Re-building rear suspension

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Ronnie Wilson
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Re-building rear suspension

Post by Ronnie Wilson »

Filled tank up, then discovered fuel leak from bottom of filler neck, a common issue.
Decided to remove tank and have it re-furnished. When tank was out, could see it left me with plenty of room to remove the suspension. Rear subframe, training arms, various brackets and exhaust away being media blasted and the powder coated in satin black. Just the English cold and damp weather slowing the process.
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Last edited by Ronnie Wilson on Sun Jan 08, 2017 1:06 am, edited 2 times in total.
Ronnie
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wattsmonkey
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Re: Re-building rear suspension

Post by wattsmonkey »

Great looking car!

Fair play to you for getting your abs sensors out in one piece! Handbrake cables probably have a tale to tell too.

Cheers,

Rob
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Ronnie Wilson
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Re: Re-building rear suspension

Post by Ronnie Wilson »

HI, tricky thing i was doing today is trying to remove the struts and springs. Workshop manual describes accessing the boot/trunk to gain access to the three nuts at the top of the strut towers. Not much room to get at the furthest nut. Other option is to remove the rear seats and speaker pods. Nightmere. :-?
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Re: Re-building rear suspension

Post by wattsmonkey »

Easy! You've done the hard bit. Two nuts easily accessed from boot, front ones via hole behind rear seat covered by soundproofing. Seat only held in by two screws at bottom
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
Ronnie Wilson
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Thanks, But i think the really tricky bit will be trying to remember how it all go back together. :-?
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Re: Re-building rear suspension

Post by 603racing »

Good luck finishing it up. I plan on doing the same thing in the next few months.
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Re: Re-building rear suspension

Post by olympia57 »

Ronnie Wilson wrote:HI, tricky thing i was doing today is trying to remove the struts and springs. Workshop manual describes accessing the boot/trunk to gain access to the three nuts at the top of the strut towers. Not much room to get at the furthest nut. Other option is to remove the rear seats and speaker pods. Nightmere. :-?
I found that using either a 13mm C or S shaped obstruction spanner made the job easy enough from within the boot .Best to remove the boot liner too .
Don
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Ronnie Wilson
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Thanks for that guys.
Tomorrow will be picking up the suspension parts that have been media blasted and powder coated. Will post some pictures.
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Brucey
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Re: Re-building rear suspension

Post by Brucey »

if you lift the parcel shelf carpet, all three nuts on each strut top can be undone in about one minute using 1/2" drive socket and a 12" extension bar.

No crawling around in the boot with spanners required....!

cheers
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Ronnie Wilson
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Thanks Brucey,
Is the parcel shelf stuck down or does it just remove when you remove the back seats.
Would you know which springs and shock I need. Want to keep as close to original as possible.was going to place an order with walloth & nesch. Bilsteins all round.
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Re: Re-building rear suspension

Post by Brucey »

the parcel shelf mountings may vary a little with model but IIRC it is usually located with (brittle) plastic pegs and may be damaged by being bent or folded, so really the whole thing has to come off to gain access. The pod hinges go through it too, and the headrests (or trims if you have no headrests) as well. So if all this is coming out anyway, great, otherwise you are making one job easy at the expense of generating another. I suppose that if this were a common task one might be able to modify the parcel shelf (e.g. with holes and blanking plugs, which might be hidden beneath the speaker pod?) to allow better access.

I've removed the rear strut top nuts both ways and in fairness it is a bit of a toss-up as to which way is faster if you have to remove the parcel shelf specially for the job. But if you really cannot contort yourself to get access through the boot or indeed don't have the right spanners, removing the parcel shelf is probably a little easier, given how easily the rear seats etc come out.

Re the rear shocks. Originally they would have been Boge twin-tube shocks with no perch height adjustment. These shocks can last a long time but some do fail (giving a bouncy rear end which is incredibly dangerous) and the damping quality is mostly thought to be nothing like so good as with monotube bilsteins; for post 5/82 cars there are a bewildering number of original Bilstein PNs for the rear shocks (and Bilstein have re-numbered their shocks at least three times since these shocks were first built.... :roll: ) but if you want a monotube gas shock the choice usually boils down to a choice of two if you are buying aftermarket; 'sports' or 'HD' (although they may also be referred to as B8 and B6). [NB Presently if you buy 'B4' Bilsteins I think you get a twin-tube shock with no perch height adjustment, but this has not always been the case I believe].

