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Subframe and Differential Bushings Selection for Lowered 325ix

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    Subframe and Differential Bushings Selection for Lowered 325ix

    Hey all, doing some light resto on my 325ix, and I have arrived at the rear end. Front suspension is already rebuilt. Rear subframe is ready to pull. I'll be replacing all the bushings back here. I am lowering the car on the 325ix specific H&R sport springs.

    I understand that the 325ix subframe bushings raise the car up .300" vs the standard RWD E30 subframe bushings, and that it can help with camber problems on a lowered 325ix to use the RWD bushings.

    I intend to run the car on the H&R springs for the foreseeable future and would like to choose subframe and differential bushings that will be ideal for this setup. Is it worth it to go with RWD E30 bushings, and if so, which should I go with and how do I set up the diff at the correct height? Also, is this going to make the front ride higher than the rear?

    Thanks!

    #2
    So I'm going to go with RWD subframe bushings and a RWD diff bushing, with the centered hole. What size spacers am I going to need for the diff mounting bolts? Anyone know?

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      #3
      I think I finally figured this out... shouldn't need spacers with this choice of bushings, but correct me if I'm wrong.

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        #4
        That's right. I would take a look at your rear shaft angle too. Make sure the slip mechanism is free and adjusted.

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          #5
          Subscribing to this, gonna need to do this in the future. Sent from my iPhone using Tapatalk
          1989 325ix Alpinweiss sedan. Auto to manual conversion. Mostly stock.

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            #6
            It is pretty simple. The "nubs" on the top of an iX subframe bushing are longer than the RWD counterpart. Lowering the iX subframe required raising the hole in the differential mount to make everything line up (from the factory). If one raises everything up to the RWD level, the only issue remaining is the driveshaft angle.

            Comment


              #7
              The simple way is to stack some washers on top of the diff between the subframe so the diff stays in the original position, and use a stock diff bushing (unless you like vibrations, I wouldn't bother with aftermarket - the original is already plenty stiff). Mine's been like that for almost as long as I've owned the car (19 years! Fuck me!). I think I used 2 thick washers which is about 3/8" - close enough to the difference in bushing length at least.

              I wouldn't just put it together without any spacers, it's going to tweak the subframe, diff bushing, bushing bracket, or all 3 - plus you don't want to mess with the pinion angle.

              Subframe height actually doesn't raise or lower the car - it keeps the trailing arm geometry aligned with the extra ride height. if BMW had used the regular RWD bushings, the rear alignment would have positive camber and toe out. So by using the shorter bushings on a lowered ix, you automatically correct issues with negative camber & toe in from lowering the car, without needing adjustable trailing arm bushings.

              Oh, there's a metal washer/spacer thing that you need to keep at the bottom of the subframe bushings. The bottom bracket that holds the subframe in place is a little different, if you don't make up that gap the brackets will be bent when you tighten the subframe bolts, or the bushing will move around because it won't be compressed fully by the bolt/bracket.
              Last edited by nando; 04-07-2021, 08:36 AM.
              Build thread

              Bimmerlabs

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                #8
                Originally posted by nando View Post
                The simple way is to stack some washers on top of the diff between the subframe so the diff stays in the original position, and use a stock diff bushing (unless you like vibrations, I wouldn't bother with aftermarket - the original is already plenty stiff). Mine's been like that for almost as long as I've owned the car (19 years! Fuck me!). I think I used 2 thick washers which is about 3/8" - close enough to the difference in bushing length at least.

                I wouldn't just put it together without any spacers, it's going to tweak the subframe, diff bushing, bushing bracket, or all 3 - plus you don't want to mess with the pinion angle.

                Subframe height actually doesn't raise or lower the car - it keeps the trailing arm geometry aligned with the extra ride height. if BMW had used the regular RWD bushings, the rear alignment would have positive camber and toe out. So by using the shorter bushings on a lowered ix, you automatically correct issues with negative camber & toe in from lowering the car, without needing adjustable trailing arm bushings.

