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View Full Version : 06 158" wheelbase Rear end Gearing ??


garyr
07-02-2019, 12:57 PM
Good Day All,
Thanks for allowing me to join the forum from Ohio.
We just purchased, last week 6/2019, a T1N sprinter out of South Carolina. 2006 Freightliner 2500HSC 158" wheelbase Converted by Gulf Stream. 53,000 miles with 15,000 miles on a German rebuilt motor. I was shown a $14,700 invoice for the motor and install in 2017; I am thinking this was because of rear end problem. 2 little scary looking rust spots at the bottom of the windshield and some orange bleeding through one of the top seams.
Drove down in our Diesel chevy cruze, bought it and tow dollied the car back to central ohio with us.
PROBLEM: The van is way way overgeared. At 70mph the motor is revving at 3,000 rpms +/- in 5th gear with the correct size 28 1/2 inch tall tires.
My experience with at least 5 diesel cars is that their "sweet Spot" is right around 1,900 rpm. 2,050rpm in this van is 51mph. Also the
Speedometer mph does not coincide with the GPS mph by as much as 7mph, with the van reading faster than the Actual.
It needs a way different rear differential ratio.
Using the youtube mercury guy's calculation I may have to go as low as 3.08/1 ring and pinion. With that will I have to
have to have the wife push ti to get it going?
Using the vin the mercedes dealer in town here emailed me the spec sheet on the van and it shows it as having a 4.11 rear.
During a brief phone call he also told me that there were only 2 rear gears offered for my van. 4.11 and 3.92 I believe.
The dealer also seemed really reliant on using the VIN to allow me to only buy specific parts for my van.
I have been a mechanic, drag racer most all of my going on 3/4 century life and rear end swaps are/were commonplace.

QUESTION:
What Options do I have available for changing the rear end and where can I find them? I am going to have to presume that for all intent and purpose a sprinter is a sprinter
and in my way of thinking, a rear from one should bolt up to another? I am fully aware that the ECU/ECM would have to be reprogrammed.
I am not against purchasing a complete new third member(that is until I see the price) I am fully capable of rebuilding this rear end with new gears but from watching a "Mercedes" tutorial video there are a whole bunch of specialty tools required which I do not possess(sp).

Can anyone of you point me in the right direction? I read some old 2010 posts on here where, back then it was a royal pain to change the rears but am hoping now not so much?
I read about the limp mode and that and I can deal with that as long as I know that the reprogramming can be done and more importantly IF the dealer is allowed to reprogram the upgrade AND if the van will accept the upgrades.

Hopefully this is not too big a can of worms. It is not fun getting whoooshed by by every semi on the freeway!
Observation: I do not think this gulf stream has one iota of insulation or sound deadening in it other than the Mercedes applied, slathered on undercarriage undercoat. Actually sort of a good thing in that I can find/stop/prevent any rust in the future.
Thanks in advance, Gary

Midwestdrifter
07-02-2019, 01:22 PM
Is this van a dual or single rear wheel? If its dual, you can easily upgrade to 16" wheels from the NCV3 sprinter. Then fit 225/75 or similar tires to lower your cruising RPM.

On your rear axle is a plate (back passenger side), it will have the gear ratio. You can also enter your vin on the website below to get your build info.

https://www.datamb.com/

garyr
07-02-2019, 01:27 PM
Sorry it is a single rear wheel/
This problem is way more than tires.
Would have to put rear tractor tires on it to solve this one!
thanks though

Midwestdrifter
07-02-2019, 01:43 PM
There are two common gear ratios, 4.11:1 and 3.73:1.

5TH gear is 0.83:1. With 225/75R16 is 689 revs per mile. with 3,73 you would be at 2488, with 4.11 you would be at 2750rpm.

You don't want the engine rpms too low, otherwise you would have no power in 5th, and be stuck in 4th/3rd on even a slight grade. The OM647 works just fine at 2500rpm, which is firmly in its powerband.

I am in the final stages of prototyping an electronic black box which can be set to correct the information the TCM receives, so that alternate gear ratios can be used. My application is for 4x4 low range, but it would likely work fine for changing rear end gear ratios. The main issue is that I don't think anything lower than 3.73:1 is commonly available. I know Mercedes offered a 3.5:1, but that may not have been sold in north america.

Aqua Puttana
07-02-2019, 02:02 PM
FWIW I agree with MWD about the 2500 rpm range being ok. The 5 cylinder T1N engines are small displacement turbo direct injection type. Some of the experiences from traditional diesel engines aren't directly applicable.

