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Brake Booster Question????

 
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Mike B  
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PostPosted: Sun Sep 02, 2001 1:47 am    Post subject: Reply with quote

I recently, with Vaughan's guidance, completed the upgrade to 4 wheel disc brakes on a '78 924...I used the parts from an '80 931 with the m471 option...

My problem is the brake booster seems to have a vacuum leak so it must be replaced...My trusty parts catalog shows the booster with part number 477-612-107F for '80 (with m471) & '81-'82 924 with the same part number...

Ideally I would like to pick up the same booster but, if I can't find one, can I use a booster from an early 944 instead???? If so which one is better...The Girling or ATE...Any help is appreciated and better yet anyone has a booster (477-612-107F) I would be interested...
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Mike B  
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PostPosted: Wed Sep 05, 2001 4:24 am    Post subject: Reply with quote

.....help.....
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kaffine krazed  
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PostPosted: Wed Sep 05, 2001 7:37 am    Post subject: Reply with quote

Are you sure the vacuum booster is leaking?

From reading the diffrent parts catalogs the ATE and Gerling vacuum boosters are not interchangeable with the master cylinder. So if you have a ATE master cylinder you can't put a Gerling vacuum booster in without changing the master cylinder to a Gerling as well.
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Mike B  
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PostPosted: Wed Sep 05, 2001 9:34 am    Post subject: Reply with quote

The master cylinder was a direct replacemment...same part number for the donor brake system from the '80 931 as was there...The symptoms are:...brakes work fine with no pedal fade while the car is moving and the rpms are above idle...At a stop light, when the car is idling, the pedal begins to fade and drop to the floor but stops short of the floorboards...As soon as I increase the rpms the pedal firms up again...The only time the pedal fades is when it is stopped otherwise it is firm and the brakes work great...A local garage, where my son used to work, stated the booster had a vacuum leak and would need to be replaced...

I don't know but the diagnosis seems reasonable...Anybody..Vaughan???
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924RACR  



Joined: 29 Jul 2001
Posts: 8322
Location: Royal Oak, MI, USA

PostPosted: Wed Sep 05, 2001 11:18 am    Post subject: Reply with quote

True, but make sure you've got it plumbed right (for vacuum)... sorry, no spares at all for the brakes...

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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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Mike B  
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PostPosted: Thu Sep 06, 2001 8:18 am    Post subject: Reply with quote

Will an early 944 booster work in place of this ATE model or should I find the same one...

I'll check all the connections but I think it is hooked up correctly...
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pst  
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PostPosted: Fri Sep 07, 2001 2:47 am    Post subject: Reply with quote

As long as the master cylinder fits the booster you can use it. Basically, there are two different boosters. A 7" and a 9". The 7" was used up to 1979 and had a slightly smaller bore master cylinder, the 9" had a slightly larger bore master cylinder. You can interchange the boosters and you won't notice much difference.
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Mike B  
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PostPosted: Fri Sep 07, 2001 7:22 am    Post subject: Reply with quote

Thanks for the replys
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kaffine krazed  
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PostPosted: Sun Sep 09, 2001 4:41 pm    Post subject: Reply with quote

I don't think it's your brake booster. If it had a vacuum leak the pedal would be hard not soft.
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