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97 Disco Transfer Case Adventure


TIm Wilson

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My 1997 Disco I transfer case "adventure" started with a gearbox overtemp light. That's the little red gear in the upper left corner of the dash, wired for some reason that makes no sense at all to me to both the transmission temp and transfer case temp sensors. High temp in either gearbox will illuminate the indicator - other than a general "something's wrong" indication, it doesn't help much with troubleshooting (any particular reason, LR engineers, you didn't put in two lights?). My transmission temp sensor failed a couple years ago, so I wasn't particularly concerned when the light came on. In this case, however, the indicator did not come back on with the engine cold as it had in that instance. I drove it for a couple days with no other indication of a problem until I started hearing a whine from the general area of the transfer case gear selector. That noise grew rapidly in volume over about 5 miles, and when I stopped the transmission refused to shift ... actually it did shift, but with a sudden slam, followed by no drive at all. While waiting for the tow truck, I tried shifting through various gears and discovered it would go into reverse and back up smoothly ... after that I could shift into drive and move forward too, though with a fairly loud grinding noise. Nice to know I could get the Rover to move, but I opted for a tow ride home anyway.

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Once I had the Disco home, I tried driving a bit in an attempt to pinpoint the source of the noise. The grinding sounded like marbles rolling around in the bottom of a tin can … a typical dead bearing “this is going to be really expensive” sort of a sound. The transmission seemed to work fine, shifting smoothly through all gears without a hint of trouble. The transfer case worked in all gears too, L – H, difflock engaged or not made no difference. I took it up to about 45 mph without a problem, other than the noise. Checked the driveshafts, front end, etc … everything was tight and there were no abnormal leaks (“abnormal” being relative, of course, given that this is a Land Rover). Incidentally, the gearbox light never came back on through all this, further reinforcing my opinion its useless as a troubleshooting aid.

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I drained the oil from the transfer case ... about 2 cups of very black fluid. Since there was supposed to be 2-1/2 quarts of oil in there, I took that as my first clue the problem was in the gearbox and not the transmission. There was no significant leakage from the box, and while the magnetic plug was covered with typical metal shavings I didn’t see any big chunks. I took the inspection plate off the transfer case but saw nothing obviously wrong … no damage to gear teeth, anyway. I put the plate back on, refilled the transfer case with 85/140 lube and drove again. No change in the noise though – the heavy-weight oil made no difference.

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I was still not certain the problem was in the transfer case, but the transmission was working fine except for that initial lockup, and since that cleared after I backed up a few feet I suspected I had somehow wound the thing up. That made me suspect the difflock had seized somehow – unlikely since it shifted in and out normally – but at any rate the transfer case remained the most probable source of the problem. I started looking for a replacement, and found a used one on eBay from a 97 with a VIN a little higher than mine and at a salvage yard pretty close to me. It arrived in a day or two. Here’s what a transfer case looks like after the UPS guy (who undoubtedly has a bad back if he didn’t before) drops it off at your door. I cringed when I saw the packaging – a crate would have saved some work later.

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The Rave CD has specific steps for replacing the transfer case, but they’re a little sketchy. They call for fabrication of a handling fixture to secure the gearbox to a transmission jack. I didn’t have a convenient way to have one of those welded up, so I opted to make one out of 1/4-inch plywood and pieces of 2x4. I wasn’t sure whether this would be beefy enough to handle the weight of the TC, but as it turned out it worked just fine. The patterns are posted at the link below for anyone else who wants to try this – print on full-sheet label paper, cut out the parts, and assemble with glue and wood screws.

http://digitalvault.cox.net/invite/login?c=74696d77696c736f6e33&i=c15e-12d7e22ba36-coxprod_gemini_canniff37&t=97a7f432776b79ef&r=mg〈=en

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Rave has the transfer case in difflock-low for removal, presumably to position the linkage for ease of access. I set mine up that way before doing anything else, only to discover, with the battery disconnected and exhaust system down, I couldn’t rotate the driveshafts to remove the flange nuts. Duh. I managed to round one of the front shaft nuts before wising up and reconnecting the battery so I could shift the transmission into neutral and rotate the driveshaft, then ended up having to cut the rounded nut off with a carbide blade in a Dremel tool. If I were doing this again, I’d drop both driveshafts before doing anything else, or just leave the transfer case in neutral – I’m not convinced it really needs to be in difflock-low for removal anyway, but if it does I’d be happy to hear from someone else who knows. I’d probably spring for the proper tool, also, available here from Atlantic British:

http://www.roverparts.com/Parts/DA1065.cfm

I found the 9/16” deep-well socket in my 1/4“ drive set worked OK for removing the nuts once the driveshaft was properly oriented, but the correct tool would have been better.

