Incorrect 1971 240z Brake Push Rod length (not adjustment)

[DaveR]

So i've been restoring my brakes and got to the point of reinstalling and checking it all. I went to check the Push rod length and adjust it for proper travel... and it seems like I have a real ways to go,

Here is an image of how it sits now, but from other images I've seen it looks like its way too short.

By my measurements the tip of the push rod at rest wants to be  .368" out from the mating surface

Currently it sits at .187" inboard of the mating surface. (picture shows it slightly pulled out so you can see the tip)   So i'm missing .555".   seems like maybe I have the wrong cap on the pushrod.

Wondering how this happened or what has gone wrong. I haven't driven the car yet with proper working brakes, but I'm fairly certain something isn't right here.  Where can I even get the proper push rod?

 

 

Edited April 10, 2016 by DaveR

[Zed Head]

That's a picture of your brake booster.  The tip of the rod sits in a cup at the base of the master cylinder piston.  Not really clear what you did or are doing.  That looks like an old dirty booster, what's new or restored?  What is not working?  What document has the measurements you're checking?

[DaveR]

Master cylinder is new.  Brakebooster is old. I did not own the car when any work was done previously, so I only know what I can see.  

So, I believe I am supposed to adjust the length of the rod shown (in the brake booster), so that it is roughly .020" away from its corresponding cup in the base of the master cylinder when everything is at rest.  So I push the rod on the brake booster in all the way, find out its offset from the mating surface for the Master cylinder.

My master cylinder is on the bench, having just been bled. I took measurements of the depth of that cup inside the master cylinder, and did some math to determine where the rest position of the rod in the brake booster wants to be when it is installed on the master cylinder.

Long story short, the tip of the rod on the brake booster needs to stick out roughly 1/2" more at rest, if it is to be close to the resting position of the master cylinder cup that will receive it.

I do not believe I have the adjustment to get it that far, and pictures I have seen of the push rods on other 240z brake boosters show a significantly longer piece.  I am thinking that is where I am losing out on my length?

 

 

[Zed Head]

Makes sense.  I've seen the problem described before but can't remember the solution.  The early 240Z's have booster and MC complications often.  Matching the right parts.  Year of car in the title will draw some eyes.

[DaveR]

Well, maybe I spoke too soon. I managed to break the adjustment rod loose and was testing how far out it went. Looks like it can go a lot further than I thought.  Seems like I will be able to get the length i need after all.

Whew

[sweatybetty]

you might try putting the m.c. in place and pushing the pedal until you feel it touch the piston, then adjust as necessary. also check the pin that holds the pedal to the rod. mine was worn almost halfway through, and the hole in the pedal was oval-ed also. that could account for the difference without any adjustment of the rod end.

Edited April 10, 2016 by sweatybetty

[DaveR]

So ultimately I got it pretty well sorted out.  The adjustment rod had a lot of adjustment available, and whoever had it before me must have not had much fun with the brakes given how far away from the MC cylinder mating surface it was set to.   I probably moved it close to 1/2" 

There is also some pedal travel that needs to be removed before I can really tell if I need more fine adjustment of the push rod,  but for now it will be good enough. I'll have to look at the pin mentioned above and that section of the assembly.

Thanks all for the quick help.

[240dkw]

I would do a search on "reaction disc" yours might have fallen down. That seems like a lot of adjustment. 

[DaveR]

One thing that was confusing was that when i pulled the adjustment rod out to adjust it (only far enough so i could get pliers onto the knurled section).... after a relatively short amount of travel it fell out of whatever cylinder was guiding it inside the brake booster. Less than half an inch of travel I would imagine.

I could tell because it was able to wiggle outside of the normally straight travel.  I was able to center it and slide it back into said cylinder after adjustment, but it left me a bit confused. I would assume that under normal brake operation it would need to extend at least that far, if not further, to fully press the master cylinder's piston. (i could be wrong though) What ensures that on the return stroke it successfully locates itself back into this cylinder? 

I have no idea if this means anything, but since the car isn't running I don't have a way to test the brake booster.

I realize that pulling out the push rod runs the risk of dropping the reaction disc, but is there another way to check if it is properly in place?  If I was so inclined can I simply remove the push rod and look?

[Patcon]

When you push the pedal, part #5 in your diagram all moves forward, pushing the reaction disc that pushes the pushrod, that pushes the master cylinder. When you let off the springs in the master cylinder force the pushrod back to keep it in place in part #5

[DaveR]

Excellent, that makes sense. Thank you Pat. 

I guess if i can move the master cylinder out of the way enough via the hard lines, I can remove the Brake booster and inspect it for proper positioning of the reaction disc.  Really don't want to have to disconnect the MC and rebleed the system, after I finally got that all sorted out.

Wish i knew the dimensions of the reaction disc (5.5mm thick apparently) , push rod cylinder that matches its size (from pictures it looks to be about 2x as thick), and the depth of that cylinder they are placed it (hard to say). If the scale of the diagram is correct it should house both items inside it fully.

I could do some testing by pulling the push rod out just far enough that it will leave the cylinder. It should require less travel with the reaction disc properly in place. If my numerical assumptions are correct.... if I move the push rod out 11mm (.433") and then it escapes the cylinder... then I have the reaction disc properly placed. If it requires ~.63" to move, then its seated further than it should be and my reaction disc is most likely floating around lose in the brake booster.

Edited April 11, 2016 by DaveR

[Patcon]

You can flex the hard lines enough to tip the master out of the way without disconnecting it. I don't know the dimension for you to calculate it and don't have a booster torn apart currently. It is easy to drop the disc down into the booster. It is possible it is already down in there. If it is, the booster will have to come off so you can shake the disc out. If it hasn't fallen down in the I use a little rtv to fix it to the end of the pushrod