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Jonathan Joseph
Expert
Date registered: Oct 2006
Location: Charleston, South Carolina
Vehicle(s): 2004 G55
Posts: 1538
| Braking/Shifting/Vacuum??? problem
Hey guys I need some help,
I have had an intermitent braking problem for some time. Occasionally when I am backing (reverse) at idle speed I loose braking power. The brakes work but require tremendous force. This is usually when on an incline (nose up) Not all of the time just occassionally.
This condition has persisted for months. Usually racing the engine in neutral has solved the problem. ( Vacuum??) Sometimes shifting gears forward/neutral/reverse helps.
BUT TODAY.....I warm the truck up begin to drive, ...brakes no good, and.... low and behold she will not shift out of second gear. I stop, shift to neutral, rev engine shift back, accelerate, still second gear. Reverse, no good, park no good, SHUTDOWN ,RESTART ...maybe.... accelerate,...... then, brakes and shifts..what's up with this?
A couple other pieces of info,
Sometimes brakes are weak in forwartd gear also just seems more common in reverse at low speed and low rpm's. (Low speed/low rpm's in forward also)
I think this problems only exists when vehicle is started from cold(ambient not cold-cold)
Any ideas? I can provide more facts if neccessary, I'm sure someone here know's what this is all about.
Thanks
Jonathan |
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DesertStar
Expert
Date registered: Apr 2006
Location: San Diego, CA USA
Vehicle(s): 85-280GE/95-G320/08-G500
Posts: 2156
| RE: Braking/Shifting/Vacuum??? problem
It sure sounds like you have a vaccuum leak somewhere in your shift linkage....curious as to whether your G stops immediatly when you turn the key off, or delays a few seconds. Irratic shifting, and motor not turning off immediately are tell tale signs of some type of leak in vaccuum system on Benz diesels. I would check all the lines going to your shift linkage at back of motor to see all is OK and work from there.
My 300SD had the symptoms I described and turned out I had a vaccuum leak in one of my climate control vaccuum elements that work the defroster flap(not applicable to a G).
Mike |
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Jonathan Joseph
Expert
Date registered: Oct 2006
Location: Charleston, South Carolina
Vehicle(s): 2004 G55
Posts: 1538
| RE: Braking/Shifting/Vacuum??? problem
Mike,
My engine doesn't stop like I would like it to when the key is turned off. It gives a little bit of a death rattle, shakes and then stops.
I will trace all vacuum lines as best I can. The strange thing to me is that it is intermittent.
BTW thanks for your advice and info on the tranny shifting situ. Maybe related for me.
Jonathan |
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Merz-Ben
Extreme Veteran
Date registered: Aug 2006
Location: Floyds Knobs, IN 47119
Vehicle(s): 230G, U1200, U1250 DoKa, U1300L, U1500, U1700, 416
Posts: 377
| RE: Braking/Shifting/Vacuum??? problem
Jonathan,
Sounds to me like either the vacuum pump or the brake booster is on it's way out. It could be either, as the booster can intermittantly loose vacuum and cause a large leak, then it eventually won't hold vac at all. Usually the Vac pump itself doesn't intermittantly fail, but it is possible, especially since RPM increase remedies the problem sometimes. Next time you have the symptoms, open the hood and check some of the accessable lines for vacuum and/or check for a sucking noise next to the master cylinder. I doubt that the leak causing your problem would be in one of the lines, since a line leak would usually be constant.
Cheers,
Ben |
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Jonathan Joseph
Expert
Date registered: Oct 2006
Location: Charleston, South Carolina
Vehicle(s): 2004 G55
Posts: 1538
| RE: Braking/Shifting/Vacuum??? problem
Thanks Ben, that's what I was thinking, a real leak would be full time. I didn't want to hear that the booster was bad. Nooooo.....
The vacuum pump is gear driven no? I'm embarressed I don't know that, should have looked at the book or engine first.....but it's outside the front door, way to far to walk...
Jonathan |
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Merz-Ben
Extreme Veteran
Date registered: Aug 2006
Location: Floyds Knobs, IN 47119
Vehicle(s): 230G, U1200, U1250 DoKa, U1300L, U1500, U1700, 416
Posts: 377
| RE: Braking/Shifting/Vacuum??? problem
The vacuum pump is driven off of a setup similar to a cam lobe on the front of the injection pump gear. It isn't that big of deal to take off, there are 6 internal hex bolts that take a 5mm alen key and one line, and the vac pump comes right off the engine. You might want to do a vac test on it and see what it is pulling before you take it off (i don't remember the figure, once you work on so many of these things you get a feel for what the vac should be  ). The pumps are pretty common because they are the same as a sedan, I'm sure you could find a used one local (or I'm sure I've got a spare or two), or get a new one without too much trouble. I think a rebuild kit is also avalible for them, but I've seen quite a few with the drive arm worn out or broken... and can't be rebuilt. If it is the booster, I think I've got a spare used one on a parts truck if you are cheap like me and don't want to buy a new one  .
Cheers,
Ben |
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dai
Expert
Date registered: Apr 2006
Location: Oregon USA
Vehicle(s): 300GD 300TD BMW R100RS Landini 80F
Posts: 2110
| Re: Braking/Shifting/Vacuum??? problem
If it is the pump and the drive arm is not worn out the diaphragm is an inexpensive part and easy to install. It does not require the removal of the whole pump housing. Isolate the problem first. See if the pump is pulling vacuum before replacing stuff.
-Dai |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: Braking/Shifting/Vacuum??? problem
You have a Mitey-Vac unit? If not, get one. Isolate the different vacuum elements and test them one at a time to see where the leak is at. Could be anywhere. -Dave G. |
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Warren T
Extreme Veteran
Date registered: May 2006
Location: Montreal
Vehicle(s): 230GE,300GD,300D
Posts: 519
| RE: Braking/Shifting/Vacuum??? problem
Intermitant vacuum problems are usualy caused by the little check
valve at the exit of the pump, clean it and veryfi that the
hair spring is not broken. If you have to remove the pump
check condition of cam lobes and roler bearing.
Cheers Warren |
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Jonathan Joseph
Expert
Date registered: Oct 2006
Location: Charleston, South Carolina
Vehicle(s): 2004 G55
Posts: 1538
| RE: Braking/Shifting/Vacuum??? problem
Thanks for all the good advice guys. I'll be sure to post the solution when I have it figured out.
Thanks |
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