THE brake story...continued...HELP!

[imported_brackie]

OK, so I got all of the air out of the brakes. Pedal is nice and hard. Then I start the motor. Pedal goes to the floor. Again, and again and again. Servo was fine before replacing the master cylinder. Switch of the motor and I've got brakes again. Any ideas??

[Volksfolks]

How did ya go bud, got me thinking hey,

Andy

[imported_brackie]

Busy day today so not time to look at the car. Well...I looked at it but that was all! Got a funny feeling that it could be either air trapped in the secondary piston (diagonally split braking system) or the master cylinder that I got had some kind of insert missing from it's push rod. The only way to check the latter I guess is to remove the master cylinder and compare it with the old one.

[Golf Loon]

I`d bleed the brakes before taking it apart again.

[imported_brackie]

I've got clean, air-free fluid coming from the bleed nipples (used different coloured fluid so I would know when it was thru') so I'm certain there's no air in the system...But wait! What do you reckon about the pressure regulator to the rear brakes? Could there be air trapped in there? If so, how do you get it out? There's no bleed nipple.

[Golf Loon]

I think the regulator is too simple for that. It just adjusts braking proportions dependant on load. As long as the angle of the car wasnt changed, sholud be unaffected. I`d put a bottle of fluid through the system to be sure its all bled up. Other than that, your taking the master cylinder apart again :shock:

[imported_brackie]

So I bled them again...... Lovely hard pedal with just he right amount of travel. Then I started the motor. Pedal to the floor. So it looks like the master cylinder comes off tomorrow and then what???

[Golf Loon]

Sounds like a bad booster

[imported_brackie]

So I took off the new master cylinder to compare it with the old. Appears the same on the outside, so I looked at the (what I thought was) the push rod. Not a push rod but the end of the primary piston. The inside of the new one was drilled out at the same diameter all of the way down. The old one has a step in it about 2/3 of the way down. "Aha!" I thought.... "Maybe the rod inside the servo is the same diameter as the smaller diameter inside the old piston but smaller than the diameter inside the new piston, giving a longer length of travel." Nope. It fits down both. OK. So I take the primary piston out of both master cylinders and I find that they are of different bores! The old one is 12mm and the new one 9mm (or as close as I can measure with callipers...Wouldn't a vernier be nice?). I'm convinced that the booster (I call it a "servo") is OK. Where to next?

[Beige76]

Can you take the booster apart? How do you remove the primary piston?

[imported_brackie]

You can remove the booster, but nope you can't dismantle it. The booster is a sealed, non-servicable item. (Not that I think there's anything wrong with it, anyway.) But I'm prepared to be wrong, How can it be tested? And what could go wrong internally that would cause this problem? It's holding vacuum and when I'm brave enough to test drive it (you should see the roads here!) it's definitely working. The primary piston is easy to remove (circlip) and the secondary is held back with a stop-bolt.

[Sharkey]

Don't know a bunch about the Audi servos/braking system, but here's my few views:

Remember that the servo is simply an assisting device, the push rod of the MC is still mechanically connected to the pedal mechanism, so in theory a hard pedal with the engine off should remain hard with the engine on. Obviously, you've disproven this.

It might be time to fall back to more extreme troubleshooting. I'd think about getting some 10mm bubble flare plugs and remove the brake lines to the wheel calipers one-at-a-time, replacing the lines with the plugs, and trying it with the engine running. If your pedal still plunges to the floor with all the ports plugged, you can bet it's a MC problem. If you get a hard pedal with just one (or more) of the ports plugged, at least you know where to start looking.

Why servo on/off makes a difference is a mystery, but it's just not possible that your depressing the pedal with the vacuum present can allow the push rod into the MC to not be pressed also.

You do have a Bentley service manual for this vehicle, yes? My A2 Bentley states that "vechiles equipped with the rear load-sensing regulator valve must have the load sensing arm held down towards the axle" while bleeding. Is it possible that the ride height of the car changes when the engine is running, making the regulator change the volume or pressure of the brake fluid going to the rear axle? Just freewheeling thoughts here...

[imported_brackie]

Thanks, Sharkey.. We don't get the Bentley manuals here. The one that I have is for the Rabbit diesel and I got that from the US :-)
The Haynes makes no mention of depressing the lever. When bleeding the brakes I had to jack the car in order to get under (I ain't a kid anymore!) so maybe you're right and I need to have it depressed or on the flat. Excellent suggestion about making the blanks. I assume that these go into the MC ports? (The Audi has twin circuit braking on diagonally opposite wheels.)
Will give the "depressed lever" trick a go today.
Great to have you on the board. Call in regularly and add to our knowledge base!

