K car Booster: A How To open thread

[brotherGood]

After my 4 year old FMJ style booster failed on me, I picked up a K car booster and master cylinder this evening for my AHB. I ordered from rockauto, using an 88 Reliant as a parts source, if you will.

My reason for using this...well, it's cheaper. Also, it's not as big as our fmj boosters, it is a bit longer though.

Everything should be here in a week or so, then it's a matter of when do I want to stand on my head to get the thing unbolted. From what I'm hearing, it uses metric bolts rather than our standard ones. Not sure if there are any other potential hurdles, but I'll post them as I find them.

I am curious..are the boosters gloss black from the factory? I know my replacement one before wasn't painted, and I'm betting this one isn't either.

 

[slant6billy]

Gator just did this for his 79 Runner. Heads up- you need metric nuts and a grommet for the stroke arm. Gator can give more detail

 

[BudW]

I bought a “turbo” booster for my ’86 5th Ave.
Without seeing yours – I can’t comment if the same or not.

A single diaphragm K-car booster is smaller in diameter and a hair shorter than an FMJ booster is.

The twin diaphragm K-car booster (generally on turbocharged cars) is longer (about an inch) but much less diameter than both the FMJ and single diaphragm K=car versions are.

The twin version “should” work fine for big blocks, or small blocks with low vacuum issues.

FMJ

K-car

Turbocharged K-car.

Note: the studs are metric. The stud centers are also in metric but will fit the firewall holes and master cylinder holes just fine.

My booster (from RockAuto) came with lock nuts

From the factory, as well as “most” factory replacement parts, the boosters came painted gloss black. Many of the newer boosters from Chrysler come unpainted (and all aftermarket).

I highly recommend getting a new booster powder coated, if possible, or at least painted. Keep in mind that DOT-3 and -4 brake fluid WILL eat paint


Personally I wouldn’t replace an FMJ booster with the same design. I would go for either of the two K-car versions. That way you can (finally) get to the rearmost valve cover screw on your 318.

Also, if replacing the booster on a ‘78 (or down) F or M-body, I would change to the ’79 and newer aluminum master cylinder. Note: some ‘79’s got cast iron for there were periods the aluminum master cylinder availability was limited. Cast iron uses 4 bolts whereas Aluminum uses 2 attachment bolts.

My wagon, I’ve been thinking about removing the booster altogether, for system is way “over-boosted” as it currently is. You apply brakes a bit hard and you and all contents is going forward.
Just trying to find the needed (booster delete) parts is not easy.

BudW

 

[slant6billy]

I bought a “turbo” booster for my ’86 5th Ave.
Without seeing yours – I can’t comment if the same or not.

A single diaphragm K-car booster is smaller in diameter and a hair shorter than an FMJ booster is.

The twin diaphragm K-car booster (generally on turbocharged cars) is longer (about an inch) but much less diameter than both the FMJ and single diaphragm K=car versions are.

The twin version “should” work fine for big blocks, or small blocks with low vacuum issues.

FMJ
View attachment 18887

K-car
View attachment 18888

Turbocharged K-car.
View attachment 18889

Note: the studs are metric. The stud centers are also in metric but will fit the firewall holes and master cylinder holes just fine.

My booster (from RockAuto) came with lock nuts

From the factory, as well as “most” factory replacement parts, the boosters came painted gloss black. Many of the newer boosters from Chrysler come unpainted (and all aftermarket).

I highly recommend getting a new booster powder coated, if possible, or at least painted. Keep in mind that DOT-3 and -4 brake fluid WILL eat paint


Personally I wouldn’t replace an FMJ booster with the same design. I would go for either of the two K-car versions. That way you can (finally) get to the rearmost valve cover screw on your 318.

Also, if replacing the booster on a ‘78 (or down) F or M-body, I would change to the ’79 and newer aluminum master cylinder. Note: some ‘79’s got cast iron for there were periods the aluminum master cylinder availability was limited. Cast iron uses 4 bolts whereas Aluminum uses 2 attachment bolts.
View attachment 18890
View attachment 18891


My wagon, I’ve been thinking about removing the booster altogether, for system is way “over-boosted” as it currently is. You apply brakes a bit hard and you and all contents is going forward.
Just trying to find the needed (booster delete) parts is not easy.

BudW

Hey Bud, what is that part number for the turbo car brake booster?

 

[BudW]

It is still in a box in my garage.
I will try to make note of it and maybe even side by side pictures.

I hadn’t check to see if the pushrod (going to petal) is the same or not – but if incorrect, I would “assume” that part can be carried over.
BudW

 

[jasperjacko]

Did this back in 91' with my 440 Mirada. IIRC the shoulder bolt was a different diameter?

 

[brotherGood]

I ordered a dual diaphragm booster..I'm assuming that's the turbo one?

 

[lowbudget]

Great info....Thanks.

 

[BudW]

I call it a “turbo” one, but I don’t think the factory did. I usually only saw it on turbo cars.
I “think” it was part of a HD braking package, or something like that, possibility.
It might have been standard on V-6 cars, as well.

It might be better to just call it a “dual diaphragm” vs. “single diaphragm”, instead of “turbo” vs. “non-turbo, or standard”, maybe.

