Cat 120g trans problem

[Nige]

The springs in the control valve I did not replace or test under load.

Were the free lengths within spec.?

All the detents, cables and linkages seemed to be ok.

Did you do the adjustment procedure.?

Also I’m really not sure how I’m going to do these test because of it wanting to stall in 1,2,3?

You could remove the axles from both tandems. If it was an H-Series or later then alternatively you could remove the lower drive shaft to the differential but you can't do that on a G.

At the very least you need results for pump pressure, direction clutch, & speed clutch in neutral. The results for pilot pressure & transmission lubrication pressure might also be revealing.
You should ensure that all machine systems are at normal operating temperature before you take pressues. If the numbers you posted above were with the machine relatively-speaking cold those measured pressures should reduce even further when it reaches operating temperature.

Did you open up the pump.? The 285psi you measured is significantly below the bottom of the spec considering that it's 310+/-10psi. I would suggest first having a look inside the pump before you go adding shims in an attempt to increase the pressure. Do you have any idea how accurate are the gauge/gauges you are using for measurements.?

 

[YellowIron25]

After testing some of the springs they are close to spec but not exact for free length. For example on the differential selector and pressure control valve
Spring 3p8042 spec calls for (.431) and what I measured was .432.
Spring 2p4547 spec calls for (.877) and what I measured was .853.
Spring 3p812 spec calls for (1.139) and what I measured was 1.131.
Spring 3p6669 spec calls for (2.796) and what I measured was 2.688.

So would you just go ahead and replace the all the springs?

Yes I did the adjustment procedure.

Also, I replaced the pump and now I’m getting 315psi +/- at low idle. My gauge is a digital gauge I got off the internet so it’s probably not the best quality.

 

[Nige]

Sorry for the delay. This one slipped off the radar for some reason.
I don't think the springs are going to affect things too much but long-term I'd suggest that they should be replaced with new.
TBH first I would suggest to get the machine up to full operating temperature and then pull the axle shafts. It only requires draining a bit of oil and two forcing bolts to pull the shafts out. See attached.
You could then measure P1 & P2 in every gear F & R and post the results. The other thing to look at when shifting from neutral to a gear, or from one gear to another, is to pay particular attention to the behaviour of the pressure gauges and how fast they recover pressure after dropping to around zero during the shift.

 

[YellowIron25]

No worries, I just appreciate the help! I will give this a try and post results when I get them.

 

[YellowIron25]

Ok so I took the p1 pressure check. At idle it is at 85psi. In all gears forward and reverse it was 197 psi with the modulated pedal pressed in. I didn’t take axles out yet. Going to do that and recheck them. The p2 at idle is reading 0. Also oil is pouring out the poppet valve on top of the control valve. Is this normal?

 

[Nige]

Also oil is pouring out the poppet valve on top of the control valve. Is this normal?

Does the oil pour out all the time or only under certain circumstances such as when when the transmission is in neutral, when the modulation pedal is depresssed, etc.?
P1 at low idle in neutral is fine, the spec at both low/high idle RPM is 90psi.
I suggest next step is that you need to get the axle shafts out. I feel that you really need to be able to measure P1 & P2 with the modulation pedal released.
Below a table of the transmission clutches for the various gears.
If speeds 1-3F and 1-3R don't work then #6 clutch is the common one for all those six speeds.

 

[YellowIron25]

Ok so I remove both axles. It still wants to stall in 1-3 forward and 1-3 reverse. It also seems like it leaks out the poppet valve all the time no matter what I do.

Speed clutch (b) p1
Low idle in neutral 82-85 psi

1-3 forward and reverse with modulator pedal pressed in Im reading 197psi low idle. It wants to stall if I release modulator pedal.

4-6 forward and reverse with modulator pedal out Im reading 315psi low idle.

Direction clutch (c) P2

Low idle in neutral 0 psi.
1-3 forward and reverse wants to stall.
4-6 forward and reverse 258psi at low idle.

 

[Nige]

1-3 forward and reverse with modulator pedal pressed in Im reading 197psi low idle. It wants to stall if I release modulator pedal.

Right there I think are the symptoms of your problem. Now that the axle shafts are removed IMHO the engine should not stall because in this condition the transmission is not driving anything other than itself.

The first possibility I can think of due to the fact that it doesn't stall in neutral but does in 1-3 is that clutch #7 is stuck somehow and is not releasing.
Refer to the table I posted above. Note that in gears 3-6 both Forward & Reverse Clutch #7 is engaged. It is also engaged in neutral.
The difference between 1-3 & 4-6 in both directions is an either/or but not both at the same time situation when it comes to the Low/High Range (#6 & #7) clutches. The lower three gears use clutch #6 and the higher ones use clutch #7.
Only one of the two clutches #6 & #7 can be engaged at any one time. So if #7 is not releasing then when you want to engage #6 the transmission will have no option but to stall the engine.

 

[YellowIron25]

Yes sir makes sense. So I guess I need to remove the transmission again and check everything is right in the 7th clutch?

 

[Nige]

Unless it's:-
1. Something in the transmission control valve that is playing up or incorrectly assembled and constantly pressurizing #7 clutch.
2. Transmission control cables incorrectly installed/adjusted.