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Rave also has you remove the starter motor heatshield (step 7), but it’s not clear to me why. It takes some fidgeting to put this back on, and I’m not sure why it needs to come off unless to improve clearance for removal of the exhaust downpipes? I couldn’t get those out completely anyway with the Rover on jack stands, and ultimately just left them hanging loose. Annoying, but no problem getting access to everything once they were disconnected. The only other significant problem I had was removal of the crossmember – it’s a tight fit and even with the bolts out, mine didn’t want to budge. I ended up pounding on it with a rubber mallet until it started to move, then kept on pounding until it popped clear of the frame with a sound that made it clear reassembly was not going to be trivial.

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With the driveshafts, exhaust system, and emergency brake assembly out of the way I took the transfer case input shaft cover plate off, intending to pull the shaft out from the rear for a look at the bearings. When the cover plate came off, so did pieces of the rearmost bearing … a couple of the rollers rattled down into the transfer case somewhere. Here’s a look with the plate off, “obviously, a major malfunction” …

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I seriously considered just swapping the input shaft and bearings with the ones from the replacement transfer case, but decided that wasn’t wise given the bearing probably failed after being run low on oil so the intermediate bearings were in questionable shape too. Running the foremost bearing in a different “used” race wasn’t a good idea either. And anyway, I’d only busted my head a half dozen times getting to this point, so was sure to miss out on more suffering if I didn’t take the whole transfer case down. Here’s how it looked before I installed my home-made handling fixture and unbolted the mounts to lower it.

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Also, a view from the front looking up towards the shift linkage …

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There are six bolts holding the transfer case in place, four installed from the rear in a roughly circular pattern and two from the front. The upper of these two is difficult to see, since it’s above the TC front output housing, roughly in line with the difflock linkage – in fact, I had to remove that linkage completely to get a socket on the bolt. It’s retained by two clips/pins inserted from the front at the actuator and mid-point pivot and a nut where the linkage attaches to the TC and was pretty easy to remove. The upper right of the four rear-installed fasteners was actually a stud, threaded into the adapter housing between the transmission and transfer case. I had no trouble getting the nut off, but did have a problem getting the transfer case to slide off that stud for some reason – the threads kept hanging up on the TC housing and it took some time to work it back and away. With the transfer case down and my transmission jack fully lowered, I found I didn’t have quite enough clearance to roll the thing out from under the Rover. I had to slide the TC off the jack and onto the floor to get it out – not a big deal, but another nuisance.

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I had seen no evidence of leakage from the transmission or transfer case before this started, but with the TC out and the back of the transmission lowered ATF started leaking around the output shaft seal and puddling on the floor. I found the shaft had a lot of free play: 1/16 – 1/8 inch, at least, in any direction. I drained the transmission, then removed the adapter housing behind it to replace the seal and investigate the free-play in the shaft. I didn't find anything significant, and since the transmission was working fine I opted to just leave it alone and put it back together free-play and all. I couldn't do much more anyway without taking the transmission down and dismantling it. The shaft is supported by the transfer gears in service, so I'm not sure the free-play makes much difference except for what it may be saying about wear in the transmission. There's surprisingly little ZF4-HP22 info out there short of buying a rebuild manual, so I'm not sure what the spec limit is -- maybe mine is completely normal. Anyone know? Here is a shot of the transmission with the adapter removed …

