Does a 1979 J20 have a dual diaphram brake booster?

[Geminiroq]

Hey guys,

I picked up a J20 and wanted to update/upgrade the brakes.

I know that you can swap out the MC/BB from a 88-91 Grand Cherokee and you can put on larger GM calipers.

Or the big boy....the Hydroboost!

So my question is this....does the 1979 J20 (8000GVW) have a dual diaphram brake booster.

Any and all advice is appreciated.

Thank you.

[Geminiroq]

Hey guys,

I wanted to see if anyone had any input on this?

I dont want to buy a dual diaphram brake booster if I dont have you.

You know we are on the cheapo side :thumbsup:

Thank you...

[Elliott]

I don't think the '79 did, but a dual diaphram... for what it takes to remove yours and install... is a waste of time and money compared to scrounging a hydroboost at the same yard and spending ~$45 to get a mounting assembly for it. Be real cheap and grab some old hoses at the same yard. Get some real brakes going for...

[Geminiroq]

Elliot,

I have heard great things about the Hydro Boost braking system.

My one concern/question is.....are they that good that they are super touchy?

If I hit the brakes will I go through the windshield or can I modulate them like regular brakes on say...a car or light duty SUV?

Please explain....I want the best but dont want to be dangerous.

Thank you...

[babywag]

Seriously....is that a real question?

Hydroboost has been/is installed on millions of vehicles, do you really think it would be unsafe to drive?

If you can drive a car, or chew gum you can modulate the brake pedal like a normal vehicle.

However if you cannot, well then maybe you shouldn't drive a car:rolleyes:

[Geminiroq]

LOL...Babywag....I guess I may have misdirected that question a bit.

The reason I ask is because it seems like the majority of the people who have put a HB on their rig say that it will put you through the window if you are not carefull.

I am in Los Angeles and I need superior brakes but those statements scared me a bit.

That is why I was asking if it is safe to put on a FSJ and not be so touchy that it throws you through the window.

I hope that is better :confused:

Thank you...

[Elliott]

I typically advise people to be sure to have their seat belt on when they first try it out, not because I give a "la""la""la""la" about the law but because the difference is so dramatic that if you think you can just slam on your brakes like you used to then you might just kiss the glass. It takes less pedal travel and comes on much stronger than vacuum brakes. The pedal feel will take a lil getting used because it's different then anything you've driven but the adjustment is made rapidly and you'll grin ear to ear everytime you use the brakes and you'll also wonder why you even thought about keeping any kind of vacuum system.:thumbsup: If you check the link in my sig I put a bunch of info in there to help folks do thier own system. You will need the mounting assembly and you will need to bush the rod end to your 7/16" pedal pin size. If you get a '94-'95 Astro HB it will have the spade shaped rod end which has the 5/8 hole, this can be bushed directly down to 7/16. If you get an earlier Astro HB it will have a 1/2 hole size and will need to drilled/reamed up to 9/16 and then bushed down to 7/16".

[Geminiroq]

Ok...thank you!

I have a better understanding of it now.

[Casey]

I am in Los Angeles and I need superior brakes but those statements scared me a bit.


:rolleyes: In that case what you need is an armored car with hydro boost and port-firing weapons.

Or an armored personel carrier, if you have kids. :D

[Serious Johnson]

No, a '79 J-20 had a single-diaphram booster. If you need a new one anyway, you may as well use a dual, but I wouldn't expect greatness from that alone. I'll eventually put hydroboost on mine because of weak vacuum from a big cam and the high altitudes at which I drive, but I consider the weak point, by far, of FSJ brakes to be the small front rotors. Pedal pressure is not a problem -- fade is. I tow 6-8,000 pounds with my Wag pretty often, and brake fade is always a concern. The rear drums are fine, but the fronts fade early, even with Porterfield carbon-ceramic pads (which did help, but sorta suck when cold). Unfortunately, I don't know of a reasonable (read "cheap") fix for that.

S.J.

[Tornado230]

All J-20's used a tandem (dual) diaphragm booster.

[FSJ Guy]

Hydroboost brakes (stock) stopped my Chevy dually just fine loaded up to the GVWR of 10,000 lbs. It should handle an FSJ just fine. As far as braking, it's the same as driving any other car.