Rebuilding M635 Bilsteins

[DRPM635CSi]

This is not a discussion about modifying or lowering suspension at all, so would appreciate discussion not being taken off in that direction. My M635CSi has 30yo shocks in it that have never seen the light of day since new car delivery to the best of my knowledge. They have all the problems you would expect of 30yo shocks. One front is completely seized and the other is visibly leaking.

I do not want to lower the car nor change any other aspect of its suspension performance beyond what BMW fitted it with new. To that end, I have heard that Bilstein will rebuild old shocks back to original specification. Has anyone in here with an M635 actually had this done with success?

I have made initial inquiries here with the Australian Bilstein distributor who indicated this was an option, but then went on to say he thought my car's shocks were fitted with rebound springs, and that if the case, then they can't be rebuilt because in today's HSE-centric world, shocks with rebound springs are now considered too dangerous to dismantle & reassemble.

This sounds like just a convenient excuse to start pointing me in the direction of installing brand new off-the-shelf shocks rather than rebuilding the old ones. Something I do not want to do.

He also mentioned he thinks the M635 front shocks have Ø12mm shafts which are NLA from Bilstein and will need to be rebuilt with Ø14mm shafts instead. I can live with that if the original shafts can't be metal-sprayed and rechromed/restored, even though a Ø2 greater shaft by virtue of reducing the shaft side piston area is going to affect the shock performance trend on rebound.

Has anyone come across this claim about Bilstein shocks with rebound springs not being able to be rebuilt before? Or were there no problems getting OE Bilsteins factory rebuilt in either USA or UK?

Does anyone have in their data collections the original Bilstein specs of the Euro delivery RHD M635CSi shocks please?

The only mods I am looking to make from factory stock are to swap the springs R<->L to even out any possible sag from the last 30 years and to fit shim plates in the strut towers to try and take out some of the in-built LHD chassis lean bias to compensate for the LHS driver, which obviously isn't appropriate in a RHD car.

Thanks for any insight offered.

[sansouci]

You may want to also post your inquiry on bimmerforums E32 subforum as Shogun has posted about shock rebuilding. Not sure if he was limited to LAD system or not. But it is worth a shot. He's German but lives in Japan.
Ken

[Brucey]

stock M635 bilsteins are ref

P36-0242 strut inserts and shocks B46-0725

I've not seen the damping spec numbers but they are rumoured to be similar to the sports shocks.

Bilstein E28 5 series 82-88, E24 6 series 83-on
rebound / compression force at 52 cm/sec

Newton pound-force (rebound/compression)
N lbf (0.2248 x N)
------------ ------------------
Front:
P36 0243 Sport 2900 / 950 652 / 214
P36 0233 HD 2860 / 650 643 / 146
P36 0239 Comfort 1790 / 650 402 / 146

Rear:
B46 0607 Sport 1605 / 805 361 / 181
B46 0608 HD 1605 / 805 361 / 181
B46 0610 Comfort 1590 / 770 358 / 173

Part numbers are now different to those quoted above but there is a conversion chart somewhere. The stroke lengths vary with these shocks as well as the valving. There are also other E28/E24-fit shocks which are not listed here; Like the M635 shocks, I don't have the valving numbers for them.

The numbers above only tell half the story; they say little about the low-speed (i.e. low shaft speed) damping values and these can really affect the handling more than you might suppose. Bilstein use different pistons, shims etc to generate a variable damping rate with shaft speed so it is quite possible to have two shocks with the same damping numbers at 20"/s but different damping at lower shaft speeds.

BTW it appears that if you bought 'Dinan spec Bilsteins' etc back in the day you got Dinan springs but you got the 'sports' shocks which came with standard 'sports' valving.... and a Dinan sticker.

AFAICT none of these shocks have rebound springs (I've dismantled rears but not fronts, but both top out the same way) and even if they did they should still be rebuildable.

Bilstein have made many, many P36 struts for all kinds of vehicles. I think that your man was full of shit to be honest. It'll be a cold day in hell before Bilstein give up making these P36 and B46 shocks and parts for them because they are fitted to so many different vehicles including many quite recent BMWs. B46 parts are numerous because the B46 piston and shaft are used in lots of race car shocks as well as road car shocks.

However there is no guarantee that the national distributors for Bilstein will continue to stock certain items, or even want to sell them to anyone. Recently several UK 6 series owners have had a real hassle getting spare parts out of Bilstein UK, and have been told that 'they don't have these parts any more' (but hey, you can still buy new shocks with them inside.... ) and/or 'why don't you use our retailers?'. These are the same retailers that don't list these spare parts, never have done, and never will do....

