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'67 Deillve Brakes / Brake booster, new issue. (Bumping this older thread)

Started by Julien Abrahams, October 12, 2014, 05:05:02 AM

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Julien Abrahams

Hey guys,
Last week I noticed that when the car is cold and running on high idle, it seems as if there is more vacuum for the brake booster: I only need very light pressure on the brake pedal to brake. However, after the car warms up and it goes to slow idle, it appears as if I need to push harder on the brakes to get them to respond. The car brakes well nonetheless.
Would this indicate a power booster being / going bad? Internal leak?
When I shut the car off, I have about 2 or 3 more vacuum assisted brake applications before the pedal becomes hard. Also, with light pressure on the pedal and then starting the car, the pedal falls. This would indicate a working vacuum system. Yes, no?
Thanks in advance.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

dplotkin

Your description of operation seems in line with normal performance, pedal should fall with your foot on it, not by itself, with the engine running. However, a small leak in a booster can show up as better performance at idle when vacuum is highest, and a fall off at high speed, I had exactly this with my 68 New Yorker.

Pedal feel and stopping power often has to do with the makeup of the friction material of the shoes, whether or not the shoes are on correctly, and/or the condition of the drums. It wouldn't hurt to pull the drums and inspect.

Dan
56 Fleetwood Sixty Special (Starlight silver over Dawn Grey)
60 Buick Electra six window
60 Chrysler 300 F Coupe
61 Plymouth Savoy Ram Inducted 413 Superstock
62 Pontiac Bonneville Vista
63 Chevy Impala convertable
63 Ford Galaxie XL fastback
65 Corvette convertable 396
68 Chrysler New Yorker

Scot Minesinger

If the booster is original with 47 year old rubber and in question, it should be replaced with good rebuilt unit.  My 1970 Cadillac similar to your booster mechanically does not exhibit a difference in braking pedal effort at idle or when running.  Have not checked it when car is not running.  It sounds like you may have a leak.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

"Cadillac Kid" Greg Surfas 15364

Julien,
It sounds perfectly normal to me.  If there was a significant leak, you would loose vacuum almost immediately upon turning the engine off. Sorry, but it doesn't seem like you have anything to worry about there.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Julien Abrahams

Okidoki ;). I just wasn't sure. This because there is a slight difference between the fast idle (just after start up) and slow idle (when fully warmed up). It appears as if there is more vacuum when the engine is at fast idle. But does that make sense? Isn't it the case that the highest vacuum will be during slow idle?
I might overanalyze this as well. The other cars I drive regularly are a'69 MG with a single reservoir, no power brake system, and my boss' 2014 Audi A 6 :). So, I have to keep in mind that it is still a pretty heavy car and the drums all around most likely do not have the stoppign power of the discs all around of new Audi hahahah  :D
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

Julien Abrahams

hey guys, took the Cadillac for a drive today. After starting it up and letting it idle for a short while, I drove down the road. The first time I applied the brakes, the front locked up almost immediately and I had to prevent my head hitting the windshield :).
That happened 2 or three times. Then, I applied the brakes again, and all was normal again.
It felt like there was something binding in the Master cylinder or something. I also thought about the piston for the rear system sticking a bit, resulting in all the brake power going to the front system. Is this possible?
Any thoughts are appreciated.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

Julien Abrahams

1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

Scot Minesinger

The brakes may work OK and be quirky sometimes.  Sounds like a problem in master cylinder.  With rubber parts in both master and booster that are 47 years old, again, I would replace them as a precautionary measure alone even if they worked OK.  If you need to stop an cannot?, ...well do I need to continue.  If a non essential system such as radio worked weird or OK but unreliably maybe I would let it go for a while, but not brakes.

In my 1970 Cadillac with 32k miles on it the brakes worked poorly and the brake warning light on dash glowed.  Since everything was over 40 year old, I replaced everything, all brake lines (steel and rubber), booster, master, calipers, drum pistons, shoes, and everything except springs and rotors which were a solid metal part that cannot really fail.  The emergency brake cables were frozen and had to be replaced too.  Now the car stops perfectly with peace of mind.

One of the biggest problems with our cars is disuse.  Drive your Cadillac once every week if you can.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Julien Abrahams

I agree with the disuse argument. But I think that goes for all older cars. If they sit for too long, it does more bad than good.
With regard to replacing everything brake related: I can imagine, but I simply don't have the budget to do so. If I would have money growing on a lttle tree in the backyard, I would most likely restore the Cad completely (except mayube for the interior, because I like to leave something that it is a 47 year old car, but that is my personal opinion ;).
But, I am trying to understand what is actually happening.
Is it possible that the rear piston in the MC is sticking somewhat causing all the pressure to go to the front system? How are the front and rear systemt separated?
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett