Hey guys I’m new here didn’t know where else to look for help. I recently purchased a 1994 cat 928f with 5200 hrs on it. Everything was pretty good on it besides a bit of a rusty cab and I had to fix some wiring issues with the lights. Now I ran the machine maybe 5 hrs since I bought it and it’s been sitting in the shop. I noticed a large puddle of what looks to be hydraulic fluid under the rear end so I crawled under and cleaned it off. It looks like it is coming from 2 small fittings on the rights side? One looks like a male air line fitting but smaller and the other is almost flat. They could be turned so I tightened them but it’s still leaking. Any ideas on what’s going on? Thanks for the help ahead of time.
First - Serial Number. Help to identify Part Numbers Take a photo and post it so we can see what you're looking at. Maybe take one from a distance as well for context.
Hey here is a photo of the serial number and a photo of what I believe is leaking. There is another one on the other side of the rear end also. It is some kind of balll valve I’m not sure what for tho.
When oil is coming out there it is an internal brake seal leaking. You can probably observe the oil coming out while holding the service brake pedal.
where the oil is coming out it is very rusty and someone told me maybe unscrew and replace where it is coming from. Does that make any sense or you belive it is a brake seal?
I ran into this once many years ago on a 928. It appears the be a bleeder fitting but it is not, it is an indicator of brake seal failure. I am not an expert on that machine . So shortly after repairing the cat axle a had a John Deere come in, every time the service brake was activated oil would come of of a similar looking bleed screw. I removed the axle and tore it down but could not find any issue with the brake seals, turns out on the Deere it was actually a bleeder screw and the only thing wrong with it was the bleeder was loose.
Left fitting bleeder for removing air from brake circuit. Right fitting is breather for axle oil. When brake disc orings leak, brake oil is introduced into the axle oil, filling up the housing. That's where the oil exits after the axle housing is completely full. Brake job time.
Great lol. I assume a brake job is a big task on this machine? Do you have any idea price wise? Thanks for your help
First and foremost, verify whether the axle is filled to the correct level. Do you have an operators manual?
I don’t have one but a friend of mine does and I’m getting it this weekend. If it was overfilled why would it just start pushing it out now? I ran it’s for about 5-10 hrs before this started happening. Thanks
Oil only transfers when the brake pressure is sufficient enough to squeeze past the worn piston seal. So, a little oil is added everytime the brake pedal is depressed hard enough.
If you want an Operation & Maintenance manual then you can download one from the web in pdf form for less than $50, probably the best money you'll ever spend I agree with HMC. The oil is likely coming from the "flat" fitting on the RH side of your photo which is the relief fitting for the axle housing. To the best of my knowledge only one side of the axle has that fitting, the other side will only have a brake bleeder like the npple of the LH side of your photo - please confirm that. If the brake piston seals are leaking and oil is going into the axle then the oil is coming from somewhere. Is the hydraulic tank level low or has oil been added to the hydraulic tank recently that you know of..? Try doing a test to prove which fitting the oil is coming out of. Clean the area of all the accumulated oil, start the engine, and then have someone press and hold the brake pedal down while you go under the machine with a light and see where the oil comes out. After that check the axle oil level, pretty well guaanteed it will be over-full.
The oil is not coming from the flat fitting it is coming from the bleeder. And it slowly drips oil when the brakes are not pressed. Just sitting it will slowly leak. I’m buying a new bleeder screw to make sure that one is not defective for some reason. Thanks
Is the oil coming from the bleeders on both side of the rear axle or just one of them..? If you have to replace it the Cat Part Number is 5H-3701. Price about US$5. A suggestion while you're in round that area. Remove the flat fitting and make sure you can blow through it from the inside. I've seen lots of them seized by paint or rust and that can cause other big $$ problems. If you want to replace it you need 8T-0336, about $2.
Just the one side I took a photo of I checked the other side and it’s dry
Have you tried turning the bleeder ? It's basically the same as a bleeder for just about anything with hydraulic brakes, be it a Cat front end loader, Ford pick-up or even my Harley Sportster, heck even my wife's Vespa has fittings like that! I would replace with one from Cat as that way you know it's the right thread and length. Also not a bad idea to replace the other "flat fitting" just to be safe. Cost to replace all them will be less than the gas money to drive to the dealer!
