Planning a drivetrain/suspension service

[IamFODI]

At some point in the next year or so, I’m planning to drop basically everything from the transmission back and refresh a bunch of stuff. The car has 149k miles on it right now and a lot of it is original, so I want to refresh it. Would love some feedback on what I’m planning to do. Also have some questions at the end of the post.

I want to replace the DMF because some clunkiness, gear rattle, etc. makes me feel like the damping mechanism is wearing out. I figure that’s a good time to refresh the clutch kit, shift bushings, etc.

The original driveshaft has been making the cowbell noise for years. Could grease the splines to take care of it, but given its age I want to just replace it.

Every bushing and joint in the rear suspension, except for the spring perches and RSMs, is most likely original. Time for a refresh. Also, I want solid subframe bushings because I’ve read the NVH/benefit ratio is just that good.

Given the overlaps in labor required for many of these jobs, I’m planning to get them done all at once.


Goals:

1. Refresh everything that ought to be refreshed
2. Improve what I can without significant NVH penalties (this car is a DD, and there’s no aftermarket exhaust to drown out noise)
3. Maximize the odds that, once everything’s back together, it won’t have to come apart again for several years and many tens of thousands of miles

With all that in mind, here’s what I want to do as of now:

1. Clutch kit (OE LuK)
2. Flywheel (OE LuK)
3. Clutch slave cylinder (OE FTE)
4. Shift kit (Autosolutions – stock throw length with a longer rod)
5. Driveshaft (rebuilt OE or aftermarket OE replacement)
6. Giubo
7. Driveshaft end bushing
8. Transmission output shaft seal (current one is weeping slightly)
9. Refinished rear subframe (thinking of buying a used one and having it powdercoated or something)
10. Diff bushings (OE)
11. Solid subframe mount bushings (Revshift)
12. All rear suspension arms & bushings (OE Lemförder/TRW/BMW)
13. Adjustable rear ARB end links (SPL)
14. Rear ARB bushings (BMW)
15. All necessary fasteners & gaskets for all of the above + exhaust

Brands are largely constrained by FCP Euro's catalog for obvious reasons.


Questions:

1. What other potential wear items are easily replaced while in there for any of this work?
   
2. What might break that I should have spares for in advance?
   
3. Any advice on what kind of coating to go for on the rear subframe? And/or anyone know of a vendor that sells refinished ones?
   
4. CF driveshaft: I really want one, but I think goal #3 precludes it. I’m sure most are fine, but between the sporadic issues people have had and the need to worry about heat shields near the diff flange (either bend, cut, or accept the risk of rubbing), CF seems like it’s not as sure a bet as OE in terms of being painless in the long run. Can anyone change my mind on that?
   
5. Looking at new/rebuilt OE-replacement driveshafts, many (all?) seem to come with serviceable U-joints. It’s my understanding that, for parts like this, serviceability generally comes with a shorter life. Realistically, I’m never going to service the U-joint. Either it lasts long enough that I might as well replace the whole driveshaft when it dies, or it’s so short-lived that I want nothing to do with it. Anyone know of a rebuilder/manufacturer that prioritizes longevity over serviceability?
   
6. Should I do the rear main seal? AFAIK, this is one thing you’re not supposed to fix if it ain’t broke, and I don’t have evidence that mine’s leaking. OTOH, 14 years and 149k miles is getting up there, so maybe it’s worth doing either way…?

Thanks for reading this far. Looking forward to people’s thoughts.

[amrazM]

Questions:
What other potential wear items are easily replaced while in there for any of this work?
1. Diff rebuild
2. Clutch pivot pin
3. Rear wheel bearings
4. You may want to freshen up the subframe itself, maybe a powdercoat if you have time.
5. Consider hitting the rear underbody with some por15 if you have any early signs of corrosion.

What might break that I should have spares for in advance?
Not much to break under these cars during a job like this, just be ready to change all the fasteners+clip nuts through the heat protection panels the hardware can rust out sometimes.

Any advice on what kind of coating to go for on the rear subframe? And/or anyone know of a vendor that sells refinished ones?
Just powdercoat your original subframe, most of these vendors have a one day turn around.

CF driveshaft: I really want one, but I think goal #3 precludes it. I’m sure most are fine, but between the sporadic issues people have had and the need to worry about heat shields near the diff flange (either bend, cut, or accept the risk of rubbing), CF seems like it’s not as sure a bet as OE in terms of being painless in the long run. Can anyone change my mind on that?
Looking at new/rebuilt OE-replacement driveshafts, many (all?) seem to come with serviceable U-joints. It’s my understanding that, for parts like this, serviceability generally comes with a shorter life. Realistically, I’m never going to service the U-joint. Either it lasts long enough that I might as well replace the whole driveshaft when it dies, or it’s so short-lived that I want nothing to do with it. Anyone know of a rebuilder/manufacturer that prioritizes longevity over serviceability?
driveshaft specialist in TX, I think its $525 now for a rebuild of the driveshaft.

