Calling everyone who upgraded to a 15/16 master cylinder

[fastzcars]

Believe it or not I ended up using the 1105 adapter, american universal version. The import universal adapter is for the single cup M/C. The americal version covers both cup's on the old datsun M/C. The picture in the main page of Motive Poducts shows the older metal version. If you go the the adapter's page you'll see the 1105 adapter. You'll like it, Just a note on using the power bleeder, FOLLOW THE DIRECTION'S, I ended up spraying Brake fluid because I didn't check the seal first before I filled the bottle. Also buy some denatured alcohal to clean out the bleeder. You can get it from you local home supply hardware store.

[jgkurz]

OK folks I give up. I know when I've been beat. I refuse to put anymore time or money into this futile upgrade. So far it has cost me 85.00 for a new 15/16 master cylinder, 49.00 for the Motive Produts Power Bleeder and 18.00 for my wasted Ate Blue brake fluid. I've done everything except replace the booster and I don't think the 15/16 is worth the trouble if that's what I have to do.

 

I will be putting my 7/8 MC back on. The 15/16 upgrade on a 280z without the 280ZX booster does NOT work.

 

Does anyone want to buy a slightly used 15/16 MC and a Motive Produts Power Bleeder? I won't be needing them.

 

Seriously, I'm done.

[Pop N Wood]

I hate to say it but you could have a bad MC. If you are bottoming out the MC then it is not the rod, and it sounds like you should have the bleed process down by now. The only other possibility is a leaky fitting, but I assume you checked all connections for leaking fluid.

 

Also the rod I was talking about goes between the booster and MC.

[DaleMX]

I could be wrong, but I think that too much rod will cause this too. If the M/C cannot return to the home position then it wont operate properly and you wont be able to bleed it correctly. This is what I think is wrong with mine, but I wont know until the monsoon season gives me a good dry break.

 

Dale

[gramercyjam]

A couple things to check - I didn't see them mentioned so I will -

 

Bleeders on MC good an tight? I've had problems with some rebuilds where the bleeders couldn't be torqued down enough to seal and I couldn't get a good bleed.

 

Proportioning valve, all the way out (counter clockwise)? I don't know if you wilwood is like mine, but with mine when the adjuster is all the way in, the pedal feels soft and goes down a lot further than when it is all the way out.

[Owen]

On the pressure bleeder...I used a similar product, DIY.

A garden sprayer (plastic bottle with a hand pump and a hose to spray the liquid-used for spraying pesticides on roses, I guess). A master cyl. cap with a brass fitting, and some clear hose.

Total cost was $12.

 

The universal caps sound interesting tho. maybe I'll get one to adapt to my system so that I can do other cars like the Motive does.

Owen

[fastzcars]

JG, I'm sorry to hear that the power bleeder didn't cure your problem. But I have to concure with Pop N Wood. You probably have a bad M/C. Have you taken apart the M/C. It's not that hard to do. There are only 4 internal parts. I found this out when I was going through the same ordeal. Take a day or 2 off from the project. to clear your mind. I've had to do this quite a few times myself just to keep me from running my car off a cliff. Don't give up.

[TOMAHAWKZ]

John this might sound wierd but the rod may be too long. If the m/c pushrod does not allow the piston in the m/c to come all the way back some of the passages will not be uncovered allowing the fluid to get behind the seal that builds the pressure when the pedal is depressed. for some good info on brake set up try the wilwood brakes or tilton web sites. they have some good info on proportioning valves also. Alot of people have them when they dont need them others have them and dont know how to adjust them. let us know what you find..

Tomahawk Z

77 280z with a rebody and reverse mount wilwood mastercylinders.......

[jgkurz]

Everyone, Thank you for the advice and encouragement. I have tried all the recommendations in this thread without success. What's strange is this is the same experience I had on my 78z years ago. I just could not get any pedal pressure built up. The car was stolen before I could resolve the problem. I chalked the problem up to a bad master cylinder but could never prove it. That's one of the reasons I was willing to try the 15/16 MC on my current 77z. The only fact vs opinion based fix I know of is to put a ZX booster on my 77 with the 15/16 MC. Since I don't feel like going through the trouble so I'm going to give the 7/8 MC a try. For some reason the 240z folks don't have a problem with the 15/16 MC. So far no one has come forward that has a 15/16 on a 77 or 78 280z without the ZX booster.

 

I'll keep everyone posted with my progress.

 

P.S. I'll probably keep the Power Bleeder. Regarding the M/C Shucks will let me swap the slightly used 15/16 for a new 7/8.

 

Later,

[Phantom]

This has been a very interesting thread - especially since I'm about to do a brake upgrade, like what Z-ya has, on my '77 280Z. I had already decided to forego the proportioning valve until after the conversion to see what the balance was like first. I think I'll also wait on the 15/16" MC too and just stick with the 7/8 for now.

[wheelman]

I'm glad I read this thread as well. I was also going to do an "upgrade" to a 15/16 MC along with the Toyota caliper swap but now I'm going to stick with the 7/8 MC and the stock 7" booster. I will use a proportioning valve because I'm eventually going to put disks on the rear.

 

Wheelman

[JMortensen]

This installation should not be a problem. I can't figure out what has gone wrong here, but this is a fairly simple operation.

