Brake System and Booster Troubleshooting (2 Viewers)

[MatthewMcD]

You sir are being VERY methodical and thorough. Soon you will be THE brake guru.

Thank you, but that I doubt. I am really hoping it's not the booster or MC. I really want to get driving and don't want to wait for more parts.

The thing about this truck I have found is once you crack open a system, you have to go all in. You can't fix half of the cooling system. You can't replace half the oil lines. So over the past year I have tried to move from system to system. I thought I was done with brakes, but they weren't done with me.

 

[MatthewMcD]

Spent the morning fine tuning the rear brakes and getting them to drag, punching the brake pedal to seat them, adjusting them again to drag, lather, rinse, repeat...now I know why folks go with rear discs. It's not for better braking...

A couple things I noticed. When bleeding the brakes, the pedal does not move when I open the bleed valve on the rear drums. I can hear the brakes activate, but there is no change in the pedal. When I crack the front caliper bleed valves, the pedal goes to the floor.

With my foot on the brake when I start the engine, there is no difference in the pedal.

Up on jack stands, with a little drum drag, I press the brake, and I can still turn the rear wheels by hand. Backing up, I slam the brakes, only the fronts lock up.

I also ran the part number for the booster 44610-60030, it says on the booster "For Disk Brake Use". But on the City Racer site it indicates that the booster is for 4 drums.

I also ordered a booster adjustment tool from a different vendor, and I was right...they should be level.

Unless anyone has any ideas based on the info above, I am going to order a booster and master from City Racer so I KNOW that I have the right parts for the job.

 

[45Dougal]

The pedal doesn't move when you open the rears because the disks take so much less fluid to actuate.
I think you'll need a different master or rear disks... unless you have the front and rear circuits reversed on the mc.

 

[aztoyman]

Sounds like a good decision. Just to let you know, it's NOT typically this much work when you have parts that are supposed to work together.

Modifications are ok as long as they are not "mismatched" components as you're finding out.

Also, what 45dougal said.

 

[MatthewMcD]

The pedal doesn't move when you open the rears because the disks take so much less fluid to actuate.
I think you'll need a different master or rear disks... unless you have the front and rear circuits reversed on the mc.

I didn't see anything specific in the Dorman guide, which is part of the reason to get a new "known good" master cylinder. I looked at the conversion kits and I'd prefer to wait on that...

@45Dougal would you recommend a proportioning valve?

 

[MatthewMcD]

Sounds like a good decision. Just to let you know, it's NOT typically this much work when you have parts that are supposed to work together.

Modifications are ok as long as they are not "mismatched" components as you're finding out.

Also, what 45dougal said.

Clean slate and "known good" parts.

 

[cruisermatt]

Spent the morning fine tuning the rear brakes and getting them to drag, punching the brake pedal to seat them, adjusting them again to drag, lather, rinse, repeat...now I know why folks go with rear discs. It's not for better braking...

A couple things I noticed. When bleeding the brakes, the pedal does not move when I open the bleed valve on the rear drums. I can hear the brakes activate, but there is no change in the pedal. When I crack the front caliper bleed valves, the pedal goes to the floor.

With my foot on the brake when I start the engine, there is no difference in the pedal.

Up on jack stands, with a little drum drag, I press the brake, and I can still turn the rear wheels by hand. Backing up, I slam the brakes, only the fronts lock up.

I also ran the part number for the booster 44610-60030, it says on the booster "For Disk Brake Use". But on the City Racer site it indicates that the booster is for 4 drums.

I also ordered a booster adjustment tool from a different vendor, and I was right...they should be level.
Unless anyone has any ideas based on the info above, I am going to order a booster and master from City Racer so I KNOW that I have the right parts for the job.

A booster is a booster. As long as it is working it doesn’t matter what brakes are on the other end. All the booster does is decrease required the pedal pressure to stop the vehicle.

Some boosters perform better or worse then others, but if it’s working properly you can absolutely use the “ drum” brake booster with disc brakes. Any booster is going to be better then no booster.

 

[45Dougal]

I didn't see anything specific in the Dorman guide, which is part of the reason to get a new "known good" master cylinder. I looked at the conversion kits and I'd prefer to wait on that...

@45Dougal would you recommend a proportioning valve?

A proportioning valve in my experience is to reduce the pressure applied to one circuit over the other.
In your case, that would be the front, because it's limiting volume to the rear, but that would reduce your overall braking capacity I think. (Edited to correct my 'breaking' typo - I hate when I read this in other posts! )
My single circuit mini brakes for example limit pressure to the rears, so they max out just before lock up, and I can push everything else into the front.

 

[MatthewMcD]

A booster is a booster. As long as it is working it doesn’t matter what brakes are on the other end. All the booster does is decrease required the pedal pressure to stop the vehicle.

Some boosters perform better or worse then others, but if it’s working properly you can absolutely use the “ drum” brake booster with disc brakes. Any booster is going to be better then no booster.

That's my challenge, is it "working". I am not sure if it's the booster or the master. I don't have the skills and knowledge to determine where the issues is.

 

[cruisermatt]

That's my challenge, is it "working". I am not sure if it's the booster or the master. I don't have the skills and knowledge to determine where the issues is.

