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  #1  
Old 06-18-2018, 03:29 PM
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1987 300TD 5 speed conversion: torque settings

Hello all,

I'm getting closer to wrapping up my 300 TD 5 speed conversion. Another list member sold me the proper driveshaft combo, which required replacement of the transmission and differential input flanges.

A couple of simple questions I can't find answers to:

- What is the torque spec for the nut that secures the trans output flange?

- What is the torque spec for the nut that secures the diff flange?

- Any special instructions before I crank down on either nut? BTW, I'd like to replace the pinion seal on the diff too.

So close!

Many thanks,

corvo gold

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  #2  
Old 06-18-2018, 04:23 PM
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Location: Modesto CA
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Quote:
Originally Posted by Corvo Gold View Post
Hello all,

I'm getting closer to wrapping up my 300 TD 5 speed conversion. Another list member sold me the proper driveshaft combo, which required replacement of the transmission and differential input flanges.

A couple of simple questions I can't find answers to:

- What is the torque spec for the nut that secures the trans output flange?

- What is the torque spec for the nut that secures the diff flange?

- Any special instructions before I crank down on either nut? BTW, I'd like to replace the pinion seal on the diff too.

So close!

Many thanks,

corvo gold

For the trans flange nut, torque is 150Nm (112lb/ft).


At the diff, the process is a bit more involved. Before removing the original flange, the running torque that is required to turn the pinion and ring gear assembly should be determined. That is best done on the bench, or if in the car, with the axles removed from the diff. The running torque is the torque necessary to keep the pinion turning after break-away.
When the new flange is installed, the nut is tightened progressively until the same running torque is achieved.
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  #3  
Old 06-18-2018, 04:35 PM
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Originally Posted by Frank Reiner View Post
For the trans flange nut, torque is 150Nm (112lb/ft).


At the diff, the process is a bit more involved. Before removing the original flange, the running torque that is required to turn the pinion and ring gear assembly should be determined. That is best done on the bench, or if in the car, with the axles removed from the diff. The running torque is the torque necessary to keep the pinion turning after break-away.
When the new flange is installed, the nut is tightened progressively until the same running torque is achieved.
Okay ... I didn't do any of that before removing the flange retaining nut.

- What is meant by "break-away"? I'm assuming when the car isn't in gear but still rolling?

- As much as I hate to ask, what is plan B? Although it may not be optimal to simply torque it on, what is a safe torque setting for the diff flange?

corvo gold
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  #4  
Old 06-18-2018, 05:06 PM
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Location: The slums of Beverly Hills
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On the pinion nut I marked the angle before removing the nut then reinstalled it to the same angle. Never bothered with the torque and that was 45k miles ago.

Are you keeping your stock 2.65 diff? I think you'll be disappointed with the 5spd/2.65 off the line especially with any load in the car or uphill. Also any freeway hill or acceleration under 70mph requires a downshifting to 4th. The wagon body is also 300lbs heavier than the sedan. I'm currently swapping a 3.07 diff into my 300D/5spd because I got tired of constantly slipping the clutch when accelerating from a stop. The 300E 3.07 already came with the smaller flange.

Good luck
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Old 06-18-2018, 06:12 PM
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Originally Posted by Corvo Gold View Post
Okay ... I didn't do any of that before removing the flange retaining nut.

- What is meant by "break-away"? I'm assuming when the car isn't in gear but still rolling?

- As much as I hate to ask, what is plan B? Although it may not be optimal to simply torque it on, what is a safe torque setting for the diff flange?

corvo gold

Break-away torque is the extra torque (as compared to running torque) required to overcome seal friction and initial lubricant drag. Both of the terms refer to turning the pinion with an inch-pound torque wrench (of the dial or beam type) with the diff assembly on the bench.

There is no published tightening torque for the diff flange nut; that said, 75-80 lb-ft should be enough to preload the bearings.

