Thanks for confirming my theory Terry. I can't agree more that people need to be honest with themselves on how they use the car. I've had more than a few customers insist on stiff 75D bushings, just to regret the decision down the road. Of course if your girl friend/wife/significant other can't stand the NVH, then solid bushings are a good way to keep them from driving your car.
Just to add one more opinion, if you stiffen the subframe, you need to consider the diff mounts too. If you are isolating the subframe with solid bushings, then it will no longer help absorb the movements of the diff. This will cause greater stress on the differential bushings. The diff and subframe bushings don't have to have the exact same bushing material, but the "stiffness" needs to be in the same ball park. I wouldn't mix aluminum subframe bushings with 90A diff bushings, for example.
I know we are talking about E36's, but on a side note E30, Z3, and E36/5 subframe and diff bushings really should be of the same material. On those cars the differential is part of the subframe support structure. The diff is solidly mounted to the subframe, the two subframe bushings support the front of the subframe, and the diff bushings support the rear. Installing a solid diff bushing and leaving stock or soft subframe bushings is a great way to cause the dreaded rear trunk floor (aka subframe) failure.
-bj
Last edited by loftygoals; 01-29-2014 at 12:40 AM.
2002 M Coupe | 2000 M Roadster w/ LS | 1998 328i w/ S54 | 1987 325is w/ M52 | 1985 735i Turbo
I repeat:
Constraining subframe motion has obvious benefits, in particular that since the rear control arms are attached to it, when it moves around it steers the rear wheels. That's not desirable in a performance application.
Constraining the diff prevents a small amount of wind-up and release when getting on and off the throttle. For a full out track car (see Terry Fair's excellent post above), fine. Tie everything down solidly and live with the banging, roaring and whining noises. But otherwise, what's the benefit?
(Note: With reference to the post above by loftygoals, I'm specifically referring to the E36 or similar setup. If the diff casing is a stressed member, different considerations apply.)
Neil
Last edited by NeilM; 01-29-2014 at 09:57 AM.
regarding your statement I highlight - So your saying it should basically be all or nothing back there? AL subframe + around 75D or stiffer diff mounts?
You don't believe in any vibration isolation back there at all for track car?
Why wouldn't it be a good idea if the diff moved more than the subframe?
Some cars don't even have subframe bushings. S2000 for example. but you could also say that it mounts better to the chasis than a E36 subframe.
98' M3/4/5 - Boston Green / modena
Forever in process - DD/AutoX/HPDE
Agreed, I assumed this was obvious but you were right to point that out! Mixing the subframe and diff bushing stiffness doesn't make sense.
Unfortunately there are a few BMW models that don't have any aftermarket diff bushing coverage, such as the E46 non-M. We've taken to tuning some Nylon bushings on the lathe for a car or two in the past, in a pinch. I've seen a few new options pop up lately, which is nice.
And yes, the Z3/E30 are a whole different animal...
Terry Fair @ Vorshlag Motorsports
Terry, For the E46 non-M, BimmerWorld site shows PowerFlex 95A and 70A options, while AKG shows aluminum, 75D and 95A options. But maybe that's what you meant by a few new options popping up.
BJ/Clownshoe: Did any of your customers say 75D subframe bushings caused too much NVH for a dual-purpose car, or were those cases of 75D poly in the FCABs, RTABs, or rear shock mounts?
Last edited by LivesNearCostco; 01-29-2014 at 12:44 PM.
^This is what I am out to achieve. I am seeking advice for the diff as while I am under there...I figure kill two birds at once. Pardon the multiple questions, but the more information I can gather the more educated decision I will be able to make. I am unsure of the benefit for tying-down the diff, hence the multiple questions. Like wise, I welcome the advice and thoughts on the subject.