Sports shocks have five perch height grooves and have a shorter stroke than the HD ones. The HD ones have three perch height grooves and a longer (matching the OEM shock) stroke. If you buy from BMW you will get the same shocks but usually with only one perch height groove.

The bump/rebound damping rates are almost identical between sports and HD, and the extra travel in the HD shock is essentially extra negative travel, i.e. it mostly affects the way the shock tops out when you are airborne or when the inside shock tops out through body roll when you are cornering hard. The latter can cause some evil handling traits if it doesn't match the front, because as the roll angle changes, there is effectively a very abrupt change in roll stiffness. If the rears top out thus (well before the fronts) I would expect the car to snap oversteer.

So:

If you want to spend the least money, you don't need perch adjustment, and are happy with the way twin-tube shocks work, buy 'B4' shocks.

Reasons for choosing sports/B8 are

1) you need five perch adjustment grooves to get the correct ride height
2) you need the short stroke to prevent dislocation of (shorter 'lowering') aftermarket springs
3) you need the short stroke to match the shorter stroke in the matching sports front shocks

Reasons for choosing HD/B6 shocks are

1) you think the damping is better than the B4s or other twin-tube shocks
2) you like the idea of having three positions for the perch height
3) you want a standard stroke shock of high quality

The correct OEM rear springs will vary with the build of the car. I went through the options for front springs here

viewtopic.php?f=17&t=16947&p=120119

and it is similar situation for rear springs, i.e. there are different rear springs with model and build spec, but there are fewer options and springs from other models that might fit are both less plentiful
and less likely to work (E28 springs will fit but E28 models are mostly heavier at the back IIRC and if you use those springs in an E24 it gives an excessive ride height).

Really you could argue that 'the right rear spring' might vary with how much junk you usually carry in the boot. You can make minor ride height adjustments by varying the thickness of the spring seating pads but larger changes need perch grooves or different springs. In theory there is a stamped part number near the end of each OEM spring; if you can still read it, you could try ordering against that as a x-ref.

If you are buying from W&N, you may only have one choice offered for rear springs at your build date. These might be identical, or they might be slightly different, in which case a shock with an adjustable perch height can be very handy.

Note that M635CSi uses slightly different shocks, different diameter rear springs etc . I think the damping rates are a little higher than in the HD shocks (because the battery is in the boot in M635CSi). You can use M635CSi shocks with standard E24 rear springs if you replace the spring perch with the correct diameter part.

Whichever rear shocks you use, you should aim to fit new bump stops (standard ones for stock ride height, M635CSi ones for any lowered suspension) and you should be sure that the protection tubes fit to them OK too; without these parts the handling will be suspect and the shock shaft will soon corrode in our lovely climate.

cheers
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Ronnie Wilson
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Thanks Brucey. :D
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Rear suspension parts back from being powder coated. Now trying to fit bushings.
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Re: Re-building rear suspension

Post by ron »

Check the OD of the 4 trailing arm bushes. You may need to skim them down. I had to use immense force to get mine in. Sharkfan and Brucey will remember it well!
They are ALWAYS rustier than you thought!!!!!!
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Re: Re-building rear suspension

Post by Brucey »

yes indeed!

Out of interest what coating is that on the exhaust system?

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Re: Re-building rear suspension

Post by Ronnie Wilson »

Thanks Ron / Brucey.

Was going to ask how you guys got your trailing arm bushes in. Made up a extractor and inserter tool for the subframe and trailing arm bushes. Used a length of 12mm stainless stud iron to try and pull out the trailing arm bush while applying heat to the outside of the trailing arm. But the force was that great it sheared off. After meeting Ron at the Nec in November, he told me to burn them out. Which I did, just leaving me to gently cut the outside diameter of the bushes. Subframe bushes just fell out when I heated them up. Putting the new subframe bush in was quite easy with the tool I made, as seen in the photo. The exhaust has been powder coated. But I only told the guy to paint the rear back box because I couldn't separate it from it's joint with the middle silencer. Not sure if the front and middle silencer coating will hold up to the heat. He said that the coating should be good for around 300*f. Would you guy know what sort of temperatures the front and middle silencers get to. If it's to much I'll have to remove the paint from those areas.
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Re: Re-building rear suspension

Post by Brucey »

I think the coating may well melt/burn on the centre box. If so, the fumes are stinky, poisonous, and I suppose there is a danger that the car will catch light wholesale (burning powder coat is surprisingly difficult to extinguish).

