I can't drive 55

[MatthewMcD]

@MatthewMcD did you find it necessary to use a rear brake proportioning valve or is there none?

I received the truck this way. I don't think there are any valves in the brake system external to the master cylinder.

 

[45Dougal]

Right, but as I said earlier, this truck has a mini-truck conversion in front. Discs in front, drums in back.

I think that's the point; you've got a 75 master that was designed for drums but you're using it with disks.

I'd be pulling the master off for inspection at this stage.

Open the bleed nipple and see if the drag goes away.

 

[pb4ugo]

@MatthewMcD did you find it necessary to use a rear brake proportioning valve or is there none?

Typically you use an adjustable proportioning valve for the rear circuit if rear disc brakes are adapted.

As @45Dougal said, it's drum master with frt discs. There should be a residual valve in both circuits, frt and rear for drums. The frt one should be removed with discs. #9.

 

[pb4ugo]

If you still have rear drums, leave the valve in the circuit for the rear.

 

[MatthewMcD]

Typically you use an adjustable proportioning valve for the rear circuit if rear disc brakes are adapted.

As @45Dougal said, it's drum master with frt discs. There should be a residual valve in both circuits, frt and rear for drums. The frt one should be removed with discs. #9.

View attachment 3752315

So undo #9 and remove the spring and check valve?

 

[hobbes]

When you stomp on the brakes do the front or rear wheels lock up?

If needed, a couple examples of proportioning valves are linked below. I went with the second one as it was simplest at the time. Now that its available, I would go with the Wildwood product since it offers adjustability.

Wildwood Adjustable Brake Proportioning Valve with Toyota Adapters for Any Toyota

Wildwood adjustable brake proportioning valve supplied with 2 port adapters that enable direct plug-in of Toyota brake lines. This new generation of adjustable proportioning valves combines the latest refinements to deliver precise pressure metering and strength from a compact forged billet...

www.cityracerllc.com

Brake Proportioning Valve for '76 to '80 Land Cruiser FJ40

OEM style brake proportioning valve for '76 to '80 Toyota Land Cruiser FJ40. Prevent rear brake lock-up and bring back your brake performance. Reproduction of OEM part # 47150-14010. Plug and play replacement for your original valve. For vehicles with stock front disc / rear drum brakes setup...

www.cityracerllc.com

 

[Pighead]

So undo #9 and remove the spring and check valve?

yes.

 

[Ocho77]

This is from a 2015 thread...seems like potentially a similar problem. I've read your entire thread, but don't remember all that's been replaced.

"I fought the same problem for awhile. It was solved by a new fuel pump. Even with the "pull the line and see how it pumps test" it seemed fine. Idled fine, ran at low speed fine. Hit 40 plus and it bogged down. I replaced the fuel pump with a OEM and its been fine since. The pumps are not cheap now but get an OEM if you can. 35 + years is pretty good for any part!"

 

[pb4ugo]

So undo #9 and remove the spring and check valve?

What @Pighead said, Yes. It should be the frt reservoir, to be sure, follow the line and be sure it goes to the frt brakes. You should only have to bleed the front brake calipers when done. I'm not sure this will stop all the dragging or not. Take it for a test drive and then check to see if the hubs and rear brakes are not hot. Slightly Warm is ok, but not hot, unless youve been riding the brakes. As I mentioned earlier, if they're hot, jack up each hot hub/tire and check if they are dragging. I still suspect the adjustment rod maybe putting pressure on the newer master cylinder.

 

[Mr. Green]

Front discs would be hot too not just hubs. If easier than fiddling with master, could test by pulling over on long straight, bleed out fronts quick and drive again without touching brake pedal to get new top speed. This master residual sounds like the culprit. I would think you’d notice it when coasting as well with clutch in.

 

[zerotreedelta]

Interestingly enough, might be an unfortunate combination of things working together. Domed heads are losing HP, so any brake drag from the disc conversion would be more noticable than normal.

 

[rkymtnflyfisher]

Locked brakes would be obvious by the smell, as well as other symptoms. My fronts locked tight after swapping a master due to the push rod being out of adjustment, there was no denyingthe brakes were tight. I'm not buying into the brakes being the issue.


I'm interested in the wheel bearings at the moment.

I'd pull one and see if they have spun on the spindle. 2 beer job tops.

 

[MatthewMcD]

I'd pull one and see if they have spun on the spindle.

Not sure what you mean by this.

 

[MatthewMcD]

What @Pighead said, Yes. It should be the frt reservoir, to be sure, follow the line and be sure it goes to the frt brakes. You should only have to bleed the front brake calipers when done. I'm not sure this will stop all the dragging or not. Take it for a test drive and then check to see if the hubs and rear brakes are not hot. Slightly Warm is ok, but not hot, unless youve been riding the brakes. As I mentioned earlier, if they're hot, jack up each hot hub/tire and check if they are dragging. I still suspect the adjustment rod maybe putting pressure on the newer master cylinder.

Making progress.

I pulled the valve from the front circuit and then blead the brakes and took it for a test drive.

Top speed was 65 MPH. Feels more nimble and certainly runs better in 3rd. In 3rd I can cruise at 40-45 at about 25-2800 RPM. In 4th I can hit 2800 RPM and cruise around 60, 65 if I am going down hill.

Hubs are still hot to the touch, but I don't think they are as hot as before.

I'll have a look at re-adjusting the push rod. I did take my time during installation and measure the depth of the push rod. May have cut it a bit too close.

Would the "right" master cylinder (like the one from City Racer) make a difference at this point?

 

[RevISK]

Making progress.

I pulled the valve from the front circuit and then blead the brakes and took it for a test drive.
View attachment 3752570
Top speed was 65 MPH. Feels more nimble and certainly runs better in 3rd. In 3rd I can cruise at 40-45 at about 25-2800 RPM. In 4th I can hit 2800 RPM and cruise around 60, 65 if I am going down hill.

Hubs are still hot to the touch, but I don't think they are as hot as before.
View attachment 3752573

I'll have a look at re-adjusting the push rod. I did take my time during installation and measure the depth of the push rod. May have cut it a bit too close.

Would the "right" master cylinder (like the one from City Racer) make a difference at this point?

You had better be making “pew pew” noises when shooting that thing.

 

[rkymtnflyfisher]

Not sure what you mean by this.

See if the inner race of your wheel bearings have spun on the spindle.

 

[rkymtnflyfisher]

The only pics I can find of mine.


Last time I was in my front axle I found signs of my wheel bearings spinning on the spindle. Most likely due to improper preload.

 

[pb4ugo]

Were the rears hot? Did you jack it up to check resistance to spin?

 

[45Dougal]

Making progress.

I pulled the valve from the front circuit and then blead the brakes and took it for a test drive.
View attachment 3752570
Top speed was 65 MPH. Feels more nimble and certainly runs better in 3rd. In 3rd I can cruise at 40-45 at about 25-2800 RPM. In 4th I can hit 2800 RPM and cruise around 60, 65 if I am going down hill.

Hubs are still hot to the touch, but I don't think they are as hot as before.
View attachment 3752573

I'll have a look at re-adjusting the push rod. I did take my time during installation and measure the depth of the push rod. May have cut it a bit too close.

Would the "right" master cylinder (like the one from City Racer) make a difference at this point?

Now point it through the hole in your wheel at the disk. Is the disk the source of heat or not?

 

[pb4ugo]

Did you measure temps on both front wheels? Rears? I'm just trying to figure out if it's 1 wheel or maybe more, so we can isolate thr problem. I think 147* is way too much.