Just bought another 1986 Toyota pickup. Occasionally when you press the brake pedal down it will pop and depress a bit more before adding more pressure to the brakes. My previous one years ago had a similar issue but I don't recall the cause. For some reason I think it may have been the proportion valve under the bed. May be a common problem. Any input?

 

Does the pop only happen when the engine is running (meaning you cannot get the brake pedal to "pop" when the truck is off)?

I recall forum member @RAD4Runner has the same problem. I don't believe he has found the cause yet.

There are only a few parts that could cause this, with the brake master cylinder or brake booster being the top suspects.

Just to be sure, check your brake pedal assembly to make sure it cannot bind while being depressed.

 

Check your brake pedal mounting bracket for cracks near the pivot.
Have a helper press the pedal while you look under the dash for flexing/movement.
If that doesn't reveal anything check your rear brake backing plates for grooves where the shoes ride on the backing plate.
either of these could cause your issue.
Do you hear a pop or just feel it?

 

I feel it. Ill have a look underneath at the pedal assembly.

 

Mine did not feel like a metallic / mechanical hard pop or snag. Feels more like a smooth notch - like the different positions of the headlight switch.
When it happens, I would go to full stop, release brake, press again, release and press. Each time, the notch would feel less and less until it is gone. I have never felt it with engine off, so more likely vacuum related. I haven;t had the chance t take things apart; would rather have all necessary parts to replace before taking things apart.

 

Rad, have you looked at your rear brake backing plates? If your rear brakes are adjusted fairly loose and there are deep grooves in the landings where the rear brakes ride it could cause what you are describing.

 

I have this problem and just found this thread. 1991 Toyota Pickup SWB FS17 front brakes with OEM 7/8 Master Cylinder. I replaced the master cylinder (which was only 2 years old) again last weekend with another OEM Advics and it's still there. I also did a full brake fluid flush and bleed as well last weekend. Not every brake pedal push and not the same every time. I'm now leaning toward wheel cylinder(s) (replaced two years ago) or maybe the rear brake valve?

 

If you mean the LSPV, definitely could be the cause. Did you bleed that (last) when you bled the rest of the system? You might want to remove it, take it apart, and clean it out. They often gather huge amounts of crud and corruption in it, even with regular flushing.
As a possible alternative to taking it off, and then apart, you can try removing the axle end of the bar that connects the axle to the LSPV, and the move it up and down through it's entire range, while bleeding the LSPV. It should only take 3-4 swings to get most of the crud out.

Worst case, if it IS the problem, replace it. Use ONLY OEM part to replace it with. It's not that expensive, really. Avoid the Chinese made aftermarket parts like the plague. They will fail rapidly.

Good luck, and keep us updated!
Pat☺

 

did you check the items I listed in post #3?

 

I forgot about bleeding/flushing that LSPV so thanks Pat! I did that this afternoon and then bedded in some new front pads. So far so good but I will know more Friday when I drive it again. Thanks.

 

My problem was 100% the LSPV. Also, heed the advice of only using a Toyota replacement. I tried a china one at first and it had a whole set of other problems. Once I installed the stock replacement everything was fixed. Sorry it took me so long to reply.

 

Hope everything is going, or stopping anyway, well for you.
Always remember to bleed out the LSPV last when bleeding the brake fluid. Move the bar going down to the axle repeatedly before, or while, bleeding the LSPV. Helps move the valves inside around, and frees up the gunk and gnrrr so it comes out with the old, cruddy brake fluid, and air, if any.

Have fun!
Pat☺

 

Folks, I had *exactly* this issue as described by the OP, and it was fixed by replacing the LSPV.