SFA rear disc conversion issue

Discuss modifications on your 1979 to late 1998 SFA 4x4 Hilux here.
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Muz
Low Range 4WD
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Real Name: Murray
Location: Linden

Fri Oct 04, 2019 7:09 pm

Hello everyone

So, discs and Audi B6 calipers fitted,Master cylinder upgraded to the 1" 80 series land-cruiser type.
Bench bleed the master before fitting,and bleed the entire system from LR,RR,LF,RF and the LSPV.
problem is i don't have a solid pedal at the first press of the brake pedal.Some travel before it feels like pressure is on the brakes.
3 pumps of the pedal and the pedal feels good, leave it for a bit and its a low pedal.
So it feels like there is air in the system but as above this shouldn't be the case.

Anyone got it right and what am i missing?
Muz
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Real Name: Murray
Location: Linden

Sat Oct 05, 2019 7:33 am

No one got it right? :shock2:
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Mud Dog
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Real Name: Andy
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Sat Oct 05, 2019 10:06 am

Murray, my thinking is that if you have air in the system you will have a "spongy" pedal all the time, no matter how many times you pump it. You say the pedal feels right after a few pumps .... this makes me think that there is an issue with the master cylinder.
When your road comes to an end ...... you need a HILUX!.

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Life is like a jar of Jalapeño peppers ... what you do today, might burn your ass tomorrow.
Don't take life too seriously ..... no-one gets out alive.
It's not about waiting for storms to pass. It's about learning to dance in the rain.
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Muz
Low Range 4WD
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Posts: 141
Joined: Fri Mar 13, 2009 1:24 pm
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Vehicle: Hilux 2.4 Raider, Suzuki SJ413, Landcruiser FJ40
Real Name: Murray
Location: Linden

Sat Oct 05, 2019 8:30 pm

hi Andy
I put a new 1 inch master cylinder after i had did the conversion. is it possible the new master could be faulty from new? To me it feels like there isnt enough fluid volume on the first push, and after the 2nd or 3rd it is ok,almost as if the caliper pistons are too big for the amount of fluid in the system.
so frustrating when all the bits should be giving a good result but are not.
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Mud Dog
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Vehicle: '90 SFA Hilux DC 4X4, Full OME, 110mm lift. Brospeed branch, 50mm ss freeflow exhaust. 30 x 9.5 Discoverer S/T's on Viper mags. L/R tank. (AWOL) '98 LTD 2.4 SFA, dual battery system. Dobinson suspension, LR tanks, 31" BF mud's.
Real Name: Andy
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Sat Oct 05, 2019 10:01 pm

A 1" master is probably not enough .....not sure, just thinking ..... the slaves on drum brakes don't need as big a volume as callipers, then you probably have two pistons per rear calliper if it's a floating calliper and four if it's a fixed calliper. Either way they use almost the same volume (the four pot will use a little more). But then you would have upgraded from a 3/4" master?

I assume the hand brake is mechanical and doesn't rely on brake hydraulics, in which case it shouldn't have any effect on the fluid dynamics. At least not unless there is a spring or mechanism that somehow pushes the pads back.

If you pump the pedal (with the motor running) until you have a solid pedal, then immediately check the level in the reservoir. Leave it stand for a while and then check the reservoir level again once you know the pedal would have lost it's solid feel. If the level has risen noticeably, then something is forcing fluid back from the new callipers.

Does the master have a dual system? One for front and one for rear?

It's puzzling. :scratch:
When your road comes to an end ...... you need a HILUX!.

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Life is like a jar of Jalapeño peppers ... what you do today, might burn your ass tomorrow.
Don't take life too seriously ..... no-one gets out alive.
It's not about waiting for storms to pass. It's about learning to dance in the rain.
And be yourself ..... everyone else is taken!
Poffie
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Town: George
Vehicle: Hilux SFA
Real Name: Charl
Location: George

Sat Oct 05, 2019 11:34 pm

Hi guys also some times air can oscillate in the system and would not come out. The peddle feels spongy remove the pipe coming from the back to the master then use a pressure bleeder and force all the air out. Then make sure your master is bled properly before you reconnect the brake line at the master. Also make sure your load sensing valve is not jammed it will definitely cause problems. To test what is bugging you around you can use a couple of vise grips and isolate the rear brakes to do fault finding. Last thing that I can think of is check that the bleeding nipples is at the top that also will give you a hard time. Hope this helps 😉
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pietpetoors
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Thu Oct 10, 2019 6:30 pm

Agree with George, I once battled with a Nissan Trokkie, each time I bled it until no air came out anymore and brakes were spongy. Drove it for a day or two, bleed again and again air came out. Only after the third bleed was the brakes solid.
Seems like the air gets trapped somewhere and only makes its wat to the calipers with time.

On this particular trokkie I also replaced the master cylinder with a new one.
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