The powder coaters will presumably have shot-blasted the whole thing which means that if you remove the coating, the exhaust will probably corrode quite quickly. I'm not sure what to suggest really.

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Re: Re-building rear suspension

Post by olympia57 »

I had some exhaust heat shields powder coated some years ago but unfortunately they rapidly discoloured and then flaked .
As exhausts corrode from within I suspect that your decision to PC the exhaust may have been for aesthetic reasons .If so I can certainly recommend Hycote VHT paint .
http://www.ebay.co.uk/itm/Hycote-High-t ... Sw-vlVjrye
I prep'd mine ( off car ) by removing ALL loose rust and prior coating and applied three coats of silver curing each coat with a blow torch . It's been on the car for over two years now and still looks as good as when i did it.
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Re: Re-building rear suspension

Post by Ronnie Wilson »

That's what I thought. I got other item that require media blasting so will get the paint around both mufflers removed and spray them with some high temp paint.
Looking at your car on the ramp, I can see that you have replaced your output shafts. I also have new ones that I haven't fitted yet, why do they come with red cv boots one end and black the other. Presumably the red cv boot attaches to the differential, the way you have yours fitted.
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Re: Re-building rear suspension

Post by sansouci »

Is the rear suspension removal a 1-man job or do I need to find some hapless soul who wants to spend an afternoon underneath a vintage BMW?
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Re: Re-building rear suspension

Post by olympia57 »

sansouci wrote:Is the rear suspension removal a 1-man job or do I need to find some hapless soul who wants to spend an afternoon underneath a vintage BMW?
With everything disconnected and a good trolley jack under the diff case one man plus gravity can remove it with a little care and patience , I found the consumption of a can of spinach prior to starting helped considerably ........
To refit it you will need the help of Bluto though. :lol:
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Re: Re-building rear suspension

Post by olympia57 »

Ronnie Wilson wrote:That's what I thought. I got other item that require media blasting so will get the paint around both mufflers removed and spray them with some high temp paint.
Looking at your car on the ramp, I can see that you have replaced your output shafts. I also have new ones that I haven't fitted yet, why do they come with red cv boots one end and black the other. Presumably the red cv boot attaches to the differential, the way you have yours fitted.
Ronnie , the red CV boots were recently replaced prior to me purchasing the car and were in perfect condition. I searched for another red pair to match them when I restored the car but had to settle for black for the hub ends.
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Re: Re-building rear suspension

Post by Ronnie Wilson »

Hi guys,
Finally managed to get those rear trailing arm bushes in. Had to buy a length of high tensile 12mm stud iron and elongated 12mm nuts.
Also decided, prior to fitting bushes to put them in the fridge freezer for 2 hours. Heated the trailing arm bush housing up with a blow tourch. To the point where the powder coating just starts to dull. Covered the bush and housing in anti seized grease, Then went for it with two 19mm spanners. The bushes started to go in quite easy, then as the heat transferred from the housing into the bushes, it began to get harder to tighten the nuts. I then had to use my foot to get the last quarter of the bush in.
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\:D/
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Re: Re-building rear suspension

Post by sansouci »

Ronnie:
Great pix! Did you use the stock bushes? What size pipe did you use for the home made tool. While it is a great rental item, I'm sure it's too heavy to cross the pond for anything reasonable.
Ken
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Re: Re-building rear suspension

Post by Da_Hose »

Hey Ronnie,

I don't know if you read my rear end rebuild document, but here it is.

https://drive.google.com/file/d/0B95IxH ... g2Nlk/view

Here is what my experience was like just trying to remove the damned bushes from my control arms.

viewtopic.php?t=9604

You are doing quite well on this project, young man. =D>

Jose
1987 M6 - My dream car
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