I mean, WTF is the point of having a rebuildable shock if you can't get the parts to rebuild it or get the people that built it in the first place to rebuild it...????

Re your strut inserts; seizure normally means that the boot has failed, water has got in, the bushings have worn and then corrosion has set in; the bushings are steel-backed and they will corrode to the damper body nicely. Once the bushings are worn the shock shaft sees side loads and this may make the seal wear and leak even though the shaft might still be OK (to start with...) . Side loads can also wear the piston inside the shock, too.

So once you look at a shock like that, you might find that you can't actually salvage many parts from it and you might be better off getting some new shocks instead. If Bilstein quote a flat rate for a rebuild that is less than the price of new shocks, they may know ahead of time that they are going to take a hiding on some shock types.

If you have Bilstein shocks that have good parts but just need a rebuild there are other people that will do this work. However they will often charge a flat rate plus parts so bad shocks can work out a lot more to rebuild this way.

IIRC Bilstein shocks are sold with a lifetime warranty in North America. If there were cheap shipping, I'd buy them from the USA, because they are no more expensive there, and they are not sold with that warranty elsewhere in the world.

hth

cheers

[/quote]

[DRPM635CSi]

You may want to also post your inquiry on bimmerforums E32 subforum as Shogun has posted about shock rebuilding. Not sure if he was limited to LAD system or not. But it is worth a shot. He's German but lives in Japan.
Ken

Thanks for that suggestion. I have sent him an e-mail. Think I bought some re-make copy E32 external door handle gaskets off him last year for my 740iL which worked an absolute treat and saved a lot of money having to buy all new complete handles since BMW don't supply just the gaskets separate for that model.

What does LAD stand for? Are you referring to the self levelling system rear shocks on an E32? If I'm successful getting the E24 ones done, then that might be the next thing I need to look into. Pretty sure I have a very slow leaking or sweating self-levelling damper in the rear of my E32 as well and replacement is out of the question at something ridiculous like $5,000 a pop down here.

[DRPM635CSi]

stock M635 bilsteins are ref

P36-0242 strut inserts and shocks B46-0725

I've not seen the damping spec numbers but they are rumoured to be similar to the sports shocks.

Bilstein E28 5 series 82-88, E24 6 series 83-on
rebound / compression force at 52 cm/sec

Newton pound-force (rebound/compression)
N lbf (0.2248 x N)
------------ ------------------
Front:
P36 0243 Sport 2900 / 950 652 / 214
P36 0233 HD 2860 / 650 643 / 146
P36 0239 Comfort 1790 / 650 402 / 146

Rear:
B46 0607 Sport 1605 / 805 361 / 181
B46 0608 HD 1605 / 805 361 / 181
B46 0610 Comfort 1590 / 770 358 / 173

Thanks Brucey, this is all excellent information I shall use to get back in touch with the local Bilstein distributor down here. This is exactly the kind of help I was hoping to get in here.

AFAICT none of these shocks have rebound springs (I've dismantled rears but not fronts, but both top out the same way) and even if they did they should still be rebuildable.

Good to know, thanks.

Re your strut inserts; seizure normally means that the boot has failed, water has got in, the bushings have worn and then corrosion has set in; the bushings are steel-backed and they will corrode to the damper body nicely. Once the bushings are worn the shock shaft sees side loads and this may make the seal wear and leak even though the shaft might still be OK (to start with...) . Side loads can also wear the piston inside the shock, too.

I am hopeful there is not too much wrong with my shocks outside of what you would normally expect after 30 years in a car. My car is a reasonably well preserved one. Southern England car below the ice/salt roads before exported to Australia some 23 years ago. Always garaged and kept in a very dry, humidity-free Perth ever since. That's not to say there is no corrosion of isolated components at all. Certainly there are some parts underneath that do reveal the UK origin & are dirtier than a Perth delivered car from brand new, but I believe it is very clean indeed for a UK car generally.

If you have Bilstein shocks that have good parts but just need a rebuild there are other people that will do this work. However they will often charge a flat rate plus parts so bad shocks can work out a lot more to rebuild this way.

I am prepared for the reality that rebuilds might well be more expensive than brand new equivalents. That's just what you have to accept as the reality in today's world where everything pushes toward throwing away the old and buying new all the time. Facing harsh facts, the truth is that I could throw away the whole car completely and probably buy a new Japanese family sedan for half as much money that has twice the performance of an ///M635CSi today too. That's probably the cold hard truth, but it doesn't make me want to swap my M635CSi for a Japanese hatchback any more either.

