Brake System and Booster Troubleshooting (1 Viewer)

[MatthewMcD]

For those of you who followed my "Can't Drive 55" thread, thank you.

The issue was an improperly adjusted booster push rod. Now that the truck "goes" I need it to stop. I am working to get my brakes to perform better. The question was asked "When you stomp on the brakes, which wheels lock up?" The answer right now is "None of them".

To review. I have a 5/75 chassis, with a mini-truck front end (discs) and rear drums.
I resurfaced the drums and replaced the cylinders and pads last year (the first work I did on the truck).
I replaced the master cylinder shortly there after. (I have removed the front circuit valve from the MC as part of the troubleshooting for the previous issue.)
I replaced the front calipers and pads about 2 months ago when I did the knuckles.
I still have the old rubber lines, that I am planning on replacing for peace of mind.

I still have the booster that came with the truck:

I don't like "firing the parts cannon" but I am wondering if it's possible that the booster or the master cylinder are not doing their job. I wanted to ask these questions as I am about to bust out the FSM and run through the whole brake maintenance section to ensure that the pedal is right and the rears are adjusted correctly. Currently I feel a little drag on the right rear and only a tiny hint of drag on the left, so I know they need to be adjusted.

How can I test the booster to determine if it's up to the task?
Should I put the valve back in the front circuit of the master cylinder?

I did a full bleed before the last test drive and saw no bubbles and nothing but clean clear brake fluid.

 

[pb4ugo]

Rear brakes effect the pedal height. When they're adjusted up, the pedal should get a little higher. You can see if the booster holds vacuum. I wouldn't exceed manifold vacuum. If the pedal gets higher when you pump it up, means there's still air in the lines. Your hoses are 50 yrs old, that would be at the top of my list. If you have a lift you should consider getting longer soft lines going from the frame to the axle.

 

[45Dougal]

You can disconnect the vacuum line to the booster and see if its worse, but I'd start by adjusting the rear drums and then rebleeding the front disks.

Stupid question, but I see lots of references to "mini-truck" and I've never heard that here - is this the same as a Hi-lux?

 

[pb4ugo]

You can disconnect the vacuum line to the booster and see if its worse, but I'd start by adjusting the rear drums and then rebleeding the front disks.

Stupid question, but I see lots of references to "mini-truck" and I've never heard that here - is this the same as a Hi-lux?

1st gen mini pick up, 1985 and earlier. Axle width was the same as an fj40, but had a smaller ring gears. The rear was centered.

 

[45Dougal]

1st gen mini pick up, 1985 and earlier. Axle width was the same as an fj40, but had a smaller ring gears. The rear was centered.

This sounds like a hilux - maybe it was called mini truck in the US initially? Or is this a separate model line?

 

[pb4ugo]

I don't recall if it ever had a name.

 

[45Dougal]

Ok thanks.
I'm pretty sure it's one of these, but reluctant to rush out and buy one without being certain

 

[1911]

This sounds like a hilux - maybe it was called mini truck in the US initially? Or is this a separate model line?

Yes, the same basic 22R-powered truck.

 

[45Dougal]

Yes, the same basic 22R-powered truck.

Thanks.
And sorry Matt for hijacking your brake discussion

 

[hobbes]

“Mini trucks” were/are good for poaching disc brakes and power steering for FJ40s. While not sold in huge numbers, they were easier to find in junkyards than late model year FJ40s.

Photo below courtesy of Bring a Trailer.

 

[hobbes]

If your booster is bad and you want to keep it, Power Brake Booster Exchange rebuilt mine back in 2018 for $230. CityRacer has a great selection of newer options. I’d probably just get a CityRacer one if I did it now. More boost.

Vacuum Brake Boosters | Power Brake Booster Exchange, Lynwood

Power Brake Booster Exchange rebuilds vacuum brake boosters and supplies hard-to-find booster parts. Find out more about our services online today.

www.powerbrakebooster.com

 

[MatthewMcD]

You can disconnect the vacuum line to the booster and see if its worse, but I'd start by adjusting the rear drums and then rebleeding the front disks.

Stupid question, but I see lots of references to "mini-truck" and I've never heard that here - is this the same as a Hi-lux?

Not sure, that's what everyone called it when I was working on suspension issues. The front axle is from a 60 series, '84ish I believe.

 

[MatthewMcD]

Thanks.
And sorry Matt for hijacking your brake discussion

I learn from every question asked, no worries.

 

[MatthewMcD]

If your booster is bad and you want to keep it, Power Brake Booster Exchange rebuilt mine back in 2018 for $230. CityRacer has a great selection of newer options. I’d probably just get a CityRacer one if I did it now. More boost.

Vacuum Brake Boosters | Power Brake Booster Exchange, Lynwood

Power Brake Booster Exchange rebuilds vacuum brake boosters and supplies hard-to-find booster parts. Find out more about our services online today.

www.powerbrakebooster.com

I will go with CityRacer if I do need to replace it, but I hate replacing parts that don't need it. Worse, I hate the feeling of working for hours only to find that the old part works the same as the new part and the problem is something else.

I prefer solid diagnostics and incremental improvement.

That said, I am planning on replacing the brake lines. That will be the last "old rubber" on the truck.

 

[charliemeyer007]

Hear Hear. The adventure is in the doing, learning new skills often translate into solving new problems faster. Everything breaks at some point and there might come a time when you can't buy it in stores, then fixing stuff will come into own.

 

[hobbes]

I hate replacing parts that don't need it. Worse, I hate the feeling of working for hours only to find that the old part works the same as the new part and the problem is something else.

I prefer solid diagnostics and incremental improvement.

1000% concur.

And I’ll add sometimes the new part that didn't fix the problem isn’t as good as the old part.

 

[MatthewMcD]

1000% concur. And I’ll add sometimes the new part that didn't fix the problem isn’t as good as the old part.

Adding insult to injury.

I am actually leaning toward the Master Cylinder as I was not aware of all the differences when I bought it. (Hence removing the front valve.) I have heard that a Brake Proportioning Valve can improve the distribution of hydraulic pressure. But aside from "trying it" how do you know?

 

[MatthewMcD]

Hear Hear. The adventure is in the doing, learning new skills often translate into solving new problems faster. Everything breaks at some point and there might come a time when you can't buy it in stores, then fixing stuff will come into own.

Critical thinking and troubleshooting is the "lost art". Many years ago I attended factory training for OMC (Evinrude and Johnson engines). The trainer spent the first 3 days teaching us troubleshooting before we started tearing down and rebuilding engines. He kept telling us that for every engine that you get to tear apart and rebuild, your will be asked to troubleshoot 20 engines. He's also say that the ECU (brain) NEVER is the problem, it's always something else, but most untrained technicians swap the ECU first. He taught us how to do the diagnostics on the engine, so you can rule it out efficiently.

Then on the final exam, we had to troubleshoot and tune 10 engines. 2 of them he had installed ECUs that he had intentionally damaged. His final lesson was "never say never".

 

[45Dougal]

Adding insult to injury.

I am actually leaning toward the Master Cylinder as I was not aware of all the differences when I bought it. (Hence removing the front valve.) I have heard that a Brake Proportioning Valve can improve the distribution of hydraulic pressure. But aside from "trying it" how do you know?

Our annual test centres perform a brake test in the shop and give you a readout of breaking force balance - I guess you have the same?

 

[pb4ugo]

Our annual test centres perform a brake test in the shop and give you a readout of breaking force balance - I guess you have the same?

No. Any testing would be done by the individual States. Some States that do testing, seem more concerned about what comes out of the tail pipe. I think there are a few that take a deeper dive into safety.