putting discs on the front

[SHADY280]

hey guys ,my first real q. i got 78 era front spindles and shock/upper a arm parts, as well as the lower control arms. im gonna cut the 75 ones off my frame to get discs on the front of this thing. my q is do i have to change my master cylinder or porportioning valve?? im trying to get all the parts together b4 i start. the rear will remain drum until i have extra coin. any help is appretiated.

[datzenmike]

It would be best, the disc brake master cylinder is different. The '75 master was a 3/4" and the '78-'79 was 13/16" (more volume). Also there is a metering valve on master cylinders used with front disc brakes and rear drum brakes. You know that the disc brake pad is normally in contact with the disc, while the drum brake shoes are normally pulled away from the drum. Because of this, the disc brakes are in a position to engage before the drum brakes when you push the brake pedal down.

 

The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve does not allow any pressure to the disc brakes until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in.

 

Having the rear brakes engage before the front brakes provides a lot more stability during braking. Applying the rear brakes first helps keep the car in a straight line.

 

The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

 

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force.

[71-521]

wouldn't it be easier to buy Beebani or Fineline's conversion brackets rather than all that welding and trying to get everything lined up right?

[lynchfourtwenty]

wouldn't it be easier to buy Beebani or Fineline's conversion brackets rather than all that welding and trying to get everything lined up right?

 

Lots easier ;)

[Bleach]

...but then you have kingpin suspension up front. Ball joints rule. :)

[]2eDeYe]

Kingpins are tough to kill though...makes lowering the crap outta your truck alot easier as well (don't have to worry about your balljoints being maxed out)

 

Saying that though, I went to ball joint's...drop spindles kick butt :D

[BEEBANI]

I went to ball joints as well...

[SHADY280]

i cant do the disc upgrade without the proper spindles (so i think) it doesnt matter what disc setup i want, i have to start with the correct parts. for me changing the frame parts is aboot 6 hours or so i figure, not to bad for what i get. i guess ill upgrade to the 78-79 master, and get a adjustable rear proportioning valve then. mike you are exactly right with yuor response (obviously you know your stuff) if i can get away without buying the adjusting prop valve it would be nice.

[BEEBANI]

I adapted the 720 booster/m/c to my truck and am very happy with it. All I had to do was modify the 620 mount and extend it. I also had to dimple the inner fender a little. If you're gonna go to the trouble of welding and cutting the frame; you should adapt to 720 suspension instead. More parts avail.

[]2eDeYe]

What BEE is saying is the 78-79 brakes suck...

 

The 720 brakes are basically the same as the nissan 2wd truck brakes all the way up to the frontier brakes. Then you can also get drop spindles and other cool brake upgrades... ;)

[RB_Shaggs]

i just have the 720 front swap done i works just fine..

[BEEBANI]

2eDeYe;11475']What BEE is saying is the 78-79 brakes suck...

 

The 720 brakes are basically the same as the nissan 2wd truck brakes all the way up to the frontier brakes. Then you can also get drop spindles and other cool brake upgrades... ;)

 

Right!;)

[SHADY280]

ah yes, but it comes down to initial purchase price. i got this stuff for next to nothing, and i get 50% off at napa (im a mechanic) so for now its gonna have to work. the future plan is to get those adapter parts and make this thing 4 wheel discs, maybe the 280zx master and booster? then it shall stop like a indy car. i really dont need much as far as aftermarket stuff goes, its only getting droped an inch, and i can always make my own parts. besides brakes are for wussies.

[lynchfourtwenty]

brakes are for people who dont like to smack they're datsuns into stuff.. lol

[SHADY280]

naw yer kinda wrong, the steering wheel is there to avoid that stuff, turn it into a drift 1 million points

[lynchfourtwenty]

yea well i enjoy my brakes ;)

[mklotz70]

As for the m/c....just use a '78 620 m/c that would have been for the setup you're going to use....but, yes, you should change out the drum/drum m/c.

 

As for the '78 parts. If you haven't measured, it's going to push your front wheels out about 1.25" on each side.

 

Yes, the '78 brakes are cheesy, but once you have ball joints on, you can simply swap spindles in the future and have a better setup. You can swap to HBody spindles/hubs/rotors/calipers....then go to dropped spindles once you've done that. They don't list dropped for the 620, early 720 because the brakes don't mount up quite the same.

[SHADY280]

havent started the dissasembly yet, and im retaining the original upper control arms, i havent measured yet either, im just plugging along. if it is going to be noticable, i can always weld the braket on a little different to compensate, or shorten the lower control arms as well. ill see when it all starts coming together. for now its collection time, parts and some great info from all of you that have put your input in. and thats what i thought, with a ball joint setup already in place, i can always swap to anything with the approximate spindle height. therfore doing my brakes some real justice.

[datzenmike]

2eDeYe;11475']What BEE is saying is the 78-79 brakes suck...

 

The 720 brakes are basically the same as the nissan 2wd truck brakes all the way up to the frontier brakes. Then you can also get drop spindles and other cool brake upgrades... ;)

 

The '78-'79 620 disc brakes were the same ones used on the first gen 200sx '77-'79, (I think) and the 720s through '83. For '84 to '86, vented rotors and a different single piston caliper and larger pads were used. In '86 to '88 there were two kinds available, a single piston, similar to the '84-'86 for 2wd with the Z24i engine and a dual piston set up for the SD25 and VG30i engines, and all 4X4 models.

[SHADY280]

mike were you at the boundry bay airport auto-x in sept. are you the one that blew yer motor?? just seems like a coincidence.

[datzenmike]

Nope, if you saw my truck you'd know why it doesn't lend itself to high speed or handling lol. With me in it, it weighs almost 1,400 lbs more than a 510!!! For the first time in about 12 years I put a wrench to the motor to change a blown head gasket this spring. Total cost.. $23, you got to love the Ls!! Anyway I plan to install a Z24 and some EFI to make it pull better...

 

http://forum.ratsun.net/showthread.php?t=684&page=5

 

Long range dream is to buy an '80 210 near me and put the old but good, or good old L20B in it with a 4 spd automatic or maybe the zx 5spd that's in it now.

 

Just realized you have that cherry 620! Very nice, optional clock AND the optional un-cracked dash!! How rare is that? I have a set of Chrysler Datona buckets that look a bit like yours.

 

http://i138.photobucket.com/albums/q251/datzenmike/01070006.jpg[/img]"]

[lynchfourtwenty]

i got the semi barely cracked version :( no clock or tach, except the aftermarket one i put in

 

[SHADY280]

mike you can have the buckets outta my truck, come on over and get em. im putting in high back, very thin rci plastic seats, im 6'0". it just dont fit with those thick seats in there!! or i may put lowback zx seats in there, saw some persons artice in here where they did that, looks good, just gotta try it.