Brake Booster failure '84 Turbo Look?

[4flyboy]

Hi guys,

My new to me factory T.L. has the vaunted 930 suspension and brakes.....not to be confused with breaks. Just sayin.

Anyway, I'm finally finding time to sort the car and the brakes are disappointing to put it mildly.

They stop the car but it feels as if I'm pushing against a firm piece of drywall. My buddy Mark here in Tampa has a vacuum gage.

He had me sit in the car and do the requisite start of the engine with my foot on the brake pedal....it doesn't soften or move at all.

We then pulled the check valve from the back of the Booster we got a solid 21 reading from the metal nipple that protrudes from the panel behind the booster with the vacuum gage..

A blow on both ends of the check valve and pipe produced airflow one direction and a no airflow the other.......

Does this mean that my Booster is faulty? Dread! Are there other tests that I may preform?

A search of our hosts parts catalog warns of one manufacturer and astronomical pricing......and indeed a new "oem" booster is well North of $800.....yikes.

Alternatives? Rebuilt? Rebuild kit?

I've done a search and there seem to be few failures....usually Master Cylinder and such?

I'd appreciate any input and suggestions.....Thanks, Scott

[john walker's workshop]

did you check that you're getting engine vacuum at the booster? the hose from the engine sometimes rots and splits down by the rear torsion tube.

[4flyboy]

Thank John,

No, I didn't check in the back but I did check behind the booster itself. I have vacuum in the trunk (nose) of the car?

Do I need to check further or is this an adequate test?

Scott

[Cory M]

I've got a booster I need to get rid of. It's out of a 1988 Carrera, I removed it when I went to a dual master cylinder set-up for racing. I'll take $50 plus the shipping. Send me a PM if you need it.

[Scott S]

There is a fitting in the engine compartment on the drivers side that is behind the motor, but not all the way to the firewall. I will see if I can find a pic. It is a snap fitting that can some loose.

I had the same issue that you are describing, and found out that I had just slightly separated this fitting when I was detailing the motor. Pushed it back together and everything came right back on line.


See the arrow:

[850carnut]

If you give the area where scott has the arrow a shot of either. You will find out if theres a leak its hard to tell just looking. The engine will pick up speed.

[john walker's workshop]

love that ether. whhooosh!! damn. maybe use something a tad less flammable?

[4flyboy]

Thanks Scott S.

Headed to the garage to find the fitting......really appreciate the help fellas.

Scott

[4flyboy]

Scott S.

Is this the fitting that you are referring to? It's a mess and looks as if the P.O. has used some sort of gunk to seal it...... John?

[LakeCleElum]

With that crimped hose, you have problems w/o a leak?

[4flyboy]

Sorry Bob,

I don't understand the question. I'm trying to determine if this is the fitting to which Scott S. is referring. He indicated that he inadvertently loosened a vacuum fitting in an area indicated above....this is a close up picture of the same area in my car but I'm unsure if we are talking about the same fitting.

Thanks,

Scott

[javadog]

Originally Posted by 4flyboy

I have vacuum in the trunk (nose) of the car?

Do I need to check further or is this an adequate test?

I'd say that if you have measured a normal amount of vacuum in the trunk, you can quit looking for vacuum leaks in the rear of the car.

A 930 initially used a different booster than the 911. It took a harder push on the pedal. They changed the booster sometime in the early 1980's, I don't recall exactly when. I haven't looked up the part numbers to see what the turbo look cars used but it may have been the same part as the 930.

I have a used 930 booster from one of my old 930's sitting on a shelf. I don't recall if it as the early one or the late one. Let me know if you decide you need a booster and I'll look and see hat I have.

JR

[4flyboy]

Wow,

Thanks Javadog. I'd dismissed that possibility though it had occurred to me.

Pelican lists a part number for the '84 that appears to be for both the Carrera and 930 Turbo.

I wrote Cory about the booster off his '88 Carrera assuming that it would fit?

Does anyone know for certain if the vacuum booster on an '84 Turbo look is the same as a standard Carrera?

Thank you everyone for chiming in here..... I couldn't afford the luxury of this incredible machine without Wayne's (our) forum.

Scott

[emac]

Scott, I agree with " lake" get rid of that kink. Start with the most obvious.
Ernie 81 sc

[4flyboy]

Thanks Ernie,

I see what you guys are referencing now......it looks as if that pipe is bent back on itself. It's a trick on the light. If you look closely it is a normal "Y" joint in the engine bay.

I used a flashlight late last night in a dark garage to take that shot! Obsessed right? Lol.

Scott

[javadog]

Look at the Ate sticker on your booster and note their part number. That will be the easiest way to determine compatibility.

Thanks,
Jeff

[4flyboy]

Jeff,

Went straight out to check it.... I'm traveling the rest of the week.

Blue sticker on back says:

3 6842-1003.4
350 3H7F





Does this answer the question?

Scott

[javadog]

The number 3.6842-1003.4 should be their part number.

The 911 originally used a 7" booster and a turbo used an 8" booster. I think the 911 may have gotten the larger booster in 1984 or 1985.

You can search through PET and compare parts numbers for the various years or look for a compatible booster based on the Ate number.

The one on my shelf is an 8" booster from one of my turbos with the part number 3.6842-1001.4. I checked the Ate web site and they don't appear to show the boosters any more.

I can't recall which turbo this booster came from. I recall changing it on one of my cars to change the amount of assist to make it similar to the other one. Years ago, can't remember the details.

One thing you might consider, since you are new to the car, is whether it's operating normally or not. I'd have someone familiar with these cars drive it, as it will have a higher pedal effort than a normal car. Brake pads can have an effect on pedal effort as well, especialy when they are cold. I'd be curious if the car were running stock pads or aftermarket pads.

JR

[KTL]

The booster in '84 is a different booster than the later and earlier 930. 78-81 930 used a brake system w/out a rear circuit pressure limiting valve and the actual booster coefficient is 3 (has to do with the internals of the booster). Then in '82 Porsche decided to add a 55 bar pressure limiting device to the rear circuit, keeping the booster coeff. at 3. Then in '84 when the Carrera came along, they decided to use the same booster and pressure limiting valve as the Carrera. P/L valve is less at 33 bar and the coeff. is reduced at 2.22. Then in '85 changed it back to 55 bar valve and booster was back to 3 again!!!

Look at teh last chart on Bill Verburg's handy brake spec page

Brakes

So should you find you need to replace the booster itself, theoretically you should be able to use a Carrera booster since your 930 is an '84?

[javadog]

I think there may be some errors in Bill's chart. What now shows up in PET also doesn't make much sense. I don't know if the part numbers have changed from what was originally fitted to suit what parts are now available but the numbers don't match what I recall.

JR