1956 Dodge Truck Build with OM617 - Page 3 - PeachParts Mercedes-Benz Forum

mach4 · #31 12-13-2014, 11:09 AM

I think you're going to be just fine. If there were ever a poorly designed drive shaft it was Mercedes, what with one u-joint at a "slight" angle incorporated in the design.

If you consider this image from Vstech's document referenced above, you have the same basic setup, only this depicts a transmission/rear end setup from the side and your setup would have the setup depicted from the top. The important thing is that the two u-joint faces are parallel.

Rock on...

By the way, if you decide to go with a one-piece driveshaft I could probably get you the CNC file to cut an adapter to go from the MB trans to a Spicer yoke.

t walgamuth · #32 12-13-2014, 12:49 PM

I am using the ford 9" from about a 72 pickup. We used the Mercedes ds and the center bearing. The rear of the back ds we cut off and Michael welded on a u joint from a corvair which matched the ds perfectly and the diff.

I should get the truck up and driving first but am thinking of swapping in something like the jag IRS.

Stretch · #33 12-13-2014, 03:38 PM

Hey up - I didn't really look too hard but I agree with John - this is going to cause trouble =>

Quote:

Originally Posted by charliebob

The front half of the driveshaft, which is "unmolested" Mercedes, is perfectly aligned with the crankshaft and transmission. The carrier bearing in the middle keeps the front shaft in alignment. The back half of the driveshaft is custom, with u-joints on both end. The slight angle of the back driveshaft is very small compared to most stock shafts. The angle is necessitated by the pinion in the Jag being offset, as are pinions in many diffs, solid axle and IRS.

It should not be a problem. If it is, I'll make a double driveshaft with u-joints on both.

...

Quote:

Originally Posted by vstech

SLIGHT offsets with a driveshaft are a bad thing... the angle needs to be in spec for the ujoint config. what is most important is the relationship between the two ends. they need to be exact, and held in relationship through the travel of the moving end...

John is right this slight angle is too much and it will probably rip out the centre bearing rubber quite quickly - this part is not meant to be used this way.

Sorry mach4 I disagree =>

Quote:

Originally Posted by mach4

I think you're going to be just fine. If there were ever a poorly designed drive shaft it was Mercedes, what with one u-joint at a "slight" angle incorporated in the design.

...

The MB design is a really good design - you have to consider the addition of the single universal joint as being there for the odd "just in case" situations (which effectively means when the motor mounts collapse!)

The design is all about resilient supports and keeping the propshaft straight. The motor is resiliently mounted; and the transmission; and the centre bearing; and the differential / subframe - these have to be aligned at the right height and in the same straight (dorsal) position along the length of the car. If this line is buggered up then you will end up with drive line vibrations. I don't think that any Mercedes (fitted with this resilient mount system) has suffered from an angle like that before.

My guess is that the system as it stands won't last long.

charliebob · #34 12-13-2014, 05:25 PM

Quote:

Originally Posted by mach4

I think you're going to be just fine. If there were ever a poorly designed drive shaft it was Mercedes, what with one u-joint at a "slight" angle incorporated in the design.

If you consider this image from Vstech's document referenced above, you have the same basic setup, only this depicts a transmission/rear end setup from the side and your setup would have the setup depicted from the top. The important thing is that the two u-joint faces are parallel.

Rock on...

By the way, if you decide to go with a one-piece driveshaft I could probably get you the CNC file to cut an adapter to go from the MB trans to a Spicer yoke.

Mach4, I would like to have a CNC file if it is easy for you to get. Thanks for the offer. I haven't searched to see if these adapters are commercially available for the Mercedes bolt pattern, but I have used this kind of adapter with a Supra suspension.

Once I get everything else done and settle on a transmission, I had planned to have a single piece aluminum driveshaft made, with u-joints on both ends and a slip-shaft on the transmission end. But if this one works, I'll just keep the money in my pocket!

Thanks for pointing out to others that the top view of my driveshaft arrangement is the same as the side view in the Spicer illustration.

It is not clear from my pics, but the driveshaft arrangement follows the rules--and was planned based on the rules. U-joints are properly phased and pinion and crankshaft/tranny are parallel.

Heck, if it does not last, all I am out is the Spicer/Dana flange I welded on to the end of the Benz shaft.

Dan Stokes · #35 12-13-2014, 05:30 PM

I completely did away with the center bearing and had a 1 piece shaft built at our local driveshaft shop. Jags That Run makes an adaptor place to allow a standard Dana Spicer U-joint flange to work. While I have yet to drive the truck I don't expect any issues with this arrangement as it's been used in millions of cars for decades. Again, you might want to check my build thread.

But on the other hand, I'd try what you have. It looks reasonable to me, you already have it, and nothing really awful can happen if it's NOT OK. I didn't notice if you have a driveshaft loop or not but it might be a good thing just in case.

Dan

charliebob · #36 12-13-2014, 05:46 PM

Quote:

Originally Posted by Dan Stokes

I completely did away with the center bearing and had a 1 piece shaft built at our local driveshaft shop. Jags That Run makes an adaptor place to allow a standard Dana Spicer U-joint flange to work. While I have yet to drive the truck I don't expect any issues with this arrangement as it's been used in millions of cars for decades. Again, you might want to check my build thread.