IIRC Bilstein shocks are sold with a lifetime warranty in North America. If there were cheap shipping, I'd buy them from the USA, because they are no more expensive there, and they are not sold with that warranty elsewhere in the world.

Yeah nice idea but the cost of shipping will kill that idea stone dead I'm afraid.

[Brucey]

I hate the throwaway society too. With a passion.

But in this case if you buy new shocks (from BMW or Bilstein) they will be made identically to the original ones. No difference there.

If you have the old ones 'rebuilt' it could be a simple job involving a few seals and wear parts but on the other hand you could easily end up in a situation where the only parts that can be re-used are the valving shims and some of the caps, (i.e. you will have a 99% new shock anyway) depending on how bad they are to start with.

If you are looking in the long term and there is a local suspension place that does good work, or you want to get stuck in yourself, you could have the shocks converted to 'tear apart' specification. In this the shock body is fitted with a Schrader valve and the shock can be pressurised (eg using dry nitrogen) and depressurised at will.

Once it is depressurised, the shock can be stripped and rebuilt very easily; some offroad racers will routinely strip and rebuild shocks this way before and after every event.

cheers

[DRPM635CSi]

But in this case if you buy new shocks (from BMW or Bilstein) they will be made identically to the original ones. No difference there.

Yeah I understand, but when you live in Australia, buying new large BMW parts is really out of the question altogether unless you have the budget of an Arabian Prince. Four brand new shock absorbers for an M635 down here would cost more than the whole car is worth. As an example, I got a quote the other week for a new genuine brake bomb accumulator. The price quoted was not far short of A$1,000 or ~£500. That's the sort of ridiculous pricing we're faced with down here.

Even if you buy from the USA where prices actually approach being realistic, we then get killed on postage+import duty+GST etc., such that on large items like a full set of shock absorbers would be, you end up pretty much paying the same if you had bought them in Australia in the first place.

We really need to restore, rebuild, refurbish as much as humanly possible down here. The costs otherwise very quickly exceed what the whole car is worth.

[sansouci]

"We really need to restore, rebuild, refurbish as much as humanly possible down here."
The Cuban Strategy...

What we need is a network of travelers who can bring in stuff in hand luggage to keep the 6'er alive without eating your wallet. Maybe a travel notice on BC so if anyone is flying down there, they can be a courier?
Just a thought!
--Ken

[DRPM635CSi]

"We really need to restore, rebuild, refurbish as much as humanly possible down here."
The Cuban Strategy...

Exactly. It's expecially noticeable for anything out of the ordinary. An M635CSi is about as out-of-the ordinary down here as you're ever going to get at a BMW dealer here. There are no Z1 or 325ix or pre-war 328 or M1 down here, so an M6 is about as far away from the mainstream as anyone has seen. In fact, most parts guys have never even seen one. You can tell by the reactions on their faces when you enquire about unique parts for one.

As a result, everything unique to them may as well be priced at $1mil for all the likelihood you'll be placing the order. And of course nothing is in stock. Their warehouse is located in Germany, so there's absolutely no incentive to place an order anyway even if price was no factor. You'll get it just as quickly ordering yourself from overseas vendors.

I'm in the market right now for a rubber diff mount for #188. A perishable you can't buy used. BMW Australia have nil stock of course and even if they did it would be A$1,000. Got one from US for a little over $300 instead.

[Brucey]

Four brand new shock absorbers for an M635 down here would cost more than the whole car is worth....

sorry, can you explain that better....?

You can place an order online with (say) Walloth and Nesch for all four shocks and it is going to be about 1000 euros plus shipping and taxes. Or about the same in USD from the USA.

If that lot comes to the price of an M-car car then they're selling for cheap where you are.

cheers

[sansouci]

LAD is the self leveling rear suspension in the 740il...

[DRPM635CSi]

Anyone know where this Bilstein part number conversion chart is Brucey refers to? I'm getting the feeling I'm going to need it dealing with the local agent down here. He is already taking advantage of my ignorance of Bilstein part numbers to try and steer me in the direction of telling me my shocks are not rebuildable and to just throw in a brand new set of HD's (which conveniently he has in stock available off-the-shelf). Why am I not surprised?

And this advice is coming from him even before he's even seen the shocks (they're not even out of the car yet!). I expected this battle though, which is why I started in here first.

