Brake Master cylinder & booster improvement (using the K car parts)

[BudW]

About the "resize bushing".
Went to my local hardware store (Ace) and found two possibilities:
Bronze and Nylon

P/N 58079. $5.25 (plus tax, US)

P/N 409900. $0.69 (plus tax, US)

A snug fit

Also sung

Both fit fine.
Either version would need to be cut for length, which would be 1/4” long (on “K” booster). Also need to find a spacer 1/16” thick to go on side of push rod.

Note: use plenty of grease when assembling to prevent squeaks – but not too much where it might drip onto carpet (or whatever floor covering).

Personally, I recommend bronze – but I'm not sure that nylon wouldn't work just as well. I'd guess this could be topic of another discussion – but if you don't mind, lets save that discussion for another day (please) or another thread.
I'll be using the bronze version.
BudW

 

[BudW]

How do you adjust the brake light switch?

A very good question.

This is from my '77 FSM (Factory Service Manual) but will apply for all FMJ's. The PDF is at bottom of page. I made photos as well (the same material).

Adjustment bolt and bracket movement.

How it looks when brakes are at rest. The switch plunger is depressed (not quite fully, though).

In this picture, the brake lights will be ON.

0.140” is very close to 9/64” (3.5 mm). I use 1/8” when I adjust brakes (0.125” - 3.2 mm) sense 1/8” is easier to find than 9/64”.

An UN-official method of adjusting the stop light switch is to bend the bracket. I don't recommend it NOR DO I WANT TO HEAR ABOUT ANYONE DOING IT. A "bent bracket will continue to bend over time to the point stop lights will stay on. The plunger needs to make contact to middle of brake petal.
Using the adjustment bolt is not hard and goes pretty quick for most people.

Note: Chrysler used several different stop light switches from '76-89. The one in my picture (above) is from an '84 Gran Fury police, so this would be a Heavy Duty non-cruise switch (if anyone wanted to know). The mounting bracket remained the same for all FMJ's (as far as I know).
BudW

 

[BudW]

The other (problem) was the top two holes in firewall were too small for the metric thread studs on the K car booster.

To be honest, I have had problems stabbing in new (original) boosters, just about every time (even 30 years ago). On just about every car I've removed the booster from, you can see the brake bracket shifts over a tad so holes are no longer round but eyelid shaped. Sometimes a person needs to get our your 5 pound (2.5 kg) and a block of wood to seat one in because you have two different sets of items to go through (firewall and brake petal bracket).

It took me a few moments to get this bracket on the booster. The bottom studs went in smooth but top studs took a bit longer. When I had originally measured them, I came up with same size. I wonder if there might be a tad difference in production tolerances or maybe a small difference from inches to mm, maybe?

I wouldn't see a problem with drilling out the firewall and brake bracket a size larger (together), if needed. Once you get one hole drilled, stick a nut and bolt into that freshly drilled hole and tighten, before drilling the other three (to keep both brackets aligned when drilling).

Finally, the threads on the K car booster that go through the firewall ended too soon (I guess the K car has a thicker firewall). Easy fix was a few flat washers on the inside under the dash.

A very good point and I had forgotten. Many of the front wheel drive cars used a thick plastic bracket for the brake petal support bracket, instead of steel (as FMJ's use). Yes a person will need to add some spacers/washers to compensate.

This picture from Aka601 shows the un-tapped portion of studs:

My booster has the same studs, so I will also need about 1/4" of washers.
BudW

 

[XfbodyX]

Dont forget to replace and lube your other wear items in the whole assembly.

 

[BudW]

A little bit of grease on those plastic bushings make a huge difference on “squeaks”.
However, too much grease causes another problem – stains on your carpet or floor mat(s).

Hehe, showoff – meanwhile I might have shorted out my keyboard from drooling looking at ‘dem bushings.
BudW

 

[volare 1977]

Rock auto or mopar has the 2467770 brake pedal bushings. I believe they were the same ones used on the dakota.
MOPAR 2467770 Brake Pedal Bushing | RockAuto

 

[brotherGood]

Wait..that's a real thing? Could bad bushings have anything to do with my pedal not coming off the switch every time I use the brakes?

 

[Mopar&vettedude]

I know its been awhile on this post, but has anyone ran into issues with their brakes being someone stiff after doing the conversion? plus for anyone that's converted to rear disc, did you have to replace the proportioning valve?

