# Felt like no servo at Snetterton today....need help.



## Von Twinzig (Feb 10, 2014)

So, after all recent the plumbing work, today, at Snetterton, was the first run out. Drive over there was okay and on track the car went fine, with one exception...after a couple of big stops the servo felt like it had run out of gas.  It would then come and go at various points around the lap.

Brakes worked fine, but the pedal would go hard, like when the engine's off. I still had brakes - just had to give the pedal a hard shove, but nevertheless it was disconcerting. Off track on the drive home, all was fine again.

When I fitted the catch can I didn't touch anything on the servo side of the PCV, just removed the 2 into 1 convoluted cam cover breather and hockey puck and connected both pipes individually into the can. The outlet from the can went into a breather filter with the TIP inlet blocked off. At half time today I removed the breather filter and connected the outlet back into the TIP - made no difference.

So chaps, what's going on and more importantly how do I fix it?

Thanks

VT


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## NickG (Aug 15, 2013)

I have seen Max write before about upgrading to a bigger vacuum reservoir for the braking system? Could be something around this.... I could be more Vauge if it will help!

Hopefully someone will be along shortly to help!


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## Von Twinzig (Feb 10, 2014)

I've done a bunch of trackdays now and this is the first time I've experienced the problem. I'm sure removing the hockey puck has something to do with it.

VT


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## Von Twinzig (Feb 10, 2014)

Did a search and found this...viewtopic.php?f=2&t=727953&p=4716849&hilit=No+servo+assistance#p4716849

Maybe? The description sounds very similar.

VT


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## NickG (Aug 15, 2013)

Worth a check definitely!! The described symptoms sound the same atleast.


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## Von Twinzig (Feb 10, 2014)

That'll be this weekends little job then. :?

VT


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## Madmax199 (Jun 14, 2015)

Ha-Ha Steve, welcome to racing a TT (you will get to enjoy it too Nick sooner or later)! I have named it the "wooden brake pedal syndrome" and it's simply a result of your servo/booster getting depleted of vacuum. At first I thought it was just my car, then I jumped into another TT at the track and it was even worse (tired suction jet pump). Any intermediate level driver (or better) that drives a TT reports the same thing, there is no way around it once you start driving with quick enough pedal transitions (even worse with left foot braking, which almost a prerequisite to be fast while driving a TT or any turbo cars at the track).

Turbo car's brakes need a constant source of vacuum (negative pressure) because most of the time they're on boost (positive pressure). When the transition is quick from full boost to the brake pedal, there is not enough time for vaccum to make it to the reservoir so you get that wooden pedal because there is no vaccum assist in these situations. Condition gets even worse with consecutive braking points with on-throttle application in-between each brake application. A bad, deleted, or tired suction jet pump also doesn't help -- on paper it's supposed to create a ventury and generate some vaccum to the booster circuit when the car is seeing positive pressure. My observation with it is that is works well enough for street driving, but not nearly suited for Motorpsort action.

Solutions are:

- An external vacuum reservoir 
- An external vacuum pump
- A TIP plumbed line to provide constant vacuum from the compressor inlet (turbo is always sucking and generating vacuum).

I have done both the turbo inlet vacuum supply and the external auxiliary vacuum reservoir. For my use, both approaches worked, but the auxiliary external vacuum reservoir is easier and better (there are sometimes a slight delay in having full assist when the OEM canister is empty and the turbo is at part throttle or low rpm). Both can be used together, but I only run the external reservoir nowadays and it's fine with no issues. An external vacuum pump would be the ideal solution, but complexity, cost, and added weight kills it IMO for track purposes.

PS: all of this doesn't change the fact that possible hardware issues need to be addressed too (check valves, vacuum leaks, and failed suction jet pump, are common occurrences on these cars).


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## NickG (Aug 15, 2013)

Do all TT's have this? I'm struggling to think where the standard one is located?

Also, maybe a link to the guide, or better yet a new thread with a how-to guide would be epic, to put in the motorsports knowledge base?


