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Thoughts on replacing entire back end (diff, axle, suspension)

Posted by Earendil 
Okay, here is what is motivating this:

1. A guy I know has a wrecked 325is (front end, 30mph into dirt bank).
2. He may be getting rid of it soon.
3. For the next 3 or so months, I'll be working within walking distance of work

My Car: 89 i, cracked axle boots for 3 years, non-LSD, original/standard shocks and springs, calipers in need of work/replacement, subframe bushings could be replaced.

His car: 87 is, Good axle boots, LSD diff, Bilstein shocks and springs.

My question is: Would it be easier to remove the diff, axles, shocks, springs, and wheel assembly as one unit and throw it on the back of my car?
If that sounds like too much, how about just the diff and axles?

I need to get to my subframe bushings at some point, and my axles need to go. However I'm afraid he may junk his car soon, forcing me to make a quick decision about taking the parts from him. Optionally, I may be able to buy the wrecked car off him cheap, and with a payment plan. My problem is determining its worth, and where I'd part it.

As I said, I am motivated by my ability to walk to work and take forever on this project. In addition, with a recent move I am low on cash, and will be for some time. I would never consider buying all this stuff refurbished/new at one time. The alternative route for me is to buy the LSD off him, and swap that out. A couple months later buy axles, swap those out. A few more months go by, calipers and maybe rotors out. And eventually spring for new suspension.

Knee jerk reactions?

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
Would it be easier to remove the diff, axles, shocks, springs, and wheel assembly as one unit and throw it on the back of my car?
Absolutely!
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Ferdinand
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Earendil
Would it be easier to remove the diff, axles, shocks, springs, and wheel assembly as one unit and throw it on the back of my car?
Absolutely!
My knee-jerk reaction is the same as Ferdinand's. smiling smiley

__________
Dave
'91 325iX
And you would recommend this even if I don't change out my front shocks/springs for another 6 months to a year?
I wouldn't expect a difference in stiffness rear to front to matter too much, but it's quite likely that these Bilstein are lowing the back end at least an inch. Would that difference in front to back height be noticeable when looking at the car? Would it cause performance/handing issues?

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
it's quite likely that these Bilstein are lowering the back end at least an inch.
If they're the black Bilstein "touring" shocks, then you should be okay.

If they're the yellow "sport" shocks, then yes the rear will be lower and stiffer. In that case you will want to get the matching springs and shocks for the front as well.

Making the rear stiffer while leaving the fronts soft would create more oversteer. Plus it will look funny with the rear dropped and the nose up in the air.
sounds good, and go for it, but realize that it's not trivial job. My suggestion would be to get all ( most ) parts at once (i.e accumulate parts over time if you can't buy them in one shot) so that you don't have to assemble / dismantle some things twice...

In order to do a swap "as one unit" ( as you mentioned ) you will have to take his rear subframe and trailing arms as well ( with exception of calipers) , otherwise you'll have to get everything disassembled ( in order to get axles out you have to disconnect them from the diff, etc.). Doing this swap as one unit will be one royal pain in the neck unless you have a lift...moving all that weight around to precisely locate holes for rear subframe during install is a bit#$. I did it with just subframe and trailing arms on the garage floor and was having quite a vocabulary ( i did it by myself - next time I'll use beer and pizza as a bribe and get another set of hands to help...).

-If you are not taking his trailing arms make sure that you don't damage rear wheel bearings during assembly.
-don't damage brake lines (including e-brake cable)
-replace as many bushings as you can while stuff is out (unless they are really new which doesn't sound like from your post)
-how are those wheel bearings - now would be perfect time to do them if you think they are going bad
-If diff is leaking now is the time to replace cover gasket
-getting access to diff bolts is a pain in a neck ( especially rear ones). Have fun properly torquing them (if you are not mounting diff already connected to rear subframe...)
-springs and shocks ( dampers) are easy - don't sweat over that
-don't forget to put lube gear in the diff before driving it. It's a LSD now so use proper blend
- most likely diff will be making strange noises at the beginning. find a big parking lot and drive the car in tight circles in both directions. Gear oil needs to work itself into clutch packs
- did I mention that this will be pain in the neck job? smiling smiley [there are few more things but I don't want to completely scare you]
rkj
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igor325
sounds good, and go for it, but realize that it's not trivial job. My suggestion would be to get all ( most ) parts at once (i.e accumulate parts over time if you can't buy them in one shot) so that you don't have to assemble / dismantle some things twice...

