Brakes questions, (runout, possible calliper rebuild)

[Rob]

Lets start with a bit of brake history on my truck. About 30k miles ago when I bought it the brakes were average and after driving enthusiastically between several roundabouts I managed to warp the front discs. I later found out that I had one rear seized calliper and the front callipers weren't in great shape either. So I rebuilt all the callipers (my maintenance skills have improved significantly since then so the job might not of been to an "acceptable" standard) and I do remember that some of the pistons on the front had some rust and possibly one a tiny amount of chrome pitting. I did not replace the discs or the pistons just cleaned them up as I was a skint student back then.

Under a long period of moderate braking or brief periods of heavy braking I feel the obvious signs of warped discs (vibration through the steering and pedal). From what I have been told there are 2 conditions where you get warped disc symptoms:

1) The discs are temporarily deformed as one side is heated more than the other due to uneven brake load from the pads.
2) The discs are permanently warped due to uneven brake load from the pads. You generally feel this even under light braking.

Generally condition one leads onto condition 2 if the cause is not addressed. Since the time when I first experienced brake warping I only get symptoms once the brakes get hot which leads me to believe that it's condition 1. As I am doing another major front axle rebuild I have finally decided to sort the front brakes. So I started with measuring disc thickness, runout and pad thickness:

Front left disc thickness: 31.8mm
Front left disc runout: 0.12mm
Front left pad thicknesses: 2.3mm and 3.9mm

Front right disc thickness: 30.9mm
Front right disc runout: 0.13mm
Front right pad thicknesses: 1.1mm and 2.6mm

Front disc thickness spec: 30-32mm
Front disc runout spec: 0.15mm max
Front pad spec: 10-4mm

Now I am a little unsure as to what I should do The disc runout is in just in spec and they are plenty thick enough.There seems to be a large variance in pad thicknesses after 20-25k miles of use. Also it seems the the right side is doing more work than the left side. Should I rebuild the callipers again? Should I change the discs even though they are in spec? Before you comment yes I will change the pads.

 

[Chris]

Rob, possibly hard to believe I know, but could your discs actually be flexing under braking leading to a greater run out than you are measuring statically? There are huge forces involved as you know and if any of the pots are not operating like the others, there will be a natural bending force on the disc. If they are crappy aftermarket ones too, there's no knowing what they are made of. Remember they are hollow, largely.

Chris

 

[Rob]

I know what you are saying Chris, even though they are in spec it may be causing vibration under certain conditions. Going by all the other parts that were fitted to the front hubs its unlikely that the discs are genuine. I am tempted to get new grooved discs anyway as I plan to fit my intercooler in the near future. But the real PITA is rebuilding the front callipers. Still do not know whether I should do them again? Is it normal for the pad/disc thicknesses to vary so much on the same axle?

 

[Chris]

Ooh, sexy discs. Where from, I'd like a pair too.

Hard to say what is actually 'normal' for discs Rob. If I had one criticism of Cruisers overall, I'd say it was brakes. I have had quite a few Yotas (we have 4 at the minute) and it seems that brakes need almost constant attention to keep them good. Off roading doesn't help I know. Have to say mine pads wear very evenly. But stopping isn't great. I would like better quality discs. I faced up a disc recently in the lathe and it was very easy to machine. Just like mild steel. other discs I have faced up have burned out tools they are so hard. Could you get yours hardness tested?

Chris

 

[Gary Stockton]

Here's a stupid question:

What, exactly, is 'run out' ? What are you measuring?

 

[Chris]

Damn, replied on the old forum Gary. Essentially it's side to side wobble, oscillation, deviation from centre line.

Chris

 

[Andrew Prince]

Rob, I think if you're aiming for better brakes overall, then a caliper rebuild or at least a tear-down to check everything is 100%, is non-negotiable. The fanciest carbon discs will count for nought if the calipers can't clamp the pads onto them.
If your pads are wearing at different rates on either side, then it suggests different braking force is being applied*. This is either due to a bulging brake hose absorbing hyraulic pressure that should be going to the pistons. Or its the pistons themselves sticking and requiring a lot more pressure to get moving.