 

My only thoughts on why it isn't working are:

 

1. The disc inside the booster that sits between the back of the master and the pin fell out (usually falls into the booster).

 

2. The rod is the wrong length.

 

3. The master is bad.

 

I wouldn't be afraid to do this swap, I'm sure it has been done hundreds of times by lots of different people sucessfully (including me).

 

The drum master has a check valve built in for the rear brakes IIRC. If you put rear discs on a drum master, then the rear could potentially drag, just a bit, all the time. I think I read somewhere that someone had removed the check valve, but I can't remember where or who said that.

[jgkurz]

The drum master has a check valve built in for the rear brakes IIRC. If you put rear discs on a drum master, then the rear could potentially drag, just a bit, all the time. I think I read somewhere that someone had removed the check valve, but I can't remember where or who said that.

 

jmortensen, I appreciate your thoughts. The above comment concerns me a great deal. I definatley don't want my brakes to drag even a tiny bit. I will be trying the 7/8 MC when I get a chance to work on the car next week. As I understand it, the check valve in question is for protection against significant pressure (as much as 1000psi) coming back into the M/C once the brakes are released. I'm not sure how this could lead to brakes draging unless the M/C was failing.

 

In my situation I believe 1) the M/C has been bled as good as it possibly can be. 2) The M/C is functioning correctly (for a 1980 280ZX) because I've tried this upgrade with three seperate 15/16 M/C's with the same results and 3) I've adjusted the rod and tested almost infinitely, again without success. In my opinion the next step would be to try 1980 280ZX booster which I will not be doing.

 

For some reason the 240z guys seem to have no problem with this upgrade.

[JMortensen]

1. The disc inside the booster that sits between the back of the master and the pin fell out (usually falls into the booster).

 

What about that one, have you checked for that? You could put on 100 masters and none will work if that disc isn't in there. I think it's called a "reaction disc".

 

My understanding of the check valve is limited for sure (a while back I talked at great length about how I thought the drums were affected by wheel cylinder size on the IZCC list and was totally wrong so don't believe everything I say when it comes to drums), but I believe it holds a bit of pressure in the wheel cylinders to keep the seals against the bores. I also believe that this valve is in the m/c itself.

[Phantom]

FWIW - I did the Toyota 4x4 upgrade on my front brakes (drums on the rear) and kept the 7/8" MC. Toyo brakes work great but you may want the proportioning vavle because now the rears don't do much, if anything.

It may be a different problem than just the upgrade becuase I've been running it for years and it initially seemed OK but I'm not going to worry about it because of the big upgrade all around coning this summer.

ALSO - I pulled out my '77 280Z Factory Service Manual and checked out the 7/8" Master cylinder - BOTH front and rear lines have check valves in them. Hope that helps a bit.

[TOMAHAWKZ]

The little check valve you are all talking about is a residual pressure valve. They are installed to keep the fluid in the lines instead of making its way back to the master cylinder this prevents you from having to double pump the pedal to build pressure. They are usually installed in both rear drum and rear disk brake set ups but the amount of pressure they keep in the lines is different. I believe the drum brakes use a 10 lb valve and the disk set ups use a 2 lb vlv. If you convert to disk in the rear and dont change the residual pressure your brakes will drag for sure causing 2 things excessive premature wear of the pads and disks and they will get hot and we all know what happes when they get hot they dont work!! They are also used when you mount a master cylinder below the height of the calipers, like on some old hot rods where the stickum below the floor keeps the fluid in the lines. I assume they are installed in one of the valves in the engine compt. but Idid not look for mine as I removed all the stock brake equipment and went with aftermarket stuff

[srgunz]

When you put the old cylinder back on, make sure you put the rod adjustment back to where it was.

Remember to carefully measure both cylinders like I said in my other reply.

If they do measure the same, the rod stay's at its origional length.

I went thru similar problem. It was the reaction disc falling out of place.

If one plays with the rod at all, the disc falls to bottom of cannister.

When it does you will NEVER get any pressure. You will need to get the booster on the work bench and put disc back. See your FSM.

[Phantom]

TOMAHAWKZ - So I could just replace the rear drum 10 lb. spring with a front disk 2 lb spring and install disk brakes on the rear, right? That way I'm not having to change out the entire MC for one that pushes about 12% more oil?

[jgkurz]

It was the reaction disc falling out of place.

If one plays with the rod at all' date=' the disc falls to bottom of cannister.

When it does you will NEVER get any pressure. You will need to get the booster on the work bench and put disc back. See your FSM.[/quote']

 

jmortensen and srgunz, I have never heard of a "reaction disk" until this thread. I looked at my 77 Service Manual and it does have a small illustration, but that's about it. If a missing reaction disk could cause my brakes to never pump up then this could be the problem.

 

Is there an easy way to determine if the disk has dropped into the booster? My 15/16 M/C is still installed and fully bled so I could unbolt the M/C and pull it back.

 

Is the "reaction" disk the piston like part that is secured to the back side of the rod? After pulling out the rod and adjusting, I have no problem re-seating the piston back into the booster.

[JMortensen]

Well it looks like Steve has actually dealt with this before, and I've just heard of it, but when I've heard of it the advice was unbolt the master, pull it off the booster, and look in there. If you see the disk put it back in place and reattach the master...