I'm going to be told anything and everything to convince me that whatever he has in stock on the shelf is a perfect equivalent replacement part for my OE M635 shocks. Everything will be about making the quickest, easiest sale of whatever they have on the shelf, rather than spending the time and effort to do the job properly as requested. This is just the modern reality of so-called 'customer service' in Australia these days. You really need to go into bargaining arrangement fully armed with all the knowledge you can possibly gather about what you want to buy or else you'll just come away buying something else you never wanted in the first place.

[m6dave]

I have three sets of front strut inserts.
Set 1
Original BMW 1987 M6 inserts. These have the following markings-
bmw roundel 31.32-2225017.2
4410242E01
when these are extended with no springs there is 138mm of shock shaft showing above the outer tube. I think they have internal springs

Set 2
Came out of an E28 I believe to have been fitted as after market replacements
They have the following markings
Bilstein stickers with part number F4-P36-0233-H002
Stamped numbers 5190233H002
I think these are HD shocks not sport
when these are extended with no springs there is 179mm of shock shaft showing above the outer tube.

Set 3
Are brand new Bilstein sport shocks.
I do not have the exact dimensions of these as they are in the car but I know that they were almost dimensionally identical to set 2.

Does this mean that only the genuine ones have the internal spring??

How do these measurements and part numbers compare with yours Dean?

[DRPM635CSi]

I have three sets of front strut inserts.
Set 1
Original BMW 1987 M6 inserts. These have the following markings-
bmw roundel 31.32-2225017.2
4410242E01
when these are extended with no springs there is 138mm of shock shaft showing above the outer tube. I think they have internal springs

Set 2
Came out of an E28 I believe to have been fitted as after market replacements
They have the following markings
Bilstein stickers with part number F4-P36-0233-H002
Stamped numbers 5190233H002
I think these are HD shocks not sport
when these are extended with no springs there is 179mm of shock shaft showing above the outer tube.

Set 3
Are brand new Bilstein sport shocks.
I do not have the exact dimensions of these as they are in the car but I know that they were almost dimensionally identical to set 2.

Does this mean that only the genuine ones have the internal spring??

How do these measurements and part numbers compare with yours Dean?

Dunno mate, mine are still in the car for now until I can establish a clear & agreed plan of attack and way forward. It's a bit more complicated being over this side of the country and all the reputable rebuilders being over there where you are. Everything is long distance from over here. I can't afford to just take the shocks out and give them to someone to have a look with no plan in place for what's to be done when it's known what there is to work with.

Can you post some photos of those 1987 spec inserts you have? Where'd they come from? US? 'M6' spec or 'M635CSi' spec? I would expect the US M6 spec shocks to be different to the Euro M635 spec ones.

[rhanley 635csi89]

The chart is on the bilstein website under downloads.

http://www.bilsteinus.com/downloads/pro ... formation/

[m6dave]

They came from a Japan M6, for all intents and purposes a Euro body spec with US spec mechanicals.
Real Oem returns this part number and usage
Part 31322225771 was found on the following vehicles:
6' E24   (07/1986 — 09/1988)

Real Oem returns this part number and usage against your VIN
Part 31322225016 was found on the following vehicles:
5' E28   (10/1984 — 01/1988)
6' E24   (10/1983 — 02/1989)

[Brucey]

I have three sets of front strut inserts.
Set 1
Original BMW 1987 M6 inserts. These have the following markings-
bmw roundel 31.32-2225017.2
4410242E01
when these are extended with no springs there is 138mm of shock shaft showing above the outer tube. I think they have internal springs

those are what is normally known as P36-0242 (back when Bilstein PNs made some sense) also as BMW 31322225016. It is possible that these are also known under BMW 31322225771. What makes you think they have internal springs?

Set 2
Came out of an E28 I believe to have been fitted as after market replacements
They have the following markings
Bilstein stickers with part number F4-P36-0233-H002
Stamped numbers 5190233H002
I think these are HD shocks not sport
when these are extended with no springs there is 179mm of shock shaft showing above the outer tube.

Yup, HD's P36-0233

Set 3
Are brand new Bilstein sport shocks.
I do not have the exact dimensions of these as they are in the car but I know that they were almost dimensionally identical to set 2.

what PN is on these?

cheers

[DRPM635CSi]

The chart is on the bilstein website under downloads.

http://www.bilsteinus.com/downloads/pro ... formation/

Thanks for that. Unfortunately neither P36-0242 nor B46-0725 is listed.

[DRPM635CSi]

They came from a Japan M6, for all intents and purposes a Euro body spec with US spec mechanicals.

