Engine/Transmission (1994 - 1998) Here is a new one for you all (I think)

[CumminsPower98]

My cousin's '97 2500 developed and bad knocking noise while he was going down the road. He had to drive it hundreds of miles to get it to me to work on. I got my steatha scope out and started probing around. The sound was loudest down on the vacuum pump so I pulled the pump and found three teeth broken clean off of the pump drive gear and no other damage to surrounding gears. The vacuum pump was still working fine as was the power steering pump. I pulled the timing cover to see if a bolt could have fallen out to cause the damage but all the bolts were still in. Even if one had fallen out it could not have done this because of the direction the gears are rotating at this point. So I am at a loss as to what caused this. It's hard to imagine anything in either of the pumps that could have bound up so bad as to break gear teeth and then continue work OK. Maybe the gear was flawed from the factory. So now in goes one of those EXPENSIVE vacuum pumps. I found all three teeth in tact laying in a groove in the gear case below the gear they came from. Anyone ever hear of anything like this before? I know I have not read anything about it.



Mark

 

[illflem]

Was the dowel pin still in place when you removed the cover?



Never seen it but about the only other thing it could be is a bad gear.

 

[CumminsPower98]

yes I have already tabbed the pin long ago and it is still in place, so all I can figure is bad gear also, who would have thought.

 

[illflem]

Someone here mentioned that you don't have to buy a new pump, the manufacturer, whose name I don't remember but is written on the pump, sells parts and rebuilts with a core exchange. Maybe an internet search will tell you more once you have the name.

 

[CumminsPower98]

Update

Update here. I got the new vacuum pump from the dealer at $820 my cost (over a grand retail). I could have bought one from Cummins for $605 but time was an issue and they had to order. Anyway once I got the two pumps apart I noticed that one of the drive tangs on the vacuum pump was broken off and just floating in it's coupling color slot. I don't know what broke first, the gear teeth or the tang. I don't know if they were even related. The power steering pump tangs were very worn also on the drive side and the pump shaft seal was leaking so it got a rebuilt PS pump. My cousin reports that it steers a lot better now so the PS pump must have been tired. Makes me wonder if something in the PS pump went wrong to cause the damage becasue it was harder to steer at low RPM. The truck seems happy now with Valvoline Synthetic PS fluid and no leaks.



Mark



Edit: the vac pump is made by WABCO. I found their site but didn't find this pump listed. A person would probably have to call them.

 

[tarussell]

Wabco - does make the pumps - You could probabley go to a industrial parts supply house to avoid the dealer mark up on parts. I worked at an industrial supply co. ( Motion Industries ) and delt with Wabco all the time - just give the serial # off of the pump and they should be able to supply all the individual parts - including the gear. HTH Thomas

 

[illflem]

Almost sounds as if the PS pump locked up stripping things out.

New one on me.

 

[drees1]

It's hard to imagine teeth stripping off before shaft breakage. What does the fracture site look like on the gear teeth and gear? Many small marks more or less parallel (beach marks)indicate a fatigue failure initiated from a crack. One of the 3 teeth may look different at the fracture line. Maybe a bad gear. A fatigue failure in the root of the tooth is a very common type of gear tooth failure. Poor machining or grinding below the case depth, or grinding burns, or a sharp nick could all be causes.



If the wear pattern on the gear and mating gear look ok then this problem probably will not repeat with a new gear.



If you posted close up pics of the gear and teeth fracture site, I might be able to tell if a brittle failure (all at once) or initiated by a crack due to defect.



Doug Rees

 

[CumminsPower98]

I did get a couple pictures this afternoon but nothing real close. My cousin said he heard no initial sound of something breaking. He said it just started making this noise while driving along and to begin with it was not quite so loud but then got louder. So to start with I would say that maybe only one or two teeth broke and then got worse as time went on. It's hard to believe the PS pump could have locked because of how smoothly it turned and the lack of noise but who knows. I put the vacuum pump in the press today to get the gear off and also pulled the back of the pump off. Everything inside looks great to me and no way it could have locked up.



http://www.pbase.com/image/9805372

http://www.pbase.com/image/9805373

 

[DieselB59]

Gear tooth failure is a funny thing. Usually it's a flaw that's there since production, and one tooth flakes, then the odd tolerance begins to smack around until the tooth breaks off, then all heck breaks loose and others begin to break off after rapping against each other when the missing tooth comes around. Finally, something else lets go, AKA the tang. Could be something close to this, but then again, since we can't see what's going on when the gremlins are playing it's just pure speculation.