[Sharkey]

Can't get Bentley manuals??? Have you tried http://www.rb.com ?? I find used bentley manuals in the used book stores here for about $12-18US a pop. My A2 manual (which I bought expressly for installing an ABS hydraulic modulator on the EV) cost me $6 at the flea market, and it was still in the plastic wrap. Sorry, just trying to make you jealous.

If you can't find 10mm bubble flare plugs, you can make your own. Go to the auto dismantelers and cop four of the (good, clean, rust-free) ends off of a scrapped-out body. Cut the steel tubing about 1-2" from the flare nut, then crimp the cut end closed in a vise. Use a gas welder to weld up the crimp and you have a DIY plug. I've found them very handy when removing brake components to stop fluid loss and cap off orifices when cleaning in solvent baths. Never hurts to have a few around. I've also made a few caps from injector pressure lines to cap off injection pumps in storage and while cleaning (never cap off an injection pump and then try to rotate the shaft, you'll blow it apart!!!).

Good luck, there's nothing all that mysterious about hydraulic brakes, at least not until they stop working. Another reason my bus had air brakes!

[Golf Loon]

Gday Sharkey. The Electric Rabbit looks great. Would be an ideal delivery vehicle for a business. I reckon.
Wise words on the brake saga, I`m gonna make me some of those brake blankers!
The Bentley manuals are great, I have one for my Saab, so much more detailed than a haynes. Not available in Australia, we have to resort to ebay.

[Anonymous]

Not available in Australia,

Yes they are. Go to any motoring bookshop.

[Golf Loon]

Great thanks, i`ll check it out. How are the brakes going Brackie?

[imported_brackie]

Nuthn's goin' Mate. Definitely not the car as it might go, but it definitely won't stop! Sent my old seals (from the original 12mm bore MC) to Hobart to get new ones. Gonna fix up the old cylinder and put it back in. If that doesn't fix it it can only be the booster. But I can't even imagine how it can be responsible. Then ...THE CRUSHER!! She's been in my shed for 2 weeks now and I can't get anything else in. Pug needs cooling system flush and coolant, blower fan overhaul, Golf should have had rings and bearings done weeks ago. And we start tearing down walls and building kitchens on Wednesday. You got a booster that would fit??

[Golf Loon]

Aaaaaargh Just cut down the shaft on an Audi Booster so that i can fit it to my golf. Only golf ones here now. Is the seal between the MC and the booster ok? Instant Gasket?

[imported_brackie]

Yeah, the seal is leaking slightly. It's an"O" ring. but I've had small vac leaks on other cars and the pedal's been OK. Are you saying that this could be the culprit?

[Golf Loon]

Put a thick bead of instant gasket over the o ring seal and try it.

[Volksfolks]

Whats the outcome Brackie, any good!! seems you are having some bad luck here..

[imported_brackie]

Nah... No outcome. I sent the seals from the old MC to ABS in Hobart but they don't have any replacements. I intended to rebuild the old MC and see if the problem was specific to the new MC. Absolutely NOBODY I have spoken to knows why I am having this problem! At the moment I'm doing building things to the house (as well as routine farm work) so it's on the backburner. I'll get back to it next week with a bit of luck. It's a good thing my trusty old diesel is still chugging away!

[20v kit car]

simple just replace the one way valve which comes off the manifold ..better still use a clamp seal it off and start the engine....brakes hard? then check if the valve hasn't been fitted arse about...sounds like the hydraulic part of the brakes are fine...the valve the valve..as it was taken to the crushes cheers steve

[imported_brackie]

Didn't know there was one! I'll check it out when I get the MC back together.

[20v kit car]

its a small cicular valve which is in line from manifold to booster...if it's missing ...thats the problem...if there try sucking thru it one way..then blow back it should seal ...sounds like the prob cheers steve

[imported_brackie]

Finally got a few minutes to look at the brakes. Checked the one-way vacuum valve but it's OK (thanks, Steve!). Carefully compared the fit of the primary pistons from both MCs onto the pushrod in the booster. Exactly the same. Can't find anything (spacer maybe??) that may have dropped into the booseter body when I took the MC off. Reassembled the "new" master cylinder so it's ready to go in. Now have to bench-bleed it. Hopefully by the end of the week????

[imported_brackie]

Bench bled the MC. Reassembled everything and bled the system. Gasket sealed the "o" ring. Brakes came up high and hard (just like me when I was a young bloke!) Then I started the motor..... To the floor. I'm now convinced it's the booster (you appear to have been right Looney) so I'll have to find another. I can't understand why it should suddenly fail as it was working fine before initial disassembly, but it's the only thing left. So who's got a booster? I reckon it'll be almost impossible to get one here in Tassie. By the way, I drove the car with the booster disconnected and the brakes worked fine except I had to push real hard. No sponginess or fade.

[20v kit car]

are you sure about the valve?????cheers steve

[imported_brackie]

Absolutely... But I'll re-check anyway!

