Product Review: RevShift M60B40 flex disc.

[Shoomakan]

Hello everyone,

Well, I've had quite the week trying this product out. Package was shipped on time, arrived in a neat little package and looks like a quality part:



The washers were also provided, as you can see. However, an installation guide would have been nice. I know, it's supposed to be obvious, but still. It would have saved me an hour. First time I tried installing this, I unbolted my flex disc, and it wouldn't come out because the driveshaft has to be removed as well. If I had known that I wouldn't have attempted it on my own.

So, installed it, took the car out, and there's a severe vibration coming from the driveline. I jack it up again, start the car and put it in gear. The center support bearing is wobbling like crazy. So, I buy a new one:



Not sure what to make of the "750i" written in marker on the bearing. Do 540i's and 750i's share this part?

Installed it, go out for a spin... Still vibrating badly. So I do some asking around, and apparently you need to install this part with the car resting on the ground, for the driveshaft to be in the correct position. So I do that, and ta da! It works great.

However, the plot thickens. I had a friend drag race last night, and after finishing the race, the vibration is back. Got back under it today, and my center support bearing had shifted its position slightly. I re-aligned it today, and it's fine now. However, it is obvious that any hard driving will force it out of position again. The solution is not over-tightening, obviously. My driveshaft is fine, I had it checked. All the rubber in the driveline is fine, as is the yoke in the middle.

So, my conclusion is that this part requires the installation of a polyurethane CSB as well for it to handle the stress. The stock rubber one simply cannot handle it. It is unfortunate, for the new flex disc really feels nice. Driveline response is noticeably improved, and feels much more solid now. It is easier to break traction, too.

I've got polyurethane motor mounts and tranny mounts, so nothing there is faulty either. I don't know if I'm going to keep this installed or not. The idea that it may dislodge my CSB at speed scares me. If anyone has any ideas how to solve this, or if anyone makes a poly or high performance CSB, please let me know.

Cheers everyone, Shoomakan

[Aradaiel]

looks like a good idea in thoery

[5mall5nail5]

So, installed it, took the car out, and there's a severe vibration coming from the driveline. I jack it up again, start the car and put it in gear. The center support bearing is wobbling like crazy. So, I buy a new one:

Installed it, go out for a spin... Still vibrating badly. So I do some asking around, and apparently you need to install this part with the car resting on the ground, for the driveshaft to be in the correct position. So I do that, and ta da! It works great.

However, the plot thickens. I had a friend drag race last night, and after finishing the race, the vibration is back. Got back under it today, and my center support bearing had shifted its position slightly. I re-aligned it today, and it's fine now. However, it is obvious that any hard driving will force it out of position again. The solution is not over-tightening, obviously. My driveshaft is fine, I had it checked. All the rubber in the driveline is fine, as is the yoke in the middle.

So, my conclusion is that this part requires the installation of a polyurethane CSB as well for it to handle the stress. The stock rubber one simply cannot handle it. It is unfortunate, for the new flex disc really feels nice. Driveline response is noticeably improved, and feels much more solid now. It is easier to break traction, too.

I've got polyurethane motor mounts and tranny mounts, so nothing there is faulty either. I don't know if I'm going to keep this installed or not. The idea that it may dislodge my CSB at speed scares me. If anyone has any ideas how to solve this, or if anyone makes a poly or high performance CSB, please let me know.

Cheers everyone, Shoomakan

Broski - all of what you describe above is exactly why you DON'T want to use this. A polyurethane CSB wouldn't solve the issue - the problem is, even on "solid" mounts, the motor, trans, and more importantly, rear subframe/differential all move. As soon as you rigid mount one end of the driveshaft the formula is destroyed. The stock rubber unit also absorbs a lot of vibration/harmonics that you don't realize. When you make the mount of the shaft rigid to the transmission the front half of the shaft is now inline, always, with the output shaft... which isn't at all aligned with the CSB, and is definitely not aligned with the rear shalf, nor the input flange on the diff. This is the issue. It all needs to be compliant to work.

looks like a good idea in thoery

That's the problem - it's actually a bad idea in theory and practice. In theory, all this does is limit the benefit of a two-piece driveshaft. The reason we need a two-piece shaft at all is because we have a rear subframe that moves independent of the engine. By making this front guibo solid you're almost making the driveshaft a "one-piece" because the front half is arrested from moving. Bad bad bad. Not to mention that solid guibo transfers high freq vibrations from the trans/engine into the guibo which has the potential to loosen the bolts. It's all downhill. Run the stock part - if my car can, others can as well.

[Sam Son]

I had one on my car for a short time. Had to get rid of it...awful

[Shoomakan]

I agree with you guys.. It's gotta go.

I'll buy a stock flex disc as soon as I can.

Thanks for the input. Jon, your example came to mind when a friend of mine was against my idea of removing it. I told him a friend on the forum is running an 800bhp E34 with the stock one and it's running fine. :P I wish I didn't pay good money on this part, woulda rather bought the poly thrust bushings.

[yardpro]

i had a terrible customer service experience with revshift and will NEVER buy from them again

[GazM3]

on the 540i i have poly everything incl engine mounts but guibo flex disk is still rubber stock
on the m5, poly in the rear and front end, but rubber engine and gearbox mounts, and rubber guibo which needs to be replaced along with the centre bearing. Not looking forward to doing so