How many inches vacuum should be at idle speed?

I get about 10 inches at idle and 20 inches when I rev engine up a litle above idle.

My problem is; when I apply the brakes, the pedal gets hard when it comes to a stop.

The check valve from top of vacuum pump tests ok.

Ac vacuum pods blocked off at the firewall.


Thanks, Tom

BUMP !!

While stationary hold your foot on the brake pedal, if your pedal slowly goes down to that hard feeling then you may have a leak in your brake booster. Try turning the engine off, if it won't you most likely have a leak in your brake booster. Replace it.

10 inches at idle is not enough. After the Car idles a short bit the Vacuum Should go up to 22-24.

If you are checking the Vacuum from the main line the first Nipple closest to the Front of the Engine; try disconnecting the Main Vacuum Line at the Brake Booster and putting your Thumb or something else like a Rubber Plug on the end of the Main line. This bypasses the Power Brake Booster.

Start the Car and see what happens to the Vacuum. If the Vacuum Is OK like that You may have a vacuum leak between the Master Cylinder and the Brake Booster or the Brake Booster has an internal leak.

If the Vacuum is still bad unscrew the Vacuum Check Valve on the Vacuum Pump and hose it out with WD-40 and re-test as before.
If it is still bad there is something in the Vacuum Pump causing an issue.

It could be something as simple as the little Disc Valves inside being gunked up or the VP could be worn out.

The below pic is one of sretch's pics. of what I assume happens when the VP piston is worn (from His thread). It might be cleaning the little Dis Valves and the gunk out would give you some temporary service until you decide what to fix.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the response.
A while ago, I was doing 40 mph and put it in n and kept the rpm's at 2000, put brakes on and it had a good pedal all the way to complete stop.
So I am going to assume the vacuum pump is bad.

I will change out the pump and report back.

Thanks,tom

Can't pumps such as in Diesel911's picture be rebuilt?

Sixto
87 300D

It depends on what you consider rebuilt.

There is 2 kits. One kit is for the Piston End and the other Kit has the Engine side parts with a new Arm and bearing.

Unless you can find someplace and get an exceptional deal on the 2 kits it is actually cheaper to buy a New Vacuum Pump and you get a new Check Valve with that and a Warranty.
Also when you are done with your Rebuild you will have no warranty and you still have the Old Vacuum Check Valve that screws into the Vacuum Pump.

More than a Few People have just bought one kit the one for the Piston End as that is the one that has to do with creating the Vacuum.

Some People have done a variation of the above and replaced the Bearing on the Arm. (Failure of the Bearing is one if the things that causes a catastrophic Failure of the Arm and parts can end up in the Timing Chain/Gears.)

But, it is the Engine side with the Arm and Bearing that if it fails often takes out the Timing Chain and sometimes the Engine itself. So by only using one Kit you only solve one potential problem.

When the Vacuum Pump is off it is a good idea to check the End Play of the Timer. If there is too Much end Play it has actually ruined New Vacuum Pumps.

MY Question on Timing Chain Failure
http://www.peachparts.com/shopforum/showthread.php?t=203364&highlight=timing+chain
In the below thread I am speaking of a Catastrophic Failure of the Arm and Bearing not the Vacuum Pump simply not holding Vacuum
My question What in particular causes vacuum pump failure?
http://www.peachparts.com/shopforum/diesel-discussion/204187-what-particular-causes-vacuum-pump-failure.html

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84 300D, 82 Volvo 244Gl Diesel

When I experienced the Symptoms that the OP listed the Vacuum Pump Check Valve was all gunked up. I removed it and sprayed it out with WD-40 and it restored My Vacuum and I have had issues for about 4 years.

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84 300D, 82 Volvo 244Gl Diesel