Brakes flagging (1 Viewer)

[IDave]

My 84 Hilux' brakes are showing some weakness. When I press on the brake I get good stopping, then the pedal slowly sinks to a lower point where I have good pedal and braking.

Typically, I'll come to a stop sign or light, stop smoothly, then, as I'm waiting with my foot on the brake pedal, it slowly sinks another inch or two. Let go, and it returns to normal immediately and we start over.

Plenty of fluid in the reservoir. No visible leaking.

Vacuum booster checks correctly (Firm pedal, sinks a little on start) but then the pedal sinks.

Stops straight. No chattering.

I'm thinking perhaps just air in the line, but I'm not sure. Is it likely to be one of the check valves?

 

[KLF]

Your Master Cylinder needs to be rebuilt. Fluid is slowly leaking past the cups. Either the inner bore of the cast part is corroded/scored, or the cups are just plain worn out, or both. You can get a rebuild kit from Toyota, the procedure is in the FSM.

 

[IDave]

That's it? Couldn't be the LSPB (can't rebuild, I know: worse outcome)?

I might also swap in the spare master I have on hand, if that's the case.

THANKS!

 

[WristPin]

the LSPV's have been known to leak. use a thumb tack to puncture a hole in the boot to check for fluid.

your symptoms are describing faulty master cylinder, too.

 

[IDave]

I'd wondered about that. We'll start with the MC.

Thanks!

 

[2ndGenToyotaFan]

I'll say MC as well, sounds like the pedal is slipping down to where the bore isn't as used and getting a good seal there maybe.....

 

[IDave]

Makes perfect sense

 

[IDave]

Well, the new master fixed it. $80 for a new US made from NAPA: that a good choice? I decided since it was my daughter's truck that that was the fastest source. So there we are. Thanks again, everyone!