Can you remove the TCV through that hole in the side of the case.?
If you do end up removing the transmission make sure to pressure-test the clutches for piston seal leakages with compressed air during reassembly.

I can't remember now whether you said you had a service manual or not.

 

[YellowIron25]

So I went ahead and removed the transmission again. After looking at clutch 7 it looks like the carrier is different than what the book is showing. I will post some pics of what I’m looking at. Also I counted my old clutch plates and disc for clutch 7. I counted 3 plates and 4 disc removed. The book is calling for 4 plates and 4 disc. I just now realized I only removed 3 plates. So I’m thinking this could be the issue? And after measuring the raised part on the carrier it is the same thickness as the plate.

How do you do pressure test the clutch’s with air?

 

[Nige]

So I went ahead and removed the transmission again. After looking at clutch 7 it looks like the carrier is different than what the book is showing.

To answer that question will require the Serial Number of the transmission. From what I can see there have been a number of different planetary arrangements, some determined by machine Serial Number, others by transmission Serial Number.

Is there a Part Number stamped anywhere on the #7 clutch carrier.? See attached. You may have upgraded parts in your transmission. Make sure that everything that is called out as being required in the procedure has actually been installed. Four friction discs and threew separator plates are correct provided all the updated parts have been installed together.

Is the Service Manual you are using appropriate for your machine Serial Number.? Apparently there are different manuals for different Serial Number ranges of 87V and to complicate matters even further all of them are Publication Number REG01654.

How do you do pressure test the clutch’s with air?

If the transmission control valve is removed there will be a number of passages under it, each one of which feeds oil to a different clutch. Whack a blow gun on to each passage in turn, put some air pressure on it, and listen for any leaks. You should also be able to hear a distinct "clunk" as the piston moves and a second one as it returns when you take the air pressure off.

Another question while I think of it. Are the 3 x 3P-0817 discs springs installed with the correct orientation.? Also do the springs meet specification.? They are what retracts the #7 clutch piston.

 

[YellowIron25]

Serial number
87v1469
Transmission serial number
3P756
Arrangement# 3P1750 3P5379(the last four are kinda hard to make out)

After reading through your attachment it appears someone upgraded the parts at sometime and I didn’t realize it. I was just going by the book. So that’s probably been the problem the whole time.

Here are the manuals that I have. Also that attachment that you sent. Is that bulletin from Cat and how do I get them?

The 3P0817 springs are the only ones I didn’t change in the transmission. Do you have the specs for those?

 

[Nige]

The 3P0817 springs are the only ones I didn’t change in the transmission. Do you have the specs for those?

For some reason that I cannot fathom they are not in your Service Manual but I found a spec for them in a manual for a different model. See below.

Here are the manuals that I have.

OK, so you have a Service Manual that is not appropriate for your Serial Number. You have SENR3655 that is valid for machines with S/N above 87V8360. You need REG001654 which is for machines with Serial Number up to 87V8359, like this one...........
https://www.ebay.com/itm/383874061233

Despite that I don't think even having the correct manual would have identified the modified (updated) parts in #7 clutch, unless manuals published after the update (which is dated 1984) contain details regarding both options (4/4 or 4/3) for #7 clutch.

The Parts Manual I can't comment because the Publication Number (top RH corner of the cover) is not visible. It does cover the appropriate range to include your Serial Number though.

Also that attachment that you sent. Is that bulletin from Cat and how do I get them?

It is, and would require access to Cat's online service system to obtain. This would depend on your dealer.

 

[Nige]

The book is calling for 4 plates and 4 disc. I just now realized I only removed 3 plates. So I’m thinking this could be the issue?

So when you rebuilt the transmission the first time you installed 4 discs & 4 plates in #7 clutch as called out by the service manual.?

 

[YellowIron25]

Yes sir, when I rebuilt it I installed 4 disc and 4 plates.

 

[Nige]

Yes sir, when I rebuilt it I installed 4 disc and 4 plates.

And there we have it ladies and gentlemen..........

Reassemble it the way the update document describes, making sure to install a friction disc right next to the carrier as instructed rather than the 4th plate called out in the Parts Manual. That should fix it, fingers crossed anyway.

 

[YellowIron25]

Yes sir, that’s what I’m thinking also after reading the updated document that you sent. I will try to reassemble today and let you know.

 

[Nige]

Basically that 4th plate you installed locked up the #7 clutch assembly and prevented it from releasing. That's why it was stalling the engine when you tried to engage #6 clutch for the lower gears.

Back to your Parts Manual. It appears you have a copy of the original version of SEBP1045. There is a later issue (SEBP1045 version 01 published in January 1985) that specifically covers machines with S/N from 87V1138-5274, not 87V1138-Up as shown the cover of your manual. As I mentioned before that later document might well contain parts details of the #7 clutch upgrade.
Here's on on eBay - https://www.ebay.com/itm/144325333206?hash=item219a75d0d6:g:3HAAAOSwxdthsrBM

 

[Nige]

Any update.? Enquiring minds are wanting to know.