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Jake brake vacuum pump

Old 12-11-2011, 12:27 PM
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Jake brake vacuum pump

I have been getting about 30 months out of these pumps. The first one to go was still under warranty. The dealer (Canada) told me that the pump was a $1200.00 item. This time around I was on my own so I did some research and the forum on this site said to expect paying $900.00. It also said that getting one from Cummins was way less expensive. I got one for $200.00 from Cummins and me and a buddy changed it in 20 minutes. Oh ya, a dealer in Mcallen TX asked for $320.00 to install it. Criminals is what they are.
But I digress. The reason I am posting is because I'm thinking of gettin a spare while I'm here in USA, but I wonder if there is any danger of the pump deteriorating over say 3 years. Will things inside dry up or get brittle, I wonder?
What do ya'll think eh?
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Old 12-11-2011, 01:20 PM
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You can get them from Genos. The hole pump is 359.00 the vacuum pump diaphragm is 169.00
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Old 12-11-2011, 04:03 PM
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I read somewhere that the ones from Geno's are made by a different company and not quite as reliable as the ones got from Cummins. And the Cummins one was only $200.00.
Also I've read that the diaphram is hardly ever the problem. So $169.00 put into a $200.00 pump don't strike me as good odds. Just sayin.
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Old 12-11-2011, 04:34 PM
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Did you use the factory hose on the install? it has several adapters and sections of plastic tubing that is prone to cracking and or leaking. Get a new fitting for the solenoid valve and run one piece of hose all of the way from the pump to the solenoid valve and cut down on the possibility of leaks. Do a search on this as someone replaced the mechanical pump with an electric pump.
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Old 12-11-2011, 08:48 PM
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Originally Posted by Colo_River_Ram View Post
Did you use the factory hose on the install? it has several adapters and sections of plastic tubing that is prone to cracking and or leaking. Get a new fitting for the solenoid valve and run one piece of hose all of the way from the pump to the solenoid valve and cut down on the possibility of leaks. Do a search on this as someone replaced the mechanical pump with an electric pump.
I agree with the above quote if you have been going through pumps that frequently you have probably got a vacumn leak. I have over 260,000kms or 162000 miles on the same pump, and the only problem I ever had was with the original hose leaking. This is hard to detect as the pump will cycle or stay trying to make vacumn and it is not designed for continuous duty.
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Old 12-12-2011, 08:23 AM
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he gets about average out of his pumps just get a bd and junk the jake. the bd has the same stopping power all the way to idle where the jake is near none also most of the time when the jake pump fails it burns the serpentine belt up before you can get off the road
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Old 12-12-2011, 07:07 PM
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Originally Posted by carl48 View Post
he gets about average out of his pumps just get a bd and junk the jake. the bd has the same stopping power all the way to idle where the jake is near none also most of the time when the jake pump fails it burns the serpentine belt up before you can get off the road
I don't know what jake you were using but mine is just as good as any BD or Pac brake I have ever driven and it does not freeze up in the winter either like they sometimes do.
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Old 12-14-2011, 01:24 AM
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I recently had a vacuum pump failure where the exhaust butterfly would not activate (no vacuum). The pump noise was different as well. I bought a diaphragm assembly for a GMC that cost about $95 and it worked fine. Unfortunately, I did not remove the pump body from the engine and lost about 1/3 of the oil that lubricates the pump lobe.

5,000 miles later it started making noise again, but the exhaust butterfly was still working, so I put on the original serpentine belt and bypassed the pump until I have time to r&r the pump to check for a failure caused by my error in losing some of the oil.

Others have reported good success with the GMC diaphragm and it has a lifetime warranty from the manufacturer. Note that $95 is for the entire pump assembly and you have to switch the diaphragms. Also, the outlet has a different orientation than the Jacobs part, but there is no problem connecting the vacuum hose to the new diaphragm.
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Old 12-14-2011, 10:35 AM
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jim we run a fleet and have several brands of brakes. the jake is old technology it uses a orifice in the middle of the butterfly to limit pressure to 60 lbs at sea level and 3,200 rpm. as you go down in rpm and or up in altitude the pressure drops to near nothing the pac uses the same orifice but closes the butterfly on a spring loaded ball that covers the hole.the spring is set that it takes 60 psi back pressure to open there fore you have the same stooping power down to 700 rpm and 12,000 feet. the bd uses a fixed pressure on the cylinder hooked to the butterfly it is set so that it holds the back pressure at 60 psi giving the same effect as the pac. the bd is better than the pac for the reason of where bd mounts the compressor. we went back and moved the pac compressors to stop the failures. i think i was told pac now mounts them someplace else
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Old 12-15-2011, 05:16 PM
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What belt driven pump? Mine is the electric motor unit from PacBrake. It is mounted on the top left of the motor in front of the air preheater. Has worked now for 2 years + with no issues. You guys that have hot pumps - use an old aeroplane trick and run a small (3/4" is big enough) cooling tube from a hole in the rad support up to the cooling fins of the compressor. Works great. And if you need to check for air leaks have the engine running or ignition on (for the electric ones) and spray all the connections and hoses with a squirter filled with soapy water solution and look for the bubbles.
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Old 12-16-2011, 01:04 AM
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Jacobs - old technology?

