So I just recently purchased a cat 120g serial #87V1469 from a auction. After getting it home I noticed that it will drive forward but when you lower the blade to cut heavy it will just stop. Acts like the transmission is slipping. But when you still have the blade lowered and put in reverse it will spin the tires. But it still seems like it’s slipping in reverse. I removed both screens on transmission. There appears to be pieces of the friction disc, some metal shaving and the oil was pretty black. So I have cleaned the screens, drained oil, installed new oil and a new filter. I tried driving it again but there was no change. So what do y’all think I need to do? Thanks
Did you take photos of the particles.? TBH even a small amount of black & burnt material in that screen is probably trouble. Black oil spells double trouble. I assume it also smelled somewhat burned.? What type of oil did you refill it with.? I can dig out the pressure testing procedures but I see a transmission overhaul in your future.
Yes, here are a few pictures of both screens. I just used 30w motor oil to see if that would help. Unfortunately not so lucky.
Don't even bother pressure testing IMHO. You just won the lotto - transmission out time. From the symptoms I would guess the forward low clutch has let go but from your photos the transmission is so contaminated internally that only a complete strip down and rebuild will clean it out. The whole powertrain oil system is going to need cleaning out as well. First suggestion. Get yourself a Parts Manual. You are going to need one. The Cat Publication reference is SEBP1045 if you want to go searching places such as eBay.
Here's one with free shipping - to buy new would be $145. https://www.ebay.com/itm/164718850421
Well how did I get so lucky! Haha No I kinda figured rebuild worst case scenario when I bought it. Yes, I have a purchased a repair manual and parts book. I also purchased another machine for parts. They said the transmission was good on it but who knows? I still have to go pick it up and get it to the house. If the transmission is good. Would you install it or just do rebuild?
For all the work necessary to remove and install a transmission on a grader would I take the chance on one from another machine being good sight unseen.? Now let me think about that for just a minute - How about nooooooooooo, or even ***k nooooooo....!!
Those transmissions are easy to overhaul once you get them on the floor. Fairly straightforward with the appropriate service manual and don’t try any shortcuts
You got that right. I have recent experience of a 143H transmission that suffered 3 consecutive failures of #7 (forward low range) clutch, of which only the first one was kosher. The 2nd & 3rd failures were the result of a half-assed mechanic (and I use that word advisedly) failing to clean the internal parts thoroughly, especially the internal oil passages and the orifices in the countershafts, when he disassembled it.
Ok, thanks Nige! I guess it’s time to start tearing it down. 56wrench I have the Cat service manual. So I will start reading through it also. Do y’all have any tips or tricks from past experience that would help?
I can suggest the following. Not an exhaustive list by any means, but you have the advantage of being able to look at the service manual. New seals, gaskets & O-Rings everywhere, obviously. 1. Control valve. Check all the springs (free length & length under test force). Replace any that are even close to being weak. If it gets to the point where you have condemned somehwere around half of them, replace the lot. Check the detents work correctly and have a good look at anything else that moves for signs of wear. 2. 9D5030 Transmission Control Gp. Replace the control cables if they don't move smoothly, along with all the small bushes, pivots, widgets, etc, in the linkages at both ends. 3. 3P0756 Planetary Gp. Considering the state of the oil you drained - new discs/plates & piston seals on all the clutches without even bothering to inspect the old ones. Same goes for the parking brake. Same comment as per the control valve for all the springs in the transmission. All new snap rings. You'll probably end up replacing all the bearings and thrust washers as well, if you're really unlucky maybe even some of the gears. 4. 3P0891/3P0892 Transmission Pump. Inspect at the very least. You might find it's toast inside.
I really appreciate all the good input! I will let y’all know how it goes or if I have any other questions. Which I’m sure I will have.
Don't be a stranger. We're here all week......
I had to remove mine one time. It only takes about 2-3 hours to pull the engine with a couple of guys and seems like around that much time to remove the whole transaxle from the frame. My differential lock had a problem with the sleeve at the hydraulic lock where somebody had replaced the sleeve with a homemade one but they failed to drill a required oil hole in it, and it wouldn't work. I don't remember why we had to remove the whole unit now. Since you already have a parts machine, it would be worth inspecting it (or have a professional inspect it) to use as a replacement. It all depends on how many hours you plan to use it each year.
Well I finally got the chance to finish the rebuild on the transmission and install back on the machine. Now it doesn’t want to move in forward or reverse through gears 1,2,3 but it will move when I put it in 4,5,6. What could this be?
Low range clutch by the sounds of it. Did you pressure test each of the clutch piston seals with compressed air after you rebuilt them to check for leaks.? What did you find (if anything) in the control valve.?
No I didn’t. The only thing I found in the the control valve was nasty oil. Should I do some pressure checks? I’m kinda lost on what to do now?
Pump pressure is at 285psi Speed clutch at neutral is 80psi
Couple of questions to get started. 1. Did you do any of the checks suggested in Post #11 above while the transmission was torn down.? If so what were the results.? 2. Did you check speed & direction clutch pressures in all speeds.? If so what were the results.?
I went ahead and replaced all the springs in the transmission. The springs in the control valve I did not replace or test under load. All the detents, cables and linkages seemed to be ok. I didn’t check the pressures in direction or speed clutch I ran out time today. Also I’m really not sure how I’m going to do these test because of it wanting to stall in 1,2,3?
Were the free lengths within spec.? Did you do the adjustment procedure.? 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.?
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.
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.
No worries, I just appreciate the help! I will give this a try and post results when I get them.
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?
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.
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.
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.
Yes sir makes sense. So I guess I need to remove the transmission again and check everything is right in the 7th clutch?
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.
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?
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. 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.
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?
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. 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. It is, and would require access to Cat's online service system to obtain. This would depend on your dealer.
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.?
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.
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.
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
Any update.? Enquiring minds are wanting to know.
And what was the endplay(clearance) of the assembled clutch pack?
Is there any sort of specification for that.? All I could find were specs for the thickness of the discs & plates plus one for the assembled 4 disc/4 plate stack - but of course that spec does not apply because of the modification. It wouldn't be hard to re-calculate it though.
There may not be a spec but it would likely be in the neighborhood of slightly less than the thickness of a friction disc. Endplay can usually be heard as a clunk during an air check of the assembly
I mentioned the "clunk" in a reply to the OP in Post #32 on the previous page.
I agree i was just elaborating on what the clunk indicates for someone who has not had an allison or a powershift or automotive automatic apart. It indicates the piston moving due to the endplay in the stack of discs
Sorry for the delay! It is running now!! It works like it should in all gears forward and reverse. No leaks when I checked with air. Thank y’all for taking time to help me getting it going!
Did you check the P1/P2 pressures again after you reinstalled it.? How did they turn out against specification.?
No sir, I was just excited that it was working. I will check them if you think I need too?
I would in your position. Then if anytrhing should go pear-shaped somewhere down the line you know exactly what you had when it was working right and can compare.