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How much testing before you change parts?

Wes J

Senior Member
Joined
Jan 24, 2016
Messages
649
Location
Peoria, IL
I was watching a heavy equipment mechanic on YouTube he got very upset with me after I accused him of guessing and winging parts at a machine. Maybe I was out of line. Got me to thinking, how much testing do you do before you condemn a part, especially a complex part like a pump, valve, or computer?

For example, he was trying to fix an issue with a 2 speed track system on an excavator. The machine has a high speed mode to track around when lightly loaded. It seems to use some inputs to the computer to control a dump valve on the pump stroke to give more flow. It was not working correctly or intermittently working.

He did some testing of the control side and found some minor wiring issues. With those fixed, he says "it has to be the valve". Next video he does some more testing and finds a default mode where the machine works correctly. He says "it needs a computer".

Finally, some folks with experience on this machine asked him to test some of the sensors. But, these are solid state sensors like hall effect RPM sensors, not like the old variable resistance sensors you can test with an ohm meter. He has no oscilloscope to test them. Finally he swaps one of the sensors and proclaims the machine is fixed.

Now, he did the right thing by not shot gunning parts. I will say that. But I think that if it was not for the comments in the video that machine would have gotten a new valve, and new ECU, and several new sensors that it didn't need.

So, how much testing do you do before you buy parts? If you make the wrong call, who eats it? Do you test sensors before changing them out (with a scope or any other method)?

From my experience, some things are really hard to test. Unit fuel injectors, hydraulic motors, some electric motors, complex units like a gauge cluster or ECU, etc. I always to rule out every other part of the system before making the call.

So what is your experience with testing versus changing parts?
 

Wes J

Senior Member
Joined
Jan 24, 2016
Messages
649
Location
Peoria, IL
I'll give some other examples from my experience doing field service work.

One time I was called in to look at a machine. It had broken several teeth off the gears that drove a multi-speed gear box. The customer had replaced the gears once and they had broken again. The gears were set up on a sliding bracket to allow you to change out the gears for different ratios and the bracket kept being pushed out of the way when the gear teeth broke. They were in the process of drilling holes in the bracket to permanently lock it in place when I walked in.

I took a quick look and it was obvious there was an internal issue inside the multi-speed gear box causing it to lock up. I pulled the box and found one of the cams that actuated the shift forks had vibrated loose and was letting two gear ratios be engaged at the same time. I replaced the damaged gears, pinned the cam in place, put it back together and everything was fine.

Another time I was called in to look at a machine with a CRT monitor that displayed some information for the machine operator. Customer said the CRT would go crazy and scramble the display. They had ordered and installed an LCD replacement to the tune of $2000 and the problem remained.

I did some poking around and noticed when I switched to a certain display screen the display would quickly switch back and then go crazy. I was able to see that there was only one way that was possible, which was by pressing a key on the key pad. So, I unplugged the keypad and the display went right back to normal. Did some more digging and found that all that was wrong is some dirt had gotten into one of the keys on the keypad and it was basically being held down. I cleaned it and put it back together and everything was fine.

One last one. I was called in to fix a machine that had a large two speed gear box. The gears were changed by hydraulically actuated clutch packs. One pack for each gear. The machine had gotten stuck in both gears at the same time and burned up the clutches. The customer had replaced the clutches, but the problem was still there. I looked over the schematic and found that the control valve had a drain port that drained oil back to the gear case. Someone had put a plug in it. The customer swore up and down that was not issue, that it was always like that, and that removing the plug would not work. Luckily, they had a sister machine there that worked correctly. I was able to use a bore scope to see into the gear box and show them that oil was indeed draining from that passage and the plug must be removed.

I have no idea how the plug got there. I have no idea if the machine did in fact work with the plug in place. But, as soon as I removed the plug the thing started working correctly.
 

JD955SC

Senior Member
Joined
Mar 13, 2011
Messages
1,348
Location
The South
I generally try all the tests I can do for an issue and all the “common sense” troubleshooting possible before throwing parts at something. So far I have a pretty good track record of dialing in on an issue to replace what is needed vs guessing. Some issues you can’t narrow it down much and have to start changing parts you think are the most likely causes.

I take pride in being able to troubleshoot and changing what needs to be changed vs firing the parts cannon. It’s what separates a mechanic from a parts changer.

Now I will note that I have the luxury of being able to have full service information, test equipment, and the calm knowing it’s not my bottom dollar being threatened by a machine down. It’s easier to take a rational approach to proper troubleshooting when you aren’t feeling like the world is going to collapse on you because YOUR machine is down

I take it this is the same fellow featured in another thread and I believe I have watched some of the videos.
 

