Braking Problem

Thadude

Well-known member
Joined
Aug 30, 2004
Location
n/a
TDI
2001 Jetta
Hi all. I'm having a problem with my car. It seems that sometimes when I start off in the morning I have little braking power until I pump the brake once. It seems to be a random occurrence and only happens the first time i set out for the day. It is corrected immediately by releasing the pedal and depressing it again. Could it be my master cylinder on the fritz? or something else? Any help would be appreciated as it can be a hair raising experience when you realize you have no brakes.


Thanks!
 

Baconbit

Well-known member
Joined
Oct 9, 2005
Location
Windsor On
TDI
2006 Jetta
Had this happen on my wife's 06 Jetta last year. Weather - foggy and high humidity. Brakes would not grab on first attempt. Car parked outside overnight. We have a long downward sloping driveway. Freaked her out !
Took it in to vw dealership. They checked it over and found no problems with the brakes. Stated that they had many calls when this type of weather was present.

Haven't had it happen yet this year.
 

Knuckledragger

Well-known member
Joined
Sep 24, 2007
Location
Green Bay, WI
TDI
2003 Jetta
Oh yeah? Top this!

I just got back from a week's trip "down south", hopped in my Jetta that had been parked outdoors in Milwaukee for the last week, and the brakes were very "soft" and spongy. I noticed that if I pumped them a few times, the pressure came back, and they seemed to work much better. But when I held the pedal down, it slowly went all the way to the floor. Very much symptoms of a blown seal in the master cylinder or a leak in the hydraulic system.

I made it home (a 150 mile drive!) in one piece, with no CEL, and didn't use the brakes at all (a lot of manual downshifting and using the parking brake when I really had to).

I'll check the brake fluid levels and see if I can cause a puddle of fluid by pumping the brake. Just wondering if anybody had some good diagnostic tips.

Weather for the last week: Mostly at or below freezing... had a lot of ice & snow on the car when I got to it.
 

NB_TDi

Vendor
Joined
Mar 16, 2008
Location
NB, Canada █♣█
TDI
2014 Jetta SE
Vacuum build up? Huh? There is a vacuum reservoir on the car, that should remain under a vacuum when the car sits overnight. If it lost it's vacuum overnight, you have a leak.

I did have a leak, twas the main vacuum line. It's hard plastic and very brittle. The one I took off was Mexican, I installed a German one. Hmmm.
 

ve9aa

Veteran Member
Joined
Dec 11, 2006
Location
Fredericton, NB, Canada
TDI
02 Golf GLS TDI 271,000kms
I had a similar problem last week when it was raining buckets all day and it was just a bit above Zero ºC and foggy. I pulled out of my parking spot at work, then put on the brakes and the pedal was quite hard and braking power was minimal. A few (hard) pumps and driving another 300' and I had full power just like always. First and only time it's acted like this.
 

NB_TDi

Vendor
Joined
Mar 16, 2008
Location
NB, Canada █♣█
TDI
2014 Jetta SE
Uncle Milty said:
Knuckle: That sounds like my car!
Don't we have to be outerspace for a perfect vacum, NB ??
Not really, just needs to be devoid of an atmosphere(ish). Removing all air from a container works fine.

But if you are loosing vacuum overnight, there's a leak.
 

NB_TDi

Vendor
Joined
Mar 16, 2008
Location
NB, Canada █♣█
TDI
2014 Jetta SE
Well a NA car produces vacuum itself all the time, on a boosted engine the vacuum must be created through a pump. Then it's "stored" in the bulb. If you have a leak the vacuum is gone and then the pump must start over again.

You start driving, the turbo acuator requires vacuum to work. So that takes some away, then you stomp on the brakes...takes more away.

To me, sounds like a slow overnight leak. My brakes haven't done this, ever.
 

pozi240

Veteran Member
Joined
May 3, 2004
Location
Halifax
TDI
2001 Jetta GLS Galatic Blue
NB_TDi said:
Well a NA car produces vacuum itself all the time, on a boosted engine the vacuum must be created through a pump. Then it's "stored" in the bulb. If you have a leak the vacuum is gone and then the pump must start over again.

You start driving, the turbo acuator requires vacuum to work. So that takes some away, then you stomp on the brakes...takes more away.