                Oh, there's a metal washer/spacer thing that you need to keep at the bottom of the subframe bushings. The bottom bracket that holds the subframe in place is a little different, if you don't make up that gap the brackets will be bent when you tighten the subframe bolts, or the bushing will move around because it won't be compressed fully by the bolt/bracket.
                Nando, can you elaborate on how the washers are placed on top of the diff? Did you place them on bolt #18 in the parts diagram attached? You said they went between the diff and subframe correct?

                https://www.realoem.com/bmw/enUS/sho...diagId=33_0124
                89 325ix coupe Diamondschwartz
                1994 Mazda Miata

                Comment


                  #9
                  Yes, bolt #18 is correct and yes they need to go between the diff and the subframe. The shorter subframe bushings move the subframe up so the diff needs to be spaced down if it's original position is to be maintained.
                  AWD > RWD

                  Comment


                    #10
                    Originally posted by nando View Post
                    The simple way is to stack some washers on top of the diff between the subframe so the diff stays in the original position, and use a stock diff bushing (unless you like vibrations, I wouldn't bother with aftermarket - the original is already plenty stiff). Mine's been like that for almost as long as I've owned the car (19 years! Fuck me!). I think I used 2 thick washers which is about 3/8" - close enough to the difference in bushing length at least.

                    I wouldn't just put it together without any spacers, it's going to tweak the subframe, diff bushing, bushing bracket, or all 3 - plus you don't want to mess with the pinion angle.

                    Subframe height actually doesn't raise or lower the car - it keeps the trailing arm geometry aligned with the extra ride height. if BMW had used the regular RWD bushings, the rear alignment would have positive camber and toe out. So by using the shorter bushings on a lowered ix, you automatically correct issues with negative camber & toe in from lowering the car, without needing adjustable trailing arm bushings.

                    Oh, there's a metal washer/spacer thing that you need to keep at the bottom of the subframe bushings. The bottom bracket that holds the subframe in place is a little different, if you don't make up that gap the brackets will be bent when you tighten the subframe bolts, or the bushing will move around because it won't be compressed fully by the bolt/bracket.
                    Sorry all, didn't realize replies were coming in!

                    Status: subframe and trailing arms sandblasted and powdercoated, wheel bearings replaced, all bushings replaced with OEM equivalent rubber. Subframe has RWD bushings and washers. Diff was also given this treatment and I selected a RWD diff bushing with a center mounted hole.

                    Nando, when you say "stock" bushing, do you mean stock IX bushing? Do I get to skip the washers/spacers between the diff and the subframe if I'm using a RWD bushing? I'm guessing the right answer here is ditch the RWD bushing and get an IX diff bushing, then use the spacers as you mentioned, so that I can maintain pinion angle.

                    Going with the RWD theme, I acquired RWD subframe brackets, the "pushrods" as BMW calls them. Even with the RWD bushings, they don't fit properly. Sadly I half-destroyed the stock brackets getting them off the car. They looked like they would fit just fine without any spacer between the bracket and the bottom of the subframe bushing, so I'm thinking of just getting a clean set of IX subframe brackets. I don't recall a spacer in that location when I was taking this apart. Thoughts?

                    Huge thanks to all who replied!

                    Comment


                      #11
                      Originally posted by lefthookz View Post

                      Sorry all, didn't realize replies were coming in!

                      Status: subframe and trailing arms sandblasted and powdercoated, wheel bearings replaced, all bushings replaced with OEM equivalent rubber. Subframe has RWD bushings and washers. Diff was also given this treatment and I selected a RWD diff bushing with a center mounted hole.

                      Nando, when you say "stock" bushing, do you mean stock IX bushing? Do I get to skip the washers/spacers between the diff and the subframe if I'm using a RWD bushing? I'm guessing the right answer here is ditch the RWD bushing and get an IX diff bushing, then use the spacers as you mentioned, so that I can maintain pinion angle.

                      Going with the RWD theme, I acquired RWD subframe brackets, the "pushrods" as BMW calls them. Even with the RWD bushings, they don't fit properly. Sadly I half-destroyed the stock brackets getting them off the car. They looked like they would fit just fine without any spacer between the bracket and the bottom of the subframe bushing, so I'm thinking of just getting a clean set of IX subframe brackets. I don't recall a spacer in that location when I was taking this apart. Thoughts?