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## Von Twinzig (Feb 10, 2014)

Thanks Max,

I was definitely smoother and therefore faster yesterday than before (wooden pedal aside) and the fact that it wasn't present on the warm up laps and then got progressively worse as each session went on to the point that it was present on both big stoppers and the bends after them every lap led me to believe it was a lack of reserve in the servo, but I didn't know why.

Is there an easy way (short of removing and checking the pipework) to check the system to the servo, maybe some kind of pressurised smoke test?

Onward from that, do you have a link to, or a write up of, your resolution please? Need to get this sorted once and for all. It definitely held me back.

Thanks

VT


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## Madmax199 (Jun 14, 2015)

NickG said:


> Do all TT's have this? I'm struggling to think where the standard one is located?
> 
> Also, maybe a link to the guide, or better yet a new thread with a how-to guide would be epic, to put in the motorsports knowledge base?


Yes, all 1.8t TT have this (nonissue on the NA cars as they never see positive pressure and vacuum is constant). The suction jet pump is located under the intake manifold. It ties the return line of the PCV with the servo system and uses a venturi to generate a decent TIP-powered vaccum source for braking assist. It's probably the name that fouls you, but the SJP is that Y looking fitting that loves to split. May look like a simple plastic Y fitting, but it has has two internal check valves in a venturi in it.









https://www.ecstuning.com/ES2681254/?gc ... hgodAbgIeA

As for a how-to, what would you guys want a guide for? How to plumb an external auxiliary vacuum reservoir? That's really as straightforward as it gets, a T fitting post check valve, one line goes to the standard canister, and the other goes to external tank. You're basically just adding volume (allowing the total volume of assist vacuum to never be near the point of being depleted).


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## Madmax199 (Jun 14, 2015)

Von Twinzig said:


> Thanks Max,
> 
> I was definitely smoother and therefore faster yesterday than before (wooden pedal aside) and the fact that it wasn't present on the warm up laps and then got progressively worse as each session went on to the point that it was present on both big stoppers and the bends after them every lap led me to believe it was a lack of reserve in the servo, but I didn't know why.
> 
> ...


Easiest way to test the servo vacuum circuit is with a handheld vacuum pump. I love my trusted mightyvac for that, just pull a good -20 kpa and see if it holds. It if bleeds, then you know you have a problem somewhere (leak or faulty check valve). I'm not a fan of pressurizing a servo system ever, so finding where the leaks are (once detected) can be a bit challenging on a fully-dressed engine.










The solution is very simple (I recommend just adding the external vacuum reservoir), plumb a T fitting post check valve and run one line to the booster and the other to the external reservoir.

T fitting (post check valve)









Auxiliary reservoir (mounted mine in the rain tray).


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## NickG (Aug 15, 2013)

Well I'm well and truly confused then, I have this pipe off of the throttle body..



It's got a valve, but I'm fairly sure that's not the right piece as it runs back to the coolant/carbon canister (can't remember which!)

I then have this setup...

Which goes to the TIP via the PCV valve

So I'm fairly sure that's not the right bit either!

So that leaves my final connection in the inlet manifold (other then FPR and DV) as this...


Which disappears after a 90degree bend behind a heat shield, probably near to the master cylinder...


But I don't see any valves in it?!


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## Von Twinzig (Feb 10, 2014)

It's under the the inlet manifold Nick.

All this guff....









VT


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## NickG (Aug 15, 2013)

Hmmm, I'm 99% sure I don't have all that down there :?

Maybe different on an APX?!


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## Madmax199 (Jun 14, 2015)

NickG said:


> Hmmm, I'm 99% sure I don't have all that down there :?
> 
> Maybe different on an APX?!


Someone likely deleted stuff on you Nick!


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## NickG (Aug 15, 2013)

How would it all work then?

EDIT: Not to say you're wrong, I just wonder what the implications would be as I'd not noticed any issues!


