Had the rear brakes replaced (shoes and wheel cylinders) six months ago at the last warrant check. This time failed on brake imbalance of 49%, the left side being low. My mechanic thought maybe the hose was collapsing internally, so replaced it. Went back for recheck and failed again. This time I had a go myself at bleeding the left side brakes, and found it very hard to do, had to really put some weight on the pedal. Went back for a recheck and this time passed, imbalance reduced to 10%. So now I have a WoF and problem over for the meantime, but it bugs me why the difficulty in bleeding this side? What else could cause this? I've heard the proportioning valve mentioned, but would that cause imbalance from one side to another, rather than front/back?
intrade,
Nov 27, 7:35pm
yes proportion valve right rear left front are on one circuit. . its why one should replace brake fluid every 24 month . only other reason i have imbalance was the drum exxeded the wear limmit. new drums cheap enough from some places i think was like 35 bux a drum or so. autostop takanini is where we got new drums from and wix oil filters just ask for trade price
franc123,
Nov 28, 9:30am
Would have been a stuck propositioning valve. It may not be a problem again who could say.
kazbanz,
Nov 28, 9:53am
How much is this vehicle being used ?
strobo,
Nov 28, 10:01am
Pressure bleeding with the motor running would have helped plenty.always bleed the entire system out the left rear a good litre of fluid until its all clear.
trade4us2,
Nov 28, 10:12am
I bought a Fiat 125 that had a brake imbalance. It turned out that someone had put a smaller brake cylinder for one wheel.
saxman99,
Nov 28, 10:47am
Crikey.
A few years ago my sister’s mpv failed a WoF check due to a brake defect; someone had fitted a smaller rotor to one side of the front brakes. Correct pads though so they were worn out across the inner half of the pad and brand new on the outer half. Words fail me.
sr2,
Nov 28, 11:13am
It will make no difference bleeding with the motor running unless you are running an older style hydrovac. Be wary of pressure or surge type bleeding as it has a tendency to aerate your fluid.
strobo,
Nov 28, 11:32am
EP91 starlet has power assist via vac booster,check if it's even working ie motor not running pump pedal 4 times until pedal is right up hard then start engine and pedal should drop about 1 inch.denoting that the assist is working correctly.My mobile pressure bleeder is 100psi in and low pressure out never had aeration problems set it right is enough to get things moving ;-)
kazbanz,
Nov 28, 11:41am
Easier done than you might think. Ie wrong disk in the box and you only work on the faulty side so don't notice the difference. Not ideal but it can happen
sr2,
Nov 28, 11:57am
You're spot on with your booster check, being vacuum suspended it should also have enough capacity with the engine turned off for at least 2-3 applications. Pressure or surge bleeding is when you pressurize the system and then release the pressure - does your bleeder attach to the mastercylinder or a bleed screw?
strobo,
Nov 28, 12:31pm
My principle is to bleed out in direction of flow from top down ,not vacuum bleed! many systems differ .air over fluid with some trucks and buses for example require many litres of fluid .I found pressure more effective than vacuum for a good bleed all round and in the process and the fluid is totally replaced with new.With pressure you have only need to bleed the circuits involved not every nipple individually unless you are trying to isolate a fault.Clutch the same ,Ive found out pressure top down works best than vacuum . Surge bleeding you say ? better the nipple is open when air applied or it will agitate the fluid in the reservoir.using low air pressure is important you can gauge by the flow rate what's is the best pressure to use , I have adjustable dial gauge on bleed bottle to control that.
marte,
Nov 28, 2:41pm
Is the brake fluid comming thru completely clear? I had a lot of problems bleeding my Cortina ( it had no problems bleeding me ) & it turned out that the master cylinder bore was rusted past the normal piston travel distance & when I was bleeding it, the seals were running over the rust & that rooted the seals. I should have figured it out quicker because the fluid was still comming thru a bit dirty & the pedal was slowly sinking if I pressed only lightly, but it was ok if jammed on hard. Reconditioned master cylinder fixed it.
I use a plastic aquarium one way valve, plastic hose & a old brake fluid container to bleed the system, one man job, quick & easy.
sr2,
Nov 28, 4:22pm
I think we may be on the same page. By air "over fluid" are you referring to direct boost(i.e. air over hydraulic actuators) or a air powered brake booster?
strobo,
Nov 28, 6:11pm
# !4 I'm not sure what you are asking? but anyway "air" refers to either pressure or vacuum. Ya need to always establish what system is in use first . it can only be either 1/ fluid over fluid ie hydrovac with a pressurized fluid actuator chamber incorp 2/ full air system as used on bigger trucks . 3/ Air over fluid referring vacuum as "air" over ,most commonly used in cars. The reserve is either in the vacuum chamber directly mounted at the master or has an inline reserve ensures to ensure good braking through out.The "air" in a vacuum system will dissipate after 3-4 applications of the brake pedal but will always replenish as long as the motor is running.Direct "air pressure" requires a compressor remember mainly to load "spring brake units to release the brakes" not applicable for cars ;-)
sr2,
Nov 28, 9:31pm
#15 - Enjoying the discussion.
No offence intended but excuse me if I pull rank on this one – spent a lot of time working on brake systems in the 70-80’s in Australia (originally trained by PBR) before returning to NZ to set up booster repair shops and train staff for APPCO brake and clutch. Left the industry late 80’s when I discovered more lucrative pastimes (long story) so sadly no expertise with modern ABS; but I’ve kept my hand in with building and running Targa cars since 97.
There are two distinctly separate forms of air (not vacuum) over hydraulic braking systems.
What we used to refer to as direct or air boosted had the brake pedal operating a control valve which fed compressed air at varying pressure into an ‘air over hydraulic actuator’ which was essentially a master cylinder powered by a pneumatic cylinder. IMOP this combined the worst of both worlds i.e. with no spring brakes loss of air pressure resulted in loss of brakes.
What was referred to as air assisted was a conventional hydraulic braking system that ran a compressed air powered in-line hydraulic booster after the master-cylinder. These are still to be seen on medium sized trucks today.
rpvr,
Nov 28, 10:08pm
A 'spare'car so not used that much - about 4000k over the past 12 months.
strobo,
Nov 28, 11:23pm
#16, sr2 Yes I remember you now ,way back in motoring you "pulling rank" lol . Group huggs and pissing contests LMHO .Firstly the loss of air in a full air syst means the brakes will come on not the other way around !Loss of air in an air over fluid system means the power assist is no longer there and more effort on the pedal to brake.The last sentence your post re compressed air inline with hydraulic booster in conjunction with master yes so true except in trucks today they are conveniently dual to comply ie 2 lots of the same or 1 larger booster in keeping with capacity. Like I said earlier identify the system in use firstly and understand how they work. I was trying to keep things in perspective relating to cars per subject to see where ya coming from with your question. Anyway impressive resume you have .Like you but I went further and turned the next page and got the later updated book so to speak ,if ya don't keep up with the later systems the "brake specialists of "old" now becomes a brake novice in today's terms.How one goes about it the correct way is most important /training etc. appco parts interpreters/sales would have been interesting to say the least.Good onya mate keep up the good work .
sr2,
Oct 17, 3:01pm
#18. All good mate, although I recently fitted a hybrid ABS system to our race car - I'm just not claiming expertise in that area!
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