Cat 924GZ transmission issues

[M&D Mechanical Repair]

Working on a cat 924GZ found bad coil for reverse and 2nd gear replaced them had a positive shift now went test and same issue came back gets warm and looses movement. When put in reverse it wants jump forward but do nothing when put in drive get same jump and no movement. Can anyone help with what might be goin on or what to test?

 

[Nige]

Have you done any basics such as cut the transmission filter element open and take a look at the media, or pull the suction screen and inspect.? If you need detailed information then we need a machine Serial Njumber.

 

[M&D Mechanical Repair]

Filter was changed and cut open it was clean. Where is the suction screen at exactly? Machine serial number is 6YW00246. I ohm solenoids from control harness found 2 that were at 20 and not the 30-65 book says pulled ohm just solenoid and got same result so replaced solenoid and stem. Tested then machine shifted positive and drove great then started doing it again where it won’t move put in reverse jumps forward put in forward jumps forward but step on throttle no matter gear no go. Got it back in shop fluid is foamy in dipstick tube, when shift only 2 solenoids that click are the 2 I replaced. Still has code FMI05 if I’m looking at the light in fuse block that blinks code. I get 1 quick flash a pause and 5 more flashes.

 

[Nige]

I ohm solenoids from control harness found 2 that were at 20 and not the 30-65 book says pulled ohm just solenoid and got same result so replaced solenoid and stem.

You may find the attached useful. 15 is the identification for a 924G. I think you need to be scrolling past that to see what else there may be in the way of Active Diagnostic Codes. To scroll requires connecting a short jumper wire between Pins 1 (wire 276-BK) and 2 (wire 202-BK - Ground) of the Harness Code connector.

I ohm solenoids from control harness found 2 that were at 20 and not the 30-65 book says pulled ohm just solenoid and got same result so replaced solenoid and stem.

According to what I see the spec for the transmission solenoid coils is below.

 

[M&D Mechanical Repair]

You may find the attached useful. 15 is the identification for a 924G. I think you need to be scrolling past that to see what else there may be in the way of Active Diagnostic Codes. To scroll requires connecting a short jumper wire between Pins 1 (wire 276-BK) and 2 (wire 202-BK - Ground) of the Harness Code connector.


According to what I see the spec for the transmission solenoid coils is below.

View attachment 352950

Thank you that is what I was trying find is the codes list and how access them everything I was finding was talking bout a screen and this machine doesn’t have a screen in it all analog gauges and roll style hr meter. The coils/solenoids I’m talking about are on the valve body right side transmission under cab this is what service/ repair manual says for checking them sir. I got set pressure gauges ordered so can check pressures in trans also. I don’t have access to them anymore after changing jobs, I priced through cat don’t have $7000 to drop on a set.

 

[Nige]

The coils/solenoids I’m talking about are on the valve body right side transmission under cab this is what service/ repair manual says for checking them sir.

There have been a number of updated Part Numbers for the (6) transmission solenoid valves. The original Part Number for the complete valve was 136-1679 (Coil 213-8760). The quoted Coil resistance at 25 ± 5°C (77 ± 10°F) ... 31 ± 3 Ohms

 

[M&D Mechanical Repair]

So it wants it to be 67° minimum to test the coils and get accurate reading? Shop it sitting in is 65° and they all tested 30-33 except 2 tested 20 ordered new ones replaced those 2 now they test 33 also. After replacing them it gets a nice positive shift into reverse actually starts go when remove foot from brake and can feel the shift into second gear those were both solenoids that ohms weren’t correct on according to giant service/ repair manual I have for the machine. It still had the 136-1679 coils in it which when replaced new coils and stems had crossed to a different number and dealer said the coils didn’t cross to working with original stems so had buy the packages deal for them. I’d have double check what the part number was on that. So I guess I’m confused the ohms on the new coils won’t follow what the service/ repair manual says now?

 

[Nige]

So I guess I’m confused the ohms on the new coils won’t follow what the service/ repair manual says now?