Yeah I tried turning it didn’t make a difference. I’m picking them up from cat 8$ each for 24 bucks it can’t hurt
When you remove the one that is leaking I would be very careful to clean out the hole and make sure there isn't some crap down in the hole or guges in the seat area for the end of the bleeder valve.
Well I went to cat and got the new bleeder valves. They were leaking but the vent is also leaking very slowly so like someone said above it’s probably the brake seals went and are filling the axel. Cat said worst case of I bring them the diff 10k awesome Friday
Well that sucks! Hate to say that if you don't have the means to safely remove and support the axle while working on it you might have to hire that job out. I came close to having to do that job on I believe a 950F. I was asked to go to another plant to diagnose the oil leak on the machine and it was just like this 928F, coming out the vent/breather. But someone in upper management decided to farm that job out, I was actually hoping to get the job. The shop at the quarry has a 40 ton overhead crane, fork truck and carry-deck crane among other tools to work with so the size of the parts was nothing we/I could not handle! Heck we had no trouble loading a 980G with a dead motor on a lowboy or swapping rear axles between two 988B loaders parked back to back in the shop among some other large things like stone crushers! Oh yea, back in the day it was nothing unusual to split 988B on two to have line boring of the center pins done! But no! I could not handle a "big" job like dropping an axle out of a 950 F! Things like that were one of the deciding factors in retiring at 65.
$10k? Is that Canadian? Dealer doing my 544Js or 426C backhoes is always under $6k. If you can get the axle out, that's the toughest part, just because of rigging and lifting. 20 hours @ $150...$3k Parts @ $1k (probably closer to $650) So, there's $4k Add another $2k if you go after axle and pinion seals. If you can get an independent, it should be less. Did you know, Caterpillar dealers can produce a formal quote.
Don’t start panicking just yet. If you had a major brake seal leak you would be losing oil out of the hydraulic tank almost as fast as you could top it up. I am assuming that this is not the case as you never mentioned it. Have you actually checked the rear axle oil level.? If it is high, drain it down to the correct level and run the machine as you normally would for a couple of days. Keep an eye on the hydraulic oil level during that time. Then go back and recheck the axle oil level. If it is high drain it back to level but this time carefully measure how much oil you drain out. Report your findings. Also mention how many hours the machine operated in that time. Another question. When was the last time the rear axle oil was changed.?
10k is Canadian . They said that’s the worst case. I’ve been busy with work but I’m going to start the process of removing the axel in the next couple weeks. Now I have a question. Why is there clean hydraulic fluid coming out of the diff if the brake seals are gone? I would assume if the brakes were shot it would be dirty old with debris in it from the brakes being shot? Thanks for the help guys .
Also do any of you know and website to download a service manual? I looked and I could only find one in French.
Please go back and read my last post #22 above, and above all - don't panic just yet . Do what I suggested in that post and report back with all the requested information before you even consider removing the axle. If it does come to having to remove the axle there is plenty of information that we can come up with to help you.
I just reminded myself that I should never assume..... In this case I was assuming that you either have an Operation & Maintenance Manual or if you don't have one that you already know how to check the oil level in the rear axle. Just in case you don't, here's how to do it..... In the 1st illustration below you are looking down from above on the LH side of the rear axle. Clean the area on top of the axle housing and remove #18. You will find that it is actually a dipstick with ADD and FULL marks on it. If the rear axle oil level is too high, carefully drain some oil out of the drain plug #17 (2nd illustration) that is located on the bottom of the rear side of the differential housing in the centre until the oil level is between the ADD and the FULL marks on the dipstick with the plug #18 screwed all the way into the axle housing . If you ever go to change the oil at any time in the future the fill plug is #1 on the same illustration.
I check the fluid. It was so full when I pulled the dipstick out oil started pushing out of there. I drained it from the drain plug now it is at the correct level.
