1994 mistral R20 rear drum brake problem

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ryalls
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1994 mistral R20 rear drum brake problem

Postby ryalls » Mon Jul 10, 2017 11:29 pm

Hi All,

Thanks in advance for any advice and/or opinions it's much appreciated.

I'll cut to the chase with all the additional info below, What PSI should I be getting from the master cylinder to the rear brakes on this vehicle???

OK, so I have been failed on a WOF for low rear brake balance as is the rear brakes are not providing acceptable braking force, the front brakes are working well.

First thought was OK need to bleed the rear brakes which i did starting with the left rear i bleed new DOT4 fluid all the way through until I had new clean fluid coming out. Next I did the same with the right hand side this was done using two people and a bleed kit and maintaining a safe fluid level in the master cylinder at all times.
Afterwards however I returned to the testing station and still exactly the same problem.

I then jacked up the rear axles to see just how little braking force I had. Engine idling and in drive with my full force on the brake pedal I can not get the rear wheels to stop turning, they do slow down slightly but they do not stop turning.

Brake drums off, inspected and measured well within spec, machined them true and flat any as a precaution and still well within limits. Slave cylinders checked, no leaks and the pistons move freely. Brake shoes a little worn so replaced with brand new shoes, adjusted up correctly and retested. Still the exact same issue can't stop rear wheels turning at idle.

Master cylinder replaced this time with a second hand unit but believed to be in perfect working order, bench bled master cylinder, everything else re-bled and this time running clear hose from bleed nipple to master cylinder. Still the exact same issue rear wheels still can't be stopped at idle.

Next I made up a fitting to test master cylinder rear brake output pressure and it reads 500PSI, does anyone know if this is correct??? or does anyone have any other ideas as to what the issue could be? I do not believe this vehicle has a load sensing valve (LSV) but I have been wrong before...

Still with me? Excellent may as well let me know what you think...

Cheers,
Dan

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Re: 1994 mistral R20 rear drum brake problem

Postby sirLachlan » Wed Jul 12, 2017 6:46 pm

Is this 500 psi at the master cylinder or down at the wheels ?
Reason I ask is does it have rear brake restrictor like a hilux has ? That applies more force to the rear wheels if the vehicle is heavily loaded ?
Has a valve on the body and a linkage to the diff . When the diff gets closer to the body it obviously has more weight on rear wheels so rear brakes can be applied harder .

Does a mistral have one and is it still working ?

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Re: 1994 mistral R20 rear drum brake problem

Postby MihiT » Wed Jul 12, 2017 7:54 pm

sirLachlan wrote:Is this 500 psi at the master cylinder or down at the wheels ?
Reason I ask is does it have rear brake restrictor like a hilux has ? That applies more force to the rear wheels if the vehicle is heavily loaded ?
Has a valve on the body and a linkage to the diff . When the diff gets closer to the body it obviously has more weight on rear wheels so rear brakes can be applied harder .

Does a mistral have one and is it still working ?


I think that would be the LSV he mentioned, and that was my first thought too. It would be pretty obvious as the rears would be tee'd off after it.

Being drums makes me scratch my head a bit more...Only thing I can really think would be a crimp in the line, but it would have to be pretty serious to stop the flow, and not blow back out and leak by hydro pressure.
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ryalls
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Re: 1994 mistral R20 rear drum brake problem

Postby ryalls » Wed Jul 12, 2017 11:16 pm

sirLachlan wrote:Is this 500 psi at the master cylinder or down at the wheels ?
Reason I ask is does it have rear brake restrictor like a hilux has ? That applies more force to the rear wheels if the vehicle is heavily loaded ?
Has a valve on the body and a linkage to the diff . When the diff gets closer to the body it obviously has more weight on rear wheels so rear brakes can be applied harder .

Does a mistral have one and is it still working ?



Does not appear to have Any kind of restrictor. And 500 psi is at the master cylinder i'm going to make a fitting this week to check pressure at the drums.

Cheers,

ryalls
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Re: 1994 mistral R20 rear drum brake problem

Postby ryalls » Wed Jul 12, 2017 11:18 pm

MihiT wrote:
sirLachlan wrote:Is this 500 psi at the master cylinder or down at the wheels ?
Reason I ask is does it have rear brake restrictor like a hilux has ? That applies more force to the rear wheels if the vehicle is heavily loaded ?
Has a valve on the body and a linkage to the diff . When the diff gets closer to the body it obviously has more weight on rear wheels so rear brakes can be applied harder .

Does a mistral have one and is it still working ?


I think that would be the LSV he mentioned, and that was my first thought too. It would be pretty obvious as the rears would be tee'd off after it.

