988b : Best transmission oil check practice

What is the correct ( or most accurate ) procedure to check the trans oil in an old 988b that has a dripping leak around the rear output shaft on the transfer case while it is working ?

I have an operators manuel that says to start and run the machine at low idle for 5 minutes then check the dipstick.
I usually start the engine and run at a low idle while I grease the non moving grease nipples on the machine, ( around ten minutes) then check the oils. But every time, the trans oil is well below the bottom mark on the dipstick so I add oil to get it into the working range markes.

But after running the machine for enough time to settle the oil temp into a happy working range temp, i park the machine again on flat ground and leave it at low idle for ten miniutes, then check the trans oil again it is rediculously overfull ( 6-8 inches above the full mark )

Is this normal or am I overfilling the trans ?

There is no big puddle of oil under the machine when sitting overnight but as mentioned, there is a drip when operating. ( have ordered new seals to fix this )

Check to see if the transmission breather is blocked.

Cmark said:

Check to see if the transmission breather is blocked.

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Thanks for the reply on this Cmark.
I have thought of that option as well. I checked the mushroom type breather at the top of the control valve box under the left side lift-up door behind the cab but it was breathing well.

Is there another breather on the transmission somewhere ?

There should also be one on the torque converter housing, not that it should affect the tranny oil level but it's worth checking anyway.

Cmark said:

There should also be one on the torque converter housing.

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Thanks again, I have just located that one as well ( top left side ) but havent been able to check it yet.

Are those two breathers all there is or is there another one somewhere that I cant readily see.

According to SIS, they are the only transmission related ones.

When you say it was working OK, how did you check it? Bear in mind that we're trying to equalise oil levels under atmospheric pressure and the slightest bit of back pressure in the tranny could theoretically affect things. Replacing the breathers is a scheduled maintenance item but if you don't do that, at least give them a wash in petrol or brake cleaner or something.

Cmark said:

According to SIS, they are the only transmission related ones.

When you say it was working OK, how did you check it? Bear in mind that we're trying to equalise oil levels under atmospheric pressure and the slightest bit of back pressure in the tranny could theoretically affect things. Replacing the breathers is a scheduled maintenance item but if you don't do that, at least give them a wash in petrol or brake cleaner or something.

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To check it I removed the breather, wiped the oil residue off the threaded end and blew/sucked some air though it. I was expecting it to give at least a little resistance, but was actually suprised by how easily the air went through it. There was literally no resistance to air being blown through at all.

But as mentioned, I will still need to check the torque converter breather as well to make sure its not offering any resistance.

I did have the idea that if the breathers were partially blocked it would cause the oil to rise up the dipstick and cause the output shaft seal to leak worse while being worked.

I just cant seem to get a consistant oil level reading by checking it the way the operators manual says to do it. The previous owner told me he always checked it at the end of the days work after it had run it at low idle for 10 -15 minutes.

I also asked a Cat mechanic today on the phone and he told me to operate the machine for at least an hour then let it run at a low idle to get the oil at a full loaded operating temp before checking it.
He said that I should be aware that there is a possibility that it has the wrong dipstick in it.
( apparently he has seen this a lot in older machine )

He recommended draining the oil, refilling with the exact amount according to the correct lube guide, working the machine till it is at full operation temp, idle it down for 10 minutes then marking the dipstick with a scribe if the oil didnt sit within the factory marks. he warned it may take 3-4 attemps as it is rare for the oil to settle at the same spot each time so 2 new marks would need to be made to indicate an ' average ' operating range if the factory marks were not correct.

I had several of those machines in various employments over my career. Oil changed in the seventies and eighties and would seem to expand with temperature. With all the older Cats, dozers, wheel loaders and excavators we went to check them all at the end of the shift with the engines at low idle. The dipsticks were marked for that. Doing that let all the machines cool for at least a few minutes before shutdown. Then every morning the operators were supposed to walk around the machines looking for evidence of oil on the ground before start up. They checked the engine oil just to make sure oil was on the dipstick and then started up.

I know all the Cat loaders I worked on the oil level would change a major amount from cold to warmed up.

Plugged breathers can make it much worse.

