Vacuum pump diaphragm failures

[Rabbit79]

All of a sudden the old Rabbit is eating vacuum pump diaphragms. I've went through 3 in about the last 2 months. The first time I just changed the diaphragm... lasted a couple weeks.... 2nd time new diaphragm and check valves... that lasted about a week... 3rd time another diaphragm and it lasted about a week again. Is there any common problem that causes this? I've been getting the parts from NAPA, which I'm sure is all made in China stuff (but then what isn't these days), could it be I'm just getting sub-standard parts?

[bbob203]

get a vane vac pump problem solved.

[libbydiesel]

I agree that the rotary vac pumps are the best solution.

If you want to stay with the pain, make sure you pre-tension the diaphragm before tightening it down. 

[ORCoaster]

How much wear and tear is on the other components of the mechanical side.  That piston wobbling around in there like a loose marble?  Bushings on other places OK.  I have two other pumps that I have rebuilt in the past so if you need another like what you have give a yell.  But honestly, IF mine goes out again I will be looking for a vane style as well.  It may be spendy but then so are the number of d phrams you are going to go through in comparison. 

Vane pump = problem solved if the pump it self isn't worn to the point of no or little pressure.

[Rabbit79]

I'll have to pull it out and check it over. I haven't really looked that hard at the pump yet, thinking maybe I just got a couple bad diaphragms, but after 3 I think the odds of coincidence have about run out. Luckily they have a 12 month warranty from NAPA so I've only had to pay for the first one. I didn't really notice anything obviously wrong with the mechanical side when I was washing it in the solvent tank, but as I said I didn't look that hard. The only reason I posted was to see if there was a common problem that causes this, but it looks like I'll have to dig into it. I've never really had much trouble with the pump, change a diaphragm every few years here and there, but all of a sudden 3 in a couple months is kinda weird. The engine is about a year and a half off a rebuild, and one theory I had was too much oil pressure, as there is a new oil pump in there (OP is about 70 at rpm, 30 at idle). However the old diaphragm lasted over a year off the rebuild so I don't know how much credence I can give to that theory. Plus I never really have looked to see how the oil flows around in there once it's in the pump. Just thinking out loud a bit on my oil pressure theory, I'm probably way off base on that. Anyway I'll take a look and post to tell what I find out.

[ORCoaster]

I don't know about that there theory of yours.  I run 110 lbs pressure most of the first couple of miles till the oil warms up then it slowly works its way down to 70 PSI running.  Some where between 30 and 45 at idle. 

I have had the little O ring get buggered up and cause the oil to seep in there and weaken the whole diaphragm.   Not sure what the flow pattern is on the oil.  Up from the oil pump itself and out the hole in the top of the shaft isn't it?  Then free fall back into the oil pan from the backside of the vacuum pump.

[Rabbit79]

Yeah I'm not all that confident in that theory myself..... pretty much just bouncing stuff off the wall on that one.

[R.O.R-2.0]

there is a big plastic bushing on the piston that actuates the diaphragm.. that piston gets loose after a while, starts to wobble around, then it starts eating diaphragms..

[ORCoaster]

Thanks for the second to my reply #3.  Has to be something loose in there. 

[92EcoDiesel Jetta]

What is the life expectancy of a diaphragm vac pump when they were new? I kinda like how easy they are to rebuild. I took my out (diaphragm pump from the Caddy) to put a new diaphragm on. I wonder if it is possible to re diaphragm without pulling pump.

[ORCoaster]

Undoing one bolt and getting it up on a bench to snap those screws loose is worth it to get it out of the car.  Really what is in the way?  Only need to be aware of getting it lined up on the notch when you put it back together.  You can spin the engine over to be sure before you fire it up to make sure it is down all the way.  Highly recommended by me.  Oil all over is just a mess. 

[fatmobile]

If you want to stay with the pain, make sure you pre-tension the diaphragm before tightening it down. 

 No mention of technique
 didn't question your spelling of pretension, ha.
Just a joke, I don't know how to spell it,.. but did he read it?

[ORCoaster]

Rather than turn the gear and get the piston to pull the rubber into the body of the mechanism wouldn't you want to turn it so it was flat across the middle of the stroke?  Get it to be at rest?  That way it is equal tension and you aren't fighting getting the screws in there and cutting up the edge of the rubber.

[fatmobile]

If it isn't pretentioned then every time it rotates it stretches the diaphram.
Compressing it is probably less straining.

[ORCoaster]

I can see how that would work.  Pull it tight and clamp it in place and then it doesn't stretch any more than that.  Whereas leaving it dead center it would pull it some and push it some but it is the pulling that makes it wear? 

Not that I plan to do another soon I will be remembering this trick if failure of the last one comes prematurely.

Thanks for splaining.