TVA

Senior Member
Joined
May 14, 2018
Messages
2,245
Location
USA
Check out thread “ungreatfull”. here on shop talk. You might be surprised.
 

TVA

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Joined
May 14, 2018
Messages
2,245
Location
USA
If you are independent then mistakenly replace costly component is a carnal thing for your business!!!
Everything rides on your reputation, you compete with the dealer who has all kinds of things going for him, information, support, parts, tools!
The only competitive edge you have over the dealer is your lower price and higher quality of service!!!
So before you call a bad component - you better be damn sure that’s what it is!!!
 

Old Doug

Senior Member
Joined
Oct 16, 2013
Messages
4,430
Location
Mo
If you are independent then mistakenly replace costly component is a carnal thing for your business!!!
Everything rides on your reputation, you compete with the dealer who has all kinds of things going for him, information, support, parts, tools!
So before you call a bad component - you better be damn sure that’s what it is!!!
Why would any one want to be a mechanic??
You have to build a network of guys you can call for help with problems. After eliminating all the easy stuff when you suspect it is something super expensive you call somebody to confirm your suspicions. In return, they call you if you have a field of special expertise they sometimes need.
This work great back when there was just a handful of diffrent brands and they didnt try to reinvent the wheel every year.
 

TVA

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May 14, 2018
Messages
2,245
Location
USA
“Why would any one want to be a mechanic??”

I ask that question my self every day! Why I always pick something complicated and hard to solve and do?!?!? Why I can’t just do teriyaki, pizzeria, or laundromat?

Best I could come up with - it’s a curse!!!
 

Birken Vogt

Charter Member
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Nov 30, 2003
Messages
5,287
Location
Grass Valley, Ca
I work on generators that are expected to work when nobody is around. There are frequently those faults that only happen in the middle of the night or when nobody is watching. When discussing with the customer you have to explain that you just do not know, nobody can tell what is wrong. Sometimes they take a wait and see approach, others will give you the OK to just start changing suspect parts until you hit the one that fixes it, but you just level with them that the cause is unknown at this time unless somebody can observe the failure directly and let them direct the course of action.
 

excavator

Senior Member
Joined
Oct 16, 2006
Messages
1,441
Location
Pacific North West
“Why would any one want to be a mechanic??”

I ask that question my self every day! Why I always pick something complicated and hard to solve and do?!?!? Why I can’t just do teriyaki, pizzeria, or laundromat?

Best I could come up with - it’s a curse!!!
Because for people like you and me there would be no satisfaction in owning a pizzeria or laundromat.
 

old timer

Well-Known Member
Joined
Aug 30, 2010
Messages
114
Location
manitoba canada
Occupation
field mechanic
Speaking from 40 years in the trade, I wouldn't do anything else!
The most important job you have as a mechanic is trouble shooting, first and last! I am continually reminding the apprentices to
"PROVE IT" give me your procedure and the results. That's the difference between a technician and a parts changer. Short story about that is I was working at a dealership, 4 of my fellow 'mechanics' and the shop foreman had thrown about 5000$ in hydraulic parts at a machine, and still had no solution. The owner who knew my dad walked into the shop and asked me what I thought. I spent 10 minutes looking at the schematics, organised 2 tests and did them. total time, about an hour. Came up with a simple solution. When I presented it to my foreman and boss, well upset wasn't quite how I would describe it but the customer was willing to give it a go. when the boss told me in no uncertain terms that my employment hinged on this, well, confidence was never lacking in my family so 4 hours work, 3.95$ seal and one happy customer later..... I made a lifelong friend, and a customer that has provided me with a lot of work when I went on my own.
There is nothing more important than troubleshooting.
And by the way, I may be old, but I saw all the good bands!
 

Birken Vogt

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Nov 30, 2003
Messages
5,287
Location
Grass Valley, Ca
working at a dealership, 4 of my fellow 'mechanics' and the shop foreman had thrown about 5000$ in hydraulic parts at a machine, and still had no solution. The owner who knew my dad walked into the shop and asked me what I thought. I spent 10 minutes looking at the schematics, organised 2 tests and did them. total time, about an hour. Came up with a simple solution. When I presented it to my foreman and boss, well upset wasn't quite how I would describe it but the customer was willing to give it a go. when the boss told me in no uncertain terms that my employment hinged on this, well, confidence was never lacking in my family so 4 hours work, 3.95$ seal and one happy customer later

Why did he tell YOU that YOUR employment hinged on a solution when 4 other guys had failed to fix it already? Did he fire them too?
 