To me, sounds like a slow overnight leak. My brakes haven't done this, ever.
Not quite, but you're thinking and I like that. All Gasoline powered cars (NA and turbocharged, doesn't matter) produce vacuum, Diesels do not, since they don't have a throttle body to "close" and produce vacuum, hence the need for a pump. NA diesels also have the vacuum pump (normally were the distributor would be on an ignition style engine would be).:)
 

Uncle Milty

Veteran Member
Joined
Feb 9, 2008
Location
Prince Edward Island, Canada eh.
TDI
2001 VOLKSWAGEN JETTA GLS TDI

NB_TDi

Vendor
Joined
Mar 16, 2008
Location
NB, Canada █♣█
TDI
2014 Jetta SE
Uncle Milty said:
Wait now, when the piston goes down it makes the vacum, I don't think it's the throttle that dictates the creation of (a partial) vacum.
Gasoline and diesel both have valves and pistons, and restrictions in the intake manifold, perhaps it's the valve overlap built into the camshaft of a diesel that governs this ?

I dunno??
http://en.wikipedia.org/wiki/Manifold_vacuum
http://en.wikipedia.org/wiki/Vacuum_servo
You forgot to read your links...:p

Manifold vacuum is present in all naturally-aspirated engines that use throttles
 

pozi240

Veteran Member
Joined
May 3, 2004
Location
Halifax
TDI
2001 Jetta GLS Galatic Blue
NB_TDi said:
I stand by my theory :)
But your theory is wrong, the key to producing vacuum, is the "throttle", which diesel engines do not have.
 

NB_TDi

Vendor
Joined
Mar 16, 2008
Location
NB, Canada █♣█
TDI
2014 Jetta SE
pozi240 said:
But your theory is wrong, the key to producing vacuum, is the "throttle", which diesel engines do not have.
How is my theory of someone having a vacuum leak wrong....?:rolleyes:

AND

I never said anything about a throttle. I said it uses a vacuum pump.
 

pozi240

Veteran Member
Joined
May 3, 2004
Location
Halifax
TDI
2001 Jetta GLS Galatic Blue
NB_TDi said:
How is my theory of someone having a vacuum leak wrong....?:rolleyes:

AND

I never said anything about a throttle. I said it uses a vacuum pump.
This is where you were wrong:
Well a NA car produces vacuum itself all the time, on a boosted engine the vacuum must be created through a pump. Then it's "stored" in the bulb. If you have a leak the vacuum is gone and then the pump must start over again.
A boosted engine (with a properly working DV valve) still produces vacuum within in the manifold much the same way as a NA engine. The opening and closing of the throttle plate is what controls the vacuum pressure (open throttle - no vacuum, closed throttle - vacuum is produced). Diesel engines (weather Turbo or NA) cannot produce vacuum due to having NO throttle plate to close the intake manifold off from atmosphere, plain and simple. All diesel engines (turbo and NA) require a vacuum pump. Its the same reason why you don't need to put a DV or blowoff valve on diesel.
I never said your "theory" of a vacuum leak was wrong, but your explanation of why his TDI needed a vacuum pump was, but I digress. :p
 

Uncle Milty

Veteran Member
Joined
Feb 9, 2008
Location
Prince Edward Island, Canada eh.
TDI
2001 VOLKSWAGEN JETTA GLS TDI
What are you talking about "Pump your brakes" ?
Are you saying to do this to increase braking performance? My car has anti-lock so I push 'em down hard as hell when I need to stop quickly.
Otherwise you are suggesting that TDI Vw's have an intermittent issue with poorly responding brake systems and they sometimes need to be pumped a few times after a long sitting period.

Please explain guys.

<edit=spellin>
 
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Uncle Milty

Veteran Member
Joined
Feb 9, 2008
Location
Prince Edward Island, Canada eh.
TDI
2001 VOLKSWAGEN JETTA GLS TDI
Seriously, I don't know what you two ment when you said pump your brakes.
Unlike the OP I don't always see an improvement when I try to pump 'em during that first non-stopping stop.
This is a very intermitent, but serious problem, the fact that it is intermitent makes it even worse.
 

Fyrman

Top Post Dawg
Joined
Sep 27, 2004
Location
Hammonds Plains, NS, Canada
TDI
Jetta, 2001, Black
Uncle Milty said:
Seriously, I don't know what you two ment when you said pump your brakes.

It's an urban slang term that means to slow down, you're going the wrong direction with whatever it is that your doing. POZI and NBTDI were getting a little heated in their off topic discussion. I was playing thread-cop.

Don't take anything I say too seriously... you'd be the first on this forum if you did!:cool:
 
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