[Golf Loon]

I`ve got a spare Golf booster. Smaller diameter than your one, but it will fit and will be better than none. Up to you.

[imported_brackie]

Took the old girl to Devonport today. No booster so hard on the right leg, but she stopped just fine! He looked at it and reckons the booster is OK. He says that there is still air in the system and that when the booster is connected the extra assistance makes the pedal go to the floor. Doesn't make much sense to me. He recommended using mole grips on the flexible hoses to isolate each wheel in turn and identify where the air lies. I'll try it tomorrow. This is ridiculous!

[el_foolio]

yeah, my girlfriends golf had no booster for a while, still stopped just fine

[Golf Loon]

Take it somewhere that has a pressure bleeder machine. Saabs are the same, keep bleeding and bleeding the system and it wont work, then as soon as you pit the line under pressure, works straight away.

[imported_brackie]

I asked him about that and he said it would blow the plastics apart. Recommended vacuuming it from the bleed nipples.

[imported_brackie]

Take it somewhere that has a pressure bleeder machine. Saabs are the same, keep bleeding and bleeding the system and it wont work, then as soon as you pit the line under pressure, works straight away.
Hey... Just an idea... What about bleeding with the engine running and the booster connected? That's really doing the same thing.
Also, he said to help get the air out of the MC, park on a steep slope (nose pointing down) and work the brake pedal. This brings the MC level (it's on an upslope to the front when the car is level) and moves the compensators so air works its way upwards and back into the reservoir.

What do you guys reckon about these 2 gems??

[Golf Loon]

Do they work?
Find someone with the vacuum machine and apply suction to all the lines.

[imported_brackie]

I thought I'd better get back to that caliper with it's bleed nipple problem. For those who've disengaged themselves form this thread (and who could blame you?....Its been a long one!) I had a seized bleed nipple that broke off and I had to drill out and plug the orifice. I discovered a retired (semi) engineer in Devonport who sleeved master cylinder and did all sorts of other magic on braking systems. I gave him the caliper and he put in an insert and new bleed nipple. So, next opportunity I get I'll go through the whole bleeding process again and hope and pray.......Oh If anybody wants this sort of modification/repair done he's only too happy to oblige. Even with postage to and from Tassie you'll end up paying only a fraction of the price of a new one. I'll put his contact details in "Recommended Repairers".

[imported_brackie]

So, I bled it again. Hard pedal at the top until the engine is strarted. (Been here before??) Decided to take Looney's advice and get it vacuum or pressure bled. Took the car to a workshop today and the guy did just that. Claims he got some air out but it felt and stopped just the same when I drove it home. So, for $66 (1 hour's labour!) I am no further forward. He said, "It's the booster". Bulls**t! There are no vacuum leaks. There is full assistance. There is no extra free play in the pedal. The engine speed doesn't change when the brakes are applied at idle. It can't be the booster. If the diaphrgm is punctured there will be a) higher tickover as there is a loss of vacuum b) no assistance because the diaphragm is perforated. There's plenty of assistance. Guy at the workshop said the booster would have to be sent to the mainland to be repaired. $350 + freight + he would have to fit it to preserve warnanty. So a $1000 job to keep a car that's worth $1000 max. ????

[20v kit car]

the one way valve ..the one way valve ......the one way valve

[imported_brackie]

Nope...It's 100%

[Golf Loon]

How did you test the one way valve?

What about the brake bias valve under the back axle?

[imported_brackie]

How did you test the one way valve?
Removed it and blew/sucked both ways. It holds.


What about the brake bias valve under the back axle?
Works as far as I can tell. When the brakes were pressure bled in the workshop he did it "on the level". Anyway, how could it be involved? I know what they do but I don't know enough about how they work. Do you agree with my logic about the booster?

[Golf Loon]

Yes I agree about the booster, but remember what the Haynes manual says.."never omitt any part from your troubleshooting even if you know it to be good"

Where else can air come into the system guys if the booster is ok?

[imported_brackie]

How did you test the one way valve?


Took out the valve altogether and plumbed direct. For some reason Audi has a complex vacuum takeoff from 3 points on he intake side. The valve itself is actually mounted on a "T" and only operates on 1 of the 3 hoses that go to the manifold :?: Duh... Should have taken a pic. But anyway, it made no difference so I put it back.

[hiho]

Hi brackie,
have you sorted out the braking problem yet? I hope so. If not, there was something in the thread that caught my attention. You mentioned that the old MC was 12mm and the new one 9mm. If you are using the same booster on both MC's then then there could be a problem. The smaller diameter MC displaces less fluid per unit of distance travelled but can generate higher pressures in the braking line per unit of force applied to the pedal. As the booster is applying extra force to supplement the muscles in you leg, it may be applying enough force to cause the smaller diameter mc to travel further.

