Booster & MC compatibility

[240z70]

PROBLEM:  Brakes too stiff. Long braking distance required.

SUMMARY: After changing adding a new booster a while 1-2 years back: Dual Diaphram 7 inch 15/16 bore and a 15/16 MC.  Had to drill new holes but it fit.  The brakes had a stiff pedal, and the bolts came out on the MC side after a while. Took the booster  to a repair expert (booster revamp shop - who took the unit apart (booster) and pressed and welded the pressed on bolts, then put the booster back together, and told me it was good.

I installed it back, used the tool to gauge the 20 mils gap between the MC and the Booster rod and installed it.  Bled MC, then all 4 breaks in order of distance.  The brakes worked but the pedal is stiff and braking distance is still too long. I have decided to change the system.

DIFFICULTY:

Cant seem to get an original/revamped booster/MC 7" for this car.  No one carries it.

QUESTION #1:  Can I just install a 75-78 280 Z booster and MC on it? Does it FIT...  It is bigger : 8.5 inch versus the 240z 7 inch.  The ZX's were even bigger: 10 inch so those are out.

QUESTION #2: IF SO WHICH YEAR IS BETTER?  Is it a bolt in or have to change holes? Does it clear Clutch MC?

QUESTION #3:  What size hose ID is the Booster to Balance tube?  I have heard 11.2mm but no one seems to carry it.  Best place to get the proper sized hose?

Car Info:

Car: Model 1970 240z Production 11/69

Engine F54 2.8L/MN47Head/SU Carbs.

Recommendations? 

 

[heyitsrama]

https://www.jbugs.com/product/N203741.html

Might work for the hose.

Why would a 15/16" master make everything more stiff, wont that push more fluid than the OEM 7/8" bore MC? Meaning less pedal input for the same fluid displaced?

 

I hear Z-Car garage has a nice brake package being that you're down in San Jose n all 🙂

Edited May 18, 2023 by heyitsrama

[Patcon]

You lose leverage with the larger master cylinder. Maybe try a more aggressive pad to make the pedal effort lower?

[Terrapin Z]

I am pretty sure you would have to drill out new mount holes for the bigger Boosters.  I have heard of people using all of those sizes with the Clutch M/C. 

Are you sure the reaction disc is in place? is can cause some strange pedal / brake function if it has fallen off the plunger. 

 

Edited May 18, 2023 by Terrapin Z
Added pic

[Namerow]

20 hours ago, 240z70 said:

QUESTION #1:  Can I just install a 75-78 280 Z booster and MC on it? Does it FIT...  It is bigger : 8.5 inch versus the 240z 7 inch.  The ZX's were even bigger: 10 inch so those are out.

QUESTION #2: IF SO WHICH YEAR IS BETTER?  Is it a bolt in or have to change holes? Does it clear Clutch MC?

QUESTION #3:  What size hose ID is the Booster to Balance tube?  I have heard 11.2mm but no one seems to carry it.  Best place to get the proper sized hose?

Re Q1 and Q2, go to 'Resources' - 'Knowledge Base' - 'Wheels, Tires and  Brakes'.  I just uploaded a summary on the topic.  Hopefully, it ill provide you with the guidance you're looking for.

Re Q3:  In its OE form, this hose (comes in two sections: 1) engine-to-check valve; 2) check valve-to-mastervac) is molded to some very shapes.  If you go with aftermarket braided hose, you'll need to figure out how to route it so that it clears all of the surrounding componentry.  It will be nearly impossible to achieve the bends that are molded into the OE hoses.

Both hose sections have the same ID, OD and wall thickness.  By my measurements, these are: 9.5mm, 17mm, and 4mm (the fittings over which the hose ends fit measure 10mm OD).  I was not able to find any aftermarket braided hose that exactly match these specs.  You can go either slightly under on ID (9mm) or considerably over (12mm).  The best choice seems to be 9mm, but you'll probably need to soak the hose ends in boiling water prior to installation to make the rubber pliable enough to stretch over the fittings.   One vendor selling high-quality braided ('Continental' brand) aftermarket hose is Bel-metric.

