Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 02-18-2005, 09:15 AM
Registered User
 
Join Date: Sep 2004
Location: San Antonio, TX
Posts: 54
1982 300SD Gets 2.47 Diff with LSD!

Hey Y'all,

I have an '82 300 SD with over 300K on it that I was on the verge of selling since it wasn't the highway car I needed it to be. It runs perfectly but simply put, it was loud! The loudness was from two things; one was that the differential gearing was too short for 80 mph cruise and the other was that one of the pinion bearings was whining and needed to be replaced. Hmmm...do I smell a project?

The project idea really arose from the fact that I used to own a VW TDI that I put a taller fifth gear in and I reduced the noise and gained 1-2mpg's at the same time while retaining the TDI's stunning 80mph passing power. I figured that the 617 could also benefit from lowering the rpms back down toward the 2400 rpm torque peak for lower noise and higher efficiency and I hoped that the torque peak would keep the car from being doggy on the highway. I could accept some compromise but not too much as I don't want to die trying to accelerate into traffic.

To predict what might happen with the diff change, I have an Excel spreadsheet that allows you to plug in tire size, diff gearing and transmission gear ratios to get engine and road speed in relation to each other. All calculations showed that by switching the 300 SD differential to a 2.47 from a Gasser 126 V8 I would lower the rpms on the highway by around 600 rpms! The big question was whether the donor rear end would have a bad pinion bearing as well and whether the lower engine speeds would turn the car into a dog. I was also a little shaky about the required yoke swap on the diffs and whether I'd mess up the drive axle boots or joints doing the swap. I did some reading and determined that swapping the whole rear axle assembly was the most time-efficient way to get the job done though I paid a little more for the axles.

Removal of the 1985 380SE's rear end was a little nerve wracking as the flex plate's dowels weren't ready to let go of the differential yoke but a properly placed screwdriver did the trick in separating them. We were careful to keep the drive axles in as straight a line as possible to keep the CV joints and boots intact. It took about 30 minutes to extract the 380 rear end including carefully removing the diff speed sensor wiring from under the rear seat in case I want to switch to ABS later. (The donor has ABS and I've done VW ABS swaps in the past so I'm not afraid of the job.)

After the donor rear axle assembly was out, I put my car on the lift and promptly removed the rear exhaust section which is so damn easy! I wish it was that easy to remove the exhaust on VW's. Anyways, I unbolted the drive shaft flex plate and found that it was cracked all the way around and didn't have long to live. I removed the center heat shield and tied some baling wire to the two rear heat shield studs to hold up the drive shaft as you don't want it to hang! Removing the heat shield was necessary to get the proper angle on the drive shaft to get the rear end out.

The outer CV joints are held in by two long 8mm bolts with tubular spacers and big washers. They are accessed by removing the center caps on the rear wheels. Four 19mm headed nuts hold the diff to the rear subframe and the differential mount is held to the body with four 8mm bolts with 13mm heads. With a tranny jack under the differential I removed all of the attaching hardware and pulled one outer cv joint out of the rear hub, angled it down and out while being careful to move the diff to keep the axles in as straight a line as was possible to avoid damaging the axles. (I didn't know at that time whether or not they would have to go back in and I don't like destroying any parts, ever.) With the aid of a helper, we lowered the assembly to a cart with the donor differential and with a deep socket I removed both 12 point 30mm nuts holding the differntial yokes to the two diffs so that I could swap them. (The 380 flex plate and yoke has a bigger bolt pattern than the 300SD's.) The 380's front seal looked o.k. so I cleaned up the SD's yoke, checked it for seal surface damage and reattached it to the 380 diff with a brand new 30mm nut from the dealer. I tightened it to around 145 pound feet and chcked for smooth turning with some resistance. Being a geek I weighed both rear axle assemblies on a commercial scale and the much larger 380 diff weighed 126.3 which was exactly 23 pounds heavier than the 300's diff. The difference in weight is due to the fact that the 380 differential has a mechanical friction plate-type limited slip mechanism inside! I was (and am) excited to think of being able to put power to the wheel with the most traction. LSD should be standard issue with a 40,000 car. (Please, no drug jokes!)

The rest of the install went flawlessly with a new flex plate and a new diff mount. I was really struck by how simple thes cars are underneath and was really ready to see if my experiment would work as planned. If the experiment worked, I would have new enthusiasm for a car that I really liked in many ways.

I set the car back on the ground, washed my hands and fired her up. I engaged drive and quietly (at least for a diesel running on 20% biodiesel could be) and motored out of the shop. Even at 15mph I could tell that the bad pinion bearing whine was totally gone. I accelerated and it was holding gears longer but accelerating quite well. The speedo moved slower than what was visually happening to the scenery but I knew that I would hafta source a speedo from a 380 or 500/560 to jibe with the 2.47 rear end. But the most incredible thing about the first drive was that the car was so much quieter! It was like it was a totally different car. My Dad used to have a 380SEL and the feeling of composure from that car was now present in my car. Even at speed, the car had plenty of power as the rpms never got above 3,000 rpms unless my foot demanded it. The torque was doing exactly what I wanted; accelerating the car without drama or excessive noise. Downshifts were easier to provoke and the acceleration was great. Highway cruising at 80mph had the engine spinning at 2900 rpms and 70mph was around 2400 rpms as verified by a hand held GPS unit.

