1966 300 convertible help!!

Ross Wooldridge

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Hmmm... you already have the correct master for the MUCH SAFER dual circuit system.

Look harder for a drum booster - but FIRST, correct the plumbing issues described with the routing, check the flex hoses front and rear (they can fail internally), check the shoe adjustments, and see if that booster doesn't work just fine before trying to replace it. You might find that you're brakes start working splendidly!

While I do not have any experience of using a disc booster on a drum system system, I have heard it works OK. There's no reason why it shouldn't work - it just might be a bit touchier, which is something you can get used to. On the other hand it just might be overboosted and call overboosted and cause other problems. It's worth a shot to find out... fix the other issues first.
 

66chry300

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1) To start, the Bendix booster is for discs - you need the drum booster. Show us a pic of your booster to be sure you have given it the right name...
Your booster should look like this:
View attachment 564348
2) As noted above, mimic the 67 plumbing - from the dual res master to a distribution block, NOT a prop valve. Your new master cylinder should be one with balanced reservoirs, NOT a later dual res one with a larger rear reservoir (for front brakes).
Your new master cylinder should look like this:
View attachment 564349
Your new metering block should look like this:
View attachment 564350
3) Lift up the rear of the car until the wheels are off the ground (use jack stands or a hoist for safety), and back off the rear drum adjusters until the shoes are barely making contact with the drums when the wheels are rotated.
4) Lift up the front of the car until the wheels are off the ground (use jack stands or a hoist for safety) and adjust the front drums until the shoes are barely making contact with the drums when the wheels are rotated.
5) Adjust the pushrod from the booster (ensure you have the correct booster) until it holds the master 1/16th of an inch away from the booster mating surface before bolting it down. This ensures the correct preload of the system. Too much, and you'll engage the brakes early - perhaps even all the time - making the fronts overheat and not grab properly, and when you do want to stop, this may make the rears do all the work and overheat themselves.

I hope this helps.
Hmmm... you already have the correct master for the MUCH SAFER dual circuit system.

Look harder for a drum booster - but FIRST, correct the plumbing issues described with the routing, check the flex hoses front and rear (they can fail internally), check the shoe adjustments, and see if that booster doesn't work just fine before trying to replace it. You might find that you're brakes start working splendidly!

While I do not have any experience of using a disc booster on a drum system system, I have heard it works OK. There's no reason why it shouldn't work - it just might be a bit touchier, which is something you can get used to. On the other hand it just might be overboosted and call overboosted and cause other problems. It's worth a shot to find out... fix the other issues first.
Everything except the actual brake lines were replaced on this car. I keep setting the adjusters back, but they keep tightening up again. So pissed because I have to get the drums returned because they all overheated and warped!!! I’ll keep looking for one and if you may come across one, let me know!
Thanks
 

Big_John

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Think I figured out the issue! Turns out this isn’t the original booster and it’s actually for a 66 Chrysler with disc brakes! Just going to convert it back to a single line since it’s near impossible to find the correct booster.

View attachment 564407

View attachment 564408
The booster isn't causing your issue.

At this point, it wouldn't surprise me if you changed the MC and you still have the same issue.

IMHO, the dual MC is a significant safety upgrade and you have everything in place... First thing is to swap those lines.
 

Big_John

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Everything except the actual brake lines were replaced on this car. I keep setting the adjusters back, but they keep tightening up again. So pissed because I have to get the drums returned because they all overheated and warped!!! I’ll keep looking for one and if you may come across one, let me know!
Thanks
Bet the adjusters are set up wrong... Possibly left on right and vice versa...

Changing the MC back to a single isn't going to fix the issue.
 

pomonamissel

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and this power booster for drums can be had as well , i'm swapping it over to discs setup off a 70 nyr

DSC03379.JPG
 

66chry300

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and this power booster for drums can be had as well

View attachment 564410
This looks c
The booster isn't causing your issue.

At this point, it wouldn't surprise me if you changed the MC and you still have the same issue.

IMHO, the dual MC is a significant safety upgrade and you have everything in place... First thing is to swap those lines.
swapped the lines and the issue transferred from the back brakes to the front brakes! I don’t think this booster is going to work
 

Big_John

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This looks c

swapped the lines and the issue transferred from the back brakes to the front brakes! I don’t think this booster is going to work
That points to the push rod not being adjusted correctly, as in sticking too far out into the MC.

It could also be an issue with the MC, although I kind of doubt it. It's not the booster giving you this problem.
 

66chry300

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That points to the push rod not being adjusted correctly, as in sticking too far out into the MC.

It could also be an issue with the MC, although I kind of doubt it. It's not the booster giving you this problem.
I do think I have the push rod on the booster adjusted a little bit too far but when I set it at the correct spot, I practically have to floor the brake petal to get it to stop
 

Big_John

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I do think I have the push rod on the booster adjusted a little bit too far but when I set it at the correct spot, I practically have to floor the brake petal to get it to stop
Well, that explains the issue. If the rod is set too far into the MC, it will hold the brakes on.

I would adjust it correctly and then find the other problem. That could be the rod wasn't out far enough, but I'm betting on it needing to be bled again.
 

66chry300

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Well, that explains the issue. If the rod is set too far into the MC, it will hold the brakes on.

I would adjust it correctly and then find the other problem. That could be the rod wasn't out far enough, but I'm betting on it needing to be bled again.
I bled them yesterday and they were fine. I’m going to try to play with the rod on the master and I will get back to you tomorrow. I really appreciate your help!
 

Ripinator

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I bled them yesterday and they were fine. I’m going to try to play with the rod on the master and I will get back to you tomorrow. I really appreciate your help!

The adjustment on that rod is tricky. It is almost a black art. . . Yer gonna hafta adjust it - drive it and adjust again, until you get it right. Don't give up. You are almost there.
 

Big_John

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Adjustment spec from the '66 Plymouth FSM, page 5-26. Get an FSM and a parts manual here: MyMopar

Gauge.jpg
 

Big_John

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This guy is a little "different", but his videos are often worthy of watching. Pay attention to about 1:30 into the second video. He shows a good way to check for the rod being adjusted too far out.


 

Big_John

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So. . . Looks like .005" less than one inch. . .?
.050 or in tech speak... 50 thousandths.

Since posting that, my thoughts are how to produce a cheap gauge to use. I have a couple ideas, but really don't want to break my retirement streak.
 
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