                      Huge thanks to all who replied!
                      Hey lefthookz! I am refreshing my ix rear end/subframe like you are. I have the subframe out and am thinking about powdercoating it and the trailing arms as well. Just curious what your experience was with that process? Why did you choose to powdercoat? Cost?
                      89 325ix coupe Diamondschwartz
                      1994 Mazda Miata

                      Comment


                        #12
                        Originally posted by E30andy View Post

                        Hey lefthookz! I am refreshing my ix rear end/subframe like you are. I have the subframe out and am thinking about powdercoating it and the trailing arms as well. Just curious what your experience was with that process? Why did you choose to powdercoat? Cost?
                        Hey Andy - basically it's a midwest car so a fair amount of corrosion everywhere, including the subframe and trailing arms. The coating is nice but the best part of the process is the shop will media blast the parts to remove every last spec of rust. In my case, there was still some pitting here and there so I didn't end up with a perfectly smooth finish, but certainly good enough and absolutely structurally sound everywhere. You end up with relatively new-looking, clean and shiny parts to install, which is always more pleasant. Plus I'm trying to future-proof the car so it lasts another 33 years, whether with me or someone else. Here in SoCal I went to Bulletproof Coatings in San Bernardino and paid $250 for the subframe, trailing arms, and differential to be sandblasted and powdercoated. Definitely recommend vs refinishing yourself especially if you're short on time - I did this manually on the front suspension with a wire wheel and Eastwood chassis coat in a can, and it takes a looooong time to do it right.

                        Comment


                          #13
                          Originally posted by lefthookz View Post

                          Hey Andy - basically it's a midwest car so a fair amount of corrosion everywhere, including the subframe and trailing arms. The coating is nice but the best part of the process is the shop will media blast the parts to remove every last spec of rust. In my case, there was still some pitting here and there so I didn't end up with a perfectly smooth finish, but certainly good enough and absolutely structurally sound everywhere. You end up with relatively new-looking, clean and shiny parts to install, which is always more pleasant. Plus I'm trying to future-proof the car so it lasts another 33 years, whether with me or someone else. Here in SoCal I went to Bulletproof Coatings in San Bernardino and paid $250 for the subframe, trailing arms, and differential to be sandblasted and powdercoated. Definitely recommend vs refinishing yourself especially if you're short on time - I did this manually on the front suspension with a wire wheel and Eastwood chassis coat in a can, and it takes a looooong time to do it right.
                          That sounds like a really reasonable price! I got quoted $85/hr for sandblast and $75/hr powdercoat (less if I do it in a batch with other stuff that is getting coated) from a local company here in VT.
                          For the trailing arms, did you remove the ebrake hardware and cables prior to powdercoat? I would rather not take all the ebrake stuff apart if I can avoid it as I was able to just slide the ebrake cables out of the tubes when I removed the subframe.
                          89 325ix coupe Diamondschwartz
                          1994 Mazda Miata

                          Comment


                            #14
                            Originally posted by E30andy View Post

                            That sounds like a really reasonable price! I got quoted $85/hr for sandblast and $75/hr powdercoat (less if I do it in a batch with other stuff that is getting coated) from a local company here in VT.
                            For the trailing arms, did you remove the ebrake hardware and cables prior to powdercoat? I would rather not take all the ebrake stuff apart if I can avoid it as I was able to just slide the ebrake cables out of the tubes when I removed the subframe.
                            Sorry, totally missed this! Yeah, I took apart the entire e-brake system, all the brake hardware, the dust shields, the bearings, everything - completely stripped the trailing arms. It's all back together now and looking much better. Though the noise I'm getting from my polymer diff mount is ASTOUNDING so now I'm hunting for a used/new rubber mount.

                            Comment


                              #15
                              New mounts are available from most vendors but be prepared to shell out big $$$ for it! Once every 30 year expense so probably worth it in the end.
                              89 325ix coupe Diamondschwartz
                              1994 Mazda Miata

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