differential ratio change for manual 240d?

[barry123400]

Have been thinking would like to reduce cruise rpms a little at 70mph. Wonder if there is a close ratio available that might help a little? Know it's a marginal ideal but I live in rural area with little traffic and no real hills. Since driving 240ds I seem a lot more aware of any hill. Before driving 240ds I used to think the world was flat. Engine does not sound particularily happy at 70 mph. I think the engine is screaming save me at 70 mph but it's too loud too understand.. Just not practical to drive slower on local highways. Any rear end experts out there? Or perhaps anyone that has tried or even contemplated this swap? My primary concern was of course any loss of acceleration but on reflection that was stupid as you cannot loose what you do not have.

[dieselgeek]

I have a 3.07 from a wagon that will lower your revs but the trade off is that in some situations you will hafta stay in a lower gear than what you would normally use.

[bennett]

Just curious here... what would my 240 be revving at (rpms) at 70 MPH with a stock rear end?
am I close to 4000 RPMS?.. insn't 4200 redline?

I'm new to 240 but mines sure seems like it revs hard at 65 let alone 70

[Brian Carlton]

Originally Posted by bennett

Just curious here... what would my 240 be revving at (rpms) at 70 MPH with a stock rear end?
am I close to 4000 RPMS?.. insn't 4200 redline?

I'm new to 240 but mines sure seems like it revs hard at 65 let alone 70

I used a 3.46 axle and 185/70/14 tires:

The engine speed for a manual transmission is 3360 rpm.

[barry123400]

Will watch this thread for awhile to see what people mention. Do not even know my present ratio mind what is available. Well aware now that with 240ds there is a varience of performance car to car. One of mine has a pretty fresh engine and is (dare I use the expression?) faster than the other one. Or is less slow more appropiate? Will check rear end ratio I have presently by checking stamp on housing as soon as I can get to it. Thought somewhere it mentioned was a 3.47. If that turns out to be the case the 3.07 sounds like a good possibility. One post (dieselgeek) mentions the 3.07 and do you know what car model it's in or is it just the standard in 123 wagons? May drop you a note a little later in this thread.. Think for my type driving it might work if the 3.47 or close turns out to be accurate. My service information is limited to the hayes manual right now. Gotta get some good manuals soon. Needless to say whatever I do will be reported on this site especially how it affected available acceleration and sound. Will do some timed runs prior and after the change. Do not have the available power to stretch the ratio any farther in my opinion. Do not forget 90% of my driving is done at close to sea level as well. My thought is every little bit helps though.

[Brian Carlton]

I didn't originally notice that you have a manual trans.

IMHO, 3360 rpm for that engine/axle combo is not too many rpm's for that vehicle at 70 mph.

Most of the discussion on the site is reducing the rpm's of 300D vehicles with 120 hp and auto trans. With 67 hp, and no torque converter, that vehicle needs all the torque to the road that you can possibly get and you should seriously consider why you want to reduce that torque.

Going to a 3.07 will make it that much more "difficult" to drive.

[barry123400]

Brian for a lot of reasons you are generally right about this. Several factors alow me to experiment a little in my area the most important being there is virtually no traffic. Felt since the effort was relatively minor to do just want to find out. Pretty well have to stay at 70mph on local highways or you hold up what little traffic there is from time to time. Mainly during tourist season. Know also the engine is not being hurt with the normal rear end ratio but some 240d owners like myself just do not like the sound. You certainly would not want to attempt this much above sea level or when living in a congested area. Or with a weak 240d manual mind the automatic version. There are less than two million total people in the four eastern provinces of canada as well and the geographical area is pretty large. Now am starting to wonder if anyones done a 240d or knows of one already converted.

[leathermang]

I see a lot of posts about people considering things like 3rd member ratio changes and 5 speed transmissions and other things....
I would like to remind yall of some things which might make your life quieter without making expensive changes which may or may not fix your complaint...and have the potential for adding even worse situations to your life... like your car being even slower than it already IS....

First remember this : Your cars are OLD !


This means things which were not present in the original car may have worked their way into your life.

First thing to check is the condition of your hood pad... this is all that keeps the noises in your engine compartment from being a DRUM ! I have no hood pad... I should know.

Some noises in items which are bolted together are hard to isolate.... a noise on one end of a frame can sound just as loud on the other end...

The Tech Service Bulletins for my 1980 list ' Modified Countershaft and rear bearing journal '... check to see if your car has updates which were not applied to your car.

Buzzing noise can also come from the 3rd member.... since it is bolted to the car instead of being sprung under the car like a live axle... there are TSB's and instructions in the chassis manual having to do with the way the 3rd member is bolted up to its mount... which needs to be checked if you have buzzing....

More buzzing is going to be sent to your car and you if the engine mounts are not correctly positioned... if your car needs the ' self made tool' for checking it's positioning while you are installing... then that may be part of your noise at speed.... but engine mounts can deteriorate just due to age, heat and engine cleaning solvents... so checking them is important.
There are about 20 plus pages dedicated to putting the engine mounts on correctly...

There are problems with flex discs on the ends of the driveshafts which need checking... and check for changes listed in Tech Service Bulletins ... they clearly had some problems and tried to fix them by changing one or more of the specs on those discs...

The noise insulation under your carpets deteriorates over the years... and better stuff is probably available than original.....this is a dirty job... but easy and very rewarding in terms of noise...

Also check your wind seal around windows and doors.....

[barry123400]

Leathermag you are also on the money. One of my 240ds is so noisy at 70mph compared to the other there is very little comparison. Maybe the right answer is to go over it totally to freshen up things that contribute to general noise. Should be done anyways. Purchased the noisy one at christmastime. Car seems happy at 60mph but not above. Drove it home the thousand miles and noticed these things. The 82 240d is the offender. The 79 with the seemingly new engine is a lot better and the friend who drove it home 1500 miles for me stated it would do 100 on the speedo on level road. I told him he was overspeeding it a little and mentioned to him at about 90 there is a mark on speedo and that is the maximum allowable speed. That 79 came home a year and a half ago and for some strange unknown reason the fuel milage is also superior to what others claim. The 82 240ds milage is substandard and so is my 77 300ds fuel milage. Hope a thorough check and tune up when I get to them will help the two substandard ones a little. Too many distractions I need a simpler life. Without the distractions life might be easier. But certainly not as much fun.

[leathermang]

My 1980 240 manual tranny loves to run 75 plus.... there are a lot of individual difference in cars 20 plus years old....