Random brake pedal travel issue
 

I have an issue with my 1999 V70 T5. I estimate that about one in every twenty times I press the brake pedal, it travels down almost to the floor. It can be quite a shock when it happens.

I have replaced my brake pedal position sensor, hoping that would fix it (I used Vida Dice - it said that it was faulty), but it still happens occasionally.

Any suggestions please as to what the cause of this issue is, and any solutions?

Cheers,

master cylinder

Master cylinder.

If there is no fluid loss, it will most likely be an internal leak in the master cylinder.

If you press firmly on the brake pedal it most likely feels normal. Try resting your foot very lightly on the brake pedal hardly pressing it at all with little more force than needed to overcome the return spring.

If the pedal slowly sinks to the floor, it's virtually conclusive there's an internal leak.

Martin

Thanks Martin, I've done what you suggested and that's exactly what happened, very helpful of you.

I'll report it to my local independent mechanic and see what he says. Any thoughts from your experience on what they normally do to fix it? The V70's probably not worth a lot of money, so I hope he doesn't say he needs to replace the entire master cylinder.

Cheers for your help.

No problems.....

The surest and probably safest option is to replace the master cylinder.

However replacement seal kits are available but these will only be successful if the cylinder bore is undamaged. If there's any scoring then new seals will have a short life.

If you are paying to have the job done then the work involved in removing and replacing the master cylinder is the same whether you are fitting a new one or putting the old one back after overhaul. Although the seal kits are relatively cheap, your mechanic's time spent overhauling the old cylinder may not be. Unfortunately he or she won't know if it can be repaired until the old cylinder has been dismantled. This cost could go a considerable way towards the price of a new cylinder

A few things to bear in mind. Your car is an automatic and it could be argued tha you are rather more dependant on the brakes than you may be with a manual transmission.

Phase 1 V70s are getting thin on the ground and are beginning to be sought after and a T5 is likely to generate some interest so it may well be worth spending the money for a new cylinder. Not that this helps in the slightest if your budget is tight!

I run a 1998 V70 Tdi auto with 228,000 mile on the clock. If it were me I'd bite the bullet and replace the cylinder but I do have considerable affection for the car having owned it for nearly 20 years and I'd be doing the work myself.

Hope this is of some help. Do let us know how you get on.

Martin

Just confirmation of the diagnosis already given really. I had a master cylinder do that on a new van intermittently between 6k and 36k miles. I inherited from one of my bosses but he neglected to tell me of the faulty brakes where the pedal would remain solid despite standing on the brakes with no braking action. As it happened so rarely and "fixed" itself immediately until the next time, it took a while to diagnose.
I've also had a few master cylinders behave exactly as your does, suddenly goes to the floor when brakes are applied, either let it return by itself or pull up with your toes and it's fine again until the next time.

Not knowing when the next time is going to be and that it could be in an emergency situation, i would strongly advise not to mess about, you have ~1.5T of otherwise unstoppable missile without brakes.

You don't want to face charges of manslaughter by dangerous driving or similar because your brakes failed and you knew about them being faulty! :nah:

It won't go away, it will only get worse so get it sorted ASAP, not just for your sake but that of other innocent people who might face premature death if you can't stop! :eek:

Hi Martin,

Thanks again, tremendous post.

Mine is also 20 years old, and I'm very fond of it too. It's given me many years of enjoyment and it's been relatively easy to work on (for a novice - with a bit of help from the internet), and rewarding to do so.

I agree that the best course of action would be to replace the master cylinder.

According to the haynes manual, the master cylinder is not a servicable item and no repair kits are available...
I suppose there is a possible solution in replacing it with a good used one...whether your garage would agree to this is doubtfull...
If you're handy with spanners and can bleed brakes you could diy, not a hard job

Most garages won't do that because they can't prove the provenenance of the used one so have no idea if it was recently fitted to the breaker car that "donated" it or whether it was on its last legs and was the reason the car was sent to the breakers yard.

Two extremes there but the only way the garage could guarantee the work is to supply the master cylinder then their insurance will cover them from any damages arising from premature failure of the new master cylinder. Of course the idea is that with a new one that won't happen...............