Master cylinder anomaly

[madkaw]

15 hours ago, Patcon said:

How did you decide on what Orings to order?

That IS the issue . It seems that EPDM O-rings are what’s best for brake fluid . Then you need the exact size . I believe the seal need to be 6x10x2 

[Racer X]

1 hour ago, madkaw said:

That IS the issue . It seems that EPDM O-rings are what’s best for brake fluid . Then you need the exact size . I believe the seal need to be 6x10x2 

Are they round cross section, or square?

[madkaw]

1 hour ago, Racer X said:

Are they round cross section, or square?

Round 

[madkaw]

The MC seals are all oriented the correct way. The Nissan unit matches up with the aftermarket fine - see pic .

So I reached out to Classic Tube since it seems their kit doesn’t have the correct line routing MC to warning switch correctly . They show 3 kits by year . The first kit supposedly goes from 1969- 6/72 . The second kit goes from 6/72 until the 280z?. 
 

Am I wrong that the earliest BMC had front and rear oriented differently and thus had the lines routed differently to the warning switch? If so - when did the MC change ? 
Classic tube wants to get this right also . 

[Zed Head]

Here's the drawing from the 1972 FSM.  It shows the big reservoir up front and shows the lines through the warning switch.  No drawing number though.

This from the very same chapter.  Seems reasonable to guess that it's an old picture from 1971..

BUT, I opened up what is supposed to be the 1971 FSM and it shows this.

[Zed Head]

I'm not sure it matters though for function.  It's just a bigger reservoir.

[madkaw]

6 minutes ago, Zed Head said:

I'm not sure it matters though for function.  It's just a bigger reservoir.

If the larger reservoir is up front then more than likely the front brakes worked off of that side. So the lines to the warning switch would have to run differently - correct . The early lines stayed separated where as the later the lines cross - because the warning switch stayed the same ?

[madkaw]

Okay- I got the word from my parts expert .

This probably old news or non-news but I’ve just ran into this and was having difficult time finding the correct info 

240z 69-8/71 used first series of BMC - E4602 plumbed F-R 

8/71 - 6/72 uses the E 8702 series BMC - it is plumbed R-F 

7/72-7/73 also uses the W8702 but the safety switch is moved so it’s plumbed a lot different .

If anyone has contrary info I’d be glad to hear. 
If not I am going to notify Classic Tube 

 

[w3wilkes]

On 1/20/2023 at 1:29 PM, Zed Head said:

I'm not sure it matters though for function.  It's just a bigger reservoir.

 

On 1/20/2023 at 1:38 PM, madkaw said:

If the larger reservoir is up front then more than likely the front brakes worked off of that side. So the lines to the warning switch would have to run differently - correct . The early lines stayed separated where as the later the lines cross - because the warning switch stayed the same ?

If what @Zed Head says is true then it seems like you could just swap the reservoirs and be done with it rather than rerouting the lines to the brake warning switch.

Edited January 23, 2023 by w3wilkes

[madkaw]

1 hour ago, w3wilkes said:

 

If what @Zed Head says is true then it seems like you could just swap the reservoirs and be done with it rather than rerouting the lines to the brake warning switch.

Whatever is done the F of the MC should go to the front brake lines- and R should go to the rear lines - regardless of the reservoir size . 

[Patcon]

36 minutes ago, madkaw said:

Whatever is done the F of the MC should go to the front brake lines- and R should go to the rear lines - regardless of the reservoir size . 

I don't know if I would dispute this but why do you think this is so?

[w3wilkes]

I must recant... Looking at the top cross section diagram with the BR212 in the bottom right corner (assuming relational distances depicted are correct) the distance from the plunger to the exit pot is greater on the firewall side chamber of the MC with a longer shaft allowing it to move greater amounts of fluid both on the input side and output side. With the difference in the shaft length sections for the two reservoirs they will move different amounts of fluid. From the diagram I can't tell if the shaft is a single piece or is it two pieces and the brake fluid between two pieces of shaft moves the further shaft from the firewall. If that makes any sense... @Captain Obvious

PS- I've never personally had one apart so I'm totally basing this speculation on the diagrams.

Edited January 24, 2023 by w3wilkes