Power brake booster for '77 911S

[tonyduc]

All

Did 77's come with a power brake booster ? Trying to figure out if this is a power brake booster ? If so then where is the vacuum line ? Just did a complete brake system overhaul and bled the lines, the brakes stop well but with some effort.

[Otter74]

Yes, they did, and yes, it is. I think the vacuum line is on the back side at about 11:00 if you're facing the booster.

[tonyduc]

Thank you !

[stevie 77 930]

here's a view of the backside

[tonyduc]

Are boosters themselves somewhat generic ? I ask because I cannot find any available for a 77 from the Porsche parts suppliers like Pelican, but I do see them from ********, O'Reilly, Advanced etc. There are plenty of rebuild kits for the MC, but not for the booster-just wondering if rebuilding it is an option.
Thanks

[spuggy]

Originally Posted by tonyduc

the brakes stop well but with some effort.

There should be some effort involved, 'coz it's a sports car... The harder the pedal, the easier it is to modulate braking effort, - and less pedal travel (sink) as pressure is varied, the better for heel'n'toe.

Traditional test for a brake booster is to, before the first start of the day, pump the brakes up until the pedal is firm and hold it, then start the car. If the pedal drops slightly as the motor provides vacuum, the booster is nominally working (might still have other issues, but you're getting vacuum to the servo and it is holding it, so should work).

[spuggy]

Originally Posted by tonyduc

Are boosters themselves somewhat generic ?

All the master cylinders interchange, and so do the boosters, AFAIK.

Originally Posted by tonyduc

AI ask because I cannot find any available for a 77 from the Porsche parts suppliers like Pelican, but I do see them from ********, O'Reilly, Advanced etc. There are plenty of rebuild kits for the MC, but not for the booster-just wondering if rebuilding it is an option.
Thanks

1977 MY used a one-year-only part, 911.355.027.00, for both 930 & 911S of that year. A guy with an otherwise original '77 930 was very happy to take my booster when I upgraded to a late 930 servo, M/C etc for big brakes, as his had failed.

1978 up, SCs, 3.2 and 930s used a different booster, 930.355.027.00. The 85- turbos switched to 930.355.027.02.

I think the 78 on boosters are 8" diameter rather than 7"; bolted straight in to my original pedestal. Pretty sure the 85-up 930 servo has a bigger "slave" or "assist" ratio, hence my choosing it (but my pedal still feels like there's a block of wood under it).

Also pretty sure I got that from information Bill V posted. He's the man to ask.

[pampadori]

For what its worth, i noticed that I have a lean condition (measured with my wideband o2) whenever I depress the brake pedal. I only have cyl 2 feeding the brake vacuum but that shouldn't matter. The lean condition goes away once I let off the brake pedal.

So i assume i have a leak within the booster. Removed it to find fluid on on the front side where it shouldn't be.
Unfortunately, I too cannot find anyone that actually has a reman or new brake booster.
Anyone have any leads on one?

[spuggy]

Originally Posted by pampadori

Removed it to find fluid on on the front side where it shouldn't be.

Yeh, that does not sound good. Although, that sounds kind of like a M/C problem; there's no fluid in the servo itself, as I understand it...

There's a Uro replacement seal kit available for the operating plunger. Maybe that's (also) worn out, and the cause of your air leak?

Just spitballin' here, sorry.

Originally Posted by pampadori

Unfortunately, I too cannot find anyone that actually has a reman or new brake booster.
Anyone have any leads on one?

Porsche 930.355.027.00 shows NLA, but the late 930 part 930.355.027.02 still shows available for order - guarantee you won't like the price. Although shopping around can bring the price down substantially (like $500), you still won't like it...

They're fairly simple devices; this guy cuts one apart and explains what it all does:



I believe all the 911 ones were made by ATE (a Continental brand now).

You can buy new ATE servos for Volvos, Saabs and the like all day long for $150-$200, seems like there should be something close enough that it'll fit/work. You may need to find specs to match up the "best" one to use...

[spuggy]

Originally Posted by spuggy

There's a Uro replacement seal kit available for the operating plunger. Maybe that's (also) worn out, and the cause of your air leak?

Found it again:

[Larry895]

Finally a definitive solution to a problem that plague ATE boosters for decades! The Mercedes M-Class vehicles was one of the most affected by this defect and until now replacing the whole booster has been the only solution available, besides adaptations not guaranteed to last long. Now we can just replace this darn seal and fix this issue in a efficient and cost effective way. Great! My Balance Now

[Raceboy]

Early Porsche 924 also uses that smaller diameter ATE booster (it is up to 1978).

[UROParts]

Hi guys, our seal kit 001 430 0708S is a replacement for ATE seal 03.7718-5028.1, which we know what used in certain Mercedes, VW, and Volvo applications.

It's possible it fits other applications, but we're not aware of it fitting any Porsche models.