Being drums makes me scratch my head a bit more...Only thing I can really think would be a crimp in the line, but it would have to be pretty serious to stop the flow, and not blow back out and leak by hydro pressure.



Yeah I had thought about that however they do bleed and flow reasonably freely so I had ruled that out. Tough one ay...

Cheers,

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Re: 1994 mistral R20 rear drum brake problem

Postby Petemcc » Thu Jul 13, 2017 6:33 am

What happens if you pump the brakes? there will be a way of holding the shoes out when not braking whether it's a non return valve of sorts or mechanical adjuster at the brake itself. If this isn't working then you will need to pump the brakes a couple of times to get the shoes out. Pedal would still be hard due to the front brakes.

Try your test again and pump it a few times

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Mehrts
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Re: 1994 mistral R20 rear drum brake problem

Postby Mehrts » Thu Jul 13, 2017 9:50 am

I just rebuilt the rear drum brakes on the Bitsalux ( Toyota surf brakes).

These have a gear and a metal tab acting like a ratchet to 'self adjust' the shoes as they wear. This metal tab is actuated by the handbrake cable in this particular system, not sure about the Mistral ones though.

When I fitted the new shoes, the adjuster was wound all the way in and I thought I'd just pull the handbrake on a few times to get the shoes to wind out to their correctly seated position.

Well bugger me, a few times ended up being around 50 before the shoes even started to make contact with the drums :lol:

Anyway, what I'm saying here is, make sure your shoes aren't still backed off away from the drum, because that would clearly give no braking effort at the rears when everything else seems good.
Toyhatsu Bitsalux

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tweake
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Re: 1994 mistral R20 rear drum brake problem

Postby tweake » Thu Jul 13, 2017 4:26 pm

to add, the likes of toyota auto adjusters are known to get worn and back off the shoes.

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Re: 1994 mistral R20 rear drum brake problem

Postby MihiT » Fri Jul 14, 2017 7:34 am

tweake wrote:to add, the likes of toyota auto adjusters are known to get worn and back off the shoes.

Yeah but mate we're talking Nissan here, none of that toymotor rubbish. :p
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Re: 1994 mistral R20 rear drum brake problem

Postby Crash bandicoot » Fri Jul 14, 2017 9:07 am

Adjust the shoes out so you have to use a rubber mallet to tap the drums back over them, secondly.. Bleed it and the load sensing valve above the diff.then at the drums..

...on a side note....swap tge drums and shoes side to side and see if ya fet tge same result. we used to have an Isuzu fsr truck that would fail one side on its cof almost every time, so we swapped the drum and shoes to the other side and went for a retest, same side failed, so we turned the truck around so it was facing the opposite way on the brake rollers and whataya know it failed the other side, turn out it was there machine. They didn't like us after that. Lol.
Waiter...there is a drought in my glass.

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Crash bandicoot
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Re: 1994 mistral R20 rear drum brake problem

Postby Crash bandicoot » Fri Jul 14, 2017 9:09 am

Also make sure the hand brake is backed off when ya bleed them too then adjust it up last as it will hold tension even if the brakes are not on.
Waiter...there is a drought in my glass.

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tweake
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Re: 1994 mistral R20 rear drum brake problem

Postby tweake » Fri Jul 14, 2017 12:37 pm

MihiT wrote:
tweake wrote:to add, the likes of toyota auto adjusters are known to get worn and back off the shoes.

Yeah but mate we're talking Nissan here, none of that toymotor rubbish. :p

they work on the exact same principle and pretty much the same design, with the same inherent faults.

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Re: 1994 mistral R20 rear drum brake problem

Postby hemi265 » Sun Jul 23, 2017 12:48 am

I've got a pr50 terrano that always does this. Never worked out what the issue is, however I try to remember to use the handbrake only to do some hard stops before the wof test and find it gives a perfect balance. First time it happened was 15 years ago when I first got it, spent the whole day trying to sort it pulling everything apart, and not being able to find anything. Just went to the aa for wof the other day, and forgot, and got a fail. Said I would be back in a few minutes, arrived back with smoke pouring off both drums, and to the surprise of the inspector resulted in perfect balance. He spent quite a while talking to all his other colleagues about it before he came back and said he was going to pass it, but he kept saying that he wasn't happy about it. I decided to pull the drums when I got home to make sure there wasn't anything obvious that needed attention, but found shoes that still look brand new after 150000km. Incidentally I'm still on front pads as well, so maybe I'm not using the brakes hard enough? Would love to know if you found your problem, as it would be nice to fix mine once and for all.

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