I've been looking for a leak in my D7 trans for a while. S/N 92V10xxx. It loses about 3/4 gal. per day. A week or so ago I had time to get it in the shop for a couple of days. I pulled the belly pan and all the access panels out of the cab. I found a few seeps and fixed. I've had it out for about 50hrs since and have dumped about 4 gal. in it. I'm starting to wonder about losing it through the rear main of the engine. The only oil leak I can find on the dozer is at the front of the engine. I haven't dealt with it yet because it doesn't look like a bad leak and the oil level in the engine stays very near the full mark, I may add about a gal. per oil change. It seems a huge coincidence that the engine would burn and leak almost exactly what the trans. loses, but I don't know where else it would go. The final drive levels are good, not over filling. My question is; is it possible for trans oil to push into the engine, and how do I test or confirm this is happening. Next, what would cause this. Thanks for any ideas.
Yes, the rear main oil seal is your likely fault. Despite the torque divider scavenge pump draining the torque divider, the small amount of pressure in the torque divider housing will push the tranny oil past the rear main, and into the crankcase. I can recall replacing a few rear main oil seals on my D7's, and they were pretty burnt up and hard. I had the same problem - tranny oil disappearing, and the engine using no oil, when it previously had been using some. A 3306 can burn a quart a day, with no problem, when they get a few hours up. I've had them burning a gallon a day when well worn.
CDUB, your tractor has a vent line half way up the torque cover so it's unlikey.you can pull this hose at the transmission fill tube to check for oil .The rear seal is a double lip seal also unlikley.If your engine is using a gallon of oil a day you should be able to see it in the exhaust.The torque oil cooler is on the left front of the engine. Good luck, Bob
That unit has an auxilliary drive gear case at the back of the engine that would most likely be open to the engine side. The transmission pump mounts to this gear train and has a shaft seal that could leak transmission oil in to the engine.
OM that can,t happen on a 3306. Auxillary drive gears are all in the converter case. on a D6 D7..; D8 and 9 yes gears are in rear of engine accesory drive. Most likely rear crankshaft seal if final drive oil levels are ok. Have seen eng oil go into trans, and trans go into engine on 3306. through rear crankshaft seal
So, if I understand correctly, there should be enough fluid or pressure in the accessory drive case to leak into engine under normal conditions, and the rear main seal is the remedy. Does anyone have any quick tips for replacement or does the engine have to come out? Would you sweat to hard about running it another 100 hrs before fixing? Thanks
Just the converter has to come out. then remove flywheel to replace oil seal and sleeve assembly. If it was mine would run 3-5 days and fix on a weekend. You might get away with 100hrs. But have to keep a good eye on everything in case things worsen. Depends on how vigilant the man in the seat is, if he can notice something happening, temps rising, funny smells etc. My views anyway.
Bob , I respect your extensive knowledge as a senior Cat technician - but I've done enough rear main seals in my D7's to know that they are a problem area after about 8000hrs. CDUB - Nope, running the tractor for another 100 hrs won't hurt anything. The engine doesn't have to come out. You unbolt and remove the jackshaft between the tranny and torque divider - unbolt all the torque divider hoses and piping - unbolt the row of bolts holding the torque divider to the flywheel housing - the slide the torque divider rearwards until it clears the flywheel, then lift it straight up. It pays to duct-tape the torque divider output shaft to the torque divider housing, so it doesn't fall out when the torque divider is being removed. The output shaft has two fragile cast-iron piston rings on it for sealing oil pressure, and these can be easily broken, if the output shaft slips out, and is then whacked back in. That's provided you're not doing a complete torque divider overhaul while it's out. As D6 Merv says, the rear main seal comprises a double-lip seal and a sleeve that is a tight fit on the hub of the crankshaft. Be very careful when removing the sleeve that you don't damage the crankshaft hub surface.
Agreed its the rear main. I am doing one on a 572G at the moment. (this is a pipelayer on a D7G platform)
You guys are a hard group to convince.....pull the transmission pump and replace seal #17. Info out of the D7G 92V2127-up with 3306 Correct me if I'm wrong but that's the way it looks to me.
Thanks for the replies guys. I'll probably think of a few more questions before I get it fixed.
Old Magnet - Sorry, I never had a problem with transmission pump leakage into the torque divider, even though it was raised as a suspicion. I owned 3 x D7's for nearly 20 years. The simple fact is that the tranny pump oil has to get past a white metal bearing, to get past the seal, to get into the torque divider housing. The tranny pump doesn't have the ability to put a serious quantity of oil into the torque divider if the pump seal is gone - and that tranny pump seal rarely fails.
The trans pump is on the front of the rear bellhousing and is driven by the rear geartrain. All this is lubed by the trans oil in the torque.
