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  #1  
Old 01-17-2009, 03:44 PM
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Join Date: Feb 2004
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74 SLC Brake Booster

Good day!
My wife's 74 SLC has been having an issue with braking.
It appeared at first, as if it were a vacuum problem, as the assist would work only for a second, and then as you continued to slow, you would have to exert a great deal of pressure to stop.

Today, I disconnected the vacuum supply hose, and read the vacuum at 18".
This pressure held for 10 minutes after the engine was stopped.

When I put my foot on the brake, and start the car, I get very little movement of the brake pedal.

Is this a rotten booster? I see them for $750 - $800, and a Cardone rebuilt for $135.

If it is booster, is this something I can replace without cracking any brake pipes, there appears to be enough wiggle room to separate the booster from the cylinder...
I've bled the car before, and it's a B#tch!

All educated replies gratefully accepted!

Many thanks!
Dan - 74 SLC - 59 Jag

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Dan Davis
74 450 SLC
59 Jaguar (Mark 1)
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  #2  
Old 01-17-2009, 03:53 PM
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Join Date: Aug 2004
Location: Blacklick, Ohio
Posts: 238
Hello,

Yes just leave the metal lines hooked up. Remove the two nuts holding the master cylinder on. You will not have to deal with brake fluid and air in the lines if you are careful.

You will have one bolt up under the dash to disconnect where the rod from the booster connects the brake bedal. After the bolt is removed a spacer must also be removed before the pedal and booster is dis-connected. In addition there are three bolty holding the booster mount to the firewall. If I recall one is unfastened from the engine compartment and the other two from under the dash also.
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Joe Alexander
Blacklick, Ohio
1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
1986 560SEC
1989 Unimog FLU419 (US Army)
1991 300TE (wife)
2002 SLK 32 AMG (350 hp)
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  #3  
Old 01-17-2009, 04:42 PM
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Thanks Joe,

That's how it appeared to me.
Do you agree with my diagnosis?
I would hate to go through the motions to determine it was something else.
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Dan Davis
74 450 SLC
59 Jaguar (Mark 1)
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  #4  
Old 01-29-2009, 06:49 PM
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Posts: 29
Good day!
Well, here's the rest of the story for the archives.
The rebuilt booster showed up Saturday morning, in a box which had been opened, and had a bunch of grease spots on it.
The booster, as well, had grease prints and scratches consistent with it having been previously installed.

I called my supplier and informed them, and had them send me a return authorization, as I could think of no reason for this, except that the unit had been previously installed - found defective - and returned.

Then my wife reminded me that she had been driving with poor brakes for three weeks now, and just how long was this going to take?
After calling around, and finding no part locally available - I decided to tempt fate and try to install it anyway.

An hour and a half later I had an answer. This booster was in fact no better than the one I was trying to replace. An hour later still, and I had the original back in the car.

There are four studs to get at from behind the brake pedal. One nut is a bit difficult to get at, but I have had much worse....
I have another booster on order, and hopefully, after all of this, I have diagnosed the problem correctly, and will get a good part, and this will do it.

Thanks for your help!
Dan
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Dan Davis
74 450 SLC
59 Jaguar (Mark 1)
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  #5  
Old 01-29-2009, 08:01 PM
ja17's Avatar
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Join Date: Aug 2004
Location: Blacklick, Ohio
Posts: 238
Hello Dan,

We are assuming that you did check the brake pads! Worn pads up against the cross springs can give the same symptom.
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Joe Alexander
Blacklick, Ohio
1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
1986 560SEC
1989 Unimog FLU419 (US Army)
1991 300TE (wife)
2002 SLK 32 AMG (350 hp)
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  #6  
Old 01-29-2009, 08:11 PM
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Join Date: Feb 2004
Posts: 29
Oh yeah!
Been there done that - Nice new pads on all four wheels.

The master cylinder as well looks fine - as I had it uncoupled for the swap, it showed no signs of leakage, and the operation without boost is nice and solid.

Many thank!
Dan
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Dan Davis
74 450 SLC
59 Jaguar (Mark 1)
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  #7  
Old 02-10-2009, 12:02 PM
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Posts: 29
Well, here's the final chapter.
After pulling the defective replacement booster, and putting the original back in the car, I went down to Pep Boys and ordered another from a different re builder.
I ordered the booster on Saturday the 24th, and was told it would be 3-5 Business days, or 5-7 normal days for delivery. No problem, a worst, it would be in by the next Saturday, and I could get it in.
Saturday the 31st, I called Pep Boys and was told, "I just called the Manufacturer. They confirm that the unit shipped on Monday the 25th and it will be delivered on Monday the 2nd."
Bugger! - Now my wife will need to drive without brakes for another week, until I can get the new booster in.
On a lark, I drove to Pep Boys on the 2nd, to pick up the Booster - Nada, didn't come in. "Hey guys! - did we get any special orders in today?" - Nope.
I took Tuesday off- then called on Weds the 4th, this time I get "Your booster is on backorder". How I ask is this possible? did they get another order, turn the truck around and ship it to someone else?
On the sly, the counter guy slips me a number of a wholesaler who may be able to help - I call him up, and he says - Sure I can have one in tomorrow.
This unit does come in, but is not an exact replacement, as it does not have the correct vacuum hookup, and is slightly narrower than the original, and about twice what I have been quoted for the imaginary unit from Pep Boys - But what the heck, in for a penny and all.
I had to cut the OEM brake hose to fashion a connection, and was able to keep the existing check valve, but mercifully, it worked!
I guess all in all, half the fun of working on your car is the unexpected adventures you get to go on. Now that I have replaced the booster three times, I can call myself an expert on the process. Anyone else need a hand?
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74 450 SLC
59 Jaguar (Mark 1)
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  #8  
Old 02-10-2009, 12:10 PM
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Location: Tucson, AZ
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You had me scared there for a minute. Then I realized you meant OEM VACUUM hose!
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  #9  
Old 02-10-2009, 12:24 PM
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Thanks Mike - Yes, after spending a few hours squished under the brake pedal, I guess I may have lost some blood to the brain.
Yes indeed the Vacuum hose!

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74 450 SLC
59 Jaguar (Mark 1)
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