... I know Mercedes offered a 3.5:1, but that may not have been sold in north america.
Many of the options for NAS aka NAFTA Sprinters are quite narrow in the offerings vs ROW.

My recollection is 4.11, 3.92, 3.73 being the NAS T1N choices.

:2cents: vic

skwoodwiva
07-02-2019, 05:58 PM
I have an older version of yours. Mine is the sideways rear bed w/ pods/bulges. Many here say I should keep the 4.11 as I am at 7700 lbs of 8600 gross.

I have 225s front & 245s rear. I think could have gone w/ 245/75 or a /85 in front & 235/85 rear that is a 32.5 dia.
I have not yet done the math to see where this set would lower my gearing.

Also the feedback I get is that the traction control should manage larger on rear, but I have yet to test it on loose roads… .

autostaretx
07-02-2019, 06:29 PM
You can download the 2006 service manual here: http://diysprinter.co.uk/reference/2006-VA-SM.pdf
If you visit that site ( http://diysprinter.co.uk/reference/) you will also find the "sub-set" 2006 manuals.
Also drop into http://diysprinter.co.uk/reference/T1N_service_scans/ to pick up about 100 training manual pages.

Adding a real-time gadget like a ScanGauge or DashDAQ would give you handy as-you're-driving info like the LOD (load) readout.
If you downshift when that exceeds 70% or so, your mileage will improve. (the Sprinter downshifts more than a bit late).

As others have said, the engine's torque and power are both at higher rpms than you'd expect (or be used to in a diesel).

--dick

garyr
07-04-2019, 11:04 PM
I have an older version of yours. Mine is the sideways rear bed w/ pods/bulges. Many here say I should keep the 4.11 as I am at 7700 lbs of 8600 gross.

I have 225s front & 245s rear. I think could have gone w/ 245/75 or a /85 in front & 235/85 rear that is a 32.5 dia.
I have not yet done the math to see where this set would lower my gearing.

Also the feedback I get is that the traction control should manage larger on rear, but I have yet to test it on loose roads… .

With the larger tires did you have to have the ecu updated to the new tires?
I can fit a LT265/75r16 in my wheelwells and am wondering if the computer will have to be
reset if I put them all around?

Can someone tell me where the sweet spot is on the OM647 engines? What is the Ideal RPM's
for that motor for long stretches?
thanks gary

Midwestdrifter
07-04-2019, 11:09 PM
The 647 has no problems with 2500rpm. Ciprian on this forum has over 700k miles of highway driving in his stock T1N (likely 3.7 gears, and 225/75R16 tires). The 647 only makes aroud 150hp in the sprinter. So it needs to have higher RPMs than the big 7L diesels, so that it doesn't need to downshift with every slight headwind or grade.

My stock 140WB with a light load would get 20.5mpg with average cruising speeds of 70mph (some stretches of 80 for hours). That's at 2,300 rpm or higher usually.

Gabe Athouse
07-04-2019, 11:54 PM
With the larger tires did you have to have the ecu updated to the new tires?
I can fit a LT265/75r16 in my wheelwells and am wondering if the computer will have to be
reset if I put them all around?

Can someone tell me where the sweet spot is on the OM647 engines? What is the Ideal RPM's
for that motor for long stretches?
thanks gary

Sweet spot for any engine is usually right at peak torque or just few hundred below.

Midwestdrifter
07-04-2019, 11:57 PM
The 647 has a very flat torque curve. Its basically flat between 1,500 and 2800rpm.

garyr
07-05-2019, 12:28 AM
Sweet spot for any engine is usually right at peak torque or just few hundred below.

Well then what id thte peak torque for this engine?

Midwestdrifter
07-05-2019, 12:35 AM
Well then what id thte peak torque for this engine?

https://sprinter-source.com/forum/showthread.php?t=57585

The 612 is essentially the same as the 647.

https://sprinter-source.com/forum/attachment.php?attachmentid=87478&d=1499347364

Gabe Athouse
07-05-2019, 05:55 AM
Midwest drifter is correct, these engines have an exceptionally broad torque curve, but I’d say the sweetest spot is around 2300. Another way to just a sweet spot is by monitoring boost. I like to keep it around 5-6 psi on the highway, any higher and you’re pushing a lot of unbranded fuel through it, losing efficiency.