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## NickG (Aug 15, 2013)

And also, what is this pipe for?


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## Von Twinzig (Feb 10, 2014)

Max...what did you use for the reservoir? Rough size/capacity? Searching interweb for solutions.

VT


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## Von Twinzig (Feb 10, 2014)

NickG said:


> And also, what is this pipe for?


That's your hose to the servo by the looks of it. Mine's different.

VT


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## NickG (Aug 15, 2013)

Von Twinzig said:


> NickG said:
> 
> 
> > And also, what is this pipe for?
> ...


That's what I'm thinking! I've found these two diagrams...









APX engine layout









BAM engine layout

Key to BAM:
(1) from fuel tank, (2) EVAP canister, (3) Check valve, (4) Turbocharger, (5) Vacuum diaphragm for boost regulation, (6) Mechanical recirculation valve, (7) Brake booster, (8) Check valve, (9) Wastegate bypass regulator valve N75, (10) Mass Air Flow sensor G70, (11) Air filter, (12) Pressure regulator valve for crankcase ventilation, (13) Vacuum reservoir, (14) Intercooler (with pressure sensor G31), (15) Fuel pressure regulator, (16) Throttle Valve control module J338, (17) Intake manifold (with Air intake temperature G42), (18) Crankcase housing ventilation, (19) Check valve, (20) Recirculating valve for turbocharger N249, (21) Check valve, (22) Intercooler.


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## Von Twinzig (Feb 10, 2014)

Can you send me/post up/link to the bam one with the key to the numbers please Nick

VT


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## NickG (Aug 15, 2013)

Have updated the post, APX is easy enough to work out from there!


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## Von Twinzig (Feb 10, 2014)

Cool. So I'm thinking the T piece goes in the line between the the check valve and the servo, a tank with a single line in?

VT


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## NickG (Aug 15, 2013)

I'd tend to agree! Seems almost too easy!

Lets do science - I'm a little confused as to how this works, it only fills with vacuum (Thats definitely not the correct phrase... forms more vacuum?! <Nope!) when off throttle?

If so it's easy to see how it could get depleted with lots of left foot braking in a row! Presumably any time you snap off the throttle, when changing gear each time Up and down, this would create more vacuum each time too?


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## NickG (Aug 15, 2013)

This may be of use VT, Prawn linked to it a while ago...

http://carparts4sale.com/lh-vacuum-...audi-a8-s8-d2-genuine-oe-443-131-541-cp021983

Might be worth a look! Can be had on the bay for a tenner too!


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## Von Twinzig (Feb 10, 2014)

I'm thinking something more like this...http://www.summitracing.com/int/parts/s ... leSwitchNo

A quick search on eBay flags up loads of vacuum reservoirs off standard cars, just a case of picking one that'll fit in the limited space. This is looking favourite to go where my carbon canister came out....

http://www.ebay.co.uk/itm/VW-Passat-B5- ... 1996043873

VT


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## Madmax199 (Jun 14, 2015)

NickG said:


> How would it all work then?
> 
> EDIT: Not to say you're wrong, I just wonder what the implications would be as I'd not noticed any issues!


With the SJP deleted, everything would still works the same.... but that's until you find yourself at the track and exceeding the vacuum capacity of the servo, then everything bit of extra vacuum is heaven sent. It's something that's not noticeable until you're driving the car very quickly (transitioning from throttle to brake pedal before the servo can be refilled with vacuum). Once you're driving at that level (as VT is experiencing), every quick brake application is meet with the wooden pedal. Very frustrating and potentially dangerous -- in my case, I couldn't take the car to the track until I had a solution for it.


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## Madmax199 (Jun 14, 2015)

Von Twinzig said:


> Max...what did you use for the reservoir? Rough size/capacity? Searching interweb for solutions.
> 
> VT


At first I made my own with PVC (tube and two end caps), then bought one of those universal ones I saw at the local speed shop. Really any reservoir (setup in single line) will work, just mount it inline post check valve (line going to the servo). That simple! The one I have is 1.5 liter in capacity, so overkill. Anything 1 liter and up will add plenty of reserve to system and provide vaccum even for the quickest inputs. You will be fine with the Summit one you linked, but I prefer the plastic units (weight concious).