CDUB, You can get a ultraviolet dye kit and put the dye in the transmission oil,run the tractor for a day and check the engine oil just to be sure your seal is leaking. Good luck Bob
OM the gear that drives that gear train is in front of the flywheel. Everything is on the converter side. Is no engine oil near the accesory drive. D342 and D353s yes they have rear gear trains that run in engine oil and the pump shaft seal there is the usual culprit rather than the cs rear seal
OK, thanks for the responses. Never was concerned about trans oil leaking into the torque, was concerned about trans oil getting into engine. Apparently this auxilliary drive is different than the older auxilliary drives that were actually driven from the engine auxilliary drive shaft like the old 17A/D339's
Does anyone have the torque specs for the bolts on the flywheel?
150 +/- 20 ft.lbs. according to the book.
Thank you sir. Hopefully this thing will go together as easy as it came apart.
Well, I got it back together, and ran it for a day. It seems to have fixed my problem. The engine oil level dropped about 1/2 gal. trans level stayed the same. If I wasn't so fat I'd do a backflip.
Well b4 you do this backflip !! post a pic or 3 of her on here for us !! Cheers
With all the D7 enthusiasts on this thread, i thought i would take a chance and hijack it. Hope yours is fixed CDUB. I am interested in the D7 size machine for use on a tile plow. Also, I have a 25 tonne float that handles my 26 tonne ex ok. Want to avoid anything bigger so i can float it. A tile plow application requires a couple things. First, you want to be able to inch forward slowly. I have been told that the cat 8h/8k don't do that well. They tend to move forcefully when the drive is engaged. As opposed to fiatallis and IH dozers that allow the use of a decel pedal to keep motion restrained. Also, the plow requires 3000 psi hydraulics, with a moderate amount of flow. I would think something like 40l/min would work fine. The longer the track on ground is the better also. For stability and grade control. How would a 7f/7g do in this application? Or should i be looking for a td20 or fiatallis Ken
CDUB - Sounds good! Do you have any pics of the old seal? They usually present as pretty chewed up and burnt, with the seal lip material becoming very hard and inflexible. Watglen - Well, for starters, I don't think you've been very well informed. All of the powershift Cats from around 1970 onwards were fitted with modulation valves in the transmissions to reduce shock engagement of clutch packs. Neither the Fiat-Allis nor the IH tractors were fitted with modulation valves in their transmissions, and some of the harshest clutch engagements I've encountered were in IH powershift transmissions. All the powershift Cats have always been fitted with decelerator pedals that allow you to engage gear at an idle. So, essentially, the transmission info you have been provided with, is pure BS and just plain speculative opinion. I've never dragged a tile plow. However, I've installed large diameter polyethylene piping using a pipe-laying attachment on a Cat D7 ripper. Smooth tractor movement and a gentle approach is the order of the day with poly pipe installation, and I never had any problems using the D7 in this application. The standard track frame on the D7 gives adequate stability without the need for a longer track. The hydraulic pressure on the Cats of this era is around 2000psi, so you may have inadequate hydraulic pressure, on that basis.
Seal was not chewed up but did appear burnt and inflexible. However it was not obvious that it was leaking. I came to this repair through a process of elimination not through certainty that I had a leaky rear main, hence my excitement that it is fixed. I'll try to get some pics up this week.
Thanks Ozdozer, In fact i haven't been well informed. I have no personal experience with these old machines. But i can say the when you search for used tile plows, there are lots mounted on HD21 tractors. Its quite likely the guy i was talking to was talking machines pre-1970, cuz he is quite a bit pre-1970. At any rate, thanks for the info, I really appreciate it. How are the 7f/7g rated for maintenance/repair. For instance, a fuel oil based TC kinda scares me because i have never heard of such a thing. Its completely out in left field for me. For starters, why would CAT use that design, what was the purpose? Compared to a tranny oil setup? Thanks, Ken
Watglen - The last Cats to use diesel fuel torque converters were the D8 and D9 of the late 1950's. From 1959, the D9G, and from 1960, the D8H - and all other Cats since - have used oil torque converters with their powershift transmissions. The early HD21's of the late 1950's also used diesel torque converters but went over to oil torque converters around 1960 as well. The diesel torque converters weren't a problem, apart from occasional leakage problems with their special carbon seals. The diesel torque converters were designed & patented by the Twin Disc clutch Company and this company supplied both Allis Chalmers and Cat with their diesel torque converters. This was "cutting edge" technology in the late 1950's. However, Cat decided they would design their own torque converter and new style transmission - the Cat planetary powershift. In conjunction with the new powershift, Cat designed and produced a substantially improved oil torque converter coupled to a planetary gearset. Cat called this the Caterpillar Torque Divider - as it divided torque between direct mechanical drive and the torque converter. The Torque Divider gives improved response to torque input and suffers from less power loss than a simple torque converter. A-C went on using the simple Twin Disc torque converters, but the newer Twin Disc torque converters used oil. These A-C torque converters were very "sloppy" - i.e. - they slow down a lot under heavy load, but produce immense torque multiplication. The effect on the tractor is that the tractor speed drops off substantially under heavy load, but the pushing ability or drawbar pull increases substantially, due to the large increase in torque multiplication. The reason why the A-C HD21 would appear as a popular tile plow tractor would be because it had plenty of HP and weight, and because it had high drawbar pull, a useful feature in tough ground where the tile plow would be heavy pulling. The D7G was produced from 1976 to 1997 - it is a very good, very reliable tractor, and would be suitable for pulling a tile plow, provided you have no major problems with tough soil types. A D7G also matches your floats carrying ability. A bigger tractor means you'll need a bigger float. Regards - Ron.
