Bizarre Vacuum Pump Damage - seizing I-shaft

[the vegenator]

After reassembling my engine and test driving my car a few times, I noticed the brakes had no vacuum assist. Today, I pulled the vacuum tube and found there was absolutely no vacuum being pulled with the engine at idle. I pulled the cover off and found stuck vanes, plus the top of the rotary assembly was marred up.

I managed to free up the vanes and I used a dremel to deburr the edges of the rotary unit. The bottom of the cover plate had some chewed up areas that were protruding, which seemed to be a possible cause of the damage. I cleaned it out, oiled it up and reassembled it. Took the car for a test drive and had good braking power for about 20 seconds, until I lost the vac assist and simultaneously heard some belt squeal and watched the oil gauge drop to zero for a split second.

I took the vacuum pump back off, and repeated the above procedure, also making a better effort to complete polish up the bottom of the cover plate. I cleaned it up and tested by hand. The unit was spinning just fine. I put it back in and took it for another test drive, lost power brakes immediately and heard more frequent belt squeals and saw the drops in oil pressure. I parked it and looked under the hood with the engine at idle - with higher rpms that intermediate shaft pull would definitely seize up. When I pulled the vacuum pump back out, it was EXTREMELY hot, and looked like this:



Obviously, I need a new vacuum pump. But this problem baffles me - I never had an issue with the same vacuum pump before. The oil pump spins fine, and the rotary part of the pump spins freely when you take the unit out. But while its in there, something is causing parts to grind together unlike before.

Also worth noting - there is about a quarter inch of play in the shaft of the vacuum pump. Up and down play, not side to side. The oil pump shaft has some wear on it - probably from the vacuum pump seizing? - and some metal shavings were found around the oil pump shaft.

Any ideas? Will a new pump solve my problems? Anything more to be worried about?

I'd love any advice or suggestions on this - I'm so close to driving this thing around!

[82vdub]

I believe there's an early and late style vacuum pump, one with a longer shaft than the other, or something like that. You may be able to search the forum and read what it was. I think fatmobile posted that comment. If this is the same pump that was in there before, then the pump isn't the issue. Either that or there's a difference in the oil pumps, one with a longer shaft than the other. My only other thought is that when the vacuum pump was installed, it wasn't properly seated with the oil pump shaft, creating up-pressure on the vacuum pump shaft when you tightened down the bolt holding the vacuum pump in.

As you found out, when the vacuum pump quits spinning, so does your oil pump. The intermediate shaft spins the vacuum pump, which drives the oil pump shaft.

[the vegenator]

The oil pump and vacuum pump both came off my old block. The replacement block is likely newer - it has the two oil drains sticking off the front. When I installed the vacuum pump, it seemed securely mounted in place. It seems like this combination - the oil and vacuum pump from a 1985 block, installed onto a hydro block - would work just fine. Which is why I'm dumbfounded.

I'll look into the post on different shaft lengths. And I will continue looking online for vacuum pumps.

[Quantum-man]

Shouldn't there be a pin that stops shaft going up and down. If free to travel up, it's bound to scrape the lid. Is the fault resulting from damage to the oil pump. Either it seizing or the slot being tapered, wedging the vac pump out.and breaking the pin [if it exists ]
There only seems to be one vac pump across the years

[the vegenator]

I'm not sure of any pin, since I don't have other pumps to compare it to. I ordered a used one on ebay which will hopefully solve my problems. I spent more buying one from the seller that had the nipple on the cover plate intact. The seller said that the other pumps (without a nipple) had a little up/down shaft play.

It blows my mind that I never had a problem with this before the rebuild. Everything seems normal and in place, but that vac pump really did just eat itself up. Hoepfully the new/used one won't have the same issues.

-mike

[Quantum-man]

Can you turn the oil pump through the hole?

[the vegenator]

Yeah, the oil pump and intermediate shaft turn freely.

I could have initially installed the vac pump incorrectly, causing the shaft to press up against the cover plate, resulting in the grinding of the pump. I have two pumps on the way from a generous ebay seller (bought one with a nipple intact, seller included an extra with a broken nipple). I'll mess around with those and see if I can get one to work properly.

[MizPahPAH]

did you check the bottom seal of the vacuum pump where the oil pump drive shaft goes in?

[the vegenator]

what would i be checking for?

[MizPahPAH]

At the bottom of the Vacuum pump where the shaft for the oil pump goes in there is a seal.



the seal is missing from this pump check the new ones that you get.

I got a new seal it is green the old one was black.

[Quantum-man]

A missing seal there doesn't makethe shaft ride high though does it?

[MizPahPAH]

This is just me thinking out loud...

The IM shaft turning the Vacuum pump will naturally force the pump up into the cover?

Without a good seal at the oil pump shaft the oil will not pressurize at the top of the vacuum pump pushing it away from the lid and lubricating the vaines and shaft top?

The other possibility is when the vacuum pump is installed say the oil pump shaft is sticking up higher than normal pushing the vacuum pump internals up into the cover?

[Fatmobile]

I always thought the vanes-style vacuum pumps were immune to this,
I thought the gear rides against a metal thrust surface on the base of the pump and wouldn't wear like the brass bushing in the old diaphram vacuum pumps.

I suppose a lack of lubrication could have caused it too.

Seems like someone thought they would try to run it without the lid on,
I think they only tried it once but can't remember why.

[the vegenator]

I got my vacuum pumps in the mail today. I installed it and got good braking power. Drove it around for 10 miles with no apparent issues. Hoepfully I'm in the clear!

The old one (along with the ones I received in the mail) all had seals in the bottom of the shaft of the vacuum pump. I don't think I'll ever understand how all that damage happened, unless it just wasn't properly lubricated when I fired it back up.

Thanks for all the help and suggestions, y'all! Keep your fingers crossed for me that this new pump continues to work well!

-mike

[82vdub]

There have been posts here about people with the vane style pump that have low brake assist boost. They find that the amount of vacuum that the vane style pump creates is dependant on oil pressure. If there's low oil pressure, the "fingers" inside the pump don't pull a vacuum like they should leading to low brake vacuum. That certainly is an interesting issue you had.