Truck Shop

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Dec 7, 2015
Messages
16,153
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WWW.
It's really fairly simple-no one is perfect nor do they know everything. In the real world mistakes happen and 95% were not intentional. But before all the trouble shooting starts
there are many questions a mechanic needs to ask himself about the problem at hand. For every action there is a direct and opposite reaction and that goes for everything.
A high percentage of it is taking the time to try and understand the problem. And plugging in is not always the answer. My 2 cents.

My issue is guys who spend most of their time thinking about chasing beans and weenies around the plate.

Truck Shop
 

Junkyard

Senior Member
Joined
Jun 5, 2016
Messages
3,607
Location
Claremore, OK
Occupation
Field Mechanic
I will exhaust every test I can perform and pick every brain I can. I can’t stand throwing parts at something. I pride myself on being a good diagnostician. I’ve literally heard our guys say they’ve never seen me stumped or brought me something I couldn’t fix. That’s a lot to live up to!!

There are times that I end up making an educated guess. Often when test results aren’t consluive but there’s certainly a malfunction of some sort. I’ve changed a few things that didn’t cure a problem but that’s a very rare occurrence and often it’s the easiest and least expensive part. Unfortunately sometimes the diagnostic process can end up being an elimination of issues by parts replacement.

I will say this....at work I have the luxury of no issues budget wise and almost always have time to dig into it or worst case a spare rig to swap with so I can take my time and fix it right. Rarely am I pushed to throw a machine back together. I think that’s mostly because I won’t do it and they know that. I might be a company mechanic but I’ve got a reputation well beyond MF and I don’t want to tarnish it.

I suppose the same experiences that have taught us how to diagnose have also given us the ability to trust and understand our gut instinct when faced with an oddball issue. The patience of Job doesn’t hurt either! We’ve all seen the random oddball issue that caused us untold amounts of grief and once we figured it out we vowed to never forget!! I’m sure that things like that help us in the future when we see similar issues.

I love to help people. It keeps my mind sharp, I do it for myself as much as anybody else. I can’t see it all or fix it all but I’ll darn sure try!
 

Birken Vogt

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Messages
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Grass Valley, Ca
Everybody has the odd problem where they do not think of the right solution the first time. And sleeping on it often brings it into focus.

My problem is that I go to a lot of jobs way out in the sticks, with high travel cost, that need to be fixed RIGHT NOW with whatever you have on the truck, and no cell service. Leaving it sit in the shop overnight is not usually an option. You got what you got in the truck and in the brain.
 

Welder Dave

Senior Member
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Oct 11, 2014
Messages
11,981
Location
Canada
Sometimes being in a hurry to fix an odd problem is the worst approach. Taking a step back, doing a little research and fully understanding the problem can often result in a faster and less expensive repair. Calling in someone with more experience with the specific problem and how to fix it is often the best course to take. Spending $500 and having someone knowledgeable fix the problem in a few hours is a lot less frustrating than spending 2 days trying to figure it out yourself throwing parts at it to no avail.
 

mg2361

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Jul 5, 2016
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4,962
Location
Pennsylvania
Occupation
Equipment Mechanic
I will exhaust every test I can perform and pick every brain I can. I can’t stand throwing parts at something. I pride myself on being a good diagnostician.

Well said Junkyard. Your whole post sums it up perfectly for those of us that take pride in what we do and want to "fix it right" the first time;).
 

Truck Shop

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Dec 7, 2015
Messages
16,153
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WWW.
I think everyone wants to make one repair and repair it right the first time, one likes loosing their thunder to someone else. But most important is not acting like
a dip sh!t when you find the problem and gloating over it, because your only one disaster away. Another thing no lab coats-dressing like {Professor Dip Sh!t}.
 

BigWrench55

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Oct 11, 2018
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Somewhere
When I first started in this field. My father told me that these parts were very expensive and you want to make damn sure that when you tell a customer that he needs this multi thousand dollar part. That you are right. I have spent the last 20years learning from others and studying how every component works. And today I have a great reputation for knowing what the problem is. It's the best feeling in the world for people to call you up because their guy can't figure it out and there machine is down and has been down. With thousands lost and thousands spent . And then you show up and fix it . The looks on their faces and the how and the hell you figure that out. Is almost as good as getting paid.
 
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