The swap was only a few days ago and now I am much more interested in fixing all of the little things wrong with the car like the cruise, windshield, door check weld, worn out seats, and questionable tires. I have all of the plans in my head for using a radiator sized intercooler and that project is back on the list of things to do to make a reasonably priced, relatively efficient, large comfortable cruiser with style and teutonic elegance.

Side note: I have yet to source a speedo head with a working odometer but my baseline mpg's was 26-27 mpg for about 7,000 miles while using the stock 3.07 rear end. I will report back to this thread as to my new MPG's with the 2.47 diff swap. I am hopeful that by lowering the rpm's down toward the torque peak my mpgs will go up a little though I don't expect a lot of change. All of the reading I have done about efficiency says that by running an engine closer to its torque peak, you decrease fuel consumption. We'll see.

Just for pleasantness alone, this swap is Absolutely worth the effort. I paid $300 cash for the whole rear end including axles plus $40 for use of the lift and help when I needed it. The diff mount and flex plate was not expensive and the new 30mm nut was $5.00. I spent about 3 hours total on the job and a coupla hours doing service manual research. The car is completely different and I really think that this diff should have come standard from the factory. I have already noticed the difference with the limited slip on loose gravel as I got the car to rotate it's rear end with the throttle. The engine is almost silent at speeds under 50mph and my hopes are high that there will be an efficiency gain. Perhaps the biggest efficiency gain is the one that made me decide to keep a car that I had put a lot of time into as opposed to selling it to buy a quieter Benz...

Jim Royston

Reply With Quote
  #2  
Old 02-18-2005, 09:25 AM
Rick Miley's Avatar
Spark Free
 
Join Date: Jun 1999
Location: Land O Lakes, FL
Posts: 3,086
Wow, what a fantastic writeup. Congratulations on a successful project!

Quote:
Originally Posted by dieselgeek
Side note: I have yet to source a speedo head with a working odometer...
Don't worry about the odometer, just source a working speedo. The odo is very easy to fix and the procedure is posted numerous times on this board. Just search for "odometer fix."
__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References
Reply With Quote
  #3  
Old 02-18-2005, 09:33 AM
Registered User
 
Join Date: Jul 2004
Location: Norwich, VT USA
Posts: 905
When I bought my '67 landrover it had a howling diff. It was the only landrover I had ever been in and I had no idea. When my cousin (an owner of an old rover as well) took his first ride in mine he siad "If this was my rover I wouldn't be driving it".....I had been driving it that way for 2 years. a week later I put it in 4 wheel drive and removed the rear driveshaft. It was like switching to an electric car it was silent in comparison...Anyway Iapologize for sharing this barely related experience...having said all that....Congrats and thanks for sharing.
__________________
Rob M
Norwich, VT USA
1980 240D Euro delivery 4 speed manual silver/blue
~160K miles
Reply With Quote
  #4  
Old 02-18-2005, 10:27 AM
Registered User
 
Join Date: Sep 2004
Location: San Antonio, TX
Posts: 54
Quote:
Originally Posted by Rick Miley
Wow, what a fantastic writeup. Congratulations on a successful project!
Don't worry about the odometer, just source a working speedo. The odo is very easy to fix and the procedure is posted numerous times on this board. Just search for "odometer fix."
Yeah, I fixed the 80mph speedo/odometer that the SD came with. Now I have to do it again on the V8 odometer...it's easy though not too cheap. My wonky tack amplifier is also driving me crazy!

Jim
Reply With Quote
  #5  
Old 02-18-2005, 10:43 AM
Registered User
 
Join Date: May 2003
Location: Boonville Indiana
Posts: 2,342
500SEL-Parts

I have a complete diff./axle(2:47)set up from a 1985-500SEL and I also have a Instrument Cluster(complete) if you are interested. Please sned me a email for more information and pics... jim16671836@yahoo.com Jim
__________________
James A. Harris
Reply With Quote
  #6  
Old 02-18-2005, 11:45 AM
Registered User
 
Join Date: Dec 2002
Location: RI shore
Posts: 2,937
one of the most informative posts I've read here. Jim, please post more info as you get it. I've been interested in this for a while. Seeing as I plan to keep my car for a long time, this may make sense for me too. Best time to do it as you implied is when you have to replace the unit anyway. Thanks!
__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
Reply With Quote
  #7  
Old 02-18-2005, 03:49 PM
Hatterasguy's Avatar
Zero
 
Join Date: Nov 2002
Location: Milford, CT
Posts: 19,307
AFAIK only the 560SEL's had the LSD's. I know the 420's didn't have them.