Yes as Oz says the twin disc AC converters had a much higher torque multiplication at stall than the caerpillar ones [although these are still made under licence from twin disc too] But your not doing any work at stall either, but they do PUSH. Cats torque divider makes them alot more lively than pure converter drive, and as oz says are alot less 'sloppy' than AC. these really slow down and speed up under changing loads. Cat still has the torque converter, but 70% of its power goes through it, 30% direct drive is what makes them lively. You can still just depress the decelerator to just keep enough weight 'leaning' on the plough to keep moving under weak soil conditions so you don,t break traction like direct drive does. HD16 was a very good tractor in its day, but is hard to get parts for and very hard to find undercarrige. TD20E was also a great performing machine, especially with its 2 spd steering; great when pushing or pulling on a curve. Its DVT800 engine was a POS, later ones have a cummins L10. But parts are still a headache. Is also komatsu D85. But have never really liked these. Big clumbersome and heavy. Just me i dont like them. Although i do like the D65. Which brings you back to a D7G. These where a good honest tractor, capable of alot of work; easy to get parts for. And at around the 23 ton mark still easy to move. Would be my choice anyway. Depending on weather plow is towed or ripper mounted, winch might be another good option too. Really depends on your soil conditions. And if you needed one
Awesome responses guys, thanks a lot. Really appreciate the explanation the the tc and torque divider. Never heard of any of those things, really interesting. When funds permit, will search out a D7g. Sounds like that is the machine of choice. Ken
CDUB, i hoped this fixed your problem but am wondering why anyone didn't say to check the final drives? at least the bevel gear housing! i have never worked on this part of this vintage of D7 but on the 46a's and 77v's the pinion seals would go out in one side or the other and the oil would run into the finals? am i remembering correctly? i can't remember for sure haven't worked on one for 10 years now......................theironoracle
Correct, but unless the final starts leaking it will level out and oil will not need to keep being added.
thanks again lee-online, i didn't think i was crazy but thought it may have been bolted together a bit different, if a person is working in mud as is common this time of year they may not see the oil coating the inside of the track if the cone seal is out too. i have seen two failed timbco finals (one still had barb wire in it)(pictures in shop talk) failed this year because the cone seal went out and they were ran dry couldn't tell because both times they had spent lots of time in the mud and never saw the oil run out. there is a scenario for everything, makes our jobs interesting.................theironoracle
I had thought of the finals, but they stay right at the bottom of the threads. The seal fixed my problem though or at least the worst of it. I have to add about 3/4 gallon of oil to the engine a day, but I feel better about that than adding it to the transmission to keep the engine full. The good news is it isn't burning all of it. There is a leak somewhere under the air conditioner compressor. It can wait until the snow flies.
One more question. I have thoroughly searched the web and elsewhere. To run the tile plow i need hydraulic pressure 3000psi or better. Flow is not so important. I know Cat used less than this on older machines. What about the D7g? Thanks, Ken
Ken - The D7G main hydraulic relief valve is set at 2250-2300psi. To obtain 3000psi or better hydrualic pressure, you will have to modify the hydraulics on the D7G. Possibly the simplest method would be to add a dedicated high pressure hydraulic pump to supply the tile plow. I'm not sure you'd be able to raise the working pressure of the D7G hydraulic system to 3000 psi, without the risk of serious damage to valve bodies, such as fracturing them. I've had a main hydraulic valve body split on a D6C, just running at the standard Cat pressures - so I don't think the safety margin in those Cat cast iron valve bodies would be adequate to handle 3000 psi and the associated peak pressure shock loads. Regards - Ron.
Hi Ron, That is a bit of a problem. The unit i am looking at is a 1993, from Japan, first sold in texas. I would of thought that something that new would have over 3000psi. I could understand it if it was older. Do these machines have a spot to add a pump? My tile plow supplier says it has been done to the older units, but not sure what is available for the d7g. Ken
watglen, i looked this machine up assuming its a 65v s# group, this machine uses a vane style pump, highest prv setting is 2500 psi. i don't think your going to get the 3000 psi out of it very easy. whats on this tile plow takes that pressure? so is there a vibrator on this tile plow or just the up and down cylinder? if its just the up and down cylinder it would be cheaper to just upsize that cylinder (if you have problems) than any other hydraulic system mods..............theironoracle
Ken - If you look below the water pump, on the rear of the timing gear cover, on the LHS front of the D7G engine - you should see a plate blanking off an accessory position - which is where you should be able to mount an additional high pressure, dedicated tile plow, hydraulic pump. Regards, Ron.
Perfect. At least it wouldn't be some cobbled up mess when it was done. Have to look into it further. Ken