OK, all good so far. Lowering the oil level will stop it coming out of the relief valve on the top of the axle, at least for the moment. What did the oil look like that you drained.? Dark and cloudy or clear and bright, or maybe something in between.? Remember that photos are always good. They help those who aren’t there to see the same thing that you are seeing. Next thing is to do as I suggested and run the machine for a few days then go back and check the oil level in the axle again. Remember to keep a close watch on the hydraulic tank oil level during that time. If you are losing major quantities of oil past the rear axle brake seals the oil level in the sight glass should visibly drop. I know I asked the question before but don’t recall a reply. Do you have an O&M Manual.?
The oil is say was pretty clean like an 8 out of 10 if 10 was brand new oil. The hydraulic tank is low right now. I’m going to top it up and see what happens in the next bit. I don’t use this machine to often I’m just trying to get it ready for winter.
Under those circumstances it may pay you to run it for a bit more than you would normally do just to get a handle on whether the amount of oil leakage you have is significant or not. Top up the implement hydraulic tank before you start testing. When was the last time the oil in the rear axle was changed.? O&M Manual.?
No idea when the last time the axel oil was changed as I just purchased it a few months back and no I don’t have a o&m manual.
Also. What is the best case scenario here? Say this is a very slow leak and it takes hours for it to fill the diff? Is this something I can leave but keep a close eye on the fluid levels? Or will this need to come out and be repaired either way? In the rear end all that is in there for fluid is hydraulic oil? I thought it would be something thicker.
I’ll post some detailed info later on how you can download one from the web. The usual price is around US$45. Regarding the rear axle oil based on your description of it I am going to advise to hold off changing it until we get to the bottom of the brake issue, because if the worst comes to the worst it will have to be drained anyway before removing the axle for the brake repairs.
The oil in the axle is an SAE50 TO-4 oil. The oil in the operating side of the brake system is an SAE10 hydraulic oil. Under normal circumstances these two oils would never come into contact with one another. Apparently what you have is SAE10 oil leaking into the axle housing, which is why it’s filling up. The $64,000 question is “how fast is the leak and does action need to be taken immediately to fix it or can the machine run for a while like it is.?”
Yep. If you could send me that link later it would be of great help. I’m going to change all the fluids in this machine because I have no idea when the last time it was done. If you can find which specific oils for each component and the quantity that would be awesome. Thanks for all the help.
OK, for an O&M manual, follow these instructions - Go to - https://catpublications.com/ Click on "Continue as Guest" Type SEBU6626 in the window at the top of the page and click "Search". You should see the illustration below - $46 for a downloadable pdf document. If you do go this route and buy a download you need to go to the top RH corner of the screen in the black bar and click on "Login". At the bottom of the popup that appears is a "Manage Orders" button. Click that to actually get your download. The O&M will contain all the fluid recommendations amongst a lot of other info. If you have any questions after reading it then post back here.
My fluid recommendations would be: - Engine - SAE 10W30 or 15W/40 meeting at least API CG-4 or better. Transmission - SAE30 oil meeting Cat TO-4 specification. Axles/Differentials - SAE50 oil meeting Cat TO-4 specification. Hydraulic System - SAE10W hydraulic oil.
If we're talking about a really slow leak it could take days or even weeks to fill up and overflow the differential. That's the idea of setting the oil level correct then running the machine for a few days to see how much the oil level goes down in the hydraulic tank and up in the rear axle. We have to know what sort of leak we're dealing with before making a decision. I've run machines for weeks or even months (under controlled conditions - in other word keep an eye on the oil levels) with leaking brake piston seals because circumstances dictated the machine in question couldn't be stopped to pull an axle out.
So I will need to do the seals at some point either way. Well I’ll see how fast or slow the leak is but I think that diff is coming out either way. I need it fixed properly I can’t just keep watching the oil every few days.
Sorry but I don't see what's so hard about watching oil levels..? TBH checking the hydraulic oil level is part of the daily pre-start check.
There is nothing hard about it. There is obviously something wrong with the seals tho. They will need to be fixed. I can’t do anymore damage by have the wrong fluid in the diff? I can’t have the machine go down when it’s in use is all. Thanks alot for the link to the o&m manual. It is a huge help.
