1977 Toyota FJ40- dragging front disc brakes. (1 Viewer)

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Can anyone help.

My 1977 FJ40 has factory fitted front disc brakes & rear drum brakes. I have renewed the braking system through including hard & soft brake lines. I fitted a new OEM master cylinder and brake booster, which I bought from City Racer. They said the booster was for drum brakes all round, but it was identical in every way to the the one fitted originally to the vehicle, so I bought it

Unfortunately, the front brakes drag.

I have tried adjusting the brake pedal and the plunger in the brake booster. I put the original booster and master cylinder back on the car, but the problem persists. I have bleed the whole system and purged any air.

What's happening is the brake pedal remains soft and requires pumping to work. However once the brakes are released the wheel stays locked. Slowly the pressure dissipates and the wheel runs free again until you apply the brake and the whole cycle starts again.

I have cracked the brake pipes at every junction and the wheels run freely, right up to the booster. If I loosen the master cylinder from the brake booster the wheels run freely. The problem seems to be with the brake booster. As I said, I have tried the old master cylinder & booster, but the problem doesn't go away.

Please can anyone help? Did I buy the wrong booster? Can it really make such a difference?
 

A10Driver

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How far down on the pedal before it starts to build pressure? Do you have the rear brakes going through the part that keeps pressure for the drums? Sure the front and rear circuits aren't switched?
 
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How far down on the pedal before it starts to build pressure? Do you have the rear brakes going through the part that keeps pressure for the drums? Sure the front and rear circuits aren't switched?
First push, all the way and then it goes hard after a couple more pushes. We checked the circuits tonight and the front circuit comes off the front of the tee on the chassis and the back circuit off the back. Is there anywhere else it could be crossed?
I'd keep adjusting both ends of the brake booster.
Both are completely backed off. The pushrod won't adjust back any further and the shaft won't wind into the pedal any more. We even spaced the master cylinder off the booster with washers. That helped a bit, the pressure dissipated more quickly, but didn't resolve the problem.
 

A10Driver

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Makes sure to trace back from the t at the chassis to the master. Also do you have the residual pressure fitting for the rear brakes?
 
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Makes sure to trace back from the t at the chassis to the master. Also do you have the residual pressure fitting for the rear brakes?
I just went out to the garage to check and the lines are correct. Yes, the original MC, which I have refitted, has two different sizes of aperture. The one I bought was wrong, it was for a '75 with drum brakes all round. Unfortunately, refitting the original hasn't resolved the problem.
 

samatulich

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@Maxdog, When you say “wind into the pedal any more” you’re threading the yoke further onto the threaded rod, correct? I just went through this myself, very similar, if not the same symptoms. With the new booster, I started with the yoke(center of pin hole) to booster spacer was 13.5cm, now its closer to 13 or 12.5cm. I shortened the length of the treaded rod in theory(I did not cut the threaded rod). I was getting a solid pedal way too soon, and the front discs were dragging, now they work great, no dragging.
 
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Messages
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@Maxdog, When you say “wind into the pedal any more” you’re threading the yoke further onto the threaded rod, correct? I just went through this myself, very similar, if not the same symptoms. With the new booster, I started with the yoke(center of pin hole) to booster spacer was 13.5cm, now its closer to 13 or 12.5cm. I shortened the length of the treaded rod in theory(I did not cut the threaded rod). I was getting a solid pedal way too soon, and the front discs were dragging, now they work great, no dragging.
Initially, I had the same problem. However, now the threaded rod is wound down (into the pedal) as far as it can be. The pedal is spongy and needs to be pumped to work the brakes. Once they are on they are slow to release. It takes a few seconds. We've tested my mates '79 and his releases immediately.
 
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Did you set all the adjustment rods (between master and booster, booster and pedal) per the FSM? It's possible that one or both of the rods are to long and preventing the master cylinder from fully retracting and allowing the fluid to bleed back into master.
 
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Did you set all the adjustment rods (between master and booster, booster and pedal) per the FSM? It's possible that one or both of the rods are to long and preventing the master cylinder from fully retracting and allowing the fluid to bleed back into master.
I'm trying to set the pushrod length using a micrometer this evening. I ordered the proper tool today, but it won't reach the UK until the New Year. I've put the original booster back in to see if that makes a difference. Unfortunately, with the new booster, the problem persisted even when I backed the push rod and pedal right off. The return spring was missing from the brake pedal and I thought that might be it. I refitted it tonight and no change.
 

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