Intersting mod though, I wonder what your mpg's will be?
__________________
2020 GMC Sierra Denali
2007 Tiara 3200
Reply With Quote
  #8  
Old 02-18-2005, 04:28 PM
dieseldiehard's Avatar
Dieseldiehard
 
Join Date: Oct 2002
Location: Bay Area No Calif.
Posts: 4,324
I had this on file:
380,500 RATIO 1:2.47

380,500,560SEL RATIO 1:2.47 ABS

420SEL RATIO 1:2.47

380SL, 560SL 1:2.47

I didn't find anything that tells whether or not these are LS.
I bellieve there is a W116 chassis (450SE?) that had LSD std. but is uses 2.65 ratio. Close enuff for me.
I sure liked it when I installed a 3.07 in my 220 gasser.
__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!
Reply With Quote
  #9  
Old 02-20-2005, 09:28 AM
Registered User
 
Join Date: Sep 2004
Location: San Antonio, TX
Posts: 54
I also wanted to post the gear ratios of the 722 transmission for the 300SD from a Mercedes transmission manual:

1st 3.68
2nd 2.41
3rd 1.44
4th 1.00

The manual states that the transmissions were designed to handle 400Nm of torque which equates to 295 lb. feet. The manual does not differentiate between gasoline powered cars or the diesel as far as ratios or torque capacity go. The overall final gearing ratios are determined by which rear end the car was equipped with and of course, tire size.

In other news and as verified by GPS, I was able to come within 4mph of the stated top speed of the car before I ran out of room. I am completely positive that I will be able to better the stated top speed at the next test track I go to.

Jim
Reply With Quote
  #10  
Old 02-20-2005, 01:56 PM
phantoms's Avatar
Senior Member
 
Join Date: May 2004
Location: Savannah, GA
Posts: 794
Quote:
Originally Posted by dieselgeek
I also wanted to post the gear ratios of the 722 transmission for the 300SD from a Mercedes transmission manual:

1st 3.68
2nd 2.41
3rd 1.44
4th 1.00
Located at this link also.
__________________
85 300CD
83 300TD
78 240D (daughter)
Reply With Quote
  #11  
Old 02-24-2005, 09:55 AM
Registered User
 
Join Date: Jul 2004
Location: North Texas
Posts: 22
Nice Write-up!

I was thinking about this myself for my 300SD. I would bet that if we had the schematics on the speedo, the timing circuit could be changed (resistor or cap) to correct the speed. Input?
Reply With Quote
  #12  
Old 02-24-2005, 01:01 PM
Registered User
 
Join Date: Sep 2004
Location: San Antonio, TX
Posts: 54
I just bought a complete cluster from a 500SEL for $23, shipped on Ebay. When it arrives I will set the two speedos next to each other to see what the diffs are (if I can discern them). I'm not an electronics guy...

I did want to get rid of my 80mph speedo anyway.

Jim
Reply With Quote
  #13  
Old 02-24-2005, 11:39 PM
Hit Man X's Avatar
I LOVE BRUNETTES
 
Join Date: Sep 2004
Location: FUNKYTOWN
Posts: 9,087
Thumbs up

AWESOME, now I'm wondering why some people on here thought I was crazy for bringing this up...

I only wish you had some pictures to go along with this writeup. It's hard to visualize what exactly I'm getting into, though it doesn't seem to bad all in all.
__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.
[/IMG]
Reply With Quote
  #14  
Old 02-27-2005, 07:03 PM
Registered User
 
Join Date: Sep 2004
Location: San Antonio, TX
Posts: 54
Hey y'all,

I just finished my first tank of fuel since my 2.47 differential swap and I got 29.42 mpg in a 30% highway and 70% city mix of driving. I used a GPS unit to calculate miles driven and the fill-ups had visible fuel right up to the filler opening both when I initially filled up and when I filled up today. The best I did before the diff swap was 27.2 mpg and that was with a little more highway driving as a percentage. Generally, my car gets 26 on every tank no matter what I do and I'm excited that the diff swap is looking like it will have efficiency advantages as well as noise benefits. I will report my next tank's mpg when the next 500 miles goes by. It is possible that this tank was a fluke so more testing is needed.

In further attempts at noise reduction, I put glycerin on my door seals today to try to get rid of the creaky sound they make and it made a big difference. We'll see if it lasts. I read about using glycerin on door seals in some owners manual but I can't remember where. So far, it seems to work and the car is quiter still.

Jim
1982 300SD Midnight Blue 312K
Reply With Quote
  #15  
Old 02-28-2005, 07:57 AM
Registered User
 
Join Date: Jul 2004
Location: North Texas
Posts: 22
I believe that I may try this sooner than planed

I found a 500sel speedo, but, still looking for a 2.47 differential. Any one know where I can find one at a resonable price? I just don't have a lot of time to spend from junk yard to junk yard, soccer season as started once again.

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
EGR VALVE 1982 300SD riske Diesel Discussion 24 10-25-2001 12:39 AM
Mercedes 1982 300D actually has a 300SD engine W107BenzW123MB Diesel Discussion 1 05-06-2001 06:56 PM
1982 300SD Power Seat Not Moving TAYJAN Tech Help 0 10-11-1999 11:09 PM
1982 300SD door panel installation TAYJAN Tech Help 3 10-11-1999 09:38 PM
1982 300SD Power Seats Not Working TAYJAN Tech Help 1 10-09-1999 10:24 PM



All times are GMT -4. The time now is 06:14 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page