Should I do the rear main seal? AFAIK, this is one thing you’re not supposed to fix if it ain’t broke, and I don’t have evidence that mine’s leaking. OTOH, 14 years and 149k miles is getting up there, so maybe it’s worth doing either way…?
You can do the RMS, try to find the bmw service tool. Maybe you can have someone rent you one.

[IamFODI]

Thanks, amrazM.

Diff rebuild: What are the common failures?

Clutch pivot pin is on the list.

Rear wheel bearings: Hmm. Good point. One has been done but maybe it makes sense to have the other one done.

POR-15 might be a good call. Might grab a can.

[IamFODI]

Was advised to do the RMS, so adding that to the list.

Diff: Other than one-tire fires or poor limit handling (neither of which I've noticed), what should I look for to decide whether it's rebuild time? It adds like $2k to an already substantial price tag, so I'm inclined not to bother unless there's a compelling reason. However, I do agree that, if it's going to get done, this would be a great time.

[Davisca455]

Rear brake hoses.

On the rear subframe there are a few plastic clips for routing of the the brake pad sensors and wheel speed sensors that are likely baked/brittle.

Personally, I don't get all excited about powder coat for chassis parts.

But if you do decide to powder coat, you'll want to convince the person applying the coating to mask the 7 precision bores, otherwise you'll be in for some extra work/expense removing the powder coat layer so the new bushings will fit correctly.

[IamFODI]

Originally Posted by Davisca455

Rear brake hoses.

On the rear subframe there are a few plastic clips for routing of the the brake pad sensors and wheel speed sensors that are likely baked/brittle.

Personally, I don't get all excited about powder coat for chassis parts.

But if you do decide to powder coat, you'll want to convince the person applying the coating to mask the 7 precision bores, otherwise you'll be in for some extra work/expense removing the powder coat layer so the new bushings will fit correctly.

Nice. Thanks.

Brake hoses have been done, fortunately.

Hadn't thought of the clips. Good call on that, and about the precision bores WRT powdercoating.

Which bores are those, BTW?

[Frostynorth]

The 4 subframe bores and 3 differential ones.

[Davisca455]

Originally Posted by Frostynorth

The 4 subframe bores and 3 differential ones.

The press fit bores for the 4 frame to body bushings and the 3 differential bushings.

[CTMike]

Following this thread with interest as I’m planning a mini version of what OP posted: Autosolutions SSK, CF Driveshaft, solid subframe bushings, powerflex purple diff bushings.

May be picking nits, but any major difference with aluminum vs. stainless steel subframe bushings?

[Davisca455]

Originally Posted by CTMike

Following this thread with interest as I'm planning a mini version of what OP posted: Autosolutions SSK, CF Driveshaft, solid subframe bushings, powerflex purple diff bushings.

May be picking nits, but any major difference with aluminum vs. stainless steel subframe bushings?

I'm not aware of a stainless option, but if there is one, I feel certain there would be an increase in cost and weight.
Raw material cost difference would probably not be the biggest issue, but run time on the lathe and the second ops on the mill would be significantly longer.

[NiBe]

>Shift kit (Autosolutions – stock throw length with a longer rod)

Why "stock throw length with a longer rod"? Why you decided for that? Thanks.

[IamFODI]

Originally Posted by NiBe

>Shift kit (Autosolutions – stock throw length with a longer rod)

Why "stock throw length with a longer rod"? Why you decided for that? Thanks.

Longer rod because I want it to be higher up so it's closer to the steering wheel.

Stock throw length because I generally don't like how a short throw affects feel (but I don't want longer throw than stock).

I've tried multiple shifters like this in other cars and loved every one of them.

[CTMike]

Originally Posted by Davisca455

I'm not aware of a stainless option, but if there is one, I feel certain there would be an increase in cost and weight.
Raw material cost difference would probably not be the biggest issue, but run time on the lathe and the second ops on the mill would be significantly longer.

Rogue Engineering seems to offer 303 Stainless, whereas most others (Turner, etc) seem to offer aluminum.

https://www.rogueengineering.com/Rog...air_p_284.html

[Davisca455]

Originally Posted by CTMike

Rogue Engineering seems to offer 303 Stainless, whereas most others (Turner, etc) seem to offer aluminum.

https://www.rogueengineering.com/Rog...air_p_284.html

Not sure why Roque uses "subframe" in the description for that part?
They say it's a replacement for the rear spindle bushing and list the BMW part number it replaces.

Cross reference the BMW part number onto the FCP site.


https://www.fcpeuro.com/Parts/?keywords=33-32-6-770-829

[CTMike]

Originally Posted by Davisca455

Not sure why Roque uses "subframe" in the description for that part?
They say it's a replacement for the rear spindle bushing and list the BMW part number it replaces.

