Help! Vacuum system down

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Oct 19, 2004
Tannhauser Gate
It seems the vucuum system went wacky all of a sudden on the way home. My stereo was shorting out, and I found out that it was the ground line being pressed under the clutch pedal. So I move the wire, and depress the clutch a couple of times to see if it is still hitting the wire (with the engine off). Turn it on, and find the clutch was real stiff, turned the engine off, keeps running. No vacuum to the clutch booster, or VSV. Had this happen to me at CMCC last year, but it cleared up before I could figure out the source of the problem. The vacuum system on the 13BT is a complete mystery to me. The Max Ellery manual (POS), doesn't say much about the vac system, and I only have the Toyota chassis manual. Where do I start? How do I test the vacuum components?
1st. See if the downloads at Birfield are working and download the 3B/13BT engine manual for future reference, however the vacuum pump detail is on BR25 of the 36262E chassis manual.

The vacuum system derives it vacuum from the vacuum pump hanging off the rear of the alternator. There are three vanes which cycle around in an oil bath. You have a small vacuum canister in the engine bay which will give you a couple brake or clutch applications, then be used up...hence your hard pedal after two tries.

Typically, if you have a small vacuum leak, even when running the pump should keep up. Follow the entire vacuum line and see if there are leaks anywhere. Pull the vacuum hose off the vacuum canister after you have run it for a while, with no applications. You should hear the air rush in, indicating there is some vacuum. If not, look to your vacuum pump. Then go to BR26 to get into the pump. Be gentle with the vanes...If your vacuum pump splines are pooched, or if the splines on the alternator shaft are not fret. They are available. Either source them yourself, or give us an e-mail. 1st thing 1st though...


Ok, I presume you know where the vac pump is. On it you have 2 lines, suction, discharge(pressure)

Track the lines to the clutch booster. Look for any check valves in the system. Possible one is blocking partly. I also do not know your system. Just trying to help.

Obviously it is not making vacuum(or vacuum drawing to where the booster or vsv get it). Start simple, by figuring out the vacuum line on the pump, pull off the line, start the engine feel for vacuum on the hose with your finger. connect the line and move further along, till you reach the clutch booster.

Also do your brakes get vacuum? These are simple lines to trace. There has got to be a block in your system. Or the pump is failed.

Start pulling the lines to see.
well, lookie here... page BR25, I never noticed that :). The brake booster was fine, just vsv and clutch booster. I say was, because the problem suddenly cleared up again for no apparent reason. I am very suspicious of that check valve, that seems to be the most likely culprit for intermittent trouble. I just stated pulling hoses and putting vac. guage on. Vsv seems to get 27"Hg, pretty impressive, 30 being a total vacuum. Another line from what appeared to be the main out on the vac. pump only read 5"Hg. But all appears normal again for now, vsv and booster working fine now???? Isuspect a blockage of some sort, as opposed to the whole pump failing, because the brake booster woked fine the whole time. Man, I only need to get another week or so out of this unit, then I'll take it off the road for total redux:)
I would look at the checkvalve. pull it off and do the blow test thru each way..see that it does whats supposed too.
Whats a vsv?

Vacuum Switch Valve. Shuts off the engine by evacuating a diaphragm which pulls a rod connected to a butterfly valve which starves the engine of air. No vacuum, no engine stop. Older big diesels have a manual rod for shut off. Vacuum system is still back to its old self, must have a piece of duff floating around in the system.
Is this where 3bs differ from most diesels? I thought the 3b diverts fuel thus starving the engine for fuel, no fuel, no run. Unlike a positive air shutdown which is required at almost every hydrocarbon plant I have worked at.


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