakes work marginally right now, barely slowing the car down.  I plan to bleed again with the next master I have coming in today and readjust the pushrod.  Also there seems to be no difference in the fluid when the pedal is depressed.  I will let you guys know how the new master looks today.  I think I also am planning to get a new booster and just stick with the 6 inch as it should be bolt in.  Oh as a side not I did pull the pushrod to make sure that the reaction disk is in place and glued it on to make sure it doesn't go anywhere. I get the very audible hissing noise from the booster and seems like its leaking from that.  The air check valve in the line is also facing the correct way, zero leaks anywhere in the system.  I really need to type shorter... sorry 

Link to post
Share on other sites

The front calipers looks like the pistons have barely any room to move with the brand new big pads.  Should I remove one pad and let the piston come out more so or would this not be an issue? I would put a spacer between the piston and the rotor so it would over extend.  The calipers are on the correct sides as well.  I'm thinking it has to be a mad master, booster, or an error in the pushrod length. I did have it set very close to where I believe it should be but no difference

Edited by ryanabab
Link to post
Share on other sites

The front calipers looks like the pistons have barely any room to move with the brand new big pads.  Should I remove one pad and let the piston come out more so or would this not be an issue? I would put a spacer between the piston and the rotor so it would over extend.  The calipers are on the correct sides as well.  I'm thinking it has to be a mad master, booster, or an error in the pushrod length. I did have it set very close to where I believe it should be but no difference

 

Why remove one pad? 

 

It is normal for pads to just skim the rotor.

 

You need to develop a systematic plan.

 

Until you are sure that you have the correct MC and it  is installed perfectly along with the booster and push rod adjustments you are just wasting time trying to guess what the problems are.

Link to post
Share on other sites

My thinking behind the pads are that one side of the pistons looks like they are almost bottomed out and if they can't expand enough could there be air pockets that are unable to be released?  I am saying that because during some research one member mentioned he did this because as he said certain "racers" would do this for a more complete bleed.  I have a new master coming in today and hopefully is the correct one.  Otherwise where do you recommend I buy it from?  The one I have now is a reman and I have heard from a few members that those are absolute junk.  I personally have had good luck in the past with them.

Link to post
Share on other sites

If the brake system has been opened and fluid  was allowed to drain out then you should gravity bleed the whole system first  to fill the lines and calipers. Or use a Motive power bleeder to force fluid through the dry system.

 

Are the bleeders on the Maxima calipers pointing straight up?   if not, the caliper has to be rotated so the bleeder is pointing up or some air may remain trapped.  Be sure to block the piston so it cannot be blown out of the caliper and then have a helper push the brake pedal while you open and close the bleeder. If you do not block the piston while the caliper is off the rotor for bleeding the piston will be blown out and you will have a very bad day.

Link to post
Share on other sites

Now that you mention it the bleeders on the rear are facing about 3 o clock and 9 respectively.  I will remove, block the piston, and then face them fully upright and re bleed the system with the new master and update everyone.  Didn't realize that would make that big of a difference with them not 100% upright but still facing up most of the way.  I will update this soon with the results.  It is still well over 100 with the heat of the day and the sun on me hahah.  Thank you for your help I appreciate it so much!

Link to post
Share on other sites

I will remove, block the piston, and then face them fully upright and re bleed the system with the new master and update everyone.  Didn't realize that would make that big of a difference with them not 100% upright but still facing up most of the way. 

Make sure that the point where the bleeder passage enters the piston cylinder (it's drilled at an angle) is at the top.  Where the bubble will be.  Be the bubble.

Link to post
Share on other sites

I pulled the new 15/16 master cylinder apart and noticed that there were the springs with a plastic underneath the flare where the lines go in, I believe for drum brakes?  Should those be removed before reassembly?  I believe they are referred to as residual pressure valves.  They were in both of the lines and I think somewhere I read about removing them for disc brake applications.  

10.jpg

I took this picture from a write up here done by z car nut and could this be my pressure problem?

Edited by ryanabab
Link to post
Share on other sites

So after using the same master that oriellys gave me with the shallower bore (both ones I got from there were identical) and a little longer pushrod from the  original booster  it is starting to look like my problem has been solved.  I took out the residual pressure valves, got pushrod length to about where I believe it should be, and put in the new booster. The pedal was rock solid after just bleeding the master.  I don't want to get too excited because there still is a brake fluid leak but even turning on the car and pressing the brake pedal felt much better.  I will hopefully be fixing the leak tonight and seeing if I can get the brakes bled (if I have enough friends at this point haha 3rd times the charm).  I'll update this if this fixed the problem once the brakes are bled so in the future people won't just be left hanging like so many other threads I read.  

 

As of now the reservoir is cracked.. in all my wisdom I overtightened it and it split on the bottom.  Also the bottom fitting that holds in the residual pressure valve is leaking and I need to pull the master to tighten it without stripping the bolt.  I am very excited to be finally driving it.. knock on wood..

Edited by ryanabab
Link to post
Share on other sites

I will try all this tonight I have a friend coming over to help as well.  Hopefully this fixes it because my daily just decided that it would rather prefer to dump all the coolant out from the front of the engine instead of keeping it inside.  Ah the life of driving a $500 miata... hey its got AC though and in Arizona that means a lot!  Will post back here if this fixed my car hopefully tonight.

Link to post
Share on other sites
  • 4 months later...

Hello, so after a semester at school I wasn't able to continue working on my car like I had wanted to, but I think I have made good progress with my brakes not wanting to act like they should.  I added an adjustable wilwood proportioning valve, deleted the block under the master cylinder that the front and rear lines go into that has the 1 wire going into it(which was an uncommon size I had to order from eBay coming from Latvia(I ordered 2 so I have a spare if anyone is interested), and then rebled everything including the master using a handheld mighty vac brand pressure bleeder (partly because I'm running out of friends that want to help rebleed the brakes for the 10th time and I was able to get some air out I believe.  I test drove the car just down the street and locked up the front tires (which are new 225s).  I just wanted to update this thread because I hate unfinished threads that never post the result.  I will be adjusting the bracket I made for the rear because the one pad is biting uneven and then possibly bleeding a little more and adjusting the prop valve for more rearward pressure.  That, as well as the inner rod in the booster may or may not be within spec but so far she is braking MUCH better than she was, there is hope for her just yet!

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...