Hj61 (12ht) vacuum pump troubleshooting (1 Viewer)

[Silveredition]

Hi all,
I have a 1988 Hj61 with the 12ht engine (5 speed manua)… this engine has the vacuum pump on the alternator which is driven off an oil feed line.
I am currently having issues (a heavy clutch and brake pedal) when idling or the revs are low.
I am wanting to do some troubleshooting before I spend money of a new alternator…
So far I have checked for leaks in the vacuum lines (as much as I can) - including spraying all connections with CRC Soft Seal which should seal up any small leak, I also removed the oil feed and return lines to ensure there are no blockages (all looks good).
I am wondering if the oil feed has a feed rate at idle (a certain amount of ml per minute???)
Also, what should the vacuum pressure (vacuum?) be at idle??

The alternator was new at the end of December and everything was working fine until a couple of weeks back when I noticed the heavy pedal of both clutch and brake….

Any thoughts or info would be greatly appreciated!!

Drew

 

[jblueridge]

Last time I checked with a vacuum gauge, my pump made about 23 inches of vacuum but it took a little time to get there. In theory, if you turn the truck off without pushing any pedals, the system should lose its vacuum slowly.
I did take my vacuum pump apart thinking to rebuild it but when I compared new parts to the old ones, they looked the same. The old pump “blades” had no wear since they are bathed in oil all the time.

Get a gauge and check the vacuum pump with everything disconnected except the gauge. Disconnect vacuum lines and plug them one at a time. It could be one of your boosters or vacuum actuators is damaged. My 13BT had a rusted metal vacuum line that I had to find.
I bought a 24V chinese alternator and it turned out to be a rebuilt Denso/Toyota with a 12HT vac pump. You can have that pump if you need it.

 

[Silveredition]

Last time I checked with a vacuum gauge, my pump made about 23 inches of vacuum but it took a little time to get there. In theory, if you turn the truck off without pushing any pedals, the system should lose its vacuum slowly.
I did take my vacuum pump apart thinking to rebuild it but when I compared new parts to the old ones, they looked the same. The old pump “blades” had no wear since they are bathed in oil all the time.

Get a gauge and check the vacuum pump with everything disconnected except the gauge. Disconnect vacuum lines and plug them one at a time. It could be one of your boosters or vacuum actuators is damaged. My 13BT had a rusted metal vacuum line that I had to find.
I bought a 24V chinese alternator and it turned out to be a rebuilt Denso/Toyota with a 12HT vac pump. You can have that pump if you need it.

Gday mate,
Thanks for the info!
This afternoon I am going to isolate each of the brake / clutch boosters one at a time to ensure it isn’t one of these… I will also buy a vacuum gauge and start to check lines one at a time…

 

[Silveredition]

In the limited time I had this arvo I:

Disconnected and plugged the brake vacuum line - still had a hard clutch at low revs. No brake light coming on and hard brakes (obviously)..

Disconnected and plugged the clutch vacuum line - hard clutch and still had the brake light coming on and limited brakes under low revs or repeated stabs of the brake pedal…

Hit everything with a hammer - still no improvements….

Sprayed CRC soft seal on everything I could until the can ran out… still no improvement

Next I will check the oil supply while running, drain while running, and anything else I can unbolt before ordering another alternator. Very frustrating!!

 

[kevin in okinawa]

Last time I checked with a vacuum gauge, my pump made about 23 inches of vacuum but it took a little time to get there. In theory, if you turn the truck off without pushing any pedals, the system should lose its vacuum slowly.
I did take my vacuum pump apart thinking to rebuild it but when I compared new parts to the old ones, they looked the same. The old pump “blades” had no wear since they are bathed in oil all the time.

Get a gauge and check the vacuum pump with everything disconnected except the gauge. Disconnect vacuum lines and plug them one at a time. It could be one of your boosters or vacuum actuators is damaged. My 13BT had a rusted metal vacuum line that I had to find.
I bought a 24V chinese alternator and it turned out to be a rebuilt Denso/Toyota with a 12HT vac pump. You can have that pump if you need it.

hello! where did you source that alternator from?

 

[jblueridge]

Next I will check the oil supply while running, drain while running, and anything else I can unbolt before ordering another alternator. Very frustrating!!