Cross reference the BMW part number onto the FCP site.


https://www.fcpeuro.com/Parts/?keywords=33-32-6-770-829

Appreciate the clarification. I just ordered the Turner aluminum ones.

[IamFODI]

Updates!

Built a huge parts list for this service. This project has ballooned in price, and not just due to creeping inflation.

I've been tracking prices every ~5 days and ordering things when they're sufficiently below their to-date average prices. Whatever's left will likely be ordered in May. Service will take place in mid/late June.

Added a rebuilt diff to the list. Current plan is Diffsonline, with the stock gear ratio and limited-slip unit, and no REM polishing. I don't think any of the other options is worth the price for my usage (mostly street, some track at novice level). Happy to hear arguments to the contrary.

My rear subframe has some surface rust. It's not bad but there's a flake or two. Anyone think this might be something to worry about WRT stiffness? Should I try to source a lower-mileage one?

[kwality]

hi - DM sent.

Originally Posted by IamFODI

Updates!

Built a huge parts list for this service. This project has ballooned in price, and not just due to creeping inflation.

I've been tracking prices every ~5 days and ordering things when they're sufficiently below their to-date average prices. Whatever's left will likely be ordered in May. Service will take place in mid/late June.

Added a rebuilt diff to the list. Current plan is Diffsonline, with the stock gear ratio and limited-slip unit, and no REM polishing. I don't think any of the other options is worth the price for my usage (mostly street, some track at novice level). Happy to hear arguments to the contrary.

My rear subframe has some surface rust. It's not bad but there's a flake or two. Anyone think this might be something to worry about WRT stiffness? Should I try to source a lower-mileage one?

[amrazM]

Originally Posted by IamFODI

Updates!

Built a huge parts list for this service. This project has ballooned in price, and not just due to creeping inflation.

I've been tracking prices every ~5 days and ordering things when they're sufficiently below their to-date average prices. Whatever's left will likely be ordered in May. Service will take place in mid/late June.

Added a rebuilt diff to the list. Current plan is Diffsonline, with the stock gear ratio and limited-slip unit, and no REM polishing. I don't think any of the other options is worth the price for my usage (mostly street, some track at novice level). Happy to hear arguments to the contrary.

My rear subframe has some surface rust. It's not bad but there's a flake or two. Anyone think this might be something to worry about WRT stiffness? Should I try to source a lower-mileage one?

i wouldnt worry about surface rust on the subframe. if you are planning to have the subframe out for like a week then just grind the paint off and around the rust area, get it down to the metal and use some rust converter and repaint it.

dude, the price of everything has gone through the roof. If I didnt do all the work on my car 2-3 years it would have been seriously tough doing it now.

[CTMike]

Originally Posted by CTMike

Following this thread with interest as I’m planning a mini version of what OP posted: Autosolutions SSK, CF Driveshaft, solid subframe bushings, powerflex purple diff bushings.

Appreciate seeing this thread come back up… life got in the way a bit this year,, just dropped car off at the shop to get this all installed! Can’t wait to get it back.

[IamFODI]

And I appreciate the continued interest. I was posting updates about this elsewhere but I guess I can paste some stuff here.

Here's (I think) the final list of jobs:

Drivetrain
- Clutch kit (OE LuK)
- Flywheel(OE LuK)
- Driveshaft (BMW)
- Differential (Diffsonline – 100% stock spec)
- Autosolutions shift kit (+40mm extended lever, 15% throw reduction)​
- Lower-mileage OE cat section, all cats in place
- Lower-mileage OE muffler, unmodified
- Re-grease & re-boot rear CVs (GKN kits)
- Rear main seal​
- Trans output shaft seal
- Shift shaft seal
- Trans input shaft seal
- Trans input shaft guide tube
- Secondary O2 sensors
- Engine mounts (Corteco)

Steering & Suspension
- All bushings in rear subframe (Bimmerworld solid subframe mounts; all else OE)
- All rear suspension arms & bushings/balljoints (OE BMW/TRW/Lemförder etc.)
- Rear ARB end links (SPL)
- Rear ARB bushings (OE)​
- Rear subframe zinc coated and powder coated
- Steering rack (new Bosch)
- Steering rack boot
- Front wishbones (OE TRW)
- Front ARB bushings

Other
- POR-15 on rusted areas
- RL wheel bearing
- E-brake rebuild (shoes, cables, hardware)
- Trans tunnel & muffler heat shields
- 513M wheels, stock 245/265 tire sizes
- Motorsport Hardware wheel studs
- PSF reservoir
- Some repair/replacement of old fasteners, studs, etc.

I won't have more than a few minutes at a time for a while but I'll post back with more updates.