Subscribing to this thread, because I was just inspecting my car on a lift and the big rear diff bushing (E46 non-M has 3 diff bushings) is cracked. Front diff bushings are Myele HD with 30K or 40K miles on them. Rear diff bushing is of unknown OEM type with 50K to 90K miles on it. Looks like I'll be selecting new diff bushings before new subframe bushings.
Oh I do agree. That's why this is a useful discussion.
BTW, mine is a track car but not a dedicated track car, in the sense that Terry Fair emphasizes in his post — and I'm quite conscious of what is is and isn't. I drive to and from the track, and retain enough comfort items (interior with sound deadening, A/C, etc.) to make a day's drive to the track perfectly acceptable (at least to me; 600#F/700#R springs aren't for everybody). That's why I know I won't ever be using solid, or near-as-damn-solid bushings. I've instructed in plenty of race cars, so I have no illusions about they are!
Neil
My track car is running AKG 75D diff bushings. Don't think "poly" when you think 75D don't think poly... think SOLID. I went with powerflex black (95A) for the subframe, RTABs and FCABs and am happy with them. 95A is MUCH softer than 75D. 95A is more of what you think of when you think of a firm poly. 75D is as hard as aluminum... seriously. Honestly, as difficult as it was to get the 75A diff bushings in, I'd be worried the subframe itself could crack from how hard 75D bushings are. The metal is very thin on the outer edges of the subframe where the bushings go in.
Powerflex purple 80A is very soft. I've ready it's actually softer than the rubber BMW used in the OEM bushings. My car is track only and handles great with 95A in the subframe but it's still forgiving enough to allow some shock absorption.
Just my opinion but I would still go 95A for subframe, FCAB, RTABs and 75A for diff bushings even on a track only car.
Hmmm... for diff mounts I could replace just the rear one with a Myele HD solid rubber one, or replace all three. On one hand, I think the rear diff bushing can be replaced without removing the entire diff, and I can do the front ones later when doing the subframe bushings. On the other hand I should learn to remove my diff anyway and maybe do all 3 then. On the BimmerWorld site, the aftermarket diff mount choices for E46 non-M are solid aluminum, 70A or 95A. AKG offers aluminum, 95A and 75D.
For the diff mounts I would definitely go firm - 75D.
You can do an E46 non-M rear diff bushing that way, but then you might want to stab yourself in the eye with a dirty screwdriver later, too. Removing the diff housing makes this job easier, actually. We have done it both ways and pulling the diff is the faster way, and let's you get to the front mounts at the same time. See you have to put a bunch of tools (pressing out the old bushing from the chassis) up in the area that the diff housing occupies... so it is easier to do it with the housing down and out. This only applies to the E46 non-M rear diff mount bushing.
Ugh, we just did this job last week on a 2004 330 (above) that had 3 oil leaks, blown bushings, blown shocks, and the rear diff bushings were shot. Of course we didn't get a picture of the diff mount R&R.
A-ha, that's another car but it shows the E46 non-M rear diff bushing, which mounts in the chassis and stays put when the diff housing is removed. You gotta press out the old one and press in the new one. Now imagine trying to get your press tools up in there with the diff in the way (or especially the diff cover). Nightmare. So you either pull the cover (which we did in the lower picture's car) or pull the diff housing (which is almost easier, actually).
Just passing that along...
Last edited by Fair; 01-31-2014 at 03:46 PM.
Terry Fair @ Vorshlag Motorsports
The reason I said this is because it puts a lot of stress on the diff mount points because the subframe can't assist in absorbing the energy from drivetrain stress. In an E36, this could lead to lots of broken from diff mounts or bolts. I haven't seen it cause problems in an E46, but that doesn't mean that it couldn't.
I was specifically speaking about subframe and diff bushings, but these were customers that wanted hard poly despite the fact that their car nevers sees the track.