Ok, easy. I only skimmed through this thread (will read it in depth later), but the quick way to test a booster:
1.Engine off
2. hold brake pedal down with foot
3. without releasing your foot, start the engine
4. once the engine starts (and starts generating vacuum), if the the brake booster is functioning correctly the pedal height will decrease.

If the pedal height doesn't change when you start the engine, your booster isn't doing anything. That may be because of a bad booster, or no vacuum from the engine.

All the booster is is a piston, with vacuum on one side (the master cylinder side), and atmosphere on the other (the pedal side). atmosphere is higher pressure then vacuum so you have the mechanical advantage of a 10-12" piston assisting you to pressure the brakes more easily

 

[MatthewMcD]

Ok, easy. I only skimmed through this thread (will read it in depth later), but the quick way to test a booster:
1.Engine off
2. hold brake pedal down with foot
3. without releasing your foot, start the engine
4. once the engine starts (and starts generating vacuum), if the the brake booster is functioning correctly the pedal height will decrease.

If the pedal height doesn't change when you start the engine, your booster isn't doing anything. That may be because of a bad booster, or no vacuum from the engine.

All the booster is is a piston, with vacuum on one side (the master cylinder side), and atmosphere on the other (the pedal side). atmosphere is higher pressure then vacuum so you have the mechanical advantage of a 10-12" piston assisting you to pressure the brakes more easily

Thanks Matt.

About a year ago I fixed a vacuum leak in the line to the booster and two things happened. The idle got better (what I was troubleshooting at the time) and the brakes got better (the problem I am working on now).

Now, I have about 18-20 "Hg at the booster, but there is no change in the pedal when I start the car.

Tomorrow, I'll recheck the vacuum and order the parts if the vacuum is still good.

 

[cruisermatt]

Thanks Matt.

About a year ago I fixed a vacuum leak in the line to the booster and two things happened. The idle got better (what I was troubleshooting at the time) and the brakes got better (the problem I am working on now).

Now, I have about 18-20 "Hg at the booster, but there is no change in the pedal when I start the car.

Tomorrow, I'll recheck the vacuum and order the parts if the vacuum is still good.

Ok, that's good info. Sounds like you need a booster.
One more question: with a axle on jack stands, engine off, spin a tire (any tire) by hand and have a helper hit the brakes, does the wheel stop?

 

[MatthewMcD]

Ok, that's good info. Sounds like you need a booster.
One more question: with a axle on jack stands, engine off, spin a tire (any tire) by hand and have a helper hit the brakes, does the wheel stop?

Fronts, yes, rears, no.

For folks just catching up. I replaced the Master Cylinder over a year ago before I knew anything about the different configurations of FJ40s. Turns out the master cylinder was for a 4 drum '75. I recently removed the front circuit valve to keep the front brakes from binding. That's why I am considering swapping to a CR master for discs and drums.

 

[pb4ugo]

I disconnected the vacuum hose to the booster and the valve works correctly. I attached a vacuum pump, drew about 10 inHg and it held that number for 30 seconds before I disconnected it.
[/ATTACH]

Bad booster? It seems to hold vacuum. Did you step on the pedal? Usually a bad booster will effect how the engine runs. You said you fix the vacuum line and it idled and ran better.

If your not getting brake fluid to the rear brakes, you need to find out why. A kinked line, bad soft line. Air in the rear master cylinder resoiviour or maybe its bad and not pushing fluid. Maybe a bad junction sucking air, but that would probably be leaking too. . When you bleed the rears, does the fluid in the rear resoiviour go down?

 

[MatthewMcD]

Bad booster? It seems to hold vacuum. Did you step on the pedal? Usually a bad booster will effect how the engine runs. You said you fix the vacuum line and it idled and ran better.

If your not getting brake fluid to the rear brakes, you need to find out why. A kinked line, bad soft line. Air in the rear master cylinder resoiviour or maybe its bad and not pushing fluid. Maybe a bad junction sucking air, but that would probably be leaking too. . When you bleed the rears, does the fluid in the rear resoiviour go down?

Yes, it did idle better, but it has been about a year. I don't feel any change on the pedal when I press and then turn on the engine.

When I bleed the rears, I see good fluid flow. I have to top up the rear reservoir, fluid is flowing.

 

[pb4ugo]

If you pump the pedal does it get higher?

 

[45Dougal]

I think you'll find that if you open the front bleed nipples so that the front circuit is left open, you'll now be able to lock up the rear wheels.
The mc piston is bottoming out on the disks before the shoes even reach the drum.
Doesn't the drum / disk MC use different piston diameters for each circuit?

 

[pb4ugo]

I think you'll find that if you open the front bleed nipples so that the front circuit is left open, you'll now be able to lock up the rear wheels.
The mc piston is bottoming out on the disks before the shoes even reach the drum.
Doesn't the drum / disk MC use different piston diameters for each circuit?

No. The pistons and cylinder are the same size.

 

[MatthewMcD]

If you pump the pedal does it get higher?

After about 6 pumps it starts to get higher, but it's a hard pedal.

 

[45Dougal]

No. The pistons and cylinder are the same size.

Ah I see, these are different to what I've worked with...
Is the front circuit always the one closest to the bulkhead then?