Good day. I have a cat d4h dozer and the transmission pressure drops after while. sn 8pb06231
Is there enough oil in the transmission, how hot is the transmission oil getting. Have you changed the filters and cut open and checked for materials in pleats of paper. Have you checked the suction screen for blockage. Can you see any hoses leaking on suction side. How many hours on this unit, any idea how old pumps or transmission are? Any previous repairs done that could help figure out. Simon C
i cleaned the hyd suction screen.fitted new hyd suction hoses.checked the hyd pump. Fitted new filter. Cleaned the priorety valve.cleaned the brake control valve. removed brakes and stearing clutches fitted new saels and bearings.(The old seals was warned out.) Re fitted brakes back. removed the transmission.Found that the bevel gear had broken some teeth.repaired it and fitted it back. Repaired the transmission .new bearins and seals.checked the oil lines found to be ok.Fitted new o ring on suction hose.asembled every thing back topped with new oil torque fluid 30. Adjuted links to speck.the transmission controle bank is also cleaned I tested the dozer and it worked fine.after while it stopped and dit not take gears. i took pressures. brakes.27 bar steering.27 bar converter in 7 bar P1- 23.bar p2- 18 bar transmissio lube2.3 bar conv ou 3.2 bar priority valve 34bar
Sure Nige may look at your test specs., and respond with some info, and some things to check. Wow, you sure did a lot on that unit. Simon C
Were the numbers below measured before or after it wouldn't take gears.?
Oh, and while I think about it, please can you start posting your pressure readings in tenths of a bar or use psi. For some parameters where the spec is qupoted as X +/- 5psi (about 0.3 bar) using whole numbers for the pressure reading is not going to tell the full story. By your posts regarding what you have done/checked it sounds as though you have a Service Manual. Please can you confirm that.
The pressures was taking after it stopped. I have sis on my computer i took pressures today and it is the same. the reason i stripped every thing is becourse the transmission was repaired by some one els and when the brakes was removed i could see the rails was broken then i desided to strip every thing. there was cuirclips missing in the transmission
The dozer did the same thing before i stripped it
Can I suggest that you lift the cab floorplate and run the machine until the transmission fails to engage gears. Then do a test by engaging each transmission gear in turn with the engine at low idle. At that point does the drive shaft between the torque converter continue to rotate with no reduction in speed, slow down, or stop completely.?
my bet is transmission pump
Possibly sucking air through a suction line leak when it gets hot.?
Good day all. Thank you for your reply. I dit the test to check if the drive shaft is turning. On low idle it does turn.When i lift the revs up and the pressure increases it stops. it does this in all the gears.
iI dit check the suction hose and it is ok
My priorety valve seems to be a little bit high.It is reading 493psi. brake and steering 391psi.The manual read that the priorety valve must open at 420psi. Do you think that my pressure could dump at steering and brakes releave valves and then struggles to open the priorety valve as it should.Do you think i should remove some shims on my priorety valve so that it could open at a lower pressure.
You could try it. Just be careful to note how many shims you remove in case you have to put them back.
Well, i had similar problem in a D5H not so long ago... my case we had to replace all seals in TXM and BRK/steering plus a new charge pump. (D4H should be same system) Thing is these dozers have some emergency features, that older tractors do not have. One is when the engine Stalls and system run out of pressure brakes apply automatically, same goes for oil leaks or cavitation in charge pumps, it always prioritize Braking and Steering. This being said u have your answer why the shaft does not turn, actually it should not turn at all, low or high idle when in gear. Well, basically the pryority valve directs oil press to release Emergency BRK, if pressure is leaking pryority valve does not open to TXM control, steering clutches also work with "pre-pryority valve, they actuate by adding pressure. The Torque Convertor rarelly have problems, as the way it is built its almost trouble free, nevertheless it does not get traction if oil press is low, TC oil press is something like 5BAR so it uses the remainder of oil flow, and from there oil goes to cooler. The thing with lowering pryority valve press, is at some point it wont release brakes, so it may drag Emergency brakes specially in 1st gear then u´ll have 2 problems , all the above plus overheating or disk burning and dadada. Knowing what i know today, i would go to charge pump, but then the clutch piston seals in the system may be leaking too much ... its dificult to get an diagnisis just by looking to pressures... they just tell u they low or not...
Just for giggles, pry the center pedal up when this occurs. My 8PB06217 did the same thing. The needle bearings in the pedal shafts were seized/ rusted. And I could've sworn it was a transmission issue. Just went thru this last year. Cold, it worked normal. As it warmed, it would get slower and slower.
