E46 Rear Suspension Mounts: Preventative Maintenence?

[dr_gn]

Guys,

I just got my '02 330i Sport back from Sytners (for an airbag recall). I asked them to inspect the boot floor suspension mounts for cracks, which they did, saying they were fine. The car is in great condition considering its age, and I'm having the wheels re-furbed and hopefully some minor rear arch rust sorted out soon. I'd like to keep the car for at least a few more years, so my question is: Are there any steps I can take to prevent, or delay, the boot floor cracking issues? For example, having the foam/resin treatment?

I posted this elsewhere, and the only reply was that if you don't do hard launches everything will be OK...

Thanks.

[optimate]

not really unless you want to pay 1500 quid to have the reinforcement/repair kit welded in

just drive it if it does crack they all don't all crack get it done later if you think its still worth keeping

what id do is change the coolant tank if aint been done as it will crack before long

and check for oil leaks from the usual places and fix them also budget for a new steering pump
and if it aint been done change the aux belt and tentioner

mines a 2004 full history when i got it 59 thousand on clock
so far
new shocks
one seized caliper
one snapped aux belt
cracked coolant tank
cam cover gasket leak
oil filter housing seal leak
shagged steering pump
leaking thermostat changed
changed water pimp while it was in bits save doing it later
changed knackered oil level sensor
changed purge valve to shut fault able not needed harmless


got to change passenger window regulator when i can be asked

all comon st with e46

Edited by optimate on Thursday 1st June 15:01

Edited by optimate on Thursday 1st June 15:02

Edited by optimate on Thursday 1st June 15:10

[dr_gn]

I thought there was some resin/foam that could be injected into the boot floor cavity to spread the loads?

Mines an '02, 117k miles, and apart form general service items, so far (over 4 years ownership) I've done:

Radiator (precaution)
Water pump (precaution)
Electric thermostat (precaution)
Coolant system drive belts (precaution)

Shocks (previous owner damaged one - replaced all four)

Clutch/flywheel (failed)
Electronic throttle body (failed)
Front suspension mounts (failed)
Anti-roll bar links (failed)
Heater thermostat hedgehog (failed)
Parking sensors (failed)

Alloys re-furbed (slow air leak due to corrosion)

I wish I'd kept a record of how much it all cost so I could estimate monthly costs compared with a new car. Pretty sure it would be significantly lower, but you never know!

ETA, just added it up from what I can remember, and worst case, not including service items etc., so far is about £50 a month, so not too bad. Car cost £3300.

Rear arches are going a bit, now, and I've had daft quotes even for a cosmetic repair...I think rust will be what kills it.

Edited by dr_gn on Thursday 1st June 16:17

[optimate]

its still a lot of labor to do the resin unless you got a lift or pit and doing yourself
i would fancy fking around doing it on Axel stands

if your are doing your self you may as well weld it properly

personalty ill wait and see plenty don't crack

mines still under 80k on the clock i picked mine up for 3k dead
some numpty dented the wing door and scuffed bumper

so i got 3.6k back insurance and had second hand door and it resprayed for 750 of a coach builder

all repair work iv done myself so its not really cost me anything bar tax and insurance and petrol

Edited by optimate on Thursday 1st June 17:37

[Sardonicus]

optimate said:

its still a lot of labor to do the resin unless you got a lift or pit and doing yourself
i would fancy fking around doing it on Axel stands

if your are doing your self you may as well weld it properly

personalty ill wait and see plenty don't crack

Edited by optimate on Thursday 1st June 17:37

This ^ I have a 325 Touring M Sport 163k no cracking subframe/body no problem to check often as I run a workshop but mine is auto not for too much longer however

[optimate]

Sardonicus said:

This ^ I have a 325 Touring M Sport 163k no cracking subframe/body no problem to check often as I run a workshop but mine is auto not for too much longer however

iv always prefer auto e46 as the dam pedals are so close together and a pain on a manual
if you got big feet

[Sardonicus]

optimate said:

Sardonicus said:

This ^ I have a 325 Touring M Sport 163k no cracking subframe/body no problem to check often as I run a workshop but mine is auto not for too much longer however

iv always prefer auto e46 as the dam pedals are so close together and a pain on a manual
if you got big feet

Already done good dough on rebuilding my ZF gearbox inc clutches etc (I had the pump plain bearing fail and do plenty of damage) I decided to rebuild my own box hardly a 5 minute job I can tell you ....but now the replacement T converter lock up clutch is failing (shuddering) 6k later so I'm out I cant justify 500+ for a gen ZF converter for my what is just a 2nd car even if my labour is free

Edited by Sardonicus on Thursday 1st June 20:41

[helix402]

Which is why my E46 with a broken auto box is getting a manual conversion! Back to the ops question. I wouldn't recommend resin injection as I suspect it may burn quite well-which is a tad inconvenient if (when) you need to weld new metal in.

[Sardonicus]

helix402 said:

Which is why my E46 with a broken auto box is getting a manual conversion! Back to the ops question. I wouldn't recommend resin injection as I suspect it may burn quite well-which is a tad inconvenient if (when) you need to weld new metal in.

Got the bits already inc correct manual sub loom/harness amongst other stuff got a spare DCM/ECU so may use this or code my existing DCM to no longer see the auto trans may save the faff of EWS keys etc ,,, sorry to take this off topic

[iSore]

Resin injection - bodge up. You might as well use B&Q expanding foam and P38.

[helix402]

Sardonicus said:

ot the bits already inc correct manual sub loom/harness amongst other stuff got a spare DCM/ECU so may use this or code my existing DCM to no longer see the auto trans may save the faff of EWS keys etc ,,, sorry to take this off topic

Your original ECUs can all be reprogrammed/recoded for a manual conversion.