But on the other hand, I'd try what you have. It looks reasonable to me, you already have it, and nothing really awful can happen if it's NOT OK. I didn't notice if you have a driveshaft loop or not but it might be a good thing just in case.

Dan

The misalignment is only 2 degrees, but it looks much more in the picture.

t walgamuth · #37 12-14-2014, 12:06 AM

It should be ok, I'd think.

mach4 · #38 12-14-2014, 12:24 AM

Quote:

Originally Posted by charliebob

The misalignment is only 2 degrees, but it looks much more in the picture.

I believe the flex disks themselves are good for a degree so I'm still in the camp of you'll be just fine...and if not, other solutions are readily available.

.

Stretch · #39 12-14-2014, 05:33 AM

Quote:

Originally Posted by mach4

I believe the flex disks themselves are good for a degree so I'm still in the camp of you'll be just fine...and if not, other solutions are readily available.
.

(Remembering)

There was a similar discussion a few years back about the alignment or the misalignment of MB propshafts - the "proper way" of doing it with two UJs was also discussed.

I was interested enough to dig out the equations of motion for a UJ =>

Universal joint - Wikipedia, the free encyclopedia

You can see that the rigid connection (third eq in that list) imposes the constraint that causes the joint to speed up and slow down during a full revolution. Without a properly phased opposing UJ there's going to be this continuous uneven running effect throughout the driveline. (The Mercedes trick is to keep the UJ straight so you reduce this effect to zero)

As the flex disc is flexible in all planes of motion (ie it doesn't have the rigid connection as described by that equation) I reckon it will die more quickly than a flex disc used in the Mercedes intended way.

I reckon it would be safer to fit a two UJ propshaft if the angle and the differential position has to be like that.

charliebob · #40 12-14-2014, 09:41 AM

I appreciate concern over my driveshaft and suggestions for improvement, but I fabricated it by following the "book." Again, the U-joints are properly phased, and the pinion and crankshaft/transmission are parallel. Moreover, the 1.5-2.0 degree angle of the second driveshaft is within spec. A Dodge truck TSB sets the max at 3 degrees. If the MB carrier bearing is not strong enough, there are stronger alternatives, like on a Turbo Supra.

Doubters should check out angles of the 2 and 3 piece driveshafts in big trucks, or the angle in many 2 piece driveshafts like on the Jag or a Turbo Supra or Lexis rwd.

The MB driveshaft may have a perfectly aligned u-joint, but driveshaft specialists recommend 1/2 degree to keep the u-joint lubricated.

If I were building a driveshaft for a high torque motor or race car turing 10,000 rpm, I would use a totally different design and construction. But this one will probably not see over 3500 rpm and under 200 tq.

As I mentioned in a previous post, I suspect that this arrangement is temporary. If not, we'll see if the "book" is wrong!

I'm always open to suggestions and concerns ... but in this case I am unconvinced that this arrangement will not work. If the shaft "shudders" on a hard launch (well, as hard as one can launch with 125 hp!) then I will go to plan B.

Bob

t walgamuth · #41 12-14-2014, 09:53 AM

As the always optimistic Red Green says...."its only temporary.....................unless it works!"

vstech · #42 12-14-2014, 11:22 AM

Quote:

Originally Posted by Stretch

(Remembering)

There was a similar discussion a few years back about the alignment or the misalignment of MB propshafts - the "proper way" of doing it with two UJs was also discussed.

I was interested enough to dig out the equations of motion for a UJ =>

Universal joint - Wikipedia, the free encyclopedia

You can see that the rigid connection (third eq in that list) imposes the constraint that causes the joint to speed up and slow down during a full revolution. Without a properly phased opposing UJ there's going to be this continuous uneven running effect throughout the driveline. (The Mercedes trick is to keep the UJ straight so you reduce this effect to zero)

As the flex disc is flexible in all planes of motion (ie it doesn't have the rigid connection as described by that equation) I reckon it will die more quickly than a flex disc used in the Mercedes intended way.

I reckon it would be safer to fit a two UJ propshaft if the angle and the differential position has to be like that.

This is what he has done.

Stretch · #43 12-14-2014, 02:49 PM

Quote:

Originally Posted by vstech

This is what he has done.

I wasn't very clear about that - I meant to say I reckon a UJ at the differential and a UJ at the transmission with a single shaft like the picture mach4 posted would be best for that offset configuration.

Another possible problem is a difference in gimbal size which will tend to push and pull the shaft.

Anyway - whatever

@charliebob

Please don't get upset with me - I am very keen to see how your project develops. You are indeed living the dream. Kind of like a fast and loud build but with out the constant whoo-ing I guess. Given half the chance I'll be doing something similar myself.

t walgamuth · #44 12-14-2014, 02:57 PM

Quote:

Originally Posted by Stretch

I wasn't very clear about that - I meant to say I reckon a UJ at the differential and a UJ at the transmission with a single shaft like the picture mach4 posted would be best for that offset configuration.

Another possible problem is a difference in gimbal size which will tend to push and pull the shaft.

Anyway - whatever

@charliebob

Please don't get upset with me - I am very keen to see how your project develops. You are indeed living the dream. Kind of like a fast and loud build but with out the constant whoo-ing I guess. Given half the chance I'll be doing something similar myself.

I hear Gimbles is a very large store!

Woooo!