 

[Mikes5thAve]

The main reason to convert the booster would be going big block when you need the clearance.

It was a nice surprise when I got a master cylinder for a truck cheap on clearance at rock auto that it came with the tank even tho it looked to be the kind that came with the aluminum part only.

 

[Duke5A]

I know its been awhile on this post, but has anyone ran into issues with their brakes being someone stiff after doing the conversion? plus for anyone that's converted to rear disc, did you have to replace the proportioning valve?

Yes, you need a four-wheel disc distribution block. Good news is there is a bolt in unit that you don't even need to screw around with the lines to put in (providing you get them disconnected in one piece). Another benefit of our cars using GM components in the steering and brakes.

Call them and verify the tube nut sizes. They list another that is really close, but is a different skew. Rear port tube nut size is 9/16". It's been a few years since I did this and it's all I remember.

1974-77 Chevrolet Corvette Four-Wheel Disc Proportioning Valve

 

[Ark]

Yes, you need a four-wheel disc distribution block. Good news is there is a bolt in unit that you don't even need to screw around with the lines to put in (providing you get them disconnected in one piece). Another benefit of our cars using GM components in the steering and brakes.

Call them and verify the tube nut sizes. They list another that is really close, but is a different skew. Rear port tube nut size is 9/16". It's been a few years since I did this and it's all I remember.

1974-77 Chevrolet Corvette Four-Wheel Disc Proportioning Valve

You ever seen one actually fail?

My brakes have been iffy ever since an autocross outing many years ago. Work, just aren't very...responsive? Part of it is the engine just not pulling a whole lot of vacuum.

I remember bleeding the heck out of all the brakes and replacing the master cylinder and inspecting everything without ever finding a real cause. This thread is a great resource, thinking about the dual diaphragm K car swap and maybe a new valve. 11.75s front drums back.

 

[Mopar&vettedude]

Yes, you need a four-wheel disc distribution block. Good news is there is a bolt in unit that you don't even need to screw around with the lines to put in (providing you get them disconnected in one piece). Another benefit of our cars using GM components in the steering and brakes.

Call them and verify the tube nut sizes. They list another that is really close, but is a different skew. Rear port tube nut size is 9/16". It's been a few years since I did this and it's all I remember.

1974-77 Chevrolet Corvette Four-Wheel Disc Proportioning Valve

I've seen some others through summit, but wasn't entirely certain on the flare nut size as well. I did find one that has the 1/2 and 7/16 for the lines coming off the master and it had the 9/16 for the rear line. Ill have to read the book later and see if it says in there before ordering. Thanks.

 

[Mopar&vettedude]

I've seen some others through summit, but wasn't entirely certain on the flare nut size as well. I did find one that has the 1/2 and 7/16 for the lines coming off the master and it had the 9/16 for the rear line. Ill have to read the book later and see if it says in there before ordering. Thanks.

Yes, you need a four-wheel disc distribution block. Good news is there is a bolt in unit that you don't even need to screw around with the lines to put in (providing you get them disconnected in one piece). Another benefit of our cars using GM components in the steering and brakes.

Call them and verify the tube nut sizes. They list another that is really close, but is a different skew. Rear port tube nut size is 9/16". It's been a few years since I did this and it's all I remember.

1974-77 Chevrolet Corvette Four-Wheel Disc Propor

Worst case i just swap the idiot light switch over from the stock valve.

 

[Duke5A]

You ever seen one actually fail?

My brakes have been iffy ever since an autocross outing many years ago. Work, just aren't very...responsive? Part of it is the engine just not pulling a whole lot of vacuum.

I remember bleeding the heck out of all the brakes and replacing the master cylinder and inspecting everything without ever finding a real cause. This thread is a great resource, thinking about the dual diaphragm K car swap and maybe a new valve. 11.75s front drums back.

Actually, I have not. Not on a anything myself or my Dad has owned.

If you're looking for 11.75" front disc parts then Doctor Diff can sell you everything. He carries the rotors and caliper brackets.

 

[Ark]

Actually, I have not. Not on a anything myself or my Dad has owned.

If you're looking for 11.75" front disc parts then Doctor Diff can sell you everything. He carries the rotors and caliper brackets.

Already got em.