2.65:1 is a ratio that was used in the 210mm diff, not in the 185mm type found in W123 & W124 chassis.
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Old 06-18-2018, 06:20 PM
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Originally Posted by Frank Reiner View Post

2.65:1 is a ratio that was used in the 210mm diff, not in the 185mm type found in W123 & W124 chassis.
The 87 300D and 300TD have a 185mm 2.65 ratio diff with the large flanges imput. The later w124 E320 has a 210mm 2.65.
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Last edited by tjts1; 06-18-2018 at 06:45 PM.
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  #7  
Old 06-18-2018, 09:13 PM
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Replacing the differential may come at some time in the future if I find acceleration to be unbearably slow.

Part of the problem is that I'm under a time crunch. I'm an Army officer about a week away from journeying to another installation, whereupon I turn around and deploy virtually upon my arrival. A crushing workload as of late and prepping for a move really impacted my progress, which is why I'm scurrying at the 11th hour to button up this project.

I ended up torquing the pinion flange to 80 ft-lbs. I know it's not optimal, but I'm afraid good enough for government work is where I'm at. The 190/260 driveshaft is in and fits perfectly. However, the bolts for the flex disc for the diff end are too long, so I'm going to have to stop into the local Fastenal in the morning since I don't think Home Depot sells 10.9 grade hardware.
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  #8  
Old 06-18-2018, 09:43 PM
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Quote:
Originally Posted by Corvo Gold View Post
Replacing the differential may come at some time in the future if I find acceleration to be unbearably slow.

Part of the problem is that I'm under a time crunch. I'm an Army officer about a week away from journeying to another installation, whereupon I turn around and deploy virtually upon my arrival. A crushing workload as of late and prepping for a move really impacted my progress, which is why I'm scurrying at the 11th hour to button up this project.

I ended up torquing the pinion flange to 80 ft-lbs. I know it's not optimal, but I'm afraid good enough for government work is where I'm at. The 190/260 driveshaft is in and fits perfectly. However, the bolts for the flex disc for the diff end are too long, so I'm going to have to stop into the local Fastenal in the morning since I don't think Home Depot sells 10.9 grade hardware.
I waited 45,000 miles to swap the diff so no worries there. Check out Ace or Orchard. Their metric Hardware section is better than Home Depot. I wouldn't worry about using 10.8 bolts. The flex disc is going to fail long before the bolts.
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  #9  
Old 06-18-2018, 09:49 PM
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Quote:
Originally Posted by tjts1 View Post
The 87 300D and 300TD have a 185mm 2.65 ratio diff with the large flanges imput. The later w124 E320 has a 210mm 2.65.
I am remiss in my research; the ratios quoted above are indeed correct.
The attached pdf. has quite a bit of useful info; if memory serves it was prepared by Stu Ritter.
Attached Files
File Type: pdf Mercedes differentials.pdf (22.6 KB, 237 views)
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  #10  
Old 06-18-2018, 09:54 PM
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Join Date: Feb 2011
Location: Modesto CA
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Quote:
Originally Posted by Corvo Gold View Post
Replacing the differential may come at some time in the future if I find acceleration to be unbearably slow.

Part of the problem is that I'm under a time crunch. I'm an Army officer about a week away from journeying to another installation, whereupon I turn around and deploy virtually upon my arrival. A crushing workload as of late and prepping for a move really impacted my progress, which is why I'm scurrying at the 11th hour to button up this project.

I ended up torquing the pinion flange to 80 ft-lbs. I know it's not optimal, but I'm afraid good enough for government work is where I'm at. The 190/260 driveshaft is in and fits perfectly. However, the bolts for the flex disc for the diff end are too long, so I'm going to have to stop into the local Fastenal in the morning since I don't think Home Depot sells 10.9 grade hardware.

CG > Command & General Staff School?
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  #11  
Old 06-18-2018, 11:36 PM
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Originally Posted by Frank Reiner View Post
CG > Command & General Staff School?
Actually, I'm 90 minutes to the west -- Senior Defense Counsel, Fort Riley, Kansas. The Corvo Gold is my gold '65 Corvair Corsa convertible (Corvo Gold ... Cuervo Gold ... I thought it was funny).

Sadly, I spent more time this year in court than in the garage tinkering on a Corvair or Benz. However, I have a week off to compensate!

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