As this 988B being talked about is I believe is the same one that is having a heating problem I would be tempted to make sure breathers were 100% clean to check the transmission oil level with it hot and drain out any excess over the "full running mark" then see if the heating problem goes away.

I believe Cat dipsticks are stamped with part numbers so checking that might be a good idea. It appears the original part number was 2V2169 and the newer number is 7V5542. According to SIS that first number was good from 50W1 to last built. Not sure what might have caused the part number to change, could be something as basic as the supplier.

kshansen said:

I know all the Cat loaders I worked on the oil level would change a major amount from cold to warmed up.

Plugged breathers can make it much worse.

As this 988B being talked about is I believe is the same one that is having a heating problem I would be tempted to make sure breathers were 100% clean to check the transmission oil level with it hot and drain out any excess over the "full running mark" then see if the heating problem goes away.

I believe Cat dipsticks are stamped with part numbers so checking that might be a good idea. It appears the original part number was 2V2169 and the newer number is 7V5542. According to SIS that first number was good from 50W1 to last built. Not sure what might have caused the part number to change, could be something as basic as the supplier.

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I seem to have fixed the heating problem on this machine by changing out the thermostats, fan belts and giving it a complete oil change. The engine sits at around 75-80° Cel and the torque converter oil seems to operate between 93-97°Cels with hard work.
( digging big buckets of virgin rock and climbing up out of the hole to dump it onto dam banks )

I suspect that I have been running it with too much trans oil by checking it after running it at low idle for ten mins at start of day. I need to change the output shaft seal so will need to drain the oil to do this.
I will refill with the exact lube guide amount ( 66 litres ) and see what that points to on the dipstick after working till hitting settled operating temp then idle down for ten mins.

Would there be any disadvantage in filling with the exact right amount, running the machine then leave it overnight, then pull the dipstick marking the dipstick with a ' Engine cold ' mark so it can be checked before starting ?

Running that transmission over full isn't going to matter much if any at all. Just make sure it has enough. It should be on the stick somewhere when you check it first thing in the morning before starting up. All that I worked on had a cold level side and a hot level side on the stick. Many if not most of the time checking the oil just after start up, it won't show at all on the stick. People than add fluid and now it's over full. But really, it's not a big deal.

John C. said:

Many if not most of the time checking the oil just after start up, it won't show at all on the stick. People than add fluid and now it's over full. But really, it's not a big deal.

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Not a 988B but I think a 966C. I recall finding one way over full and figured someone started it cold and then went by the "Running" level and topped it up! Forget if it was having a problem but recall I hooked up a hose to the pressure check fitting on the filter and let it idle while filling a five gallon pail at least one time to get it down to the full mark!

I do seem to recall some machine, might not have been a Cat, that due to too much oil in transmission it caused the drain back line from the converter to be restricted and it pushed oil out the breather in the converter. That was long ago so I may have some details missing!

John C. said:

Running that transmission over full isn't going to matter much if any at all. Just make sure it has enough. It should be on the stick somewhere when you check it first thing in the morning before starting up. All that I worked on had a cold level side and a hot level side on the stick. Many if not most of the time checking the oil just after start up, it won't show at all on the stick. People than add fluid and now it's over full. But really, it's not a big deal.

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This dipstick only has a ' low idle ' set of marks on one side of it about 4 inches from the bottom.
If I check the oil hot after low idle for ten minutes, the oil is 6-8 inches above the full mark. I was worried that if working it with too much oil, I could cause the gears to splash thus causing the oil too collect air. ( there is tiny air bubbles in the oil on the dipstick after working it to full working temp )

The trans. oil was overfull when we bought our used 950H.
It would become aerated as well and looked terrible but returned an A level sos test result.
I find it easier to measure the oil in after an oil change to find an accurate starting point.

ajginger said:

This dipstick only has a 'low idle' set of marks on one side of it about 4 inches from the bottom.

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Does it have a Cat Part Number marked on it..? Refer to KSH's post above.

ajginger said:

Would there be any disadvantage in filling with the exact right amount, running the machine then leave it overnight, then pull the dipstick marking the dipstick with a ' Engine cold ' mark so it can be checked before starting ?

