Unbalanced rear brakes

[muppetlab 0]

Just replaced my rear discs, pads, bearings and mk4 caliper upgrade. Did each side a day apart as its my daily and had a bitch of a job stripping the old stuff off. Had a problem with a soft pedal and suspect there may be air in the system possibly of maybe thats how the MK4 calipers make it feel? Anyway its pulling slightly to the nearside through the rear brakes (not the front as its not felt through steering). Wondered if this is because one side has an extra day to bed in or wether its more likely that there is air on one side and not other? What do people think? should i swap the pads over? Have covered about 300 miles since fitting so would assume both side should be bedded in pretty well :scratch:

thanks

[Bruno 4]

Just replaced my rear discs, pads, bearings and mk4 caliper upgrade. Did each side a day apart as its my daily and had a bitch of a job stripping the old stuff off. Had a problem with a soft pedal and suspect there may be air in the system possibly of maybe thats how the MK4 calipers make it feel? Anyway its pulling slightly to the nearside through the rear brakes (not the front as its not felt through steering). Wondered if this is because one side has an extra day to bed in or wether its more likely that there is air on one side and not other? What do people think? should i swap the pads over? Have covered about 300 miles since fitting so would assume both side should be bedded in pretty well :scratch:

thanks

 

The MK4 calipers dont make it feel soft. New pads can do that. Did you bleed the brakes with the beam at full drop? If you did, you effectively closed off all pressure to the back in the bleeding. Jack up the car, put it on stands on the back and front, then put the beam on stands to make sure that the brake proportioning valve thinks the back of your car is fully loaded. Yes thats five stands at least. Run the engine, keep pressing the brakes until the hub is a little warm at the back on both sides, then stop the engine. Turn the ignition off and keep pumping the pedal until all of the pressure is loaded out of the ABS system. Then load the pressure bleeder,and bleed from ns/r, then os/r, then os/f then ns/f. Its best to clear all the fluid when you are working with a caliper swap. Stop. leave it for an hour. Go back and check the pedal when the engine is running...if in doubt, repeat. If after 5 goes you cant clear it, you need to check the calipers for a stuck piston, or admit that your bleeding technique is not effective.

 

If you are still of the opinon that it could be an air problem.... sometimes, depending on how you started your original bleeding cycle, it is true that you can get air stuck in the abs reservoir. The only way I know out of that is to take it to a place which has a bleeding machine which works by suction, and where they induct a brand new cycle of fluid. Most back road garages know someone who can do it swiftly for you whilst you wait.

[muppetlab 0]

Thanks for all the info, have failed on a front flexi hose now so am replacing all front and mid hoses with braided too so will have another good go at bleeding with my ezibleed. Mot man also said the pedal was spongy so must be air in there somewhere. :mad2:

[pete_griff 0]

if of course you don't want to go through that mammoth task of jacking up the rear beam with extra stands etc etc you could just undo the 13mm bolt that holds the bias valve onto the rear beam, then hang a set of mole grips etc off the pivot from the bias valve to ensure it stays fully open when you bleed the system!

 

edit - just read theabove post fully (no offence meant here btw bruno) - there's absolutely no need whatsoever t go through all that elaborte process - all having the engine runnning does for the brakes is activate the vacuum going to the servo and give you servo assistance - the actual hydraulic braking system is completely independent of the engine!

 

if you ensure the bias valve is fully open (as bruno says, though i would suggest my method!) and bleed the system thoroughl using an eezibleed kit, then you shouldn't have any problems.

point when doing the bleed - don't forget there are two bleed nipples on top of the abs pump and one on the master cylinder itself - don't forget to include these when you do it.

hope you get it all sorted. :)

 

 

and for the record - you've almost definitely got air in there - if there i an imbalance to the rear brakes (as you say) then the car will noticeably pull the rear end out of shape. this strangely will sometimes also happen if your abs is on the blink!

[muppetlab 0]

cool thanks. i do remember playing with it when i had it up on a friends ramp when i did the exhaust mounts. I was concerned as the previous owner lowered the car and i thought the car was thinking there was weight in it as it kept locking the rear wheels under heavy braking. Just to be clear if i undo the adjustment bolt, do i need to push the bracket up or down to open the valve? When i adjusted it i thought i had it fully adjusted as far down as it would go to limit rear flow so i would need to push it up against the spring to "open" the valve??

[pete_griff 0]

when you undo the bolt te pivot should be pulled down towards the floor - look at the way it moves with the rear beam. when the beam is upper most (closest to he floor of the car), the pivot arm thingy on the bias valve is down the most.

simply just undo he bolt and hang a set of decent size mole grips off the pivot arm.

 

if the car is lowered once you've got it all back together, it might be worth getting an mot testing station to set the bias back up for you - they'll have brake testing rollers, so they'll be able to the the front-to-rear bias up somewhere near what it should be for the ride height of the car.

the pivoting arm on the bias valve has a nice long slot in it to allow for the adjustment.

[pete_griff 0]

for the record as well, from what i can see having had it apart before, the spring there doesn't actually serve much of a prupose.

 

i can see it perhaps saving the bias valve from damage due to over-extension etc, but it just serves as a link between the beam and the valve mainly...

[muppetlab 0]

Okay thanks, from memory i had to fully adjust it to get the rear brakes to stop locking up too early. The car is pretty low!! cheers for the help.

[Bruno 4]

if of course you don't want to go through that mammoth task of jacking up the rear beam with extra stands etc etc you could just undo the 13mm bolt that holds the bias valve onto the rear beam, then hang a set of mole grips etc off the pivot from the bias valve to ensure it stays fully open when you bleed the system!