(*of course there are other variables like quality and consistency of brake pad material, hardness variation between discs, build-up of abrasive matter between disc and pad (think Lincomb grit!) but assuming you're using quality OEM or equivalent pads, then some of this can be ignored)

As you know, base-lining everything and fitting quality parts will remove most of the variables. Tearing down the calipers, replacing seals/boots and polishing up the pistons, (red)greasing everything, and checking that everything is sliding smoothly on the bench before refitting will give you the best shot of good brakes. Of course there's also flushing and filling with new brake fluid, including the LSPV, replacing brake hoses or upgrading with braided hoses, new discs and so on are all part of the deal.
Kind of an all or nothing deal! ;-)

I'm sure you're on top of it but I guess wheel bearings with insufficient pre-load would also allow the hub to wiggle around its axis which would introduce vibration under braking. I doubt this is your issue but worth mentioning and double-checking for completeness

 

[ajnabi]

Hi Rob,

re: calliper rebuild
I've just finished rebuilding my front callipers, the truck was pulling to one side, mileage is 80K miles, brake parts were all standard OEM 80 Series.

I also found uneven pad wear (one down to metal), and partially rusted inside surfaces of both discs, so I bought the calliper rebuild kit and rebuilt the callipers.
Found 2 pistons that had pitting on the seal contact surface, and 2 torn boots, plenty of "gunk" caked onto the other pistons and some rust building up on the "lip" of the bores, past the slot for the seal.

Replaced the 2 pistons, and installed new OEM Discs and 100 Series Pads (without anti squeal shims).
Was going to go for DBA Slotted discs, but got a really good deal on OEM.

The brakes are now smooth and the truck now stops straight and true, with a much better feel on the brake pedal.

My advice is pay particular attention to cleaning the area where the seal sits, and also the bores for each piston, including the lips as mentioned above.
The idea is to clean and not to grind, as to take too much metal off.
I spent a lot of time on this, using 1200/1500 grit wet and dry from Halfords.
I think some attachment on a tool such as a dremel would have been less painful and time consuming.

And as Andrew says, full brake fluid flush is a must, inc. LSPV, inspect brake hoses, etc.
Don't forget the all important red rubber grease, when rebuilding.

You should be able to lock your front tyres or get the ABS to engage(where fitted), with the OEM setup, on dry tarmac.
There is no point moving on until you can achieve this.

re: brake discs
As you mention your disc thickness is fine but the run out is suspect
However the run out is similar on both sides, so is probably not the reason for the uneven pad wear.
Due to the vibrations I would change out the discs too, and for the uneven pad wear (and your possible reinstall of a pitted piston), I would rebuild the callipers.

IQ

 

[Rob]

Chris, not sure what discs I will go for. Will update as soon as I decide which ones to get.

Andrew, looks like a complete strip down is the smart thing to do but with all this overtime I am doing now, the big trip soon and a front axle to rebuild (including diff, discs, stub axle bushes, 1 new speedi sleeve) adding calliper rebuild to the list makes it a very long list. My bearings are definitely done up properly. Been using OEM pads so slightly concerned by the uneven wear. Braided hoses you say (now where is that thinking smiley?)

Ajnabi, I have no problems locking up the wheels in the dry (I have been driving with ABS disabled recently as missing the front prop). The brakes work fine but they are not spectacular. The calliper rebuild process you have described is essentially what I did however I did not replace any pistons, although if I did it now I would take a bit more care.


Admins, any chance we could merge the thread from the old forum with this one?

