RE: {Chrysler 300} 300K Midland Booster

>When disconnecting booster vacuum from the intake and plugging it, the problem wasn’t there. The rebuilder advised it shouldn’t be the booster and let it break in a little.

I don't know who your rebuilder is, but I would advise finding someone that knows what they are doing. Boosters don't need to 'break in a little'. They are not like a new pair of shoes or jeans. LOL. Either they work or they don't.

If you are not inclined to rebuild the booster yourself, then I would recommend Booster Dewey, who has now been joined by two other rebuilders and changed their name. Here is their website: https://www.powerbrakebooster.com/ I assume that the quality is still the same. But YMMV.

Danny has good points. It could very well be your master, or booster. I will say we had this problem recently on our K, after installing a new dual reservoir master with a rebuilt booster. When disconnecting booster vacuum from the intake and plugging it, the problem wasn’t there. The rebuilder advised it shouldn’t be the booster and let it break in a little.

Turned out the booster had been damaged by UPS in shipping, had gone back to the rebuilder (due to the box being trashed), they checked it and then resent it to us. When we installed it we had the sluggish pedal rebound I mentioned (could lift pedal from underneath with foot, or it would come back on its own after a second or two but brakes were engaged until pedal was back up). After a few miles of seeing if it would break in, it did get a little better, but then while trying to drive to the club mini meet the brakes became suddenly jammed (pedal would not depress). Used the parking brake to stop, disconnected the booster vacuum and plugged it, turned around and drove back home fine on manual brakes.

Sent the booster back to the rebuilder and installed the old booster the K came with in the meantime. Problem went away. (Why did I switch out the booster in the first place? We we were changing over to Dot5 and the old booster already had peeling paint from Dot 3 leaking on it).

So in our case, the booster not only was causing insufficient pedal rebound, but also jammed the brakes after not many miles. And all that while thinking the booster was rebuilt so should be good. I say this because you might consider disconnecting your booster and trying manual brakes until you can rule in or out whether the booster is safe.

D&K

Sent from my iPhone

On Jan 22, 2023, at 1:33 PM, dplotkin <dplotkin@xxxxxxxxxxxxxxxxxxx> wrote:

James, I once experienced a similar failure on my 60 Buick. Pedal went to the floor seemingly held by vacuum. Pedal came up with engine off.

Is your pedal returning with no vacuum, when engine is off,?

Most master cylinders have a spring inside to bring it back. I see this external spring and bracket stuff when boosters or cylinders are wrong or poorly repaired. I see lots of Treadlevacs that way.

Say whether the pedal is held by vacuum or gravity.

Dab

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------

From: 'James Douglas' via Chrysler 300 Club International <chrysler-300-club-international@xxxxxxxxxxxxxxxx>

Date: 1/22/23 1:12 PM (GMT-05:00)

To: "Chrysler 300 List Server (chrysler-300-club-international@xxxxxxxxxxxxxxxx)" <chrysler-300-club-international@xxxxxxxxxxxxxxxx>

Subject: {Chrysler 300} 300K Midland Booster

I just went to pull the 300K off the rack, I have the steering all back in with the temp box. I went to back up and the brakes were locked.

The pedal did not return. Now I had the booster off. It looked like it had been rebuilt at some time in the last 20 years. There was some surface rust on the can and also some on the plunger. I took the can apart, just the two shells and I cleaned everything on a wire wheel and gave the parts some zinc paint. Nothing on the inside. I put it back together and that was it. I reinstalled it after the steering was in.

Now one thing that has not worked well is the brakes since I picked it up. I do plan on an entire rebuild, but that is after the steering. There was a funky return spring and bracket on the brake pedal arm that I took off. It did not seem to affect anything. But now I see why.

Anyone have any ideas? The service manual does not have anything on pressing the pedal down and and it staying there. I can pull it back with my foot.

I doubt it is the MC but anything is possible.

Help!

James

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