I had the truck in the shop for power steering pump replacement as existing one leaked fluid (2nd replacement).
During the repair, the techs saw a crack in vacuum pump housing/adapter. So this component was replaced as well. The housing/adapter is made of aluminum and it lasted 23-years before failure.
There are only 2 bolts at the adapter flange that failed, so i suppose over the years, there must have been some movement/vibration of the power steering pump to cause the failure. Keep in mind that cold climate likely impacts the power steering pump. The fluid used in power steering pump is a synthetic ATF as it is better than the power steering fluid.
What turned out to be a $300 job ended up being $950. Ouch!
Here are the photos taken of the failed component and a screenshot of the overall installation from the repair manual.
The PS pump seems to be cantilevered from the end of the Vac pump, making a long assembly sticking out. Do you think that played a role in the failure of the flange?
yes, coupled with only 2 bolts which allows for adapter movement perpendicular to bolt axis. the techs say that after 23-years with normal engine vibration could have an impact as well. Seems that adding gusset or a 4 bolt flange would have been a better design.
although rare in occurrence, extremely cold starts resulted in about 10-15 seconds of rough engine operation (cough, spit, and splatter) until all cylinders fired.
i’m grateful that these techs are observant and found it as a catastrophic failure was likely imminent.
My though is all of the above, plus a microscopic casting flaw exacerbated .by a poor design.
If the failure was only design related, after 23 years in service, that assembly would have a reputation for failure.
Anecdote alert;
Background;
I like the gear drive on the power steering pump.
When I was pulling new travel trailers from Indiana to Alberta, many of the axle assemblies had been in outside storage for a year or more due to COVID issues.
A layer of surface rust would form on the internal brake drum surfaces.
It took a long time to scrub the surface rust off.
It was not unusual to be into North Dakota before I had usable trailer brakes.
I really liked the Chevy Duramax engine, except that both the alternator and the hydraulic pump are driven by the same belt.
And as well as the power steering, the power brakes are powered by the same pump.
The drive pulley on the alternator has a centrifugal clutch to prevent excess speed of the alternator.
The incident;
I had pulled into a small town in Minnesota for a 20 minute power nap.
I was headed back to the Interstate and was making a left turn in a wide, traffic light controlled intersection.
As I started to turn left, a woman pushing a baby carriage stepped off of the curb into the cross walk.
No problem, she has the right of way, and I have lots of room to make a gentle stop.
But, just then the pulley on the alternator failed and tore up the serpentine belt.
With the belt gone I had no power steering and no power brakes.
That truck really needs both. And right ahead is a woman with a baby buggy.
I had an angel riding with me that day.
I had lucked out and had a trailer that had working brakes and the trailer brakes brought me to a safe stop.
The woman had no idea how close she had come to a close encounter.
now that i think about it, my truck has 1 serpentine belt, so i would have like not had power steering as the power steering unit bolted to the adapter from vacuum pump. sure would have made a mess though.
i would think your truck has emergency brakes?
i occasionally practice stopping my truck with the emergency brake. mainly to make sure they work and to familiarize myself with them.
I think of mine as a parking brake rather than an emergency brake.
It is not very good as a parking brake and I would not even think about it in an emergency.
But your drawing shows a gear drive. That’s what I liked about it.
My three ton has a gear drive hydraulic pump and a backup electric-hydraulic pump, both charging an accumulator, for the power brakes.
As soon as you turn the key on, the electric pump starts and charges the accumulator so that you have full braking available to hold on a hill if you release the parking brake before putting it in gear.
And it also has a better parking brake.
