2002 Mercury Mountaineer Front Differential

[asergio]

Morning, all: Just last night my Mountaineer started making a clunking noise in the front end. Based on what I know and what I read on the internet seems the front differential is toast. Before I go to a junkyard I wanna make sure I'm pulling the right part; junkyard guys don't generally like returns and also I don't want to make multiple travels to the yard because I didn't do my homework.

Ok, to the chase: My Merc has an axle code D4, meaning a 3.73 limited slip differential but I think it means the one in the back. Any way to know which front diff it has? Stands to reason it must have a 3.73 gear ratio as well and I'm pretty safe pulling it from a vehicle with the same axle code. But I'd like to hear some opinions first. That setup seems common to many Ford/Mercury trucks and I don't want the junkyard guy to tell me they don't have it when there is an Explorer with the same part sitting in the yard. Thanks to all.

 

[drdoom]

Correct, just get one with the same axle ratio. Code 46 will work also.

 

[asergio]

Correct, just get one with the same axle ratio. Code 46 will work also.

Thanks! Though it says here code 46 is an open diff. Does it work also? It would mean no matter the diff on the rear the one in the front is the same as long as the gear ratio is the same.

 

[drdoom]

Yes all the fronts are open.

 

[asergio]

Yes all the fronts are open.

Much obligued sir!

 

[imp]

Thanks! Though it says here code 46 is an open diff. Does it work also? It would mean no matter the diff on the rear the one in the front is the same as long as the gear ratio is the same.

@asergio If it were my vehicle, I think I would verify differential trouble before buying a replacement. Is this an AWD? I would remove the front driveshaft and see if the noise disappears, to eliminate possible driveshaft issues. You might be surprised! imp

 

[asergio]

@asergio If it were my vehicle, I think I would verify differential trouble before buying a replacement. Is this an AWD? I would remove the front driveshaft and see if the noise disappears, to eliminate possible driveshaft issues. You might be surprised! imp

Yes, it seems like the u-joint is the culprit. This evening I went under the truck and tried to move the driveshaft with my hand and there's play.

 

[imp]

Yes, it seems like the u-joint is the culprit. This evening I went under the truck and tried to move the driveshaft with my hand and there's play.

@asergio I do not know if 2002 used the C-V joint at transfer case end of front shaft. My 2004 has it. Remove shaft carefully, do not damage the "cup" part of the yoke fastened to the transfer case. I had trouble with the front U-joint bolts, and replaced them with Allen (socket head) cap screws when I replaced the front U-joint. If you buy a used shaft, and it is from an all-wheel-drive vehicle, it's parts may be worn more than a regular 4X4. Take old shaft with you to compare length. imp

 

[asergio]

@asergio I do not know if 2002 used the C-V joint at transfer case end of front shaft. My 2004 has it. Remove shaft carefully, do not damage the "cup" part of the yoke fastened to the transfer case. I had trouble with the front U-joint bolts, and replaced them with Allen (socket head) cap screws when I replaced the front U-joint. If you buy a used shaft, and it is from an all-wheel-drive vehicle, it's parts may be worn more than a regular 4X4. Take old shaft with you to compare length. imp

No, the 2002 has a regular joint not a CV one. Just to be sure I'll change the u-joints at both ends of the shaft and be done with it. I was fearing the diff were a goner but everything seems ok except for either one or both U-joints. Now with that behind I'll stop playing the armchair mechanic and take it to a garage (there's a reputable one just a couple of blocks away) and have that fixed for good. Just to assuage any possible guilt over not greasing the joints I looked at them and look of the sealed type.

All in all it's natural as the truck is nearing 200K mostly trouble-free miles.

 

[TechGuru]

Ya the "Dana" front diff outlasts the rear "Ford" diff by far, lol.

I wish there was a Dana that could be put in the rear...

 

[asergio]

I suppose that since that Dana design is both time-tested and sturdy Ford found it cost-effective to simply put in their cars rather than designing their own from the bottom up.

 

[imp]

I suppose that since that Dana design is both time-tested and sturdy Ford found it cost-effective to simply put in their cars rather than designing their own from the bottom up.

@asergio The basic design of Dana driving axles dates back 70 or 80 years. They built among the very first front driving axles having steerable knuckles. Many car and truck makers have used their axles as OEM Original Equipment Mfr.) in their own products. My friend had a 1965 Volvo which came with a Dana rear end.

The smallest they build, I think Model 25, was used in early Jeeps, larger units go 28, 35, 44, 60, 70, and up to large heavy truck axles. I believe the front in Explorers is Model 35, rear I am not sure of, it may be based on Ford's 8.8.

The correct name for them is Dana Spicer Division driving axles. Spicer also builds U-joints and heavy truck transmissions. imp

 

[asergio]

Dana 30, as I have it. It dates from the 1930s and it's actually used not only by Ford but also by Chrysler in their Jeep line, whose users are *****in' all the time it's not strong enough and plan to switch to the Dana 44 or even the 60... which powered muscle cars of yore such as the Charger.

 

[asergio]

@asergio I do not know if 2002 used the C-V joint at transfer case end of front shaft. My 2004 has it. Remove shaft carefully, do not damage the "cup" part of the yoke fastened to the transfer case. I had trouble with the front U-joint bolts, and replaced them with Allen (socket head) cap screws when I replaced the front U-joint. If you buy a used shaft, and it is from an all-wheel-drive vehicle, it's parts may be worn more than a regular 4X4. Take old shaft with you to compare length. imp

In the end you were right. Indeed it has a CV joint off the transfer case and I had it replaced. Transfer case itself, differential - both alright. It'll cost a pretty penny but not as much as I feared.