It happens sometimes. A part gets updated and the specs change. Is there an electrical schematic on your service manual.? What spec does that give.?

Get into the Codes and see what pops up is probably the next step.

 

[M&D Mechanical Repair]

Yea there is it’s the cat service/ repair binder that’s bout 6” thick. It gives same spec of 30-65ohms. I’m not finding in the manual where the suction screen is and been 6 years since I worked on one and can’t quite remember where it is?

 

[Nige]

it’s the cat service/ repair binder that’s bout 6” thick.

You were saying earlier that what the manual you have contained about reading Codes was different ("everything I was finding was talking about a screen and this machine doesn’t have a screen"). Does the spine of the binder include your S/N prefix (6YW1-Up) and what is the Cat Publication reference.? I see RENR3500 as being the appropriate one for your machine.

I don't know if it is relevant but I see your 6YW00246 machine Serial Number as a 924G not a 924GZ. Maybe that could explain the difference in the dash panel.

’m not finding in the manual where the suction screen is and been 6 years since I worked on one and can’t quite remember where it is?

It should be included in the Operation & Maintenance Manual which forms part of the service manual binder. See attached.

 

[M&D Mechanical Repair]

No what I was told by somebody else and found on Google said for codes wasn’t able be done on this machine when looking for way check codes cause didn’t have a bunch time to search the manual (with customer watching me) for the procedure so I tried find it elsewhere on my time quicker using Google. I don’t know why, that’s serial number on machine and machine number on side is 924G z. When I put serial number in cat online for parts it shows up as a Gz? It’s the manual was bought with the machine when it was bought new from cat, when I go check trans pressures I’ll check the manual for matching to it. The machine only has 2000hrs 2 owner. I’m thinking we are having a miss communication here sir, I’m saying the numbers your giving me for the factory original coils wasn’t same as book was giving me

 

[Nige]

It’s the manual was bought with the machine when it was bought new from cat..........I’m thinking we are having a miss communication here sir, I’m saying the numbers your giving me for the factory original coils wasn’t same as book was giving me.

And there may just lie the problem. The machine dates from 1999. If the service manual was purchased at that time then the information it contains will be even earlier than that, maybe by a couple of years. So any changes to specifications, etc, that may have taken place in the online system in the intervening 25+ years will not be reflected in the paper manual. As I mentioned above the current spec shown for the solenoid valve coil resistance for a 136-1679 Valve Assy is listed 31 ± 3 Ohms.

Please cany you take a look at the top RH corner of the cover page of the section of the manual where you found the information about the coild resistance and post it up. I would like to compare it with what the system lists now. I suspect it will be SENR1218-xx but the kicker is what the "xx" is.

Here's how 6YW appears for me.
What I also found is that machines up to 6YW00946 (end of 2002) were fitted with analogue gauges and would require the use of the Harness Code connector to pull Diagnostic Codes. It was only after S/N that the all-electronic dash panel appeared.

 

[M&D Mechanical Repair]

That very much could be an issue. Book says 30-65ohms but they all fall right between 31-33 now with the 2 new coils. Since then have done more testing found all my pressures are in line with the manual and I believe what you shared, I found the 2 forward stems weak. Upon replacing them coil and stem only way cat shows do to a cross to an update new coil stem number is 186-1525. Replaced those and now machine stops trying go forward when forward pressure was loss and I no longer completely loose pressure I only loose pressure in forward gears return neutral or go reverse they come back. I swapped the low side coil with 3rd gear cause it gives me fits in reverse also at times and now I got good 1-3 reverse but forward gotta play with it and can get pressure back randomly to 1-3 forward but always had 4th gear which fwd high and 3rd gear are running new coil/stem. Is it really possible with 20+ year old that was really watery like consistency, 2000hrs on machine that all the coil/ stems are bad? I keep getting a little closer to solved every time I swap out an old coil/stem but I can’t wrap my brain around them all going bad like that? I have bench tested stems and they click very soft unlike new ones that have a fast hard to see valve move in the holes click. I will check that page reference number next time I’m at machine probably be Friday

 

[Nige]

I have bench tested stems and they click very soft unlike new ones that have a fast hard to see valve move in the holes click.

