Urgent help please! Lost power to brakes!

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Hi,

I was changing over my front brakes to the 312mm upgrade on my Leon earlier today and I think air might have gotten into the ABS pump (or that's what google seems to suggest with the symptoms the car is having). The fluid level may have run quite low, I have bled the rear brakes using the brake pedal method with a friend, and also the front left caliper which has been changed to the 312mm setup. The pedal is horribly spongy and I have no braking power at all (handbrake does however work).

I haven't yet fitted the new brakes to the front right side, will changing over the brakes cure the pedal problem I've been having or have I let air into the ABS pump?

I understand there are two bleed nipples on the brake cylinder? What is the correct method for bleeding these cars? Is it Rear left, Rear right, Front left, Front right, Master Cylinder, ABS pump?

I have not yet bled the master cylinder or ABS pump (I don't have VAGCOM access)

Many thanks,

Amjad
 

car.crash

Active Member
Jun 22, 2012
302
0
slough
Holy ****!! Why are you removing calipers If you don't know how to bleed them.
You need to fit your new calipers and hoses. When you have finished you will have to bleed all 4 corners of the car. Which one you start with I'm unsure but I always go furthest from the master cylinder and work to the shortest. Do you have a pressure bleeding kit?
More importantly do you know someone who knows how to do it and get them to lend a hand. If you have a accident through faulty equipment your liable.
 

cleverspoon

Active Member
Sep 17, 2011
686
2
Bleeding the brakes with the pedal damages the master cylinder, you need to either bleed using vacuum bleeder or pressurised bleeder. Iv read you can bleed using pedal but you must not push to floor, only about 1/4 or 1/3 the way down. The best way is to use an easy bleeder which uses presurised air from spare tyre.

Im sure some one will confirm or ammend this as im not 100% sure, but some one did have very similar problem and every one said master cylinder due to impropper bleeding.

I think you also have to bleed clutch aswell.
 

feast130

Keeping it Standard :)
Aug 17, 2012
111
0
Stamford
surely the clutch system is totally different...unless i read wrong and he broke into that system too
 
Last edited:

Muttley

Catch that diesel!
Mar 17, 2006
4,987
29
North Kent
If your profile is accurate you have a Cupra TDI 150, so I assume you are changing from 288mm discs to 312mm. Both these setups use the same calipers so there is no need to change them and get air into the system at all. All you have to do is change the caliper carriers for the larger ones from the 312mm setup.

So unless there is something wrong with the caliper, don't take the offside one off (I assume that by left front you mean nearside, passenger side).

If you have spongey brakes, son't drive, get a friend to get you to Halfords or wherever you can get the necessary bits from. You'll need brake fluid and an Easibleed-type pressure bleeder. At least 1 litre of brake fluid, probably two.

As far as bleeding goes, I can only give you the whole nine yards, based on experience plus the Haynes golf Mk.4 manual - which you should get hold of if you contemplate any more DIY. Haynes 4169, Golf and Bora 2001-2003.

Sorry this has turned into a bit of a lecture. But there are no safe shortcuts. Anybody reading this who finds a mistake - let me know, I'll repost it and/or get the moderators to make the change. Maybe even make it sticky if we can get all the details right.

Brake and clutch bleeding on the Golf Mk.4 platform

Hydraulic fluid should be changed at intervals of two years or less. The fluid deteriorates by absorbing water over time: mileage is not a factor. If it's more than two years since it was done, aim to change the whole contents of the system. I've not done this on a Mk.4 and don't know the quantity; the change is performed by bleeding in the correct sequence until the fluid coming out of the caliper changes colour. Use Dot 4 hydraulic fluid.

Always keep the fluid level in the reservoir at or near the full mark. If you let air into the system you have to start all over again.

You should run at least 0.25 litres of fluid from each caliper or slave cylinder. You will need more than 1 litre of fluid to complete a full bleed of the system.

It is not recommended to bleed by pumping the pedal, as there have been many instances of master cylinder seals being damaged using this method. If the master cylinder seals are damaged the master cylinder must be replaced.

I understand that people have succeeded in using the pedal method, without damaging the seals, by not pushing the pedal all the way to the floor.

The failure seems to be that the seals are caught and flipped round, so they fail to seal any more. I assume that there is a ridge worn in the master cylinder at the bottom of its normal stroke, which you go past once the resistance of the caliper or slave cylilnder is removed by opening a bleed nipple.

Use a pressure bleeding kit (Gunson Easibleed or equivalent).

The Clutch System
The clutch is fed from the same hydraulic reservoir as the brake system. Its master cylinder is fed from a pipe coming off the reservoir side, a small distance up from the brake connection which is in the bottom. This means that the clutch will fail first if you have a hydraulic leak. This can be a warning sign - if you get clutch disengagement problems, check the hydraulic fluid level.