-bj
2002 M Coupe | 2000 M Roadster w/ LS | 1998 328i w/ S54 | 1987 325is w/ M52 | 1985 735i Turbo
Thanks, Terry. I guess the DIY I heard about for doing it without dropping the diff must have required removing the diff cover. Looking at my records, the diff fluid was last changed 3 years and 42,000 miles ago, so looks like it's due for a change, but the cover is so nicely sealed right now... as you said probably easier to remove the whole diff casing.
- - - Updated - - -
Thanks, BJ. I do track my car, but over the last year it's become more of a daily driver too, so I have to balance things.
98' M3/4/5 - Boston Green / modena
Forever in process - DD/AutoX/HPDE
All right, do me a favor and tel me the proper maintenance schedule for a dual purpose car that sees 8-10 track days per year? When do you change oil, transmission fluid, diff fluid, coolant, PS fluid, and brake fluid? Do you go by miles, event, or hours? Is the recommended diff fluid interval different for an E36 M3 clutch type LSD vs. an E46 open diff? I changed the "lifetime" transmission fluid 3 times in 50,000 miles... is that often enough for your taste or is it car abuse that condemns me to using only transmission mounts?
I have admittedly overlooked the diff fluid... changed it when I got the car, had it changed it again 10,000 miles later while re-doing the cover, then changed all the other fluids a few times (coolant, PS ATF, oil, transmission, brake) but forgot about the diff. I guess that means I'm not allowed to use poly bushings on it, eh?
Edit: The BavAuto guideline for diff fluid changes is every 50,000 miles or 2 years, and I assume that does not include tracking the car. I've emailed Mike Miller for his old school maintenance schedule, but looks like I'm overdue for a change anyway at least on years, so today I changed it. Now time to find some poly diff and subframe bushings.
Last edited by LivesNearCostco; 02-02-2014 at 10:34 PM.
Personally, I change the PS fluid, rear diff and tranny once a year at beginning of each season. Track days aren't as brutal as a wheel-to-wheel. Brake fluid I change twice if I boil it. If not, then it's once in the beginning. Engine I change every 2nd track day, though my car is strictly a track car, the only street it sees is to and from the track, which is 25-30 min for the local track and 3 hour drive for the furthest ones, 1-2 track days a month if time/money permits.
Unless you're using the Jiffy Lube discount dino oil of the day that's likely to be way more often than needed for engine oil, especially since the E46 M3 has a factory oil cooler. Do yourself a favor and invest $25 in an engine oil analysis at Blackstone Labs. I doubt you need more than one mid-season oil change, if that.
Neil
Just bringing up the facts. Once you go race bushings, there needs to be more inspection and maintenance typically. It appeared that you were having an issue with changing the diff fluid at around 42,000, so I was just trying to help. Sorry for making my comment a little personal. You are very active in many threads, so I know you like to get all the information you can out of threads. Just trying to spark a bit of a reality check with maintenance when you get into the racing mod world. Cars can start to see things rattle loose that you wouldn't think of. When I went hard engine mounts and spherical bearings on one of my cars, certain bolts/nuts started to come loose. Had to replace some with new.
It looks like you found some good information on maintenance for fluids but it really does come down to how you use it, how hot it gets, current condition of components and how anal you want to get with maintenance. Example. A motor that has a lot of blowby and or oil dilution with fuel and water, you might want to change after every 2 track days and XXXX miles (not autocross). Solid motor, could go 4,000 miles of double duty with 4 track days (If the oil isn't getting sheared a ton and oil temps are kept in check). Blackstone labs or other place could shed better light on this. I like yearly trans and diff fluid changes on a double duty car but again, if it's know that the temps get super hot, more often might be needed and you could probably even feel an operational difference in short intervals.
- - - Updated - - -
I've seen some lab results from even boosted Audi S4 motors that didn't need changes after 6 track days and 4,000 miles. As always, YMMV. Whatever makes you feel better about your car. Competition requires being prepared mentally. If frequent oil changes allows your mind to be at ease and gives you that sense of readiness, then do the oil change as much as you can afford! New socks, new gloves, new undies haha, whatever works lol!
