Hi,

I have noticed recently that the performance of my brakes varies during a drive. Sometimes the pedal travels much further than normal. The brakes seems to work ok in terms of stopping the vehicle - its just sometimes I need to press the pedal further/ harder. I've changed the front pads recently but not looked at the rear yet - but since it stops fine I'm assuming the linings are ok. I see no leaks from any of the cylinders so wonder if its the master cylinder piston seals worn.

Also I note the elbow on the power booster where the vacuum hose from the intake plenum is connected seems a little loose. If vacuum is leaking at this point would I expect the excess pedal travel as discribed? Can this elbow be removed and the seal replaced??

I'm considering buying a new master cylinder but its not going to be cheap importing one from the US to the UK so if there is anything else to check it would be appreciated.

Also the pedal seems firm when depressed so I don't think its air in the system.

I do not get any warning lights on the dash (other than the test as startup) so I assume its not an pressue imbalance or a RABS fault.

 

It could be a master cylinder - usually this will cause a slow leakdown when holding the brake pedal at a light. Mine did give intermittent symptoms when it was on the way out. Wiggle the elbow at the brake booster while the truck is runnng to see if it leaks - the seal is replaceable if you can find one. a hard pedal is the symptom of a failing brake booster. Let me know if you need help finding one. Over here, the master cylinder is a common replacement part - they're very inexpensive. I've shipped ebay stuff to France before - it might not be too bad.

 

Thanks, that might be a good option - Autozone quote $50 (including the core charge) whereas it'll probably be over $100 in the uk. I'm after some other bits (rear shoes, O2 sensor etc so maybe a combines shipment would be a good deal)

 

Sounds like the master cylinder is on the way out. If so, it well get much worse quickly. Replace it now before you end up somewhere with no brakes.

 

I also had brake problems like yous. I replaced everything and i was still getting low pressure at different speeds (like there was a fluid leak) The rabs is the only thing left to replace and there is no code when the valve inside goes bad. Only the sensor will give a code. When the rabs is bad it siphons off fluid that is supposed to go to the rear brakes and doesn't engage them all the way. You may only be using the front brakes. Rabs are not cheap but i am replacing mine this weekend. Its the only part left and i'm not getting a code.

 

Take some carb cleaner and spray around the vacuum elbow and see if any engine rpm change is noted. It does sound like a master cylinder, though. They may be rebuilt for a fraction of the cost of a new one and while you're at it get the kits for the rear wheel cylinders. Same hone will do both, generally. Kits will also ship marginally cheaper or should actually be mailable. Get a list and make a Bronco "Care" package and minimize the cost of shipping multiple times. Cut you logistical problems where you are able.

 

I checked out the hose and elbow on Friday and it seemed ok. Although the elbow was able to rotate in the powerbooster inlet (or is it an outlet as its a vacuum????) the seal looked ok. I'll try the carb cleaner trick later too.

I am thinking more and more its the master cylinder - I was trying to work out in my head what the problem was and can only think it is the piston in the master cylinder getting stuck in the bore and not returning under spring pressure - hence why sometimes the peddle hits the floor before any resistance is felt. Sometimes you feel pressure with only slight pressure on the peddle.

If it were the RABS then I would still expect the same pressure on the peddle as the mastercylinder is dual circuit. As you say the RABS would bleed it back to a reservoir but the front would still be fully operational and since the front brakes do most of the work the truck would still stop as quick (expect for when it is loaded/ towing etc).

If it were the powerbooster then I would expect the vehicle to be difficult to stop as I would obviously have no assistance to my foot pressure on the brake peddel.

I'm gonna try and call autozone today and order a kit plus some other bits etc. and combine shipping.

Only worry about the rebuild kit is if the bores are scored I'd still need to change the whole lot and make another order and more shipping costs.

Do you know any reason why I shouldn't buy the remanufactured master cylinders from autozone?

 

MP,
Remember that the master cylinders offered may be rebuilt units. I'd order a kit as well if I had your logistical issues. I see no reason not to do a direct swap. The pedal going all the way to the floor is an indicator of a failed master cylinder or a blown wheel cylinder. Is there any evidence of brake fluid at any of the wheels?

 

Not had a very CLOSE look but first impressions are the cylinders are ok. Changed the front pads a week or so ago and all was fine there. Not loosing any fluid from the resovior so I think they are ok. Will try and get drums off this week and check them.

Just doing some sums to see if its better to get a whole package of parts from the US or just buy the cylinder from the UK and then get everything else afterwards.

Its so annoying that so many places charge so much for shipping to the UK- even for small "no weight" parts.