In order to do a swap "as one unit" ( as you mentioned ) you will have to take his rear subframe and trailing arms as well ( with exception of calipers) , otherwise you'll have to get everything disassembled ( in order to get axles out you have to disconnect them from the diff, etc.). Doing this swap as one unit will be one royal pain in the neck unless you have a lift...moving all that weight around to precisely locate holes for rear subframe during install is a bit#$. I did it with just subframe and trailing arms on the garage floor and was having quite a vocabulary ( i did it by myself - next time I'll use beer and pizza as a bribe and get another set of hands to help...).

-If you are not taking his trailing arms make sure that you don't damage rear wheel bearings during assembly.
-don't damage brake lines (including e-brake cable)
-replace as many bushings as you can while stuff is out (unless they are really new which doesn't sound like from your post)
-how are those wheel bearings - now would be perfect time to do them if you think they are going bad
-If diff is leaking now is the time to replace cover gasket
-getting access to diff bolts is a pain in a neck ( especially rear ones). Have fun properly torquing them (if you are not mounting diff already connected to rear subframe...)
-springs and shocks ( dampers) are easy - don't sweat over that
-don't forget to put lube gear in the diff before driving it. It's a LSD now so use proper blend
- most likely diff will be making strange noises at the beginning. find a big parking lot and drive the car in tight circles in both directions. Gear oil needs to work itself into clutch packs
- did I mention that this will be pain in the neck job? smiling smiley [there are few more things but I don't want to completely scare you]

All great advice, you should also consider, first, are these parts good. It would be a drag to do all that work only to find a noisy bearing or a rumbly, whining rear end.

What's the mileage on the doner car, how's the fluid level and what does it look like; a little work before can save you a lot of work later smileys with beer does this car roll?

Rick
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Ferdinand

If they're the black Bilstein "touring" shocks, then you should be okay.

If they're the yellow "sport" shocks, then yes the rear will be lower and stiffer.

The "Heavy Duty" Bilstein is also yellow, but it fits stock springs. If you find yellow Bilsteins in that car just get them all. I put the HD shocks in my car and I love the way it feels. Of course, I also love the way it feels to drive a '65 VW Bus with a king pin / link pin front end, so take that into account when you read my advice. smiling smiley

John
Thanks for all the responses!

I'm pretty sure the shocks are yellow/blue. unfortunately the current owner did not install them, and cared little what they were.
I'd guess that if a person were to install new shocks on a 325is they would opt for the "sport", unless perhaps they got a deal on the heavy duty.

Ferd, wrong answer. I was looking for "It works perfectly and looks sexy. And it adds 50hp!!". Oh well, better luck next upgrade smiling smiley

igor, thanks for all the tips. I don't have a lift, but I now work at a a company in the aerospace arena. There are a number of engineers around here who can be bribed with pizza and bear, even if they know nothing about cars smiling smiley
I also managed to do the drive shaft without a lift, so I'm familiar with the vocabulary set required to do similar jobs smiling smiley

Rick, The owner said he thinks it's all in good condition. 180K + miles on the car. At the very least he knows the diff wasn't making any noise. I'll make sure I do some looking over and checking before I commit to it. Currently the car has been sitting for 18 months on flat tires. Last time I saw the car there were about 50 paper wasps that thought they owned the place...and they were right. In any case, IF the diff has good fluid, and knowing it has fewer miles than mine does, it's probably pretty good. The axles can't help but be better than mine, and obviously the shocks are. Bummer that I have to remove the axles from the diff to avoid taking the subframe/control arms. That's one of the big things I was hoping to avoid.

John, My only issue with taking the front shocks/springs as well, is that the front end is wrecked. This doesn't give you a good idea what the condition of the shocks are, but it does show the front end damage.

I know that the front wheels were not bent, and that the wheel assembly was in one piece, though I doubt it's all still true.

I wish I could provide you guys with a good story to follow immediately after your advice. Sadly, as I said, I am looking for advice so that if I have to make a quick move, I can. I am however trying to get a hold of him to see if I can go take another look at the car. I'll provide more pictures if that's the case.

Is there an easy way to tell the difference between sport and heavy duty shocks?
What about the springs? I went looking online for Blistein springs, and they don't seem to make it, or at least sell them through the common BMW channels.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil


Is there an easy way to tell the difference between sport and heavy duty shocks?
What about the springs?

Sport = lowered, Heavy Duty = stock ride height. If the car has been lowered the springs will be shorter too. The right way to do it is to buy lowering springs which are are shorter than stock. I guess there may be some hacks out there who cut stock springs, but that's a mistake. You can probably tell if has been lowered just by looking at how the car sits compared to a car you know is stock. Measure the gaps between the fenders and tires if you can't be sure by looking.

