Brake problem

[Dave_EH]

Hi,

I have an HR disc brake front end, appropriate drum rear and remote VH40 booster with disc brake m/c.

All components bought brand new or reconditioned 2 years ago and have done approx 1000 miles.

The car has seen very little use in the last 3-4 months and only covered 100 miles or so.

Firday I adjusted the wheel bearings, and then enocuntered the following problem immediately afterwards in a test drive:

1) brake pedal was firm before start up
2) after start up, the fisrt instance I braked there was significant travel
3) after 1-2 pumps, the brake pedal retruned to standard travel and firmness.
4) several moer seconds of motoring, and the situation repeats itself
5) a moderate "clanking" noise occurs when moving, obviously caused from rotor.

I have not had too much a chance to look at his problem, however I bled both front calipers before a very short test drive and the problem did not change.

I'm still to bleed rear cylinders and booster.

There appears to be no leaks, as I cannot force the loss of fluid through heavy pedal application.

Any ideas on where to start?  (i'm hoping to sort it out one night this week in preperation for an early start saturday).

Dave

[ACE]

Hi Dave,
It's hard to say what it is without having a look at the car.
My guess is that you haven't adjusted the wheel bearings properly if the problem wasn't there before you adjusted them. From what you have said it indicates that the wheel bearings are loose or you have a collapsed wheel bearing.
Hope this helps.
Regards ACE  

[mcl1959]

Bleed the booster and wheel cylinders and try again, When the pedal will "pump up" as you describe, this is a sign of air in the system.  As Ace describes - if your rotor, due to bearing sloppiness or some other effect, pushes against the brake pad, this pushes the piston back into the caliper.  Then when you next go to push the brakes, you get a long pedal until the piston is pushed back.

Ken

[Dave_EH]

Thanks Ace and Ken.  Always very helpful and a great resource to have!

More developments...

Yesterday afternoon I had a chance to examine the brakes in daylight.

Everything was tight, no fluid leaks.

On removing wheel and closely watching left hand front rotor/pads there is movement, that pushes the inner pison in.  This would be where my pedal travel is coming from.

This is my theory: bent stub axle or warped rotor

Before I got the car on the road, there was an incident where the front left wheel fell off at low speed on a test run (don't ask!).  This flat spotted the rotor, so I replaced rotors, wheel bearings, ball joints etc and also had the calipers machined and recoed as well as new pads.

On fitting new bearings, the front left hub needed a bit of a tap to slide onto the stub axle.  At the time I wondered whether or not it had been slightly bent.  Since then I've done a bit under 1000 miles, in which I've always had a quiet squeak coming from the left front which went away under light braking.

My theory is that when I tightened the wheel bearings up one adjust ment on the weekend (to try and get rid of the squeak), this decreased the tolerence between the pads and rotor and created a bigger problem.

Either way, if its not a bent stub axle, it has to be a warped rotor?

The rotors were brand new and have been hardly used, so I doubt the rotor is the problem.  I can check this by using a straight edge or putting on an old rotor and spinning.

My only conern is why the piston is moving in and out, as if the stub axle was bent slightly you would think it would permanantly push on the inner pad rather than in and out.

Conclusions:
1) Does anyone have a spare HR stub axle in Brisbane?
2) Is there anything else that could be bent that would cause this?

Sorry for the long winded story, I hope someone can help me out.

Dave

[fccool59]

its probably hard for a hub to bend being a small chank of hardened steel but are they still the same hubs you had when the wheel fell off?
are all 5 screws tight between the rotor and hub?
did all the outers of the bearings seat in properly?
I agree, as you said the one piston would constantly be pushed if the stubb axle was bent unless a bent axle has not allowed all the bearings to work properly.
is the pedal pulsating when you brake?

[Dave_EH]

No Leon, the pedal has never pulsated.  This is another reason why I think the rotor is not warped.

THe hub is the original - I didn't think there was any chance of it being damaged but I could give it a good look over.

The hub-rotor screws are tight, as I made sure of that when I checked the bearings.

I'm thinking along the same lines as you - the stub axle is causing poor alignment of the bearings.

It must be very minor though - jsut enough to cause the brake problems, as I took it to an older style steering specialist who did the alignment after the front end work and he said it all came up really good and said everything was in top shape.

Thanks for you help.  Hopefully Ken might be able to shed more light on it.

[HARKO]

Its the slides in your caliper , Causing the caliper to skew ,
Hold your foot on the brake untill you come to a stop keep your foot there put in in reverse ,move back a little and see what happens.

[Dave_EH]

Thanks Harko,

Is that process for diagnosis or a remedy?  So I'll have to heel and toe it in reverse with my foot still on the brake?

By slides, are you referring to the two pins that hold the pads in place?

Have you had this happen before?

Dave

[HARKO]

Yep its happened to me in the past Dave ,
Sorry mate I was forgetting you may have a manual .
Those pins yep ,I replaced my caliper to fix the problem but it had all the same symptoms .
That reverse trick should help you diagnose if it is that but like all said its easier to be there and looksee.
Or is it easier to sit here and send out wild goose chases Hmmmm sounds fun hehe

[mcl1959]

Dave the stub axle shaft itself could be bent rather than the stub axle body.  If the shaft is bent then the rotor will not run centrally in the caliper and will push the pads back.
Also, what do you mean when you said the calipers were machined?  There should be no need to machine the calipers ever.

Ken

[jimmys57]

Gees,this is getting really interesting...I cant wait to find out what the problem is.....somebody must surely know somewhere!......good luck.....jimmys57

[Dave_EH]

Hi Ken,

From memory, I thought the part of each side of the caliper that bolts together was faced (machined) slightly.

I can see why you shouldn't mill too much off as it would upset all the tolerances.

This may not be correct - I just pulled them off and asked for a reco at a local engineering/brake shop called Power brakes and Engineering.  Cost was $220 from memory.

I could call the shop and check, but this was approx two years ago.

I guess the next step is to try another rotor/check the existing one and report back for more direction then?

I'll try and get this done one afternoon this week if work/daylight allows.

Any other ideas?

Cheers
Dave

[Brad]

Dave
       You could turn back the bearing nut and live with the squeak .
   Or I have a stub axle and rotor in poor condition that you may borrow to check out some of the theries. If your intrested send me a e- mail or phone 0412  226 960. I'm  on the southside near Capalaba.
        Brad.

[Dave_EH]

Brad,

Thanks for your kind offer.  I've managed to buy a good second hand set of stubs and I have some rotors in good nick, so I'll have a play when I get the chance.

Appreciate the help
.
Dave