brakes again and again and again

G

Guest

Guest
Hi Guys
Does anyone know how to test for a warped brake disk.
Julian you told me about some pipe to check in the engine bay regarding the
vacum for the brakes.
Would that be the black pipe about 6ins long at the rear of the brake fluid
resovoir.
What do I need to check for as there is no fluid anywhere on it to indicate
a leak.
My brake pedal vibrations are coming back again.
Just another one of those really annoying hard to find problems.
cheers
john 92HDJ 80 1HDT
 
G

Guest

Guest
JB,
I think we have gone through this before, but no worry.
The best sign of warped discs is pedal reaction. So drive the car
wearing a thin soled slipper on your right foot. Do a few miles to
get the discs warm and then notice the feedback you get in your foot
when you brake at a junction, preferably after you have had a gentle
slow-down from a straight stretch of road. This is best done out in
the countryside where you have time to experiment without interfering
with other drivers, and you can concentrate on the pedal as you slow
down at that junction.
You should feel the pedal pushing back at you in a pulsating fashion
at a speed that slows as the 80 slows down. That will just confirm
that there is a problem on one of the four discs only though. If the
80 is unladen and you are driving and braking gently, then the
chances of it being the front axle discs that are worn are the
greatest as the LCV will divert little pressure to the back axle.
So I would look at the front axle first. Jack it up both sides and
remove both wheels. If you have PT 4WD then disconnecting the hubs
makes life very easy. Otherwise if you have permanent 4WD you might
have to disconnect the driveshaft flange at the transfer box. (I
don't have this system so Julian will surely correct me here). There
will be a test procedure in your manual that will show a special dial
gauge to check disc 'run-out'. All very good and fancy but not so
good for you working on your front drive. So lets get agricultural about it !
All you need is to see if there is some warp on the disc, not measure
it. In fact, as you have ventilated discs you may be unlucky to have
them so worn that when you look at the surface at an angle you will
see some extra shine on the surface coinciding with the ribs cast
inside the centre void of the disc. If you see this on the surface
then you can guarantee that the disc is shot and not even worth
having them skimmed on a lathe.
So, get hold of a heavy weight, something like a 56lb potato scale
weight or a large chunk of scrap railway line. To one flat side weld
or clamp a piece of steel bar something like 40mm by 10mm with a
squared-off end. A sturdy bar anyway. This should be welded at about
a 60 degree angle from the horizontal away from the weight, with the
corner of the top end of the bar about the same height as the centre
of the shiny braking surface part of your disc in line with the
centre of the axle and opposite the brake caliper.
With the steering set straight ahead you now need to have the corner
of the angled bar just touching the shiny surface. Then you want to
slowly rotate the disc and see if the bar remains in constant contact
with the surface, or if it is pushed away or a gap appears between it
and the surface. If it does either then you have a very good - but
rough - indication that your disc is warped. The handbook, even
Haynes will show the permitted tolerance against which you can judge
if replacement is needed.
Turning the rotor has to be done very carefully, made easier by
removing the opposite wheel. But if you find it hard to turn without
disturbing the disc's position, then you need to get a helper to turn
the propshaft for you, thus eliminating any wobble on the disc
invoked by your hand pressure. Naturally you will have plenty of
support under the 80 if your mate gets under, unless you are working
in an inspection pit.
(You could leave the wheel on the opposite side and turn it to turn
the other end being inspected, but you might risk moving the axle
sufficient to affect the visual error you are trying to observe.
Twisting the outer end of the propshaft is less likely to move the
axle. But I might be getting too critical here!)
I said it was agricultural but this is a common field procedure where
one needs an indication and not a precise measurement. The
alternative is to remove the discs and take them to someone who can
measure the warp. Not your favourite Yaris expert but a skilled
machine shop that deals with rotating equipment or uses lathes. I
have a mate on my marina who makes components for F1 gearboxes, its
amazing what favours he can do for me at times as he has gear at work
that he can use for other purposes at lunchtime!
Anyway, once you have confirmed that the disc is shot then you have
no choice but to buy a new pair for the affected axle - usually the
front one. I have Italian Brembo discs fitted and they are giving
good service at a fraction of the Toyota price.
This procedure is not difficult and easily rigged-up with a mate to
help out, and in your situation the costs are suitably minimal. HTH
Cheers
Jon
Tring, Herts
'92 HZJ80 ex UN Bosnia surplus - (pleased I prompted Julian's
thoughts on your IP problem).
 
G

Guest

Guest
Hey Jon
Thanks for all that info.
But I cant weld anything to anything and was just wondering if there was a
simple way to check for warped disk.
My disks are only a few months old, I think from last summer.
I got them from Milner, I also replaced all the pads and the rear two
calipers, which in my stupidity thought this would cure the brake pedal
jumping.
But as usual I was wrong .
thanks
john 92HDJ 80 1HDT
 
G

Guest

Guest
Hi John,
They are unlikely to be warped if they are that new unless they were
fitted incorrectly.
The easy way to tell if the disks are warped is to remove the wheel and
then turn the hub by hand, you will hear the pads rub against the disk
- if it sounds uneven as you rotate the hub they could be warped and
worth further investigation.
The next thing would be to rotate the hub as you look through the hole
in the brake caliper - should be able to notice warping by eye.
What are the disk surfaces like?
Do you get any vibration in the steering wheel under normal use?
I would also be keen to double check the wheel bearings before you
remove the wheels to see if they have worked loose - quite likely if
not bedded down properly when put together last year.
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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G

Guest

Guest
Hey Julian
Thanks for that, ill have a look soon and see what I can see, or not as the
case may be.
I do get the odd vibrations in the steering wheel but I think its when i
brake.
I also changed the wheels around front to back only last week and no
bearings hit me in the head so does that rule out the bearings not being
bedded in.
cheers
john 92HDJ 80 1HDT
 
G

Guest

Guest
Hi John,
You need to hold the wheel at the top and bottom and then push and pull it
to see if there is any movement.
Sometimes you will get a little movement with a metallic thudding sound -
this is due to loose bearings.
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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