The thing I would want to know is does it take one day or one month to leak a gallon of oil in to axle. If it is passing a gallon a day I would make it a priority to get the leak fixed. But if it takes a month or more I would be looking for time in the work schedule for myself and who ever you are going to have do the work. Might be able to plan it for a time when machine and mechanic both are more or less free. That way you don't have to air freight in a part that you did not expect you would need.
Right now is the slow time with the loader. That’s why I am going to see how bad it’s leaking. Like you said if it takes a month to lose a gallon it might be able to wait.
I'm sure that you are all aware that the leak is most prominent when the brakes are applied. Right way is to disconnect feed line to one side a pump it up with a porta power and gauge. With knowing test spec, I'd call 750psi a good number. If it holds, test other side. Odds are that only one side is leaking, but there is no way I'd only reseal one. Does Caterpillar have a brake lining inspection hole on each side like on my Deere machines?
Yes there is a inspection hole to check the brake measurements I’ll do doing that this weekend to see how they are. I ran the loader for 3 hours today and the fluid has not risen any that I can tell on the dipstick. I’m going to keep running it when I have time to see how long it takes to start filling up.
That’s what I was alluding to in asking how long since the rear axle oil was last changed, because I’m betting that was the last time anyone looked at that dipstick. Obviously because you only recently bought the machine you don’t know. However if you were to discover that the oil was last changed say 18 months ago (for the sake of throwing a number out there) I imagine that might change your perception of how urgent it would be to get into the axle to replace the leaking seal in the brakes, because that would be the length of time that the amount of oil you drained the other day had taken to accumulate. The oil in the rear axle should be an SAE50 TO-4. To mix small quantities of SAE10 with that wouldn’t do any harm in the short term, especially if the SAE10 was also a TO-4 oil.
Well I’m going to play it out the next while and if it does not seem to be going up to fast I’m going to drain the axel and fill it with the correct oil. And hope it takes 18 months to fill back up. And if it were my guess I’d say it’s been a long time since it’s been done based on the amount of crud and such on all the drain plugs and the dip stick.
I think that's a sensible attitude. Until you have a handle on exactly how much oil is leaking in what time frame IMHO it would be impossible to make an informed decision on how urgent it is to make the repair. When it comes to removing the axle there will be plenty of help available to guide you through the process.
And if you do come back to ask for the "Remove Rear Axle" instructions be sure to include the S/N in that request even if you have posted above in this thread, save who ever sees the request from having to scroll through several pages of the thread trying to find it. I would also suggest you do post that request right on this thread to keep continuity to the problem. good Luck!
Well I ran the loader on aug 28th for about 3 hours and it’s just been sitting since. The oil on the dip stick for the rear diff has risen about 1/2 and inch. It must be a bad seal leak if it’s leaking while it’s just sitting right? If I run the machine I thought it would fill up faster while I’m running it and using the brakes. It seems to fill up faster when it’s just sitting.
It can't leak "just sitting" in my opinion. It will only leak when you actually apply the brakes, because it is hydraulic oil from the brake operation side that when you press the brake pedal is leaking past the brake piston seal into the axle housing. How much did the oil level in the hydraulic tank go down in the same time..? See the illustration of the differential and one of the brake packs below. The hydraulic piston for the brake is #6 and it has two seals (circled) on it. When you press the brake pedal those two seals are going to be what's leaking, either on one side of the machine or both I don't know. Either way it would be normal to replace the seals on both sides at the same time. The BIG problem about disassembling the brake packs is that it requires the axle to be removed from the machine and stood up in a vertical position, it can't be done horizontally.
I’m going to check the hydraulic fluid later today. But it definitely leaks while it’s sitting. The diff keeps getting fuller.