Yeah that's what I feared might be the case. I think the US cars were a bit softer and more comfort biased with also heavier luxury equipment levels, which might have meant a slightly different spec damper package than the Euro-spec cars. That's not a fact at all and just my surmising. Happy to be shown to be wrong.

[rhanley 635csi89]

See if these help. I could not find anything on B46-0725, is this the correct part number?

http://cart.bilsteinus.com/productsearch/p36-0242

http://cart.bilsteinus.com/search/setting=M%20Series

[m6dave]

those are what is normally known as P36-0242 (back when Bilstein PNs made some sense) also as BMW 31322225016. It is possible that these are also known under BMW 31322225771. What makes you think they have internal springs?

I don't actually know they have internal springs but thinking this because the open length is so short. They are a real PITA to assemble the struts because you have to compress the suspension spring so far to get them on. AFAIK when you release the spring compressors the inserts come out further.

Set 3 I got from Bavauto their part number 34-181546

[Brucey]

OK you have got me wondering now.... I might have to build up a strut and see if that is really true or not.

Other struts with negative springs in them (eg the Boge ones fitted to E24 models for example) usually have a fairly soft transition into the negative spring, so that you can tell if there is one or not by simply trying to extend the shock by hand. The Bilstein ones are certainly not like that.

The rear shocks have a rubber top out bumper inside the damper assembly, and the top out of the (bare) front struts feels very similar to the rear, very much a clunk rather than anything else. If you try pulling (pretty hard, but not spring force admittedly) on the insert, it doesn't really move.

These things tell me that if there is a top out spring in there, it is a very stiff one. Quite why one should stop you from disassembling a damper is quite beyond me anyway; maybe I'm missing something here, but all these shocks are gas pressurised and the end caps want to come out with a force of several hundred lbs and it is that which makes dismantling one of these shocks tricky, not any internal spring, surely...?

BTW the part number issue is complicated by the fact that Bilstein have changed their part numbers not once but twice in recent times, and then some importers have chosen to (quite randomly) not bother listing certain part numbers even though Bilstein still make them and they can certainly get them if they really want to...

So for example

B46-0725 = BMW 33522225020 = Bilstein 24-007252 = Bilstein EAN
4025258498054 = not listed in Bilstein US's latest part number conversion.

P36-0242 = BMW 31 32 2 225 016 = Bilstein 34-002421 = Bilstein EAN
4025258639389 = not listed in Bilstein US's latest part number conversion.

Both the above are also listed as B6 shocks but this is a fairly arbitrary designation; when listed for one model a given shock may be called B6 (or B6 sport) but the exact same part can also be called B8 (or B8 sprint) in relation to another model of the same car.

This site allows searching by various old part numbers (but not by Bilstein US's latest concoctions, I think)
http://web1.carparts-cat.com/default.as ... 004&12=130
This site doesn't recognise BMW 31322225771 so it either isn't perfect, or that PN is perhaps not a Bilstein shock after all.

The Bavauto PN 34-181546 is a Blistein part number that means 'B8 sprint' = 'sport' (in US) = P36-0243. IIRC this insert should have a shorter travel than the HD part.

Searching by EAN also gives some interesting results e.g.

http://www.ebay.com/itm/Bilstein-B6-Spo ... 1169739754 -will ship to Australia (NB the image is generic I think)

cheers

[Brucey]

OK, I helped a chum refit his P36-0242 inserts yesterday and they do have a negative (top out) spring in them and it must be very stiff.

As M6dave says, they do extend when the strut is assembled; we measured another ~45mm of travel in extension that appeared as the spring compressors were backed off.

cheers

[DRPM635CSi]

See if these help. I could not find anything on B46-0725, is this the correct part number?

B46-0725 = BMW 33522225020 = Bilstein 24-007252 = Bilstein EAN
4025258498054 = not listed in Bilstein US's latest part number conversion.

From RealOEM, I've got my rear shocks coming out as being BMW part number 33522225150. Does that mean they're not these B46-0725 model?

Thanks for all the good info & research provided on the front inserts. This is really good and is exactly what I need to give to my workshop guy to try and keep him on the right track. If I can give him the same info on the rears too, then I think I'll be all set.

Cheers

[bpoliakoff]

Anyone thinking Bilstine will honor the life time warranty may be in for some bad news. Bilstine will only warranty the shocks if you have the original bill of sale showing they came from a retailer. Reason being they don’t want to honor the warranty if ther shocks were bought on Ebay etc, but if it is a parts place they will then honor the warranty. Again a purchase receipt is required.