Brake Booster Question

[datzenmike]

Smaller booster will reduce the braking assist I would think. However the 80-'82 brakes are pretty much the same as the '78-'79 620 that used a smaller booster so .... ?

[Charlie69]

You are welcome Frank and thank you sir.

[DanielC]

How is the brake booster removed from a 620?

Are the nuts removed from inside the cab?

 

[datzenmike]

The booster can be unbolted from the pedestal on the fire wall. If the push rod and clevis pin are disconnected from the brake pedal it just lifts out. The pedestal has nuts on the inside of the cab.

[wayno]

I have used the 73/74 Datsun 620 booster on all but one my projects and it works fine when you can find a good one, my first project(521 kingcab) I used a Ford Courrier booster which is slightly larger.

The thing about the 1980 Datsun 720 booster is that it is almost slammed against the firewall already, the smaller booster will not change the location of the brake master.

[datzenmike]

The '80 720 had the L20B so the intake manifold would be in the way of a large pedestal/booster/master. On the '81 and up with the Z series and just a slim exhaust manifold the booster is way out in front and there is a dent in the inner wheel fender for clearance. This later booster is massive for the later improved and larger brakes.

[DanielC]

Thanks for booster, and pedestal removal tips, guys!

 

[Charlie69]

Here is some pictures of the small brake booster.  Might help people to understand what is involved in removing the pedestal and the booster.  I bake the master cylinder mounting nuts, brake lines, and booster mounting nuts loose before I pull the the clevis pin and the nuts under the dash inside the cab.  I find it easiest to pull the pedestal, the booster, and master cylinder as a complete unit.

 

 

 

 

 

[Rat-a-tat-Dat]

As with my '80 720 w/L20B, it incorporates front disc brakes too. I'm understanding the situation but need verification regarding this particular set up.  

1) Smaller brake booster size determines brake application force. 2) Pedestal may require some modification or fabrication. 3) Fitment issues vary depending upon model and year and 4) Possibility of used brake booster repair. If additional comments apply, please respond and promulgate your expertise. Thanks!

[datzenmike]

Vacuum is used on both sides of the diaphragm and outside air is bled in by the pedal providing push on that side moving the diaphragm forward against the master cylinder. A larger diameter diaphragm has more surface so more push. I believe multiple smaller diaphragms will also work where a larger diameter booster won't fit. Don't forget the clutch master is right there beside it and the steering column just below it, so diameter is limited. A long pedestal can be used to move the booster away from the fire wall if it doesn't place the master into the engine.

 

A 4 1/2" diaphragm has 15.9 sq. in. of area  X 20" of Hg (@ .5 lb per sq/in = about 155 pounds of added braking to the driver's effort on the master cylinder.

[wayno]

Personally I don't think you will know the difference between the 1980 booster and the 1973/74 booster, I believe my builds with the 620 booster stop better than my 1980 Datsun 720 kingcab.

The pedestals also appear to hold the boosters about the same distance away from the firewall, you may be able to re-drill your 1980 pedestal to except the 73/73 Datsun 620 booster, maybe it will bolt right on the way it is, I have never looked into it as I don't do much with 720s anymore.

The big deal with the 73/74 booster is that they are available rebuilt, but my experience has been that 50 percent of them are bad within 3 months if not bad right out of the box, also they do not come with the spacer between the booster and the brake master, so unless you buy a used one with everything on it you will need to find that spacer for between the booster and the brake master.

Here are a couple photos of my 1980 brake pedestal/booster, sorry about the turbo piping but I didn't want to remove it to get the photos.

 

[DanielC]

Thanks again for tips on removing brake boosters from 620 trucks.  The local Pick-n-Pull has a 1979 620 truck, and this morning I removed the brake booster, and master cylinder from that truck. 

 

I also got the differential carrier, hoping for a 4.11 rear axle.  Yesterday, I removed the speed pinion, it was red.   After bringing the differential carrier home, I did the math, 35/8.  It is a 4.375 ratio.

 

I think this is the bigger booster.  Can I use the pedestal with the booster I got with the smaller brake booster?

Edited February 16, 2019 by DanielC

[wayno]

Daniel, the easy way to find out the gear ratio on early Datsuns  at the wrecking yard is to pin one of the rear tires/drums so it cannot move, put it in neutral, release the e-brake, then mark the tire/drum on the side your going to turn and then mark the driveline, then turn the tire/drum 2 complete turns and count how many times the driveline turns, 3.5 turns is 3.50 gears, 4 turns and a little more is 4.11 gears, 4 and a third turns is 4.375 gears, and so on, if you happen to find an LSD then you count how many times the driveline turns on one complete turn of the tire/drum as both sides turn, you will not have that issue very often as I have only found one LSD in the wrecking yard in all the years I have been looking and it was in a 93 Nissan D21(Hardbody), from 1981 on the rear axle gear ratio is marked on either the tag in the engine compartment(720) or on the tag near the door jam(D21), I spin one of the tires/drums on everything Datsun/Nissan with an H190 to see if it is a LSD. 

 

Edited February 17, 2019 by wayno

[datzenmike]

All PL521 were 4 speed and 4.375

'73-'78 PL and HL620 4 and 5 speed were 4.375

'79 4 and 5 speeds were 4.11 with optional 4.375

'73-'74 automatics were 4.625

'75-'79 autos were 4.375

 

'88-93 4 cylinder D21s had H-190 and optional LSDs

[Rat-a-tat-Dat]

Stellar enlightenment gentlemen.

 

Procurement of one pre 80's brake booster consequentially dictates affirmative action. Thus, an acquisition is forthright!

 

Do any followers obtain such an item? Or know the whereabouts of this desired treasure? Mainly, a 5" brake booster set up?

Not much variety in AB to choose from, you know. Plus, everything is covered under snow.

 

Many, many thank you's

[FrankRizzo]

I just bought a rebuilt one on Rockauto a couple of weeks ago, but now they are out of stock:

https://www.rockauto.com/en/moreinfo.php?pk=258893&cc=1210105&jsn=368

 

I was trying to eliminate the booster all together. Today I unplugged and capped the booster vacuum line and went for a test drive/ I like the way it feels and brakes soo much better (I have 4 wheel disk)....plus it  would clean up the bay. None of the online eliminator plates would work because of the funky 3 bolt pattern on the firewall, so I would have to keep the pedestal even without the booster.

 

https://bloxracing.com/shop/index.php?route=product/product&product_id=389

 

.

 

 

[Stoffregen Motorsports]

You could make an adapter plate out of some aluminum pretty easily. I would think a 5/8" or 3/4" thick piece would handle all the torque of the brake pedal without concern.

[Rat-a-tat-Dat]

Additionally, without complicating matters, an alternative brake booster has been found! A 1972-1974 Datsun B210 has reared its magnificent and prolific engineering properties, which illustrates the brake boosters dimensions are equivalent to the 610's but the mounting studs attached to the rear of the booster are longer than its successor. The pedestal is a visually solid structure with internally bored channels for these longer studs that extend through the fire wall and mount from the inside the cab ( an over sized spacer? ). Conversely, adequate modification is required but regardless, a notable and doable alternative. It appears that FrankRizzo's comment states the 535311's are 'out of stock', so this substitute is found on RockAut, p/n: 535300.