I think there could be a clue. When energized those solenoids should activate with a fast and hard "clack" noise.
Have you tried giving the valve parts a spray with something like brake cleaner to get the oily residue out of the inside of them.?
I wonder if something in the transmission oil could be causing the symptoms to the old coils.?
What oil is in it and when was it last changed.?

 

[M&D Mechanical Repair]

I wasn’t sure if I sprayed brake clean inside the stem part if would hurt it. That’s what new ones do old ones click but it’s not a hard click or fast. I can see old ones moves new ones move so quick can’t see it. Transmission fluid was changed at beginning this and suction screen cleaned.

 

[Nige]

I wasn’t sure if I sprayed brake clean inside the stem part if would hurt it. That’s what new ones do old ones click but it’s not a hard click or fast. I can see old ones moves new ones move so quick can’t see it.

It can't do any harm to the "old" ones because if you can't get them to click hard and fast then they are going to need replacing anyway. If you can see the spool move when the solenoid is energized then it's moving far too slowly.

Transmission fluid was changed at beginning this and suction screen cleaned.

What I was trying to get at is what brand, type, and viscosity of oil is being used in the transmission, or maybe even some insight into what oil was used in the past. If the oil is not the correct type or viscosity, or both, it could be gumming up the solenoid valves internally which might go some way to explaining why all six have gone bad at the same time.

 

[M&D Mechanical Repair]

Not sure why my reply never posted other day. I can’t comment on previous oil in it current owner hasn’t changed it and didn’t know if previous owner did either. Machine has 2000hrs total on it. It now has cat TDTO 30 oil in it. I went ahead and replaced last 2 after moving them around found they weren’t working right. Now I have all reverse gears, high side fwd and fwd low cold. Once starts warm up I keep all reverse and fwd high gears now I longer loose everything. But I’m loosing all fwd low side gears still which I think the slog valve from what I’m following in the book would be blame for that cause when shift gears can see tires on machime rock forward but no pressure to engage fwd low clutch. Is there away without pulling valve body to pull that spool and slug out since I can access the cap to remove with valve body on machine?

 

[Nige]

Is there away without pulling valve body to pull that spool and slug out since I can access the cap to remove with valve body on machine?

Officially no but you might manage to finagle it out. It needs to be stood in front of the machine to form an opinion yes or no.

I can’t comment on previous oil in it current owner hasn’t changed it and didn’t know if previous owner did either.

So in that case where nobody seems to know when it was last changed my honest suggestion would be to change the oil & filter, at the same time cutting the old filter open for a detailed inspection of the filter media. That would be after whatever disassembly/inspection is done to the control valve. From your description it certainly sounds like the moving guts of the valve are gummed up.

 

[M&D Mechanical Repair]

I did go ahead and change the oil and filter after I found out they just changed the filter not both. Unfortunately they cut the old filter open before I was called about job said seen nothing and pitched it. I Checked and cleaned suction screen and magnet. Then retested machine got same results. That’s when I went checking and found solenoid issues. Replaced them as I tested them to find all bad. Got so I don’t loose reverse or it try to turn into drive and I don’t loose drive in 4th gear. Just loosing it in fwd 1-3 pulled valve body found debris in it and slug/dump valves dragging and hard move cleaned them and they now will come out without having pull slug valve out with pliers. Did the chemical check for cracks and found none in any of the sections of the valve body and no issues with the center plates either besides the dump valve on outside had corrosion making issues with the small separator plate. Gonna get new seals and put it back together and give it another go. Only thing left after this is drive low side clutch in trans

 

[Nige]

With all the contaimination you found in the control valve gumming up the works I wonder if there might be something similar deeper in the bowels of the transmission where a similar situation exists.? All it needs is for a passage or orifice somewhere to be partially plugged and all the pressure does it to force the contamination tighter into the hole to present the symptoms you are seeing.

I don't know how you would confirm it but based on what you found my suspicion is that they were not using the correct oil in the transmission.