Offroad-Express

Hello

I have recently rebuilt my rear brakes, slave cylinders, machined drums, brand new shoes

I am getting some really bad rolling brake test results failing a wof, 70L/30R (VTNZ)

From inspection I can tell that my right leading shoe has less friction material/contact on the drum then the left leading shoe. So that makes sence. So I have a friction contact issue. I gave em a bit of a emery scrub over the contact area and put the drums back and adjusted accordingly.

My new shoes are going to need some bedding to conform to the larger diameter of the machined drums that are in tolerance.

So my question is, How long can I expect my braking to firm up in the rear ?

I have done the whole drive up to 60, hit the brakes as hard as you can without locking up.. releasing and driving on.. It feels like they are bedding in but that might be in my head.

Check the drum diameters as I suspect that if they are different or out of specification this will have an impact on the brake preformance.

Also
Have they been assembled correctly?
Is the brake pedal firm/system properly bled?
Has the brake back plate been bent?

churchill wrote:Check the drum diameters as I suspect that if they are different or out of specification this will have an impact on the brake preformance.

The drum diameter I am assuming is in spec because I had it machined by Waikato clutch and brake.

The feel is firm, but not stiff and not spongy I bleed the entire system to rule out that factor as I did have to replace the slave cylinders.

So assuming the drums are in spec, and the new shoes do not yet conform to the larger diameter of the drums.

I am just wondering how long does it take to bed in, or should I just dissemble the brakes and take them in for profiling (I cant be arsed being the major problem) It will cost $$ and more nights in the cold shed that I am growing very un-fond of and after a very hard working day

Its certainly not my first shoe replacement on vehicles So this one has taken me by surprise at its failure...

Mind you.. I have never replaced slave cylinders out of reaction to a wof fail ... have only changed them out of run away down hill fails...

So I am %100 certain I have done it correct, but what was over looked was the new shoe profile vs machined drums and bedding in time.

Rubbing brake linings with Emery paper is a waste of time.

Get a hacksaw blade and drag it across the lining in a criss cross pattern to get a good scoring on the lining.

Bedding in rear brakes are always a pain on light vehicles.

Can you wind your load sensing up to get full pressure to the rears?

Driving round and pulling on the handbrake while keeping your foot on the gas helps bed them in, as long as you don't get it too hot.

There used to be a product called 'fullers earth' that you put in the drum and made massive difference in brake performance(temporarily) but I doubt if its used anymore.

Hope one or all of them tips help

Weemsy wrote:Get a hacksaw blade and drag it across the lining in a criss cross pattern to get a good scoring on the lining.

Bedding in rear brakes are always a pain on light vehicles.
Can you wind your load sensing up to get full pressure to the rears?

Thats a really good idea!!! I could trick it indeed Moahaha!! Or I could laden the rear down with some river stones That's a really good tip man thanks!

Driving round and pulling on the handbrake while keeping your foot on the gas helps bed them in, as long as you don't get it too hot.

Yeah I can tell it's helping a we bit To get the process started indeed!

There used to be a product called 'fullers earth' that you put in the drum and made massive difference in brake performance(temporarily) but I doubt if its used anymore.

Hope one or all of them tips help

You have given me a good picture of how much effort is required to bed one's shoes in at a fast rate . I will see if I can safely trick the proportioning valve to bias the back rear some more during the process... but in saying that...

What "If" my problem is with this unit.

Do you know if the proportioning valve needs bleeding too ?, I did not have a good look at it last time I was under there for a nipple.

If that is the case, then I presume the order of bleeding is this value first, then the rear left slave/wheel cylinder

Can't remember if there is a bleeder on the load sensing or not, but you should have a poor pedal (excess travel) if there's air in the system

If there is a bleed nipple on there, bleed it before the wheel cylinders

I think my problem is not the same but one of you may have an idea.

I have a Suzuki Escudo 91 and the drum was very hard to remove from the axle. (The handbrake wasn't on) when I put the drum back on again it was very hard and needed some hammering. Is this normal?

now spinning the wheel I get about 80% of freewheel until it gets very hard to turn the wheel and then frees up again. I have done a few k's in it now to see if it would free up but its still the same.

Any ideas? Thanks

It sounds like you have a warped drum, or maybe a hotspot on the braking surface?
When it's in the 'free' part, does the drum come off easier?

Also, is there a lip on the drum? If the drum is worn it will leave a lip on the edge, making it difficult to get over the shoes.
Are you adjusting the shoes before and after removing/refitting the drum?

kiers117 wrote:I think my problem is not the same but one of you may have an idea.

I have a Suzuki Escudo 91 and the drum was very hard to remove from the axle. (The handbrake wasn't on) when I put the drum back on again it was very hard and needed some hammering. Is this normal?

If in turns %80 then locks up, I would expect vibration during braking. It is quite normal for drums not to be perfectly round There will normaly be some contact during a full rotation, the trick is as long as it's not binding and can turn freely.

I would consider it a problem if you felt shuddering during breaking. Just my opinion.


And now for my problem, of friction and bedding.

Solution : Carry on as I was, but as mentioned earlier be more aggressive in the bedding process. So last night I thrashed the brakes a little Sanded off the contact spots, then trashed it to the WOF station. Yesterday I got 70/30 on my pedal test. Today I got 90/90 and 140/140 on the handbrake test. Perfect! And they are feeling more and more better each time I take the car out.

So morrel of the story, every known and again you will get a car where the shoes take alot longer to bed in before braking performance is restored.

So thanks all for you advice! It kept me on the right track

Weemsy wrote:If there is a bleed nipple on there, bleed it before the wheel cylinders

I found it last night be left it alone on account of having good pedal feel And you where right on the amount of bedding required

Pass the WOF no worrys today Thanks man!

Sweet as no worries