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## NickG (Aug 15, 2013)

On a little research I've found that the APX doesn't have all that gumpf under the inlet manifold. Presumably my pipe off the inlet manifold will have a one way valve at some point, which fills the reservoir with vacuum?

This little diagram has also helped me understand how the system works...










It does beg the question, why is it needed? Surely it just makes the brakes lighter to operate, rather then making them more effective?


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## Madmax199 (Jun 14, 2015)

Nick, you maybe right that the APX didn't come with a SJP, but I doubt it. My car is an AMU which I believe is the USA equivalent of the APX, and had the SJP. I have no way to confirm, but I doubt Audi wouldn't use the vacuum boosting function of the SJP on one variant while it's US-bound counterpart has it.

As for function, the brake assist uses vacuum to boost the effort needed to generate X pressure. It's like a pedal effort multiplyer, without it you'd need to exponentially increase the pedal effort to get the same braking force (think braking without the engine running). The servo has a storage capacity to keep vacuum around for repeated use until the engine generates more. Our problem, using the car in Motorsport, is that we're exceeding what the system was designed for (especially in the absence of the SJP which helps with vacuum generated). The engine generates it's own vacuum, but being a turbo (which often is seeing positive pressure) our storage at some point becomes too small for track use. That's why adding the auxiliary tank double the storage capacity to eliminate the problem.


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## Von Twinzig (Feb 10, 2014)

We are just increasing the total vacuum capacity to bridge the gap between fills, in effect creating a bigger bucket to draw upon. The problem with our RH drive cars is that there's a lot of kit stuffed into the RH side of the engine bay so I feel some more grazed knuckle moments in my future :? :roll:

VT


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## brushwood69 (Dec 17, 2012)

VT, this chap had a similar problem and removed the ABS stuff.

http://audittracecarproject.blogspo...d-max=2016-01-01T00:00:00-08:00&max-results=7

Max have you removed the ABS?


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## Madmax199 (Jun 14, 2015)

brushwood69 said:


> VT, this chap had a similar problem and removed the ABS stuff.
> 
> http://audittracecarproject.blogspo...d-max=2016-01-01T00:00:00-08:00&max-results=7
> 
> Max have you removed the ABS?


If you read the blog post about it, his issue was a soft pedal. The issue we discussed here is a rock hard pedal with zero brake assist. The owner in that blog also seem to have removed the ABS only to find out that it was not the issue (problem remained).

As for me I still have the ABS fitted and plan on keeping it. It is not intrusive at the track, and can bail you out of trouble in slick conditions. No ABS also means that you loose EDL, and Haldex function need to go standalone, or permanently-running (loosing the intelligence of the system).


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## Von Twinzig (Feb 10, 2014)

TT brake CSI day today.

Now I'm no Colin Chapman, but I'm thinking this is not helping my brake problem....










:roll:

VT


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## NickG (Aug 15, 2013)

And I don't know who he is... But I'd tend to agree with your evaluation!


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## Von Twinzig (Feb 10, 2014)

Nick....Colin Chapman....really? Google him then hang your Motorsport head in shame. :roll: 

VT


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## NickG (Aug 15, 2013)

:lol: in my defence, he was worm food 8 years before I was born!

But then again, I do know of Enzo Ferrari...


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## NickG (Aug 15, 2013)

Finally looked into my setup on the APX today, it is literally just a pipe off the inlet manifold to the servo, with a valve hidden in there just before the servo;



So presumably if I want to increase capacity I just need to T-in between the valve and servo.


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## Von Twinzig (Feb 10, 2014)

Yep.

Those plastic pipes are tricky fellows to work with, I changed the lot.

VT


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