So I'm starting to hear clunking in my drivetrain when I shift, and the axles are new so it better not be them. (I only get sideways in the dirt, stockish 240D and all.) Probably the flex discs, and after some time of canyon runs and other foolishness I don't doubt it's probably them.

I was looking on the 'No More Flex Discs' thread, and the simplest way to eliminate the discs is to have some solid ones fabbed up. Basically take a used but not destroyed disc into a machine shop and have them make a disc with the right holes in the right place. At about 90 bucks for a pair of new replacement flex discs I'm sure that figure can be matched and possibly beaten walking into Joe's Machine Shop, bonus being that it only has to be done once and you don't have to look at your watch waiting for the driveline slack to take up.

V8 discs have been mentioned but I'm not cutting up a driveshaft for that.

There's some small risk of 'adding to driveline wear' but I'm not all that concerned, mostly because of the low stock power and that the flex discs have been absorbing driveline shock the whole time. Take a new diff from a setup without flex discs, calculate it's approximate life span, halve that and that's probably the miles one can expect from a pumpkin after this, barring other considerations, like making real power.

I'm heading to the yard anyway tomorrow, maybe I can pull one real quick, swing by a machine shop and see what the damage will be.

Check the rearend support bushings and the midship support bearing. The flexdiscs do have their purpose, I don't see it being advantageous to not having them. Afterall, whats more expensive, the discs or your drivetrain.

http://www.superturbodiesel.com/std/no-m...t-783.html

With only 1 u-joint in the system, it needs to have some flex at each end to allow for body, subframe and engine movement.

The stock flex discs are already very good. Most that are coming apart are doing so because they are over a decade old. $80 every couple of years isn't a big expense compared to what most everyone is investing elsewhere on their cars. I could have replaced mine 10x over with what I've spent on turbos alone.

It was my impression that the flex discs flexed along the circumference to absorb shock in the drivetrain for smoothness, not to act as a quasi u-joint. A U joint and a slip yoke - both present besides the discs themselves - should take up the very little movement perpendicular to the length of the shaft.

However, I suppose they could be doing just that. I somehow doubt that's their purpose, though.

I need to recontact my old boss, a factory trained tech would be of much use to us in cases such as this.

you might look into this, kind of a marriage of both ideas. This is a tiny picture, but this is one of the discs for the driveshaft that runs between a toyota previa central mounted engine and the accessory cluster under the hood. Its an aluminum disc with smaller rubber seated bolt locations. Don't know if it would be harder or softer, but interesting none the less.
   

OOOOOoooOOOO. What are the dimensions on the holes?

Not sure, Its a VIN ordered part according to the dealer. We'd have to grab a disc or VIN from a yard to play with.

Also not sure what its designed to handle for load, there are two on a short forward facing driveshaft that turn all the accessories and optional supercharger under the hood, but the actual drivetrain used standard slip yokes. May not hold up moving the weight of a vehicle.

previas are a PITA in my opinion, especially if you get saddled with a repair on a 4x4, supercharged version. Still, theres a lot of interesting stuff on em, I have a couple of the super short 2 ft rear driveshafts off the 4x4s with a slip yoke built into them.

(01-18-2010 09:03 AM)dropnosky Wrote:  you might look into this, kind of a marriage of both ideas. This is a tiny picture, but this is one of the discs for the driveshaft that runs between a toyota previa central mounted engine and the accessory cluster under the hood. Its an aluminum disc with smaller rubber seated bolt locations. Don't know if it would be harder or softer, but interesting none the less.

Hah! Toyota cribs another piece of MB's bag of tricks, only the materials are reversed.

I am entirely certain (perhaps foolishly so) that the pumpkin will be fine. I haven't heard of anyone breaking one yet - those 500 lb ft Finnish OM617s don't mention anything about a special diff.

Every RWD car I've driven besides this one didn't have flex discs. Just u-joints which while not entirely without slack are practically there compared to the slop in this system. Since the Genesis sedan was obviously trying to be a cut-rate Benz, and the Genesis coupe gets criticized for it's sloppy drivetrain...I'll bet they threw some flex discs in there. I almost never hear about real criticism for RWD drivetrain slack and most don't use a torque tube.

Also, not only were the diffs designed to hold up to a variety of engines including V8s and diesels making their torque down low, think about a Camaro. Nothing special going on there in the driveshaft. That larger, OHV V8 makes a lot of torque immediately off the line and those rear ends hold up ok (the stock 10 bolt is just a weak, junky rear, period, serious drag racers go with a 12 bolt or a 9 inch). A 5.0 Mustang might be a better example since the 8.8 inch rear is pretty much bulletproof behind a stock motor. No flex discs there, and no driveline slack either, at least nowhere near the degree in our cars.

Besides, in the diff swapping threads weren't y'all telling me how cheap and easy it is to swap out these diffs with another from the yard? I doubt MB is going to over engineer the durability of every other component and not do the same with the differential, which could leave the car stranded if it failed.

All I'm saying is every piece of shit junky pickup truck with a stick I've ever driven didn't have this kind of fuck-up-my-rhythm slack no matter how badly it was neglected, but my more expensive than a Corvette damn near as expensive as a 911 240D has it. Oh, wait, the trucks, my POS Celica, Mustangs, Camaros, etc don't have flex discs.

I don't doubt that the flex discs do exactly what they were designed for and very well but they're doing something I neither want nor require.