If you can find NOS hoses, that would be the best way to go (but expen$ive).

Good luck.

Edited May 18, 2023 by Namerow

[Tirnipgreen]

I got my booster from this guy in Canton, Georgia

https://harmonclassicbrakes.com/

[Patcon]

I bought a rebuild kit from him

[inline6]

Hmmmm - Interesting - very close to me.

[SteveJ]

9 hours ago, inline6 said:

Hmmmm - Interesting - very close to me.

I think Chet knows him.

[Tirnipgreen]

[240z70]

On 5/18/2023 at 4:01 AM, Terrapin Z said:

I am pretty sure you would have to drill out new mount holes for the bigger Boosters.  I have heard of people using all of those sizes with the Clutch M/C. 

Are you sure the reaction disc is in place? is can cause some strange pedal / brake function if it has fallen off the plunger. 

 

Well that was my original thought before my dual booster bolts failed.  They were only pressure fitted on the vac canister.  When I took it to the shop, he opened the unit and I waited while he pressed new bolts and then welded them on the inside of the canister.  I mentioned to him about the reaction disc and he said no, it was not missing and showed me the little black piece inside the tube. 

I had several possibilities for the hard pedal condition:  1-The booster was bad...but that makes no sense.  I unhooked the vacuum line and it swooshed air in.  Then I put a vacuum pump w/meter to it and vacuumed it up to 22/Hg.  It held for about 15 minutes without a drop.  Then I ran the engine with a vacuum gauge connected to the other side of the hose and it produced 20/24 Hg (idle/rev 3000), so the engine is producing adequate vacuum in the manifold.  The check valve is new (Z Depot).

I know that with the larger MC I lose pressure on the calipers while gaining more volume (which is really not needed since they are stock).  But maybe that is why the pedal is hard.  The calipers cant accumulate more volume so the pedal is harder, and since it is bigger (MC) then I actually have less pressure at the calipers which might explain the slowness of the braking...  The booster is a DUAL Diaphram so its supposed to give me more pressure on the MC so I thought it would compensate for the larger MC... Maybe not.

I am getting frustrated and may just see if I can find an original 7" or maybe a 8 or 8.5 inch booster (hence the original question of compatibility and whether or not the 8 or 8.5 clear the clutch MC on the 240z).  If I find it, then I will probably just get a 7/8 MC and stick with it.  Not sure, just looking at options and availability.   Also don't want to pony up all that cash for the all slotted disk and wilwood options.

By the way, the aftermarket universal vacuum hose can be had from Amazon.  It's Gates 27232 Power Brake Vacuum 11/32 inch x 36 inch (85 PSI) Hose - 3 ft for $18.15 - Looks and fits perfectly.

https://www.amazon.com/Gates-27232-Power-Vacuum-Standard/dp/B000CRHL5S/ref=sr_1_1?crid=3OIUGPOCDN3NX&keywords=gates+27232+power+brake+vacuum+11%2F32+inch+x+36+inch+85+psi+hose&qid=1684941954&sprefix=gates+11%2F32+vacuum+%2Caps%2C123&sr=8-1

ANOTHER QUESTION:  Not sure if this has any impact, but on the MC the front brakes are connected to the rear port and the rear brakes to the front as called out on the MC = R__F,  but it is common knowledge that on the 69 thru mid/late 71 the ports on the original MC 7/8 were actually listed F__R and the F port was on the front of the MC and was connected to the front breaks....  Would it make a difference?  The new MC is connected according to its R__F functionality/identification. 

 69/70/71  F__R port designation

72 and on R__F port designation

ANOTHER QUESTION:  The brake indicator light is always on on the tac. I have not been able to shut it off.  I checked the handbrake switch and it works, and there is no wire connected to the distribution  block on the firewall.  That is the only two connections that the light is supposed to have... Ideas?

 

 

[Yarb]

Here’s what happened in my situation. I was having the same issue’s similar to what you’re experiencing. Without getting into great detail. I changed out the booster check valve in the midst of going down the rabbit hole. Come to find out I had installed the new check valve backwards. There is an arrow on the valve. I had it pointing in the wrong direction where I was not getting any assist from the booster.