1993 Vacuum pump failing?? Help!!

[crazeejames]

Have 1993 c1500 with 6.2L, only 150,000miles. Developed a loud metallic knocking sound the other day. Using a stethescope, determined it is coming from the vacuum pump on the lower passenger front of the engine. Removed the belt and ran the engine, noise is gone. Can turn the pump by hand, feels smooth and no noise..........Can this be the pump? What is the pump used for, can I just get a shorter belt and bypass it? Anyone know what size belt I would need if that is possible? It's a 1993, so I assume all the hvac controls are electric controls........
Any info would be appreciated, as this truck rarely gets to sit still........and don't want to wreck anything by continuing to drive it.

[Robyn]

The Vacuum pump is used to run the EGR system on the 1500 trucks.

If the pump spins free by itself with no noise check the other stuff on the front including the vibration dampener and the serp pulley setup.
The serp drive pulley is rubber isolated with a bearing in the center and if the rubber breaks loose they can make a helluva noise. Also look the vibration dampener over real good. These do fail over time and can be a serious issue is allowd to go on this way.

This sort of thing can lead to crank issues.

The water pumps can get noisy but usually its a grinding vibration and this can be seen with the belt off by wiggling the fan and hub.
Knocking or rattling is usually a Vac pump or the isolator setup.

Now if nothing seems bad put the belt back on and run it and see what sort of vacuum the pump is producing.
The pump has the drive portion with a shaft, cam and bearing setup and then there is the vacuum pod assembly with the diaphram.
The pump should have some resistance as the diaphram is actuated and this should come and go as the pulley is turned. If it spins free the pump is toast.

Check it out and get back to us.

Robyn

[crazeejames]

O.K, I'll go double check it this aft, but the noise sure seems to be the pump when I use the stethescope.............with the belt off when I turn it, I can feel the diaphram pumping............I'll pop the belt again, and check the other pulleys.......but it sure sounds like the vacuum pump hammering......

[DmaxMaverick]

And.....

If you aren't sure if your EGR is functioning properly (most don't after about 5 years), you can bypass the vacuum pump altogether, for testing purposes. A non-EGR belt will leave the pump out of the loop (an additional idler pulley may be required, but they're not expensive).

Be careful, though. You may find a smoother engine with a little more power (less accessory drag). I recommend this for testing purposes only. Many folks also replace the EGR intake with a non-EGR intake during the test period. However, there is no hard rule on how long you should test this. We cannot recommend any modification of emission systems, and it should be in compliance during any state required inspections. In CA, we do not inspect Diesel emissions, and I've been "testing" my 1985 for about 20 years. I should have the results of the test very soon. No conclusions yet, but I'm confident I should have the "test data" at some time in the near future.

[restoguy]

Yup. Mine's hammering too. I took it apart and cleaned the area around the cam lobe and plunger, put some oil in it and put it back on but it's still making noise. I'm afraid that I may have to replace it. What did you find?

[opto]

Is the vacuum pump ONLY for EGR, nothing else at all???

[Robyn]

On that truck it serves no other function.

Robyn

[Roachie]

Here in Australia, I have a 6.5 Chev in my Nissan patrol 4x4. It has a belt driven vacuum pump. My rig has a 5 speed manual transmission and the vacuum is used for the brake and clutch boost as well as an aftermarket cruise control I have fitted.

The vac pump failed a year or so ago and a new one was fitted but I occasionally notice the same symtoms (as I was suffering when the pump failed) and I am concerned that this near new pump is also going to fail soon.

Because the pump is located in an awkward spot (as regards the bottom radiator hose access position for example), I am seriously thinking of removing it altogether and fitting up an electric unit like this:

http://www.summitracing.com/parts/SUM-760150/

or possibly this:

http://cgi.ebay.com/ebaymotors/Ford-F-250-F-350-F-450-F-550-Electric-Vacuum-Pump-_W0QQcmdZViewItemQQhashZitem51929f2279QQitemZ35035 2253561QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries

So, I'm just wondering if any of you learned folk in the states know what the "HG rating is for the Chev/GM vacuum pump, so I can try to match the electric pump with that please?

I note one of the sites that sells the Ford vac pump (the 2nd one listed above), states that it only puts out 17"Hg and as such it is not suitable for operating brake boosters; but this particular advert does not mention that.

Any thoughts would be greatly appreciated.

Thanks,

Roachie (down under)