Thank you all for the advice. i have done every thing you just told me. checked links and pedal. done all seals
In that case it would appear that an attempt to adjust the priority valve pressure is your last hope before tearing into, or replacing, the pump.
Good day. I adjusted the priority valve. The transmission pressure went up. The thing is when the dozer is at low idle the pressure drops on the priority and p1. if i rev it up a little bit the pressure rise up to spec. before i removed the shim my p1 dropped to72 psi still the drive shaft stopped when i selected it in to gear after removing the shim the p1 pressure went up to 217 psi and when i tested on high idle p1 was 319psi the priority was 420.I removed the priority and cleaned it out and tested again same thing. It seems that every thing is working fine on high idle but not on low idle. it looks like i have a flow problem but i dit strip the pump and i could not find any thing wrong with it. i was thinking of checking the transmission control valve I dit check the park brake link and adjustment again to day and it is working fine
The there are two specifications for the priority valve pressure with all systems at normal operating temperature. Low Idle (390+/-5psi) and High Idle (420+/-20psi) What values are you measuring at this time.? The same criteria applies to P1. the spec is 370+/-15psi at High Idle and a measurement of no more than 50psi less than the High Idle value at Low Idle. Again what are your measurements.?
priority= low idle 348psi =high idle 4230psi p1 =low idle 217psi high idle 319ps
Based on those numbers either you have (multiple) leaking piston seals inside the transmission, or the pump is not producing the required oil flow. Time for a pump I think, as @Dave Neubert commented way back.
ok thank you will check
If you install a replacement pump I would suggest replacing whatever shim(s) you removed from the Priority Valve BEFORE you crank the machine up for the first time.
Good day all. I replaced the pump still same problem is there a way to blank the steering and brake system ?
I have had the metal lines that are in the housing crack they have to be patched or welded in this was in a d6 but I bet it has the same set up
Thank you Dave i will check the lines. I made a test plate to blank the brakes and steering. Started and tested found that my transmission pressure stays constant even if it reached working temp. I think it is leaking through. Today I am going to make a plate to test the brake control valve. If the valve is not bypassing at the park brake I have to check the metal oil lines and brake seals. I am not sure how to determine if it is the left hand or right hand side. I will keep you updated. If you have any suggestions, please keep me updated.
Daniel, I sugest u go directly to brake/clutch module before loosing time with valves and such. Opening track and remove modules takes 2h for a 2 person crew, (u can´t do it alone). Resealing Brake/clutch pistons cost 100USD tops, wile doing it u can inspect the frictions too, these are not prone to fail... Even when u have Brake/Clutch modules resealed and inspected, probably u´ll have to reseal the TXM, as the system is same tech. This system, is prone to SEAL failure, Maintnance books even call for resealing at a certain hour intervals, even if the sealing prove not to be the main cause, then u know that this modules are free of problem. Good Luck
Thank you for the reply. I have resealed the brake and clutch modules with new seals
And it still show low pressure when hot? well signs of leakeage?
l blanked the brake and clutch completely and after long time the transmission pressure dropped again..
Well, the modules are made to leak... as some of the lubrication comes from that leakeage. Nevertheless it should not leak too much as will come a point where the pressure needed to operate pistons plus the leaks overwelm the pump flow and then i starts to decrease press. In your case, looks like u have a heavy leak somewhere that show specially when hot. I bet is somewhere in the TXM or the Brake Modules. This cause this modules TXM or the BRK are the parts that contain seals prone to failure. It may also be a broken line, but that is highly uncommon.
I keep thinking on the cover on transmission where you remove to gain access the transmission valves there is a accumulator there was a problem with the bore wearing and causing pressure problems.
That may be, but u can check the O rings!! When one removes the cover u can check them out. Sure the D4 has an acumulator? We're talking about a D4H power shift TXM.
l blanked the brake and clutch completely and after long time the transmission pressure dropped again..
This sorry the cal it a resonator
We've seen trouble with them before.......... The plug has been known to unscrew itself and as a result the guts fall out. Worth a look if nothing else, just to eliminate the possibilty.
Thank you. I removed the cover to day the valve is still in one peace. I will strip and clean the Valve tomorrow I removed the transmission control valve will strip and clean it in the morning.
Check to make sure bore is still round in valve. Also look at orfice for load piston it is plastic and comes apart and plugs the orfice
Where is the orfice located.I
Where is the orfice located.Idit not see a plastic one
It’s in the transmission valve
Where is the orifice located. I did not see a plastic one
Is it in the spool?
I came across a breakdown of the resonator, just in case you need any parts.
#12. It is actually part of a plastic screen. Well known for plugging up.
