whats the largest MC you can Bolt in a 620

[lynchfourtwenty]

ok so once again im asking.. whats te biggest mc i can put in my 620.. i believe its the 79/80 all wheel disc 280zx mc but im not positive..

 

sorry my internets really unstable as im using my cell as a modem lol

[INDY510]

I remeber a disscussion on some forum about whether pushing more fluid into the same calipers actually does any good

 

 

If you are upgrading to bigger brakes then it makes sense to upgrade the master....... talk to beebani

 

 

We want pics of your brake upgrades...... it looks like there are 2 different size masters for the 280zxs.... both have brake boosters,, but diff reservoirs:

 

[Braden]

i liket the one on the right alot better, can you get one without wires and shit in the cap???

[mklotz70]

15/16" bore is the biggest that I know of that will BOLT IN. The one on the right of the pic is not a bolt in. You'd have to double check to see if the '79 m/c is a disc/drum or disc/disc unit. I know '80 is disc/disc....not sure about '79.

[datzenmike]

Some m/c have an adapter that will bolt to the vertical truck firewall.

[mklotz70]

You are most correct good sir :) Might need a new pushrod with the adapter if it won't adjust out long enough. I'm not familiar with the stock dual res m/c on the 620.

[datzenmike]

I think this is off an S110 and has the adapter.

 

[mklotz70]

The challenge is that to use the m/c on the right, that adapter would have to fit in a position 90 degrees from that mounting. I don't think the studs of the adapter fit in the other m/c and I don't think the holes in the adapter will line up with the firewall holes. We'd have to measure an adapter to see if the holes and studs are the same distance apart.

[lynchfourtwenty]

indy i have pics of the upgrade i did a few years ago, theres a thread here somewhere about it..

 

problem is i've always had to double pump the brakes even tho im using a 720 mc.. i've bled these suckers a million times, replaced stuff, an the brakes still blow.. im using pathfinder 2 piston calipers on the front an stock drum crap on the back, but its all new, well except the wheel clyinders which prolly do need replaced.. idk tho, could it be the booster?

 

im thinkin about takin the dive these year (again i know) an finally upgrading the trucks power plant since i dont really want or need to go much further on my car.. an i want a reliable braking system..

 

thanks for the replys guys, appriciate it

[lynchfourtwenty]

so went an looked (been so long) looks like i got a 13/16 720 mc on there now, so the 15/16 should be a tad bigger.. perhaps big enough to help push them big 2 piston calipers..

 

did a little research an found thatthe pathfinders (which is what i got my calipers off of) run a 15/16 bore mc.. but they are all wheel disc.. so is the 79+ s130's anfrom the looks of it the 79 mc will bolt on with little to no mods..

 

Question is will the all wheel disc mc be to much for the rear drums? would i need to ditch the proportioning valve or leave it? hmmmm

[datzenmike]

Yup, moving up 2 sizes will make a big difference. The 720 used 0.938 or 15/16" masters and they had drum rears.

[mklotz70]

The diff between the disc/drum and disc/disc m/c should simply be the residual valve. I think you're ok using disc/disc m/c on a drum setup....but not the other way.

 

Seriously....my bet would be on your rear brakes not being adjusted tight enough. Pull your ebrake up until it just engages. Drive forward and see if you still have to double pump. You may have to the very first time you stop, but after that, you should not have to pump.......if it's the rear brake adjustment that's the prob.

 

You could jack up the front and look at the pads...if they're up against the rotor, the pumping is not because your m/c is too small. If you have a large gap between the pads and the rotor....there's something hinkey with your front brakes. But, I doubt it's your fronts.....rarely is. Do you stop good once you've pumped them up?

[lynchfourtwenty]

i will try the ebrake trick mike thanks, it stops oookkk on the second pump, even better the 3rd.. an last i checked i ha pleanty of pad left an they're seated pretty well :)

[datzenmike]

The danger of having to pump the brakes several times is that is in a panic situation, where you know positively that you are going to hit something, it's impossible to even think of pumping the brakes. First there isn't time and second it's PANIC... both feet on peddle and ass off seat!!! and hang on and wait.

[mklotz70]

The ebrake trick should highlight poor rear brake adjustment because it mechanically holds the shoes out close to the drums. The first time you press the pedal, it fill the slave cyls up and since the springs can't put the shoes back in and compress the cyl, it will stay filled up.....so the second time and ever time after that, it will give you a good pedal.

 

Mike's def right....you don't want to be in a situation where you have to pump your brakes.

[lynchfourtwenty]

thats very true guys, which is why the truck doesnt really get driven much, shit i had to jump start it the other day cause it had been sittin so long the battery went dead

[yello620]

Lynch, the zx master that you want is the one that you pictured on the left, with two reservoir caps. It bolted directly to my 1976 620 booster, and i would assume that it would do the same to all years of 620's.

 

So my truck has the early 15/16th zx master, twin piston truck caliper up front and stock drums in the rear. Works great, been this way for over four years now. Excellent pedal too. I am aware that this master is for disc rear brakes, works perfect with rear drums.

 

With that said, i think that you have two problems with your brakes system. Master cylinder being one of them. The other is either rear brake adjustment, front caliper/pad/rotor contact, or air somewhere. Just cause you have bleed them sixteen times does not mean that you got all the air out.

[lynchfourtwenty]

awesome thanks for te info jason, as soon as i get some tags on the truck im gonna figure it all out.. i got a bunch of aluminum to scrap so it should be real soon

[mklotz70]

Best indication of air in the line is a spongy pedal. After you have pumped them up....if the pedal is rock hard, they are bled well enough. If it's spongy, re-bleed them. Pumping is always an indication of the slaves requiring more fluid than the m/c provides in one stroke. Since the pads up front are normally in close contact, it's not typically the front calipers. You can check the fronts if you have a 2nd person......jack up a front wheel....have them slowly press the pedal down while you're spinning the hub with the wheel off. You watch for drag and they watch to see how far the pedal goes down. The fronts won't lock up until there's good pressure in the rear circuit....which won't happen until the shoes are in good contact....but turning just the hub by hand, they may seem locked up.

[lynchfourtwenty]

my thoughts exactly.. thanks guys, cant wait to get some tags on the bitch so i can test out some of these methods

 

edit i guess i dont need tags for that method, but i wanna drive her lol!