The clutch will need to be bled if you change the slave cylinder on the gearbox or if air gets in by letting the level get too low. There is only one bleed nipple, at the slave cylinder end.

For cars with a five speed gearbox the slave cylinder is on the outside of the gearbox with an obvious bleed nipple.

The six speed gearbox has the slave cylinder integrated with the release bearing, inside the bellhousing and mounted around the gearbox input shaft. There is a bleed nipple on the outside of the bellhousing, close to the gearshift mechanism. Pressure bleed, then with the pressure kit still in place, push the pedal down and release it quickly to get any small bubble out of the long pipe to the middle of the bellhousing. Now bleed some more fluid through.

After bleeding, pump the clutch pedal up to pressure before starting the car again.


The Brake System

If you have any doubt at all about there being air in the master cylinder, bleed it first. There are two bleed nipples, one for each circuit. You should then bleed the front left and right calipers simultaneously, then the rear left and right calipers. This is to get any air out of the master-cylinder-to-ABS-unit pipes.

All the manuals say that the correct bleeding sequence depends on the type of ABS system you have installed.

The two possibilities are Mk.20 or Mk.60.

The Mk.20 unit is mounted flat, with the hydraulic unit on top, and has six hydraulic pipe connections on the left-hand face of the hydraulic unit. The two topmost are from the two halves of the master cylinder.

My 2001 Toledo TDI 110 SE had a Mk.20 unit.

The bleeding sequence for the Mk.20 unit is
Right (offside) rear
Left rear
Right front
Left front.​

This is furthest-to-nearest, as the ABS unit is on the nearside of the engine compartment.



The Mk.60 is mounted on the nearside wing with the hydraulic unit towards the engine. The two pipes from the master cylinder enter the uppermost side of the hydraulic unit and two pipes go to the rear brakes from the top of the hydraulic unit just below. The pipes to the front brakes are attached to the opposite side of the unit, and can only be seen from the bottom of the engine bay.

My 2004 Toledo TDI 150 Sport has a Mk.60 unit.

The bleeding sequence for the Mk.60 unit is
Left (nearside) front.
Right front
Left rear
Right rear​

I assume that this is because the unit is mounted vertically and the front brakes are fed from pipes attached to the lowest part of the unit.

If air has got into the ABS pump then VCDS or a dealers diagnostic computer may be needed to exercise the ABS unit and remove the air bubbles.
 
Last edited:
  • Like
Reactions: m0rk

feast130

Keeping it Standard :)
Aug 17, 2012
111
0
Stamford
this is what shocks me tbh...people seem to think that as soon as they join a forum they then become an instant mechanic :( bloody dangerous if you ask me. I have been a vehivle mechanic/technician for almost 16 years now and im shocked at some of the questions being asked. I joined the forum to get some ideas but all its done really is scared me with what is out there on the public roads...
 

traumapat

Leon Cupra IHI
Jul 24, 2005
5,928
4
sunny sussex
this is what shocks me tbh...people seem to think that as soon as they join a forum they then become an instant mechanic :( bloody dangerous if you ask me. I have been a vehivle mechanic/technician for almost 16 years now and im shocked at some of the questions being asked. I joined the forum to get some ideas but all its done really is scared me with what is out there on the public roads...
sort of agree but at least he can now do it right or get a garage to, without the forum he wouldnt have a clue which is more dangerous imo.

anyway doubt he'll be going far with a buggered MC :)

EDIT feast I dont type fast enough!
 
Last edited:

Muttley

Catch that diesel!
Mar 17, 2006
4,987
29
North Kent
feast130 wrote

this is what shocks me tbh...people seem to think that as soon as they join a forum they then become an instant mechanic :( bloody dangerous if you ask me.
Did you mean me? I hope not - I'm not an instant mechanic, I'm very slow about it. :p To be fair they are asking for help rather than just going on the road with spongey brakes. There is only one way to learn, and that's by doing it. You will make mistakes, and need to be prepared for that, leaving the car until it's fixed. I hope that the original poster has a friend or a pushbike or something that they can use to get around on until the car is back in order.
I have been a vehivle mechanic/technician for almost 16 years now and im shocked at some of the questions being asked. I joined the forum to get some ideas but all its done really is scared me with what is out there on the public roads...​
It isn't the ones asking on here you need to worry about, it's the ones with no clue who bodge it themselves without help. They have always been there, too. You very rarely meet one on the road though - they usually self-select by making the car undriveable. I can't remember seeing a headline along the lines of "bodged repair causes accident", and it surely would be a headline, papers will publish anything to sell copies.
 
  • Like
Reactions: feast130

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Thank you to those who posted helpful replies!

Okay so a bit of an update!