I am not sure how the constant supply of oil fits in with how the pump works. The alternator shaft does the most work. If you connect a gauge to the pump and plug all other pump inlets, that will tell you if the pump is bad. I am serious about giving you the vac pump I have here. See pics below.
The only way the alternator itself could affect the amount of vacuum is if the shaft broke or if oil was leaking into the alternator's internals.

hello! where did you source that alternator from?

24V alternator The link is in this thread. The short answer is China via AliExpress. It was actually a rebuilt Denso unit with one critical flaw that had to be fixed here.

 

[Silveredition]

I am not sure how the constant supply of oil fits in with how the pump works. The alternator shaft does the most work. If you connect a gauge to the pump and plug all other pump inlets, that will tell you if the pump is bad. I am serious about giving you the vac pump I have here. See pics below.
The only way the alternator itself could affect the amount of vacuum is if the shaft broke or if oil was leaking into the alternator's internals.


24V alternator The link is in this thread. The short answer is China via AliExpress. It was actually a rebuilt Denso unit with one critical flaw that had to be fixed here.
View attachment 2960447

Thanks heaps for the offer!! It is really appreciated, but I thing the freight and time from where you are to the South West of Western Australia might be a bit too much!!
I will carry out another couple of tests this weekend - then it might be a new alternator!

 

[Silveredition]

Well, I have just purchased a vacuum gauge, and carried out a few quick tests….
I assume that the readings (at 850rpm - 13 in-hg, at 1000rpm 15 in-hi and at 1200rpm 17 in-hg are all lower than what they should be?? I have read at idle that it should be 26 in-hg. Is this correct?
Also, can I unbolt the vac pump from the back of the alternator and take the vac pump apart easily to have a look inside?

The alternator was new at the end of Dec, so is still under warranty, but I don’t want to replace it only to find I have the same issue!!

 

[jblueridge]

Yes there are 3 bolts and the oil drain line to get loose then the pump can slide off the shaft. Oil will spill when you get it loose from the alternator so have towel ready beneath. Inside the pump are 4 small planks of carbon that can slide outwards and inwards. The manual tells you the dimensions they should have so you can measure and see if they are worn. My pump "vanes" had zero wear after all those years.

Maybe check this first:
At the top of the vac pump is a fitting of multiple tubes to attach vac hoses to. That mini manifold has to be tight to the pump with copper washers above and below it as seals. Look to make sure copper washers are there and check top bolt tightness. It could be the manifold itself has a cracked tube or something.

 

[jblueridge]

If you do remove the pump, be careful with the thin o-ring that is between it and the alternator. It is an oil seal. Spaghetti thickness and maybe 70mm diameter.

 

[Tufve]

@Silveredition any progress on the issue? I have a similar problem. Changed calipers+pads, master brake cyl and exchange my oem brake booster to a dubbel diaphragm booster. Tested vac all good with 26 in-hg of vacuum. As soon as I hit the brake at idle vacuum drops to around 5 in-hg and starts to rebuild. This gives me 1 good brake application and poor 2nd and a very poor 3rd.
I do suspect the pump not efficiently build up a vacuum pressure quick enough to give me multiple brake applications. Could be a low rpm vacuum pump issue, ie shaft issue?

 

[jblueridge]

Most probably it is because the larger brake booster uses more vacuum than the pump was designed for. I added another vacuum reservoir which helped the problem.

See post #17. vacuum

 

[Knowbuddy]

I am not sure how the constant supply of oil fits in with how the pump works. The alternator shaft does the most work. If you connect a gauge to the pump and plug all other pump inlets, that will tell you if the pump is bad. I am serious about giving you the vac pump I have here. See pics below.
The only way the alternator itself could affect the amount of vacuum is if the shaft broke or if oil was leaking into the alternator's internals.


24V alternator The link is in this thread. The short answer is China via AliExpress. It was actually a rebuilt Denso unit with one critical flaw that had to be fixed here.

View attachment 2960445

View attachment 2960447

Any alternator shop could rebuild your original alternator if you still have it. Is your 61 internally or externally regulated?

 

[Knowbuddy]

I actually do have an oem extra Alt but I’d be super hesitant to let it go.

 

[Silveredition]

I have been meaning to follow up on this thread…

I ended up taking the car to a mechanic. They confirmed that it was holding vacuum at all points it should, there was very little vacuum at idle and increasing with revs. They also found out that oil was being supplied to the vac pump - but not returning to the engine (a blockage in the vac pump).
I returned the alternator to Repco (was still under warranty) and fitted the replacement they gave me and it has been perfect since!!!

 

[jblueridge]

Thanks for the update.