Hi Carl48,

I have heard these claims before but have never understood the actual magnitude of the pressure difference caused by the fixed orifice of the Jacobs butterfly compared to the spring relief of the Pacbrake.

It seems that the diameter of the hole on the Jacobs is less than 5/8 of an inch, with the overall diameter being about 4 inches. So the area of the hole is .625*.625 * 3.14 = 1.227 sq in. The overall area of the butterfly is 4 * 4 * 3.14 = 50.265 sq in. That means the hole on the Jacobs is about 2.4% of the overall area.

I don't see how 2.4% equates to a significant loss of braking force, unless the pressure differential across the butterfly is very low.

From http://www.trident.on.ca/orifice-air-flow.htm, the maximum flow through a 5/8" orifice at 60 psi is 359 SCFM. At 15 psi, the flow is 154 SCFM.

Also, the spring loaded relief could fail closed, causing excessive pressures or fail open, giving lesser flow restrictions compared to the Jacobs part, which is mechanically simpler.

Do you have retarding horsepower curves for the Pacbrake at various rpms and altitudes for a 5.9L ISB application? The only claim I have seen in writing is "1/3 more retarding HP at 1500 rpm".
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Old 06-14-2012, 03:13 PM
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I know this is an old thread; but, Can anyone share a part number for the GM assembly?

As for their effective braking. An actual comparison needs to be made. Both designs have their merits. edtyler, you are correct with your calculations (At least at a glance....) but carl48 is also! What happens is that the back pressure in the exhaust before the brake butterfly will decrease as RPM's drop. It does this because the engine is putting out less cfm as the RPM's drop. By simply having a set orifice, as the cfm drops, so does the back pressure. By design the brake with the spring loaded gate (Basically a variable sized orifice!) should have more braking power at lower RPM's than one with a fixed size orifice.

My vacuum pump failed recently. I have it apart and have found the part that failed. It is about a 50 cent piece so there is no way I'm buying another complete pump at about $240. (Cummins has the best price on these).

Here is a shot of the failed 'mushroom' rubber check valve inside the Jacobs vacuum pump:

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And it goes in here:

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Anyone know where I can source something like this? It measures about .800" in diameter and is supposed to have a 'tit' in the center to hold it in place.
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Old 06-18-2012, 10:33 PM
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Jake Brake Punp

Hi Millco,

What was the symptom you saw when you started to troubleshoot the failure?

This is the information from my Rock Auto order:

1999 GMC K2500 PICKUP 6.5L 395cid V8 DIESEL FI Turbo (F) OHV DORMAN 904801 (904-801)Vacuum Pump$ 92.89

In my case, the sound from the pump was quite loud and there was no actuation of the brake dashpot. I was worried about a possible vacuum leak causing damage pump, so I used a MityVac and proved the system would hold 24 in of vacuum indefinitely.

I wonder if Dorman would provide parts?

As to the difference between fixed vs. spring loaded orifices, I have yet to see proof of real world differences and what, if any failure modes exist for the spring loaded device. Imagine if it rusted closed and then over pressured the exhaust manifold and overrode the valve springs.

Overall, it seems the best use of any e-brake is to run the engine in the same gear going down hill as going up, which means 2000-2400 rpm as suggested by Cummins. At low ground speeds the energy required to slow the vehicle and trailer decreases with the square root of the speed. It takes a lot less to slow from 30-10 than from 60-50. Therefore the low rpm performance may not be very relevant.

However, carl48 likes his choice and I respect the positive experiences with other e-brakes. I like the simplicity of the Jacobs unit. To each his own. However, I don't like the failure of other e-brake manufacturer's to provide braking curves make me wonder why. Jacobs provides curves for their unit in the operator's manual. Do the others?
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Old 06-22-2012, 12:05 PM
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I have heard, a electric vacuum pump that came on the 2003 Dodge CR Cummins can be used and mounted in about the same place as it was in 2003. Price less than 200 bucks.

Ford also used one on alot of the trucks prior to 2009 so there should be something out there that will work in lieu of the belt pulled pump.

Good thing about it is, you can turn it off until you want to use the EB.
Should last forever.

Dave
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Old 09-02-2012, 09:07 PM
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Folks just to clarify this thread.

The brake units use pressure not vacuum so don't go buying a vacuum pump to operate the butterfly type exhaust brake.

My PAC valair unit keeps blowing the fuse after about 1/2 hour. Might have to replace it and mount it in the cool air up front somewhere as heat kills electrics.
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