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The problem is that there is no "right amount". All the manuals have a table entitled "Approximate Refil Capacities", note the use of the word "approximate". IMHO the value in that table is a ball-park number to enable the machine to be safely started after an oil change, then use the dipstick to determine if any further addition is required. I have seen instances in the past where the quantity in the table for a particular compartment was waaaaaaay off.......... YMMV.

Nige said:

Does it have a Cat Part Number marked on it..? Refer to KSH's post above.
The problem is that there is no "right amount". All the manuals have a table entitled "Approximate Refil Capacities", note the use of the word "approximate". IMHO the value in that table is a ball-park number to enable the machine to be safely started after an oil change, then use the dipstick to determine if any further addition is required. I have seen instances in the past where the quantity in the table for a particular compartment was waaaaaaay off.......... YMMV.

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I got a chance to check the part number on the dipstick. It is 7V5542.

I also check the mushroom shaped torque converter breather . It was blocked with dust/oil residue so I washed it with petrol so it was easy to blow air through. ( will be ordering some new ones ).

Not sure yet if this will make a difference with the consistancy of the oil level or the oil leak on the output shaft.

So the dipstick is the correct Part Number. That removes one doubt.
Regarding checking the oil level at idle, to me it shouldn't make any difference if the machine idles for 10 minutes or 10 hours the level should still remain constant after the initial drop that occurs on engine startup.
I wonder if the oil is being somehow "lazy" to drain back from the converter housing to the transmission drop box for some reason.? To investigate the converter return hose & fittings would most likely require the powertrain oil to be drained.

ajginger said:

I got a chance to check the part number on the dipstick. It is 7V5542.

I also check the mushroom shaped torque converter breather . It was blocked with dust/oil residue so I washed it with petrol so it was easy to blow air through. ( will be ordering some new ones ).

Not sure yet if this will make a difference with the consistancy of the oil level or the oil leak on the output shaft.

Click to expand...

So it appears to have the correct dipstick and now that breather has been cleaned that should help also.

I would check the level after working machine good but not excessively hard with water and trans temps about half way up the green zone on gauge and see how it reads. Adjust to oil to put it just at the top of the running level on stick. Then next morning check it cold to get an idea where it is before starting. Then after starting check again cold but running. I imagine when cold and running it is going to be way lower than when worked hard. I always used the "running level" to be when oil was at operating temperature and the "engine stopped" level to just be a safe starting point after an oil change.

Once you have it toe where it is at the hot running level you can use that as a guide to know where it should be in morning before starting or where it should be after starting but before working. This would be one advantage of getting to know a machine close up and personal!

I don't think the transmission would be extremely sensitive to the exact oil level as other than the pump itself everything is ball and roller bearings. So as long as the pump can get enough oil to work the clutches and shift correctly I feel everything else should be good to run at least long enough to warm it up whether a bit on the low or over full side. The pressures you are dealing with in the transmission are about one tenth that of the hydraulic system. Not saying I would just run it for weeks or months at a time way high or low but that a couple hours should not be a major problem as you have probably done that sever times already!

from memory that dipstick has the metal top. Check to see that it hasn't broken off in the past and been refitted, may be a bit shorter

Nige said:

So the dipstick is the correct Part Number. That removes one doubt.
Regarding checking the oil level at idle, to me it shouldn't make any difference if the machine idles for 10 minutes or 10 hours the level should still remain constant after the initial drop that occurs on engine startup.
I wonder if the oil is being somehow "lazy" to drain back from the converter housing to the transmission drop box for some reason.? To investigate the converter return hose & fittings would most likely require the powertrain oil to be drained.

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I 'm not recalling mention of the level changing after sitting at idle. Maybe I miss read something?

Other than the initial drop when first started the only other thing I could see making a difference in the reading of the level would be the level going up as the oil got hot and expanded. But if the oil level did continue to drop with engine running, say after a couple minutes, a low idle then I could see where there might be a restriction in the drain back to the transfer-case from the converter. Or if there was a problem of plugged breather either on the converter or transfer-case. I know some machines had one on each and seem to recall some machines with one one the converter with a tee and a hose going to the transfer-case.

A bit of a side note I just recalled:
One problem I found that was caused by plugged breathers is very slow draining of oil when doing an oil change on the transmission!