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  #1  
Old 07-15-2008, 01:00 AM
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rear diff replacement questions

I would like to get lower rpms on the freeway in my '85 300cd. I have never messed with this kind of stuff before, so bear with me.

I read from a search that there is a list somewhere of stock diff ratios. From there, what car(s) would have my best bet for a replacement part? Is it just pop the old one out and the new one in?
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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

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  #2  
Old 07-15-2008, 01:14 AM
minimike
 
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I'm under the imperssion that the 85's have the 2.88 diff. you can crawl under the car or put it up in the air and find the ratio stamped on the drivers side of the diff case just foward of the rear cover at about the 7 oclock position standing behind the car looking at the diff. Use some brake clean to wipe the grease off the housing and you'll find it.

As far as removal and installation. First you need to be able to remove the fill plug. If you can free that up, then drain the diff oil from the lower plug. This is a precaution in case you need to keep what you got. You'll need then to refill the diff.
Once drained, remove the rear cover. The axles are held in place with circlips. Axles won't slide out from diff unless you remove them from the backing plates of the rear brakes. So you've got disassembly on each wheel to remove the axle. Once the axles are out of the back plates, Big nut in center of hub, you can manuever the axles away from the diff. Next you need to disconnect the driveshaft. Good time to renew the flex disc if needed. then there are 4 big bolts that hold the diff into the floor. Also I think there is a rear diff mount. that's about it, but do a search. I think Lawson the pilot did a real nice pictorial on the diff r & r.
Make sure the car is supported so it won't fall on you, best on a lift to remove the 4 bolts. and wear eye protection. take pix for all of us.
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  #3  
Old 07-15-2008, 01:32 AM
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No prob on the pix...I'll do a writeup if I can't find one else ware. Thanks for the info so far...I'll climb under it tomorrow and see what I can find.

Anybody have a line on where to get a replacement?
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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
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  #4  
Old 07-15-2008, 02:32 AM
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your 85CD does have the 2:88 Diff.

the 2:47 Diff from W126 81 - 85 V8 gassers will fit. do some searches on the topic.
as far as I know, there isn`t a spedo that is calibrated for a W123 with the 2:47. that would slow the spedo about 9 to 10 mph?

now if I figured it out corectly 2:88 minus 14.2361% = 247.00004. so that is close to 2:47. that would be a 420 rpm drop from the 2:88 Diff.

charlie
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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

http://i30.photobucket.com/albums/c3...ilys/boobs.gif


Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #5  
Old 07-15-2008, 04:52 AM
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isnt there more to this than just dropping the axle and swapping the diffs? I can recall that there is a special tool for installing the diff bushings as well as some super expensive alignment/torque (?) tool as well.
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  #6  
Old 07-15-2008, 09:04 AM
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What did you use for seam sealer and where did you get it?
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  #7  
Old 09-22-2008, 08:48 PM
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Does anybody know what ratio a w126 gasser (86+) has? Would it fit in a w123?
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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

Last edited by lowriderdog37; 09-22-2008 at 09:11 PM.
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  #8  
Old 09-22-2008, 09:36 PM
Banned
 
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Quote:
Originally Posted by lowriderdog37 View Post
Does anybody know what ratio a w126 gasser (86+) has? Would it fit in a w123?
They won't fit the W-123.
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  #9  
Old 09-22-2008, 10:09 PM
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The 86 and newer have a totally different differential mounting, and the sub frame is redesigned.

If you go with a 126 Diff. you will have to change the flange and replace it with the 123 flange. the flex disc are of different size. 126 larger.

as a side note the 1/2 shafts are different also. I pulled a good set off a 91, and they will rub on the diff from the 83 2:47 I have.

Charlie
__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

http://i30.photobucket.com/albums/c3...ilys/boobs.gif


Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #10  
Old 09-23-2008, 07:40 AM
lowriderdog37's Avatar
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fair enough...I almost went to pull one out of the junk yard, I'm glad I didn't now. I'll just have to wait for the earlier 126 diff.
__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
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  #11  
Old 09-23-2008, 01:32 PM
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Location: Out in the Boonies of Hot, Dry, Dusty, Windy Nevada
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the 126 you look at has to have the 4 studs mounted up on top into the sub frame like the 123.

If you see a large mounting set up off the left rear of the Diff., move on.

look in the DIY articles, DELIVERY VALVE has a good write up and pictures how to R & R.

you will have to change the flange, here is a thread how to determine the friction preload when doing this. I thought I could whip it off and on.

www.peachparts.com/shopforum/showthread.php?t=233540

Charlie
__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

http://i30.photobucket.com/albums/c3...ilys/boobs.gif


Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #12  
Old 09-23-2008, 03:55 PM
lowriderdog37's Avatar
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Join Date: Mar 2007
Location: Viera, FL
Posts: 665
Yeah, I saw the writeup from delivery valve. That is what has me motivated to do this. Just need to find the diff.
__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior
Reply With Quote
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