Have to agree with Nige, seems strange that you say it is filling up more when parked than when being used. Can't see why there would be any pressure going to the wheel brakes with it parked and engine off. Could it be that the side of the axle with the dipstick in it was just lower than the other side? Maybe when you checked it the first time the dipstick was at the high side and the next time you checked it it was at the low side of the axle. I thinking the only way to prove it is leaking while parked would be to drain down till it was at the right level and then without moving or running the machine check it after a day or two. I can see finding the oil level to go up slightly while parked if one was to check it right after running and then check again after it had set for some time which might give time for oil to drain back from planetaries and off the inside of the housings. Careful checking of both hydraulic and axle oils is important to be sure what is going on. And check it with machine nice a level every time. As an example we had a Mack truck at the quarry that when parked in shop and oil was checked right at the full mark. Then when parked outside next to shop it would show below the add mark. The dipstick was at the rear of oil pan and where the truck was parked outside looked level to the eye but was actually a very slight grade and truck was facing towards the low end of parking space!
Thinking aloud I wonder if there is a leak somewhere in the brake accumulator side that is causing a slight residual pressure in the brake system that is just enough to weep it past the piston seals..? To the OP. Run the machine. Set the oil to the correct level in the rear axle dipstick and carefully note the quantity of oil you drain out. Also note the oil level in the hydraulic tank. When you have shut down the engine press the brake pedal numerous times until it goes "hard" under your foot. That means that the brake accumulator has been completely discharged. Note how many pumps of the pedal it takes for this to happen. Leave the machine stand for a few days in one spot and go back and check the hydraulic tank and rear axle oil levels again.
Ok will do this weekend. I drained it the first time to get it to the correct level and I drain out roughly 25L to get it to the correct level. But the hydraulic tank was not low 25 L it was down maybe 12L but I’m not sure what the previous owner was doing.
Good once you get a solid baseline to make judgments from it will be much easier to make an educated guess at how bad the leak may be and how soon you need to be looking into a major repair.
Ok. So I drained about 10l for oil from the diff so it was at the bottom of the add mark. Let it sit. And it is still filling up. Any ideas? I didn’t touch anything else because I wanted to see it was actually leaking when just sitting. Does the park brake have anything to do with these brakes or is it a different setup.
Did you do as suggested by Nige above?: To the OP. Run the machine. Set the oil to the correct level in the rear axle dipstick and carefully note the quantity of oil you drain out. Also note the oil level in the hydraulic tank. When you have shut down the engine press the brake pedal numerous times until it goes "hard" under your foot. That means that the brake accumulator has been completely discharged. Note how many pumps of the pedal it takes for this to happen. Leave the machine stand for a few days in one spot and go back and check the hydraulic tank and rear axle oil levels again. At least give us an idea how much and how fast it is "filling up." Also is the hydraulic oil also going down? As for the parking brake, going by SIS it is located on the drive-line just forward of the transmission. A basic drum type brake that is actually your simple mechanical brake. Lever should be to left of operators seat.
No I didn’t not do exactly what he said. I drain it and did not want to start it or touch the brake to see if it leaks sitting. It filled up about 8l in 3 days. 2.5 days. The hydraulic oil was down a bit yes. Where else could the oil come from? I know the seal leaks I’m just wondering why it leaks while sitting. Everyone says it should leak when the brakes are being applied
If the seals are really bad, or the piston is cracked, remember, the feed line to the brakes is higher than the axle, and siphoning can occur. As an aside, does a Cat loafer have recircultor pumps, screens, and coolers like my later Deeres? If the recirculate pumps are hydraulic driven, could that be the source? Is there a rear differential lock, and, if so, is it hydraulically activated? Could that be a leak source? It would seem as if the easiest course of action is to disconnect the brake feed to the rear axle and pressurize the brakes with a porta power. Someone else will chime in if the pressure for testing should be 750 psi or not.
By not going through the procedure I suggested above you did not remove any residual pressure in the brake system between the cab and the axle, so there is no way of telling how much pressure you had in the system that could cause oil to leak into the rear axle. Just saying.
Axle oil cooling is optional on some Cat loaders but not on this particular model. No differential lock fitted. The cutout pressure for the brake accumulator charging valve is 2100+/-50psi. Pressure testing with a Portapower to anywhere over 500psi and watching the pressure decay IMO would indicate whether the brake piston seals were leaking big time or not.