John
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John Yust
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Earendil


Is there an easy way to tell the difference between sport and heavy duty shocks?
What about the springs?

Sport = lowered, Heavy Duty = stock ride height. If the car has been lowered the springs will be shorter too. The right way to do it is to buy lowering springs which are are shorter than stock. I guess there may be some hacks out there who cut stock springs, but that's a mistake. You can probably tell if has been lowered just by looking at how the car sits compared to a car you know is stock. Measure the gaps between the fenders and tires if you can't be sure by looking.

John
\
You may have missed where I said that the car is sitting on 4 flat tires. Its ground clearance is currently well below stock tongue sticking out smiley
However, if the tires are seemingly inflated at the top (i.e. holding their shape), I may be able to compare the distance from tire to fender.
And thanks for explaining that simple distinction between the two shock types. I had failed to make that observation before smiling smiley

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 02/05/2010 02:40AM by Earendil.
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Earendil
You may have missed where I said that the car is sitting on 4 flat tires. Its ground clearance is currently well below stock tongue sticking out smiley
However, if the tires are seemingly inflated at the top (i.e. holding their shape), I may be able to compare the distance from tire to fender.
Measure from the lip of the fender to the center of the hub. That distance is unaffected by anything the tires are doing; it's affected only by the suspension.

__________
Dave
'91 325iX
you may want to get new rear subframe bushings while you're at it. was the 325is auto or manual? that will determine the diff ratio.


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Dave_G
Measure from the lip of the fender to the center of the hub. That distance is unaffected by anything the tires are doing; it's affected only by the suspension.

You know, I believed you. I went out to the car, and measured his car only to find less distance between my back fender and center of wheel (i.e. mine was lower). Visually mine looked lower too. So I went to my tool box which was under my jack stands in the trunk of my car....doh! That's why my rear end was lower smiling smiley
He also didn't have a spare tire in his trunk.

The front was different though. His was a little over an inch lower than mine, and maybe had 20lbs of components missing from under the hood. I was able to see some very visible yellow and blue on the shocks up front. The back I couldn't tell without jacking up the car.
The springs are anyone's guess. But it sounds like if they are the "sport" shocks, that he would have to run different springs? Or at least should have.

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daniel
you may want to get new rear subframe bushings while you're at it. was the 325is auto or manual? that will determine the diff ratio.

It's a manual. I believe I already checked to see that it was a 3.73. I was hoping to see a 4.10, but I'm pretty sure it was just a 3.73.
And if I end up doing this I will certainly tackle my sub frame bushings.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

you dont want a 410 unless you have a 4-banger or an automatic. 3.73 is perfect.


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daniel
you dont want a 410 unless you have a 4-banger or an automatic. 3.73 is perfect.

I don't know if you remember this, but the M20 is a lot closer to a 4 banger than to your S52 B)-
An M20 with 250K on it, even more so B)

The only people I've heard complain about a 4.10 in their cars are those people who do a lot of freeway miles. the 3.73 spins the engine up on the freeway as it is, a 4.10 would just exaggerate that.

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
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daniel
you dont want a 410 unless you have a 4-banger or an automatic. 3.73 is perfect.

I don't know if you remember this, but the M20 is a lot closer to a 4 banger than to your S52 B)-
An M20 with 250K on it, even more so B)

The only people I've heard complain about a 4.10 in their cars are those people who do a lot of freeway miles. the 3.73 spins the engine up on the freeway as it is, a 4.10 would just exaggerate that.

the motor doesn't have much to do with it, really. it is the transmission gear ratios. the M20/getrag 260 was paired with the 3.73 for a reason. If you want to get the 4.10 be my guest. you'll have better acceleration and worse highway mileage. you would basically be making 5th gear a non-overdrive gear.

and for the record, my S52/ZF320 is connected to a 3.25 diff, and i wish i had a 2.93 or 2.79 even though i am driving 90% of the time off the highway, so maybe i am biased toward longer gear ratios.


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daniel
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Earendil
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daniel
you dont want a 410 unless you have a 4-banger or an automatic. 3.73 is perfect.

I don't know if you remember this, but the M20 is a lot closer to a 4 banger than to your S52 B)-
An M20 with 250K on it, even more so B)

The only people I've heard complain about a 4.10 in their cars are those people who do a lot of freeway miles. the 3.73 spins the engine up on the freeway as it is, a 4.10 would just exaggerate that.

the motor doesn't have much to do with it, really.