Thanks, I found the screen, with the orifice, everything is clean and the orifice is open. On the attached photo, there are 3 holes, 1 hole is plugged, 2 are open. Is this correct?
Is there some thing else that i can check in the control bank
yes that's correct
You can pull the small plate off the selector valve remove spool marked 1 in Niges post of the valve remove slug and check if snap ring came out over part marked 2
Lost track of things, u mention this Did u reseal the TXM? can´t understand why u bother with the valve block(resonator) when the possibility of having a problem there, besides debris from components, is rare. really lost track...
I heve resaeled all the seals in the drive train. Replaced all clutch plates an discks. There is no more seals to replace. The reason i removed the transmission control bank is to check if there is any problems with it.To check for blocked orifice etc
Ok, so whats the problem after all that replacement? I guess u static tested TXM Clutch Packs? They should leak , a litle ...(damaging a seal on assembly is easy, easy). From previous posts understood u have a new charge pump? Tractor TXM brakes and clutches are not operating right? whats the the simptoms?
WHen i start the dozer and it is cold.the pressure is ok.After it heats up.The transmission pressure drops.when the machine is at low idle it drops to low.When i ref it up to 1200 rpm the pressure is ok again
Question what does sis say for transmission primary pressure??
370 psi high idle Low idle max50 psi less than high idle
No there should be a lower pressure listed that you get by either blocking load piston or pulling a plug to take oil away from load piston
Ok, then u have too much leak off flow. Since u resealed the BRK/ Clutch and TXM its safe to assume u did static leak testing after resealing? If so it should be time to search for broken ring either in the filter/ PV assy, and or in the brake valve assy. After that piping conections!!! U can try that out with compressed air. The TXM valve assy also leak off , it leaks off when clutch pistons are on , that leak of goes to TC. Its a good idea to check TC intake flow. TXM valve assy has no rings , but galleries to it do. I so sorry it is beeing dificult to trace it out. U'll find it. Just make sure basics are ok.
My low pressure is 480kpa it should be 535 This is with the plug removed.
Is that pressure what it drops to when hot?
Spec is 530 +/-35 kPa (77 +/- 5 psi) at Low Idle with the transmission in neutral and the oil at normal operating temperature. So at 480 you are not a million miles away from the low end of the spec (495) provided the oil was at the appropriate temperature when the measurement was taken.
Nige,this reminds me of the unfathamable D9R saga. We cured it in the end with a new controle valve group I think.
That was ahead scratcher that's for sure. Unfortunately the fix wasn't cheap.
Before I would condemn the pressure control I think I would change the orfice and polish the spools and the slug in the end of load piston with crocus cloth
Just out of curiosity have the metal tubes in the transmission case been inspected.
He’s had the brakes blanked off for testing and the problem still exists, so I don’t think a crack in one of those tubes could be the cause. I think this is where your diagnostics may be going off track. All pressure specifications call for measurements to be taken at normal operating temperature. So to a certain extent what the pressure measures when cold is not really relevant, it’s what it does hot. All pressures are going to drop back a bit when a system warms up. The only pressure that is specifically stated to be measured with cold oil is converter inlet. I just read through the entire thread again and have a couple of questions. You said that you resealed all the transmission clutch pistons. Cat seals or aftermarket.? Did you inspect the condition of each clutch piston outer surface and the associated housing bore for signs of wear and/or damage.? When you rebuilt the transmission did you test the clutch piston seals for leakage by applying compressed air to the port for each clutch before you completed the transmission reassembly.? Did you disassemble the resonator assembly to check out the state of the internal parts.?
Thats the thing Nige, 2 or 3 threads ago i asked if he did static test of clutches in TXM and BRK packs and he did not replied, either he does not understand or he didn't. I remember that cutting a seal in assembly is not that dificult specially that that brake piston inner seal.
@Daniel Pretorius - If you have the control valve removed at the moment you could easily check the clutch piston circuits for leakage. The ports that feed the clutches are located on top of the powershift assembly right where the control valve bolts over the top of them. Also while I am thinking about it, was the condition of the large O-Rings #9 and the sleeves #10 in the illustration below ever checked.? The flanges of the tubes can wear resulting in a lack of support for the O-Rings.
Good day i have been working out for a while today i will be working on the dozer again. I will start by testing the clutches while the control bank is out.Thank you for every one so far .
Have you solved your problem any good news? I have the same sympthoms on my cat d5h
No not yet
I suggest to start another thread starting with your Serial Number and giving a full description of the symptoms. First queston would be do you have pressure gauges.?
Ok thank you Nige going to list all pressures and post a new thread