Thread: Should I replace a badly leaking (oil) vacuum pump?

Originally Posted by Young Angus

Vacuum pump leaking oil pretty badly...should I replace this or just keep cleaning up the mess and leave cardboard under it?

If you're good at DIY then try some repairs.

The pump uses engine oil to lube the plunger. In normal operation some oil gets past the plunger into the cylinder, and gets returned to the engine block along with the air being evacuated from the booster. Oil in the pumping system is not a sign of pump failure, although if excessive could be a worn piston o-ring.

The most common leak is between the cap and main body caused by stretched rivets. There are articles on replacing cap rivets with tensile bolts, although the bolts will also eventually stretch and need re-tightening. An easy fix.

There's less information on fixing leaking welch plugs. If you can, then find better replacement welch plugs. There are two large welch plugs on the cap and one small one on the side of the main body. I threaded the two cap holes on a lathe and made some giant threaded 'grub screw' type plugs to fit, firmed up with some wraps of plumbers tape. The small hole on the side of the main body was easy enough to hand tap and fill with a bolt. Make sure air flow in passage ways are not blocked by what ever repair you undertake.

I think you can also buy plunger o-rings, but is an issue I've not had to deal with yet

There are two poppet valves, one under each welch plug in the cap. Only when a poppet valve fails do I consider throwing the unit. If the crimping fails then the poppet will drift loose and get smashed to pieces. Sometimes the poppet will remain in place, but fails internally. I've not found a source of replacement poppets; and also there is little 'meat' on the rim of the hole in which they sit to use as crimping material to secure new ones. If you have oil coming out of the left welch plug in the cap then its more than likely the poppet underneath has failed - oil should not normally go that way, toward the booster. You can expect oil out of the right welch plug in the cap and the small plug on the side of the main body, as this is the correct path for the oil/air mix returning to the engine block.

If the unit is also noisy or banging then there are two grub screws at the back of the unit that may need re-tightening. They sit in two small holes, and if it weren't for them drifting loose and exposing themselves you would not know they were there. From memory they secure a collar, which if comes loose starts to bang in response to the movement of the piston.

A new unit is no guarantee of securing a leak free environment. A new unit leaked on me from the outset, through a very loose welch plug.

Some owners replace the cam driven pump with an electric unit.

Wow. What a fantastic reply. There i was thinking they were just a basic cam driven piston hunk of metal and now it suddenly seems much more interesting. Thank you for that. It’s nice to learn the finer details of these machines. Thanks to OP for posting original question too.

Originally Posted by Fausto79

Wow. What a fantastic reply. .....

+1

I had a leak, which left over a couple of months appeared to be a bad one.
But cleaned up every week(just wiped with a rag) .. it wasn't so bad. Just a single 5c drip on the ground over night.

I just cleaned up the around the welch plugs thoroughly, siliconed them over, and leak gone(or stopped .. or kept internally).

On a drive the leak was incessant enough that it'd spray oil all the way down the side of the block and onto the tans and transfer case .. making it look like everything was leaking badly.

Originally Posted by AK83

+1

I had a leak, which left over a couple of months appeared to be a bad one.
But cleaned up every week(just wiped with a rag) .. it wasn't so bad. Just a single 5c drip on the ground over night.

I just cleaned up the around the welch plugs thoroughly, siliconed them over, and leak gone(or stopped .. or kept internally).

On a drive the leak was incessant enough that it'd spray oil all the way down the side of the block and onto the tans and transfer case .. making it look like everything was leaking badly.

i think i may have that now. driver side is very dirty and there seems to be a mist of spray all over steering shafts and aircon lines etc. and lots of oil down near gearboxes (possibly from different leak). i thought maybe one of the lines to oil cooler has small split, even though they are only 2 years old.

might have to check the pump then. i know a few weeks ago when idling or going slow in first or reverse that i would lose vacuum assistance on my brakes, but that seems to have gone away now. i thought might be due to vacuum leak somewhere or one of the two bigger components on it's way out.

I am in process of upgrading brakes to vented and was going to change a lot but wanted to keep booster and vacuum pump until the brake issue appeared. now it's gone though i am thinking to just check out VP and fix any leaks and to replace all the vacuum lines and see how that goes.

really sorry young angus. i know it's your thread.

I used the copper coloured Permatex silicon on my VP welch plugs.
The thinking was .. 1. that's all I had .. and being copper coloured it'll show the thick black coloured sludge usually associated with diesel engine oil!
So whenever I pop the bonnet, it's now easy to see if there is any blackening on the 'two large orange dots' on the VP now .. so far so good .. close to 12 months or so now.

Being all matt black originally, in the pump it's hard to distinguish freshly dripping oil until it's too late, and it's all over the place.

Originally Posted by Fausto79

... i would lose vacuum assistance on my brakes...

Do you have ABS? One of my vehicles has ABS and was the cause of loss of braking when first starting after a prolonged stand ie next morning going to work or after work going home. The lack of brake lasted for 50 to 100 metres before some banging noise from the ABS unit restored braking. This ABS issue could be mistaken for lack of servo assist.

If your booster diaphragm is punctured then sometimes this may be confirmed if you hear a faint whistle coming from inside the footwell where the brake pedal goes through the firewall. Harder to hear on the engine bay side with engine running, although the noise may persist for a bit when engine is shut down.

Originally Posted by AK83

I used the copper coloured Permatex silicon on my VP welch plugs.

I'm puzzled why the pump can generate forces sufficient to stretch rivets or replacement tensile bolts holding the cap, yet doesn't blow out poorly fitting welch plugs on the route to the engine block. Could the poppet or channel on return to the engine block be too small for the task?

From memory the pump shaft is spring loaded against the cam. Some recommend putting extra gaskets between the engine block and the pump unit. The idea is that the extra gaskets move the pump unit further away from the cam, taking some pressure off the cam and piston shaft contact, and consequently pressure off the cap.

Fantastic discussion and info, wow, who knew!

I was more just asking if it's something you should replace because it will fail soon after leaking badly and leave you with no brakes, or something like that. I'm not in a place right now to be able to do repairs myself but one day I'll have a garage again I can make a mess in. So I'm just getting the garage to replace it.

Great discussion though!