Good news is I have braking, bad news is its too much! And not in a good way lol


Basically the MS was bled with an eezibleed, then the front brakes and the rear ones. Loads of air came out to each stage. Pedal feel was nice and firm afterwards. Took it for a test drive and after about 5 mins we realised the brakes were sticking. This is with the new calipers that were fitted. Shut the car off and a few hours later the brakes were fine, so it only occurs once the brakes have warmed up and I'm guessing the discs have expanded?


We took the brakes apart again to switch the new calipers with my old ones (288) with the old pads, but still using the new carriers, discs. The piston was compressed using a g clamp and a block of flat wood (brake line banjo bolt and bleed nipple were both closed, dunno if this is okay?).


Rebled the fronts and went for a drive, once again the brakes started sticking after about 5 mins. So much so that I couldn't hold it in 4th gear at 30mph without it struggling majorly, and the brakes were smoking badly!


I don't understand how two sets of calipers can seize so badly? Having just spoken to a friend, he suggested that it may be the end brake lines that may be at fault (perhaps due to bleeding via pedal method). He said to release some fluid from each bleed nipple at the front, and if the caliper retracts, allowing the disc to spin, then it proves the caliper isn't at fault?

Any ideas guys?

Just popped into kwik fit and they suggested the sliders might be a bit stiff, or the master cylinder could be at fault.

Are either of these likely problems? Can I just lubricate the sliders with some copper grease? Could it also be the hoses? May they have been damaged when pumping the pedal?
 

grahams81

Active Member
Oct 14, 2010
1,165
5
County Durham
Before you compressed the pistons with the g-clamp did you remove the brake fluid filler cap ???? this to let the excess fluid out as when you push the pistons back the fluid needs to return to the tank and if it's too full already then it can knacker the master cylinder.

Personally i would doubt that both calipers were sticking, you've probably knackered the master cylinder... so it's not letting the fluid flow back out of the system to let the pressure off the calipers.
 
Last edited:

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Ah can't believe I forgot to do that :(

I think it was still connected up to the eezibleed and pressurised!

So I may as well order an MS then I guess? Are they all the same on the MK4 chassis regardless of engine? Think I'll just order a used one off Ebay as new ones are a bit pricey
 

Muttley

Catch that diesel!
Mar 17, 2006
4,987
29
North Kent
Are the brakes binding all the time? It sounds as though the pads are staying in contact with the disks.

Check the calipers to make sure that the sliders where the pads sit are clear of corrosion and smooth. Clean them up with a file if they are not. Do this every time you change pads, as a minimum.

Check that the pads are in straight, are the correct pads and can slide freely.

A very small amount of copper grease may help if all else fails, but only a very light smear, and make sure it stays away from the pad material.
 

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Having said that though, when we fitted the new calipers we didn't need to compress the piston as it slid straight on the disc with the pads. We did bleed it with the eezibleed and then disconnected the eezibleed at the MS. And it was sticking then?

So then thinking about that, maybe the master cylinder was damaged by pumping the pedals before we got the eezibleed on there?

I thought that if the master cylinder had failed then we would nose all pedal feel and braking power?
 

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Yes the pads are in contact with the disc, but only really when warmed up, when the car has sat for a few hours they are free and the brakes are not sticking.

Not sure whether to just check the sliders and where the pad sits now or just to order a new master cylinder?
 
Last edited:

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Okay so after taking apart one side once again, I inspected the sliders and where the pad sits. They were a little rusty but in better nick than the old carriers, so pretty much ruled out sliders being the problem.
Been reading up online a bit and it sounds like the master cylinder has indeed gone. Something to do with too much residual pressure I think it was?
Anyhow, has anybody ordered a master cylinder off of one of the breakers on Ebay? There seems to be quite a few listed for around the £30 mark and I can't really afford a new one at this point in time (insurance and a recent major service have left the pockets quite empty!).
Lastly is there a guide on how to change the brake master cylinder? The engine bay is a lot more cramped than my other cars which I work on more frequently, don't wanna be struggling all day lol
 

Amjad

Active Member
Oct 26, 2010
92
0
Cardiff/Southampton Uni
Okay so after taking apart one side once again, I inspected the sliders and where the pad sits. They were a little rusty but in better nick than the old carriers, so pretty much ruled out sliders being the problem.

Been reading up online a bit and it sounds like the master cylinder has indeed gone. Something to do with too much residual pressure I think it was?
Anyhow, has anybody ordered a master cylinder off of one of the breakers on Ebay? There seems to be quite a few listed for around the £30 mark and I can't really afford a new one at this point in time (insurance and a recent major service have left the pockets quite empty!).

Lastly is there a guide on how to change the brake master cylinder? The engine bay is a lot more cramped than my other cars which I work on more frequently, don't wanna be struggling all day lol
 
Last edited:
Adrian Flux insurance services - discount for forum members.