[bmwmike]

My e46 had boot floor done in 2008 by BMW and the dealer asked for it back a year later for a "quality check" at which time they injected foam. If I buy another e46 I'd get the foam injected if reasonable cost.

[E-bmw]

For the following reasons I would not use the foam.

1. I am not sure how effective it would be. If steel is cracking under stress how will glue prevent this? Yes, I understand it will spread the stress loading, but will it really actually stop it.

2. If my worries above are founded then how the hell can you then repair with weld when the void is full of epoxy?

I had the issue on a previous e36 325 & did the repair myself over 2 days on axle stands & minimal tools, with a welder. I took the opportunity to change all the rear bushes too & drove out a completely different car.

[xjay1337]

£1500?

I swear a company in Bristol does it for half that.

[SebringMan]

xjay1337 said:

£1500?

I swear a company in Bristol does it for half that.

Redish do it for £1500 in Bristol and they have the waiting list to match the price. ETA in Brands Hatch do it for £800. But TBH you'd want to change the subframe bushes at the same time ; I am shocked at the difference they made going to Poly items here.

FWIW here is my take in a nutshell below, and then my experience below:

Despite what BMW tell you they WILL crack. The question is not if it has cracked, but whether it is saveable/viable to repair. That last bit means alot more if the floor has cracked too far. It doesn't matter if you have a 316i Compact or an M3, they are all susceptible, albeit the higher powered cars moreso ; My friend has a repaired mount on his 328i.

As for my M3:

-In 2014 mine was checked by BMW ; all was deemed well on the subframe
-In late 2016 it was checked again : the car was given the all clear again bar the tyres and the HID

When I checked the mounts myself I could not see it being obviously cracked ; I even cleaned around the rear mounts ; that is the loose dirt. Checking the N/S Front mount on a n M E46 is easy enough but it's almost impossible to check the O/S Front mount without removing the factory shielding and possibly even dropping the subframe down

I then gave it to ETA as I had one or two knocks from the back ; I suspected my subframe bushes. When he checked :

-The N/S Rear mount was cracked but only under the underseal once it was fully removed ; I would be pissed off if someone did that to my own car as I suspect would other people!
-The O/S Front was cracked undeneath the bush (this is impossible to see with the subframe in position) as well as around it.
-I "think" two or three spot welds had popped.

Here's my car having the work done:

https://www.pistonheads.com/gassing/topic.asp?h=0&...

The BMW foam fix is a nice idea but it leaves two problems:
-The front mounts which also cracked are still left to crack and they are the second most common place to crack. By the BMW method the only way to deal with these (if they were ever checked which it seems they are not) is a new boot floor.
-An issue with the inner wheel arch separating from the rear axle carrier panel (RACP).
-It doesn't deal with popped spot welds ; it's these which lead on to a number of cracks.

I have the BMW bulletin if anyone wants it forwarding on. I don't see it mentioning the front RACP mounts once regarding checking for them bar saying it's a rare occurance (the Redish videos seem to prove otherwise...)


ETA and Redish deal with those aspects ; they weld the RACP more onto the inner arch allowing the stresses to be spread more. I believe Redish are beginning to brace the two chassis legs and attaching that onto the RACP as a further method like I believe MwStewart has here.

It's funny how people say the subframes don't crack ; they don't. It's the RACP that does.

[Krikkit]

E-bmw said:

For the following reasons I would not use the foam.
1. I am not sure how effective it would be. If steel is cracking under stress how will glue prevent this? Yes, I understand it will spread the stress loading, but will it really actually stop it.

Lots of manufacturers are using resins to increase spot-welded structure stiffness, if you get the right stuff there's no reason it can't be a permanent solution. Applying it correctly might be tricky, however.

[iSore]

The cracking (esp rear passenger side mount) is caused by the threaded block - the bit the subframe bolt screws into - breaking loose. The axle twists under acceleration and the pressed steel lower boot floor skin cracks as it's unable to take the street. To sort this properly requires cutting the upper boot floor skin open inside the boot itself and welding this block back into place. I had this done on mine (323i) and it took about 2 hours including welding up the cracks visible underneath.

Welding big plates on underneath whilst the threaded block is still broken away smacks of an expensive sticking plaster.

By far the best guy to repair and reinforce these (inadequate) boot floors is Dan Harboro.


https://www.facebook.com/pg/bmconversionsuk/photos...

Edited by iSore on Friday 2nd June 23:14

[dr_gn]

iSore said:

The cracking (esp rear passenger side mount) is caused by the threaded block - the bit the subframe bolt screws into - breaking loose. The axle twists under acceleration and the pressed steel lower boot floor skin cracks as it's unable to take the street. To sort this properly requires cutting the upper boot floor skin open inside the boot itself and welding this block back into place. I had this done on mine (323i) and it took about 2 hours including welding up the cracks visible underneath.

Welding big plates on underneath whilst the threaded block is still broken away smacks of an expensive sticking plaster.

By far the best guy to repair and reinforce these (inadequate) boot floors is Dan Harboro.


https://www.facebook.com/pg/bmconversionsuk/photos...

Edited by iSore on Friday 2nd June 23:14

How much is the repair and how long does it take? Thanks.

[pidsy]

Had mine done using a reddish plate kit. It went to deutschtech in Milton Keynes. It was £800 iirc. Got a lot of photos from them too - whole process start to finish.

[iSore]

dr_gn said:

How much is the repair and how long does it take? Thanks.

You'll need to ask him.