Brake Booster Question

[FrankRizzo]

It seems like there are two different sizes for the brake booster on the 620. The one on my truck seems huge, and I noticed a smaller model while looking at the 620's at the JCCS. I was talking to Seeker at the show and he thought the smaller one is the factory model and most common on the 620. Can anyone shed any light because I'd definitely swap mine out for the smaller one if it is as easy as ordering on RockAuto - but they dont give any dimensions.

 

Also - for extra bonus points - has anyone deleted their booster? I'd love to just go full manual but don't know how to go about mating the MC to the firewall as the bolt pattern does not line up.

 

Thanks in advance.

 

Smaller one:

 

My HUGE booster:

 

 

 

 

Edited September 30, 2018 by FrankRizzo

[datzenmike]

A larger diaphragm should make pedal effort less. Anything that reduces driver fatigue is good.

[Farmer]

Doesn't it the years determines the size? Both my 74s have the smaller. My 78 has the larger.

[FrankRizzo]

9 minutes ago, Farmer said:

Doesn't it the years determines the size? Both my 74s have the smaller. My 78 has the larger.

 

Thanks. This helps, i might just order a 1974 and see what I get.

.

[wayno]

To me it appears you have the 73/74 booster, but I can not tell for sure without seeing a close up photo of where the brake master mounts to the booster.

The first photo appears to be of a 1972 Datsun 620 booster, I have only seen a couple of these but I have not been looking either.

I use the 1973/74 booster on all my 521 builds, it is just small enough to clear things when mounted on a modified 85/86 Nissan 720 pedestal.

If what you have clears everything, stick with it, I have found that buying boosters online has a 50 percent failure rate, they work for a short time and then fail, it is kinda a pain to remove/install them, well it is for me, I have bought mine off ebay(Autozone & some other place), the Autozone failed and if you do not have receipt and the box it came in you cannot return it, I have heard others talk about this high failure rate issue also.

Edited September 30, 2018 by wayno

[FrankRizzo]

Thanks Wayno. From what I could find online (not that this is accurate...) the 521 thru 1974 620 are listed as the same booster.

It helps that that the smaller booster is "not in stock" right now ? so I'll leave it alone...with your advice.

 

.

[wayno]

I am just saying that if you can use the one you have, stick with it as that smaller one will not likely work as good as what you have.

I have never seen a 521 with a stock brake booster, but again I have not been looking.

[Stoffregen Motorsports]

I send my boosters off to Power Brake Sales in Sacramento to get rebuilt. They usually only charge $175 or so per rebuild. SO if you find a used one that you think may or may not be good, it's not the end of the world if it goes bad. If you do find a small one and it looks like crap, send it out for rebuild before you remove your larger booster.

 

Booster delete isn't a horrible idea. Some guys like the analog feel of manual brakes. You may need to play around with master cylinder bore size to get the brake feel right though. The pedal ratio might be off too, and that's not so easy to change. To bolt it to the firewall, you're obviously going to need to do some fabrication. You could probably have someone make you an adapter plate out of aluminum that has both bolt patterns in it. I bet it wouldn't take two hours to machine from scratch.

[Charlie69]

I have both sizes.  The smaller one was on the early 620s 72 to 74 and the larger I know was on the 78/79 with the front disk brakes.  I am not sure what was on the 75,76, &77 trucks but I suspect the larger diameter.

 

I am using the larger 7" diameter booster on my 66 520.  The smaller booster is approximately 4" diameter.

[FrankRizzo]

Boom!

 

5 - 3/4 diameter booster in stock at Rock Auto.

 

As Chas points out above - this is the correct booster for 72-74 620's. I like it because it is smaller and looks a little cleaner.

 

[wayno]

The issue you are going to have now is finding the spacer for that booster as it is a 2 year part, it's the spacer between the booster and brake master I am talking about.

Edited January 23, 2019 by wayno

[FrankRizzo]

Fuk me!

I thought it bolted to the firewall like my current (oversize) booster!!!!

?

[wayno]

You should likely find a pedestal also, but I was talking about the aluminum spacer, I made one out of other ones.

 

 

 

This is the 73/74 pedestal.

 

 

Edited January 23, 2019 by wayno

[FrankRizzo]

Thanks Wayno.

I think I have something like that. It came with my 15/16 Master Cylinder in case the orientation was for another Nissan vehicle, but it does not look like it will be thick enough. I saw you stacked parts, I assume that extra space was needed. I'll pull down the part box and look.

 

Without the pedestal, it wont directly to the firewall without modifications? This is looking like a PITA. I might just send it back!

[FrankRizzo]

found this....

 

[wayno]

The spacer is 3/4s of an inch thick, the pedestal is angled on one end, that is likely because of the firewall is also angled, I have a few of them that I do not need as I make my own pedestals for my 521 trucks, but I have no spacers.

I believe I made my spacer out of two 720 spacers stacked, and the smaller one had the sides cut off to match the 1979 620 master brake cylinder as I have front disc brakes on everything I own, I thought I had an extra spacer somewhere to get a photo of one but I cannot find it.

Here is a photo of one on my 521 work truck.

[wayno]

I finally found the thing/part.

 

 

And here is the one I made beside a real one, I did use this home made one till I found a real one.

Edited January 23, 2019 by wayno

[FrankRizzo]

thanks. 

This is becoming a huge PITA. Its going back to Rock Auto.....

[datzenmike]

Ahh but when you're done it's so sweet driving it with your own hand built mods.

[FrankRizzo]

13 hours ago, datzenmike said:

Ahh but when you're done it's so sweet driving it with your own hand built mods.

 

Thanks for the encouragement, but Im not sold.

 

I dont have access to a welder to make the pedestal so i'd have to go to a machine shop to have it fabbed and  the spacer needs to be angled so the M/C sits level.

 

Im just going to take of the large one and just clean and paint it.

 

.

[wayno]

You need to look at what you have right now, look at the pedestal holding the booster you have right now with the larger booster, does it have 3 mount bolts holding it on the firewall, is it angled?

It may be you have what you need right now, just measure how far apart the bolts are holding the big booster on the pedestal, if it is the same your smaller booster might bolt right on with what you already have, then all you need is a spacer.

Now if the pedestal is correct you could possibly take the spacer off the larger booster and drill it to mount on your smaller booster, then all you would need is to find another spacer to make the smaller piece like in the photos I posted in my last post.

[FrankRizzo]

Thanks Wayno. I'lll check, but since my truck is a '74 - I assume it came from the factory with a smaller booster. I can order the spacer above and add my 15/16" spacer and might get it t work.

 

thanks for your help!

[Farmer]

Heres what the 74 suppose to look like. Pics from Funtana and my other 74.  Im having to replace the booster too on Funtana

 

 

 

I can give you the pedestal  on from parts truck, just pay shipping

[FrankRizzo]

Thanks. Charlie hooked me up.

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[Rat-a-tat-Dat]

I too am modifying my brake booster which requires replacement of a 10" diaphragm to a much needed smaller version, 5 3/4". However, it's a 1980 720KC and the clearance is for adding a Cannon intake and two Weber carbs. The closest carb to the fire wall won't fit an air cleaner attached to it or air horns and filters. Thus the smaller diameter brake booster is required. I'm following this thread with interest.