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I managed to tear the paper gasket between the housing and transmission and had to wait a couple weeks for a new one. I cleaned and inspected the replacement transfer case while waiting on the part. I took the temp sensor, neutral and difflock indicators off my TC and put them on the replacement, since I knew they were working and wasn’t sure about the replacement. I’d had occasional intermittent speedometer dropouts in the past, so I put a new speedometer sensor on while the TC was down. Also removed the large inspection plate and the one over the difflock mechanism to look for anything abnormal and set the position of the difflock indicator. The replacement TC turned freely, but I found the front output flange mud shield had been dented in shipping (here’s where a good crate would have been nice) and it was scraping on the housing. I removed the flange entirely and replaced it with the one off the old TC. A pneumatic impact wrench made quick work of the flange nut – it came off easily. Shipping had not been kind to the housing, either, and the upper right corner (viewed from the front) was dented just enough that the transmission adapter housing shear pin wouldn’t fit in the hole. I reshaped the hole with a grinder bit in a Dremel tool … several grinder bits, actually, because this took some time to get right.

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Since I had to unbolt the shift mechanism from the transmission adapter housing to take the housing off anyway, I pulled the mechanism down, cleaned and repacked it with grease. Mine has never frozen up, though I know that’s a common fault with Discos. Not sure why LR didn’t put a rubber boot over this to keep dirt and water out. Couple pics of the mechanism here …

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And before someone asks, no I didn't pack it with the Vaseline shown off to the right in that picture. I used Valvoline bearing grease.

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More work while waiting on the gasket: I installed a new Optima battery, replaced the mudflaps (one had already cracked and fallen off and the other was on its way), and cleaned and re-taped the TC wiring harness. And in a show of true anal-retentiveness, I made a useful laminated decal to replace the badly peeled and not-useful “use only genuine Land Rover parts” decal in the engine compartment.

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And here’s the replacement transfer case, on the jack and ready to go up. I replaced the transmission input seal at the last minute, just to be sure. Although it’s the same size as the aforementioned adapter housing shaft seal, it carries a different part number, LR part ICV100000, and is significantly less expensive … another Rover mystery. The two seals I removed were exactly identical. I left both output seals alone, since there was no evidence either had been leaking and they’re pretty easy to get to with the transfer case installed. Also note, the front output flange was still off when this shot was taken … I put it back on after I had the transfer case up so I could torque the nut properly.

post-28412-0-89824200-1297772224_thumb.jpg

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New battery … why is there no rubber boot over the negative terminal? Is this factory-normal, or is mine missing?

This is normal as there is no need for a battery negative cover. The chassis and bodywork are connected to the negative terminal, so if anything in contact with them were to touch the positive the whole truck would be short circuited, hence the cover.

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A view of the transmission ready to receive the transfer case ...

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I made the alignment pins out of three 180mm long M10x1.5 hex bolts … cut off the heads just behind the hex, then cut a groove for a screwdriver tip using a carbide bit in the Dremel. Bolts are available (in the US, anyway) from McMaster-Carr, here: http://www.mcmaster.com/#91280a674/=b3ud5z . Unfortunately, I found they were about an inch too long and I couldn’t get the transfer case in place with them installed … I should have used 150mm bolts. Rather than cut them again, I took them off, positioned the transfer case so the transmission output shaft was lined up, then inserted the alignment pins through the holes in the transfer case and wiggled things around until I could get them started in the transmission housing again. Then I worked the transfer case into place, wiggling the output flange back and forth to line up the splines in the transmission shaft with one hand while using the other to ensure the threaded shaft of the shift linkage, shown at the arrow in the pic below, engaged the linkage on the TC ...

post-28412-0-54849900-1298159342_thumb.jpg

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Seems like the thing should just slide into place once the shaft splines have engaged, but mine would not. And no amount of wiggling, prying, pushing, or anything else helped. I wanted to avoid taking the input cover off because I wasnt sure I could get it sealed up again (thought I was pushing my luck as it was), but eventually gave in and removed it and the input shaft entirely. With them out of the way, I was able to slide the transfer case into position against the transmission easily and start the attach bolts. I torqued all six up, then tried to slide the input gear back into place. Problem is, it wouldnt budge ... the transfer case was locked solid and the intermediate gear teeth would not engage those of the input gear.

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