3B Vacuum Diagram/Problems (1 Viewer)

[torqueluvr]

Hi All,

I have a FJ75 with a 3B in it I'm trying to get up and running, and I'm having some issues with the brakes. Symptoms - very squishy pedal, but full braking power at end of stroke - pretty unnerving driving it. If I pump the brakes I loose all vacuum assisted braking and loose all power brakes. New parts:

- Brake booster
- Brake master cylinder
- Front calipers, pads and rotors
- Rear drums, wheel cylinders and shoes - adjusted properly

I'm thinking there's something wrong with the vacuum system. The pump on the back of the alternator seems to be working because when I pull the rubber line off (I pulled it off the brake booster on the other side) there seems to be good vacuum - it sucks my thumb good. However, I don't see any sort of vacuum storage canister in the system.

The PO swapped the 3B into this Troopy allegedly from a BJ60.

Is there supposed to be a vacuum canister to store vacuum? It seems like there's not enough vacuum for the booster - either a bad vacuum pump or no storage canister to store vacuum?

 

[Bandit_guy]

You need a reservoir to hold vacuum, the pump is insufficient to keep up. It does sound odd to say but you need a tank to store emptyness. The toyota reservoirs are often rotten out, you can replace it with 1 gallon air tank with fittings to install the pressure switches, or leave them out. Check the lines for leaks as well. With the engine off you should have five or six pumps before running out boost.

 

[torqueluvr]

Awesome, thanks. Sounds like I have some work to do.

 

[lacalvette]

There is usually two vacuum outlet on the vac pump. One for brake and one for clutch.
The outlet doesn’t have the same size, brake is bigger

 

[M1A1cruiser]

Related question, and hopefully not a hijack.

Is the vacuum reservoir literally just an empty tank?

That is, are there no check valves internal to the tank?

I know there's a check valve on the brake booster (at least the one I got from City Racer). And I understand that there are bungs on the tank (at least the Toyota one that I have mounted currently) for a vacuum switch that is wired in to the brake system warning light (along with pressure switches on the brake master cylinder if one has that style), but I'm curious about the internal requirements of a replacement tank, and/or ensuring that my original tank is doing what it's supposed to.

I suppose another way of asking the question is: does it matter which hose (FROM the vacuum pump, or TO the brake booster) attaches to which port on the vacuum reservoir?

Thanks for any clarification. I'm just not sure - after only having taken my project for a couple of test drives - if my vacuum assist is functioning properly or if I just have 40 year-old braking system (albeit with discs up front and all new components on the rear) that stops like a tractor!

 

[lacalvette]

There a check valve on the vac pump.
Not sure about réservoir but I don’t there is anything special on it. I may be wrong, I’ll have a look.

 

[Bandit_guy]

The tank is just a tank, nothing else but the fitting holes for the switch hose, connections and a drain hole. I replaced it with a small cylindrical tank and it works real nice. One small hole in the hose or steel lines and you will lose vacuum fast. To check if you have a vacuum issues on your breaks is to pump the pedal with the engine off until it's hard, start it with your foot on the pedal and feel if it goes down. If it doesn't move no boost, if goes down a bit turn off the engine and you should get 2 or 3 assisted applications and then rock hard. If you have vacuum leaks you will get a little breaking then after pressing down the pedal for a little while it will stiffen up but the breaking will suck. With front discs you get good stopping even with big tires.

 

[M1A1cruiser]

Thanks @Bandit_guy and @lacalvette .

Like I said, I'd read a dozen other threads on the vacuum assist for diesels and the tanks, but was never really sure if there were check valves within the tank that would help regulate the vacuum. Your test will be a good one for me to understand if my system is working effectively; I never really know if I'm just feeling 40 year-old brakes, or if there's something amiss.

Thanks to all for this valuable forum!

 

[Bandit_guy]

Here is the tank I put in. I still have to paint and mod some amour for it for wheeling but for driving around it's fine.

I have a hand vacuum pump for bleeding brakes/Clutches ect, (nothing fancy, bought it at Princess auto) but connected to the hose right off the altenator vacuum pump It's able to crate vacuum within a short while and I see the vacuum hold on the gauge. The pump isn't perfect so it bleeds down a bit but it's enough to see if the system is tight. I had a tiny crack in my Toyota tank and pin hols in the steel line and it was enough to give me some boost but after a short stop at a traffic light or repeated break use it was done. Let go of the break for a half a minute and just enough to give you confidence but than gone again. I replace the steel lines with 3/8 stainless and new hoses and if I stomp on the pedal all four wheels lock up even with my 33"s.

 

[lacalvette]

The vacuum reservoir also have check valve