 

[Chris]

Rob, interesting by product of fitting my lift kit last week. I got new brake hoses from chassis to axle and there is a noticeable increase in pedal pressure - no other changes. I suspect that on an old bus like ours, new hoses never mind braided hoses would make a difference. Another cheap trick (or cheat) on the brakes that I do, is give the pistons a work out. I pull one pad, turn it 90 degrees and slot it in to block a piston then press the brake pedal to push the free piston out. You can give it a clean round check the boot etc and then push it back in. I do the same for the other three. Essentially, it gives you an idea of how they are all performing. If you have a slightly reluctant one then cycle it a few times.

Worth looking at before you get to the point that you have the calipers off and get the big tools out. Uneven wear can also be caused by hard spots in the disc itself. Brought around by cheap discs. I was looking at the Brembo ones. It's a name a know, but whether this is Brembo China division or not, I have no idea.

Chris

 

[Rob]

Worth looking at before you get to the point that you have the calipers off and get the big tools out.

Too late for that unfortunately. Both callipers are off and ave already removed one CV. These hubs can be stripped in a matter of minutes if you have the right tools and experience, I wish they went back together as quickly. Been striping the front axle for the last 2 days after work in the hour or so of light I get and seem to spend more time taking tools up and down the stairs to my flat...

How much for a set of new braided hoses then? Where do I get them from?

Will have a look at discs now.

 

[Chris]

I don't know Rob, I haven't researched new hoses, I simply got some in the lift kit. But I do know there have been several sightings of braided hoses on various threads. Maybe someone will be along soon and point us to some.

Chris

 

[Rob]

http://www.landcruiserclub.net/forums/showthread.php/44958-Brake-discs?
I am tempted to get the Nitrac discs from here: http://www.motorsportworld.co.uk/ Front discs only for now. I would prefer not to have to replace them this decade so seems like a good choice.

 

[Chris]

They look nice Rob. Hmm.

Chris

 

[Rob]

Question is which Nitrac ones should I go for, non grooved heavy duty ones, cross grooved, 8, 12 or 16 grooves? How much are the Brembo ones?

 

[frank rabbets]

Hi Rob

Runout will not cause judder unless there is a lot of play in the wheel bearings which there isn't. Runout with good bearings and constant thickness disc just makes the pistons in the caliper to move in/out but they cancell each other out and there is no feedback to the brake pedal, just between the 2 sides of the caliper which you won't notice.Soft spots a cheap disc can cause judder especially if they have got very hot. Also unequal thickness in a disc can cause judder with the pedal moving up/down. I just recut my rear discs and one of them varied in thickness by 0.0015" and now I can feel the pedal move up and down!

As other hydraulic problems do not cause rapid fluctuation in pressue these will not cause judder, just softer or harder pedal.

All my cars over the years have suffered from unequal pad wear. The inners are exposed to water dirt more or less than the outers. Also the nearside often runs in wet when the offside road is dry.

Frank

 

[AndyCook]

disc runout will lead to judder in the long run though, since it will cause high-spots to get worn more on each disc rotation and lead to unequal thickness in the disc

 

[fridayman]

On bikes you can clearly feel judder (from warped discs) through the lever, so I would have thought it is possible to feel it through the brake pedal too.

 

[Rob]

Missed the last few posts, not familiar with the new forum yet...

Thanks for the comments. Frank, the discs are almost certainly not genuine as they were apparently replaced just before I bought it along with non genuine bearings, stub axle, cam belt, oil filter and fuel filter. I have not measured if the thickness is consistent all the way round but one of the discs has deep grooves on one side only and the other one seems fine. They are off and not going back on the truck.

Tested the callipers and 2 pistons were sticking as striped them and it seems that 30k miles of off road use has taken a toll on the pistons. There was evidence of mud under 3 pistons outer seals and all but one piston is in perfect condition so will be replacing all 8 pistons as well. This pistons were damaged previously but I was too skint to change them back then. Will order discs soon, just got to figure out which ones I want/need.

 

[Paul_Humphreys]

http://www.llama4x4.co.uk/ for custom pipes.