 

edit - just read theabove post fully (no offence meant here btw bruno) - there's absolutely no need whatsoever t go through all that elaborte process - all having the engine runnning does for the brakes is activate the vacuum going to the servo and give you servo assistance - the actual hydraulic braking system is completely independent of the engine!

Fair point Pete. My post was really quite silly. Although I wasnt confused about the servo and ABS systems, I made an even more silly mistake.

- I didnt make it plain that the point of running the engine was to warm the back hubs to enable the balance to settle, the new pads to takeup the undulations of the disc...but that would mean driving it for 10 mins... Old rear hubs can be a problem. The way I wrote it- it would give the impression :cuckoo:

that by running the engine in gear - somehow the back wheels would be turning

 

Sorry about that folks. Please put it down to being tired and getting old and stupid.

[muppetlab 0]

Well i am having a mare with these brakes. for the last 4 days i have been crawling around under the damn car, nothing was easy. The middle hoses are a bitch and had to replace two sections of copper pipe due to corrosion. The front porsche calipes were a bitch as i was sent the wrong banjo bolt which then snapped off in the caliper and now to top it all off i have bled nearly two litres of fluid through the brakes, master and abs pump and they still feel soggy. I am about to cry as its been off the road for a week after the mot fail and i need it back on the road. The Brakes have felt poo since i put the mk4 calipers on, is this a common thing are they a bigger piston or something as i just cant get a hard pedal :shock:

Have tried 30psi in my eezibleed and still not getting any air out of any where since the initial first bleed. :censored: car i am about done with it, its really annoying me now especially as its probably going to fail the retest for soft pedal. :bad-words: :bad-words:

[muppetlab 0]

Well after a very early start this morning and 4 litres of brake fluid i have what can only be described as brakes! Only took 4 days and a lot of swearing. Finally got it running and on its wheels again to find that the abs actually works now i have fixed all the sensors. Think i even have traction control as when i went to light the front wheels up today it was hopping all over the place. And as an even better friday present it passed the retest so i have another years ticket :clap: :clap:

Although now i have plugged the abs light back in it does not want to work. As my abs has been faulty since i owned it i thought it was supposed to come on with the ignition but now nothing. it used to be on all the time. Strange as the abs actually works now?? If the light is faulty would it cause an abs shut down or does it not check the light? have tried another bulb across the contacts and that does not work. is there anything on the abs circuit to actually break just looks like a bulb to me?

Anyway i am going to have a few well deserved ales this evening and ponder some corrado spend now shes back on the tarmac. :D

[Bruno 4]

Well after a very early start this morning and 4 litres of brake fluid i have what can only be described as brakes! Only took 4 days and a lot of swearing. Finally got it running and on its wheels again to find that the abs actually works now i have fixed all the sensors. Think i even have traction control as when i went to light the front wheels up today it was hopping all over the place. And as an even better friday present it passed the retest so i have another years ticket :clap: :clap:

Although now i have plugged the abs light back in it does not want to work. As my abs has been faulty since i owned it i thought it was supposed to come on with the ignition but now nothing. it used to be on all the time. Strange as the abs actually works now?? If the light is faulty would it cause an abs shut down or does it not check the light? have tried another bulb across the contacts and that does not work. is there anything on the abs circuit to actually break just looks like a bulb to me?

Anyway i am going to have a few well deserved ales this evening and ponder some corrado spend now shes back on the tarmac. :D

 

The light on the US/LHD version plays a different role to the one on the RHD version. In our version it has no part in the trigger of the ABS relay, just offering a status of whether the ABS brain has taken control of the pump. So:

- before you start the engine to listen for the sound of relays behind glove box kicking in.

- if you dont hear the sound, then it may be that the ABS brain hasnt engaged;

- if you hear it wait and then kick in, then the ABS brain has engaged; if it then clicks again, it means that the pump has not completed its comms with the brain, and the brain has turned off to prevent damage to the valves.

 

Putting a new bulb is relatively easy, pull the lamp holder, carefully take it apart, and check the bulb for continuity. Once you are sure it has failed, one can obtain the bulb from an RS (Radiospares) spares dealer or, failing that, an LED with a resistor should be used to replace it. Not a big deal, but it does take time to get the bulb. If I remember correctly its unusual, something like 3.2v....

 

Try and borrow a vagcom and put it on the diagnostic port and see if you get any abs fault readouts. clear them, and check again. If a fault appears, you need to follow tha. Hey- you really should be proud of yourself, you are unlikely to get this again for a long time.

 

One small thing. Get a bottle of copydex solution and paint the joints upon the pipes you had recently replaced - both the metal pipe ends and caliper ends. It produces a milky waterproof, rubberised surface that dries to an almost transparent state. It prevents further corrosion. You can use to cover any surface which is exposed to water but you need to protect. When you need to open the nuts one can grab the rubber coating and just tear it off.

[muppetlab 0]

Wow thanks Bruno thats some great info. I know the abs works as a quick thrash along the back roads near me had the pedal pumping and it stops a treat. Did not realise the bulb was 3.2v, that might be why when i put a 12v led across the terminals it did not light? I can hear/feel the pump doing its checks on ignition turning on so its all okay so must just be the light. Brilliant tip with the copydex, will try that will be good on those new unions. Will try and get a replacement light and try that. Many thanks, i am just relieved to have it back after the nightmare of brake bleeding. They really do feel brilliant now with fresh fluid and braided hoses all round. Felt good to be back driving it again after a week without it. Made me realise i would miss it if i sold it and that it was worth the frustration and effort to get it back right. Cheers Jez