I beg to differ. Gearing has everything to do with the torque/power of the motor and what kind of output you want.

Though when I wrote what I did I was thinking strictly of how short 1st and 2nd would be. In a 4 banger you get to (read: have to) spend some time in those gears. With an s52 I don't suppose you'd spend more than a literal split second in 1st gear if you had a 4.10.

I have no doubt that BMW engineered this car beautifully, including how the power gets from the motor to the rubber. However they engineered it with a purpose and use in mind. That purpose and use may not be the purpose I have in mind, or how I want to use it smiling smiley

All that said, I'm far more interested in an LSD than I am in a 4.10.

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Those pictures I promised of the springs and shocks, as well as the damage to the front left wheel.
If anyone wants to take a wild guess at the cahnce that that front shock is still good, please do. I know they towed it on all 4 wheels to get it home. It looked like the tie rod on the drivers side was bent, but there was no noticeable damage to the control arm, knuckle, spring or shock. The Shock tower was not in the correct position, but whether it was pushed out of place by impact to the shock, or if the rippling of the corner caused it to move, I don't know.




Such a sad sight.







And here I am thinking "How much damage can there be when the wheel looks that good!" smileys with beer








Dang... I had to spoil my hope by looking in the trunk, and finding what I can only assume is the wheel that was attached during the wreck. thumbs down
Of course they would put the spare on (they rope towed it 15 miles up curvy roads to their home). Silly me for thinking otherwise eye rolling smiley



This project has now taken a back seat to the brain surgery I'll end up performing on my M20, and those silly valve springs... sad smiley

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

I'd forget about that shock and rather pay for a new one. We often bend shocks at work by impacts, need a long straight ruler to check for bending, in the long run you'll end up replacing it again.

If you want to re-use parts from a crashed car, go for the parts that were in the non-impact zone.
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Michiel 318iS
I'd forget about that shock and rather pay for a new one. We often bend shocks at work by impacts, need a long straight ruler to check for bending, in the long run you'll end up replacing it again.

If you want to re-use parts from a crashed car, go for the parts that were in the non-impact zone.

Might there be any negative result from using 3 older shocks with a brand new one? I know, your question is probably going to be "how much older?" which isn't an answer I have yet. Obviously orn out shocks has a negative effect(compared to brand new), I just don't want to amplify that problem by having one stiff shock.
I'm also assuming that the spring, even if on the damage side, is okay.

Thanks.

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
Might there be any negative result from using 3 older shocks with a brand new one? I know, your question is probably going to be "how much older?" which isn't an answer I have yet.
OK, I'll ask a different question: What kind of driving do you do? If you're just driving it at 30 MPH to church on Sunday morning, then you'll never notice anything. If you're pushing the car at all, you might notice some odd handling behaviors. Personally, I would always replace shocks at least in pairs.

I drove around for a while once with two completely blown shocks on opposite corners. There was no problem just puttering around town like that, but whenever I pushed it, or went over a bump, the handling characteristics became, well, "interesting." smiling smiley How much of a problem that is depends on both how different the odd shock is, and on how hard it's being asked to work.

__________
Dave
'91 325iX
rkj
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Earendil
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Michiel 318iS
I'd forget about that shock and rather pay for a new one. We often bend shocks at work by impacts, need a long straight ruler to check for bending, in the long run you'll end up replacing it again.

If you want to re-use parts from a crashed car, go for the parts that were in the non-impact zone.

Might there be any negative result from using 3 older shocks with a brand new one? I know, your question is probably going to be "how much older?" which isn't an answer I have yet. Obviously orn out shocks has a negative effect(compared to brand new), I just don't want to amplify that problem by having one stiff shock.
I'm also assuming that the spring, even if on the damage side, is okay.

Thanks.

That car took a good solid hit; a lot of things can bend from a hit like that, even things not in the crumple zone.
Just think about it this way: how much is your life worth compared to a set of brand new shocks? Would you rather pay with your whole life rather than an arm and a leg?
If you don't know the history of the right hand side shock, consider it scrap. And what's the use of going through a shock replacement when not having 'new' characteristics, even unknown characteristics. If it's bad, you'll have to do it all again.
rkj
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Michiel 318iS
Just think about it this way: how much is your life worth compared to a set of brand new shocks? Would you rather pay with your whole life rather than an arm and a leg?
If you don't know the history of the right hand side shock, consider it scrap. And what's the use of going through a shock replacement when not having 'new' characteristics, even unknown characteristics. If it's bad, you'll have to do it all again.

Yes, doing things once is bad enough smileys with beer
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