If you have a 9mm mc then you may not need the vacuum assistance at all as you now can generate higher brake line pressures for a given pedal effort, the trade off being longer travel.

On the subject of brakes, i have several GLD's that are being prepared for roadworthy. I have measured the discs and i have thicknesses of 7-8mm. this seems to be very thin. Do you know what the wear limits are for the GLD's? Also, if i go to a wrecker, are there any other cars with better fromt brakes that i could adapt to the Golf?
Thanks
Matt

[imported_brackie]

Hi brackie,
have you sorted out the braking problem yet? I hope so.


It came good! I gave the car to our dairy hand and she's been driving it without mishap (apart from a duff water pump) for a few months. Can only assume that there was air trapped in some obscure place and it vented itself :?:


If not, there was something in the thread that caught my attention. You mentioned that the old MC was 12mm and the new one 9mm. If you are using the same booster on both MC's then then there could be a problem. The smaller diameter MC displaces less fluid per unit of distance travelled but can generate higher pressures in the braking line per unit of force applied to the pedal. As the booster is applying extra force to supplement the muscles in you leg, it may be applying enough force to cause the smaller diameter mc to travel further.

If you have a 9mm mc then you may not need the vacuum assistance at all as you now can generate higher brake line pressures for a given pedal effort, the trade off being longer travel.

Good stuff! Yeah, your logic is good and this sort of info is good to have on our database. I still have the larger master cylinder re-sealed and in good order.


On the subject of brakes, i have several GLD's that are being prepared for roadworthy. I have measured the discs and i have thicknesses of 7-8mm. this seems to be very thin. Do you know what the wear limits are for the GLD's?

No, but I'll bet that someone on the forums does!


Also, if i go to a wrecker, are there any other cars with better fromt brakes that i could adapt to the Golf?

Look in "Interesting Articles" for the posts on

Hi brackie,
have you sorted out the braking problem yet? I hope so.


It came good! I gave the car to our dairy hand and she's been driving it without misshap (apart from a duff water pump) for a few months. Can only assume that there was air trapped in some obscure place and it vented itself :?:


If not, there was something in the thread that caught my attention. You mentioned that the old MC was 12mm and the new one 9mm. If you are using the same booster on both MC's then then there could be a problem. The smaller diameter MC displaces less fluid per unit of distance travelled but can generate higher pressures in the braking line per unit of force applied to the pedal. As the booster is applying extra force to supplement the muscles in you leg, it may be applying enough force to cause the smaller diameter mc to travel further.

If you have a 9mm mc then you may not need the vacuum assistance at all as you now can generate higher brake line pressures for a given pedal effort, the trade off being longer travel.

Good stuff! Yeah, your logic is good and this sort of info is good to have on our database. I still have the larger master cylinder re-sealed and in good order.


On the subject of brakes, i have several GLD's that are being prepared for roadworthy. I have measured the discs and i have thicknesses of 7-8mm. this seems to be very thin. Do you know what the wear limits are for the GLD's?

No, but I'll bet that someone on the forums does!


Also, if i go to a wrecker, are there any other cars with better fromt brakes that i could adapt to the Golf?

Look in "Intersting Articles" for the posts on
Hi brackie,
have you sorted out the braking problem yet? I hope so.


It came good! I gave the car to our dairy hand and she's been driving it without misshap (apart from a duff water pump) for a few months. Can only assume that there was air trapped in some obscure place and it vented itself :?:


If not, there was something in the thread that caught my attention. You mentioned that the old MC was 12mm and the new one 9mm. If you are using the same booster on both MC's then then there could be a problem. The smaller diameter MC displaces less fluid per unit of distance travelled but can generate higher pressures in the braking line per unit of force applied to the pedal. As the booster is applying extra force to supplement the muscles in you leg, it may be applying enough force to cause the smaller diameter mc to travel further.

If you have a 9mm mc then you may not need the vacuum assistance at all as you now can generate higher brake line pressures for a given pedal effort, the trade off being longer travel.

Good stuff! Yeah, your logic is good and this sort of info is good to have on our database. I still have the larger master cylinder re-sealed and in good order.


On the subject of brakes, i have several GLD's that are being prepared for roadworthy. I have measured the discs and i have thicknesses of 7-8mm. this seems to be very thin. Do you know what the wear limits are for the GLD's?

No, but I'll bet that someone on the forums does!


Also, if i go to a wrecker, are there any other cars with better fromt brakes that i could adapt to the Golf?

Look in "Intersting Articles" for the posts on Commodore/Magna conversions. I believe that Camira brakes can also be adapted. If your Mk1 diesel appears to have poor brakes check the vacuum pump. The diaphragms may be perforated (especially if you have excessive blow-by.)