Last edited by berny2435; 02-03-2014 at 10:54 AM.
98' M3/4/5 - Boston Green / modena
Forever in process - DD/AutoX/HPDE
Berny (and Neil & Inflame),
Thanks for the advice. I do appreciate it. Just got Mike Miller's "old school maint. schedule" and he recommends diff fluid and transmission fluid every 30,000 miles, so I changed my transmission fluid a little earlier than that (20,000 miles) and my diff fluid late (42,000 miles). Oil (Total synthetic) usually gets changed every 7,500 miles. Coolant gets a complete drain every 3 years and partial drain every 18 months. Bleed the brakes about every 6 months, depending on track schedule. PS fluid changed about every 2 years.
I have used Blackstone several times for oil, once for my transmission, but never for the diff. I didn't grab samples for either this past week. The transmission fluid didn't smell burnt and was clear but was no longer red (it was Redline MTL) like the new fluid. Shifting is slightly (very slightly) smoother with the new transmission fluid. The diff fluid looked pretty dirty, so just by looks, I waited too long on it. I did 3 track days in hot (102F) weather last summer and that might have helped cooked both fluids.
Last edited by LivesNearCostco; 02-03-2014 at 12:28 PM.
Cosco,
For what it's worth, I have dedicated track e36 M3 that's been reinforced front and rear (in fact, Clownshoe helped with the welding) and has AKG 75D throughout, except the engine and maybe also tranny (I think one or both are 80A). My car had an interior for about a month with the 75D suspension bits installed, and the NHV increase was nominal. It was noticeable to me, but probably not to anyone else in the car - like maybe the difference between nice tires and tires that make a bit more road noise or driving on new asphalt versus chip seal.
The engine mounts is really where the NHV gets unbearable for a daily driver. Currently, I've front carpet, dash and door panels, but nothing in the rear (no trunk carpet, no rear seats, no bulkhead). It's an hour and a half to both the tracks I drive at, and the 75D in the suspension doesn't bother me. I do hate the NHV the engine mounts generate, but only at stop lights and in staging.
I have had a similar experience. The move to 75D subframe mounts yielded negligible increases in NVH, and a slightly more "connected" feeling.
I could see both sides of the fence on this one:
It wasn't enough of an improvement from a performance standpoint to fret over durometer...just get something not squishy and/or worn out and you'll be fine.
Conversely, the NVH increase was barely perceptible, even in a stripped car, so why not go with something less compliant. Full disclosure: I have stock diff bushings...combining stiff diff AND subframe bushings will increase diff noise transmitted into the cabin.
I say let the diff bushings do their job and isolate the subframe from drivetrain shock loads (lengthy in impulse duration) and let the subframe act as a good foundation upon which the suspension is mounted and let the suspension do its job. Subframe does not need damping or compliance. Other components of the system have been designed expressly for that purpose.
Thanks for the shout out!
I'm the same way, I barely notice it. It's probably because I spent so much of my life driving crappy worn out cars. In fact I'm more bothered when I get into a brand new Lexus or even BMW--I feel isolated from the road. It's as if I'm driving a video game instead of a car. With that said, some people are very sensitive to NVH. Maybe the right solution in to spend some time in a E30 stripped race car with solid suspension, solid drivetrain mounts, and an open exhaust w/o a muffler. After that, everything will seem quiet.
-bj
2002 M Coupe | 2000 M Roadster w/ LS | 1998 328i w/ S54 | 1987 325is w/ M52 | 1985 735i Turbo
Except that on a race car the drivetrain load is altering the suspension geometry unless you solid mount it to the chassis. A solid mount on the chassis is the only way to minimize the changes of inflection caused by changes in drivetrain load. It's better to drive all the twist into solid mounts and distort the chassis slightly than to have your alignment change with every change in throttle directly. Fatigue not withstanding. ("Better" meaning more predictable results)
#54 GTS-3/CM E30 Race car
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