I didn’t have time to do all that when I was there. I’m going to try today. But if there was no leak wouldn’t there always be pressure from the cab to the axel? So by pressing the pedal till the pressure is gone am I not just pushing all that fluid into the axel from the brakes?
I was thinking about that too! Pump up to even 300 psi and see if it drops off. With the reported leaking I'm thinking just trying to build any pressure will not be easy!
The idea is to release pressure from the brake hydraulic system accumulator THEN drain the axle oil to the correct level and monitor the level for a couple of days. And my apologies - I got the sequence the wrong way round (I set to set the axle oil level then release brake pressure) when I told you the first time.
No worries. I’m going to run it for a bit in the next couple days then I’ll pump the brakes till there feels like there is no pressure then I’ll set the oil. Now if it is still leaking oil into the axel is there anything else that could be the problem or is it my brake seals and I just need them fixed.
Ok guys so Ive decided to just re build the brake seals and see if anything else needs and work in the axle. im going to be keeping this loader for a few years to come so the investment is worth it to me. now i need some help with a service manual. Or if you guys could give me some guidance on how to get the rear axle removed. Serial number for my machine is 2xl00721. 1994 Cat 928F. I have lots of big lifts and equipment to move everything around and lots of blocking to safely get the machine up. Any help would be awesome. Thanks.
Guess my question would be are you just wanting to get the axle out or do you plan on attacking the problem yourself? If just needing to drop axle start a conversation with me and I'll see how big a file that would be. If you are planning on keeping this machine for a "few years" it may be to your advantage to invest in a service manual for it. You can go to " https://www.servicemanualpro.com/ " and do a search under your serial number and down load a manual for $410.00. or order a paper version for $672.00. I believe there is someplace in that process where it will ask you to"Log on" but there should be an option to "Continue As Guest". I think the $410.00 will seam cheep compared to what the dealer will be asking just to disassemble and reseal that axle and even if you do still let them do that work I would guess that over the next several years the book will pay for its self.
for now im just planning on getting the axle dropped out of the machine. A friend of my dad works at cat here and is going to give me a great deal on rebuilding it depending on what is all wrong. I will be purchasing that service manual asap. there a huge help. how do i start a conversation with you? im pretty new on here not sure how it all works. thanks.
Well I got the rear axle out today. Took about 2.5 hrs not to bad. It’s going to cat on Monday I’ll let you guys know how much she sets me back in the wallet.thanks for all the info in here.
Hoping it's mostly a handful of seals and orings and a bunch of labor and no major hard parts.
Well guys I just got a call from cat. Brake seals were completely shot. And the brake discs were pretty worn so I replaced them. Everything to be fixed is about 3700 Canadian. She’ll be good as new now.
A bit less than the CAN$10k that I think was originally bandied around for the repair - maybe that included overhauling the diff as well. You must be pretty happy. With only 5200 hours it's likely that's the first time that rear axle has ever been out. Now all you have to worry about is the brakes on the front ………
Yeah it was a good price. The 10k was for a total over haul. They said everything looked really good otherwise. They said I could of left the brakes and they would of lasted a little longer but I figure while it’s out and there i paid all the labour already so figured I’d get them done. Thanks for all the help.
No point going in there and not doing the brake discs at the same time as replacing the failed piston seals. What type of oil are you planning on putting into the axle once you get it back in the loader again.?
Glad you were the one to bring up that point! I was thinking that for some time.
Usually the brakes on the front axle wear faster than those on the rear because of the weight transfer to the front. So either the front brakes have already been done by now, or if not and they have worn more than the rear ones they’re just about on the point of letting go.
Speaking of the oil to be used doesn't this machine also need to have additive added to the axle oil for the wet brakes? I thought I saw reference to that at one point but can't seem to find that information again! Believe it called for .5 liters of the additive. EDIT>>>>>>>>>>>>>> Did some more digging and found part of what I was looking for in the section in the maintenance manual on changing the axle oils: 4. Add 0.5 L (.53 qt) of oil additive to each axle. See Axle Lubricant in the Lubricant Specifications of the Maintenance Section. Only problem is I'm not seeing it mentioned in the Lubricant Specifications section.