BTW, I forgot to take pictures last night. Will try to sneak out to the garage and do so tonight.
BudW

 

[brotherGood]

Received my booster and master cylinder yesterday..didn't receive any hardware. Anyone know what size I'm after?

 

[4speedjim]

BudW is there any chance you have grease or oil on the shoes, possibly pads? That makes brakes grabby. Just a thought.

 

[BudW]

is there any chance you have grease or oil on the shoes, possibly pads?

Not a chance.
It is just too much booster for a stripped down (plain Jane) car.

The car feels like it weighs in a 3000 pounds where as my 5th Ave feels like 4500 pounds (no, I hadn't weighed them, and weight exaggerated for effect).

You can not slam on the brakes on my wagon, or you and all contents in rear will be hitting you in the head.

Light braking also feels “overpowered”.

I don't think the wagon ever needed a booster (well, not yet, but will once my other plans materialize).
Get some better tires, then I can go brake with the better of them.

That car will get 11¾” front disk and 11” rear drum upgrade anyway – for you can never have too much brake.
BudW

 

[BudW]

Received my booster and master cylinder yesterday..didn't receive any hardware. Anyone know what size I'm after?

8mm-1.25 thread, lock nuts (6x).

I took some pictures of my booster this morning (burr - its cold outside . . . ).
The old booster is from a '84 Gran Fury police car (but same booster size for all FMJ cars).

Roughly about 12" diameter.

Not quite 9"

About 5" long

About 5" long

Side by side stud (horizontal) comparison

Side by side stud (vertical) comparison.

 

[BudW]

Received my booster and master cylinder yesterday.

Is the booster you received the same one as I have pictured above?

Be sure to shoot some paint on it before install, for it might turn a couple shades of . . . rust, sooner rather than later.

I would also recommend reusing your existing vacuum check valve, than the style that my replacement booster came with.

A large screwdriver and patience, and it should pop out.
You should also hear a “swoosh” from air entering into the vacuum chamber, when the valve pops out of the grommet. If not, then you have a bad booster.

Make a gasket to go between the booster and firewall (or reuse the old gasket) will help with popping noises when brakes are applied. Ask how I know . . .

 

[brotherGood]

Are you saying the new check valves go bad quickly? The booster that went bad in my car is only about 4 years old...could it be the valve? Nevertheless, this is something I had wanted to do anyway...I'll just keep the other as a spare.

Then, if thats the case, where can I get a valve that's actually worth putting on there.

Any specific kind of paint I should use? And what about the gasket. I don't think this new one came with one of those either

 

[BudW]

My booster also did not come with a gasket.
The booster bolt pattern is same for pretty much any Chrysler booster from mid-60’s to mid ‘90’s.
I would say reuse existing one or make one. Material type is not that important as long as it’s not metal against metal. Paper/cardboard might not be the best material to use.


The check valves rarely go bad – except for breakage.
The one with the hose that sticks out towards the front of car is a pain to work around. I’m always hitting it by accident (and have broken a couple).
The original design is out of the way for most things and layout wise, just works better.

If you pop the old valve off, then you don't have to remove any hose clamps. Just push it right back into the new booster.

If you want to test the valve, then pop old one out (can be done with engine running – but a chance engine might die once valve is popped out). Having two people do this might be easier.
Stick thumb over end of valve and you should feel a strong suction force.
Turn off car. Your thumb should stay stuck to valve for a very long time (you will have to pull thumb away from valve – but it won’t hurt or cause damage).
If booster is good, that valve is designed to leave booster with enough vacuum for at least one power assisted stop.
If no vacuum is held, then (most likely) a bad booster or (less likely) bad check valve or restricted/leaking hose.


Paint – pretty much whatever you want to use (or none, if you like the "rust look). Paint made for metal might last longer and look better in the long run (like for metal outdoor furniture, etc.).
Factory paint color should be a 60-80% gloss black paint (or powder coat).

There is not a paint out there, that I know of, that will stay on if DOT-3 or -4 brake fluid gets on it – so be careful with that.
If you are changing the booster only, there is no reason to loosen the brake lines.

Now with that said, brake fluid really needs to be changed/flushed every couple of years – even if car sits a lot.

Brake fluid absorbs water moisture over time. When brake fluid gets above boiling point, the water boils out of the fluid. The water moisture and iron/steel = (equals) rust - which generally occurs at the source of heat (brake caliper and wheel cylinders) – which generally causes brake calipers to seize up and wheel cylinders to leak.
BudW

 

[brotherGood]

Been a while since I've posted in this, but I'm finally gonna do the switch. Pulled the old booster earlier today after work and got the new booster mocked into place. It doesn't seem to want to just slide into place, I'm hoping I can draw it down with the bolts

 

[Gator]

It will draw down I did this swap last summer only thing I changed I had to get metric nuts and pedal bushing diameter was different

 

[brotherGood]

Well..only took 5 hours, but i got it finished. In the process, I made the executive decision and took the dash out. I should be getting my new custom gauge bezel soon, so I figure id might as well prep the dash for a complete rewire.

I love how much smaller that booster is.. after I finish the dash project, I'm gonna just go ahead and flush the system and put the new master on as well..thatll leave the only things I haven't changed being the front brake hoses.

 

[Gator]

Awesome you get so much more clearance fir valve covers