I’ve just broken the third set of rear shocks on my car; it happens every 5 years or so. the first time I attributed it to the bump stops being absent, the second time tired springs (which I replaced). This time I’m out of excuses. The shock(s) break when it hit a depression where both wheels drop in at the same time and the rear squats down. The depth of the depression does not have to be extreme and is one that any car should handle quite easily. Also the speed at which this occurs is not high, this time I was travelling at about 45 mph.
The breakage occurs where the rod of the shock mounts to the top of the rear end sub frame, a few inches below the mounting point. In the past it has been one shock on the LHS that has broken, this time it was two shock one the LHS and the other on the RHS.
The shocks are standard Boge shocks and the spring are about 5 years old. No suspension modifications, the entire set up is stock.
Has anyone else experienced this? Is it possible possible the that the rear end sub frame is somehow out of whack and and is creating uneven stress points under certain conditions?
What bushings have you got installed in the shock eyes, and is there any indication that your Diff or Inner Fulcrum mounts are moving around?
I can sort of imagine breaking the rods where you describe if there was zero compliance in the shock bushings, but with the regular rubber shock bushings I would think the cage would have to be visibly out of whack to put enough loading on the shock rods.
Are you replacing with exactly the same Boge shocks, and what number are you using? If the shocks are too short then you might be hitting the internal stop when a wheel droops, but I wouldn’t expect that to break the rods.
No similar experience in 35 years of ownership. Longshot: how solid is the IRS mounting and stabilising arrangement - the four mounts and the trailing arms? How sound are the caged roller bearings in the swing axles? Is the IRS cage moving backward suficiently to apply a shearing moment to the shocks?
When I lifted the rear end the first time with the cage hanging by the four mounts I found one where the rubber was completely separated from the steel. When I rebuilt the rear assembly the caged roller bearings were worn to an extreme.
Thanks for the replies Andrew and Nick. Since this only happens when the rear drops into a trough or depression rather than a bump lends some credence to Nick’s theory that the whole unit is moving backwards and applying a shearing moment. I’ll get it up on a lift and report back.
I’ve driven a couple of E’s where one cup had separated from the floor. These wandered so significantly in a corner or on acceleration that even if you didn’t know what proper e-type handling was like you’d still think “Something is seriously wrong behind me.” and stop the car immediately.
A torn or perished Donut might give enough movement to get some cage flex, But I doubt that alone would be enough to result in a bending moment on the shocks.
If the shocks are correct, and the bushings have some compliance, then if something is loose or bent I would expect it to jump out at you.
Perhaps power washing, then spraying some Christmas “Window Snow” paint on all the connections between the various bits then going for a drive would reveal things sliding about.
This is not a problem I have heard of. I agree that there must be something significantly awry with your rear end.
I reckon that if you had enough fore and aft movement between the top mounting point and the lower wishbone to break a shock you’d surely notice when driving the car. I’d expect it to be pretty much undrivable and noisy.
Similarly I’m not sure that looseness with the radius arms would cause enough flex; the cage is pretty rigid.
Given that they break when going over a bump, I’d guess that the shocks are being over extended or over compressed somehow. Have you since refitted the bump stops? What is your rear camber like? Do you have issues with uneven rear tyre wear?
I just wonder whether at some point your IRS may have been reassembled with incorrect components.
I had exactly this problem with exactly the same company, on an XJ6 (1995 version, so different IRS).
Where the bottom fixing was a spherical bearing originally, Boge fitted a hard rubber shock eye…where the upper mount was stiff foam between dished convex washers, Bove supplied hard rubber ronuts between flat washers. The were OK for a few months until I started working with a client fifty miles away along country lanes. After a week of gradually increasing speeds I started catching air on the run home, and a week later as I landed there was a bang and the left shock rod had snapped. The weak point was the root of the first thread.
The Jag IRS lets the wheels go forward/backward as well as pivoting up and down - hence the spherical bearing - to permit full deflection in two planes but the normal rubber bush only allowed pivoting in one plane around the fixing bolt. The lack of fore/aft pivot meant the moving suspension transferred those loads up the rod to the top mount. The top mount was far more rigid than Jag’s version and so the increased loads in a design less able to absorb them, was never going to end well. Boge agreed to a refund and changed their X300 etc. design.
I don’t quite see what the parallel snafu could be but if the break is actually at the first thread Root there’s something going on!
That makes some sense Pete and that in fact is where the break occurs. What to do however as it seems all the after market shocks have a rubber bushing and not a spherical bearing and it seems as if other Series 3 owners haven’t had this problem. Maybe there’s something slightly out of line with the rear suspension that exacerbates the situation. HopefullyI’ll know more after the unit is dropped.
I believe I know what the reason for the rear shocks breaking. It happened to me as well with Boge shocks bought from SNG.
The problem is actually that the top mounting bush is too close to the top spring flange. This results in the top spring landing interfering with the IRS cage. When the wheels go up, the shocks rotate outwards and this interference can become quite substantial, so much so that the shocks can actually tear the IRS cage before they eventually break. This picture shows an IRS that was torn in this way. (Click on the"doubl-arrow" bottom right of the pic and then press F11 for a very good view of the picture)
I reported this problem to SNG and got the usual “Never had this before” answer…
Fortunately I have someone locally who built me a set of shocks from Bilstein base units. His first attempt ALSO had this interference issue, but the second attempt was successful.
Hi Philip…what was the condition of the top mount bush and did it have the metal sleeve fitted in it…i have never see a standard set up with Boge shocks that touch the cage, mine definatly dosnt…Steve
How many V12 E’s have you checked Steve? Due to the wider track within the same width cage, I think the spring-damper units are more splayed (due to wider - i.e, longer - wishbones/half-shafts).
Hi Peter…i fitted a set of Boge to a S3…the top definatly did not touch the cage…are you saying that they should…?.if not then something must be wrong with the photo Philip posted…a worn bush or missing sleeve could cause the shock to touch the cage…otherwise every setup with Boge shocks would have the same problem… Steve
Ps…think i did question at the time when this was posted on the UK forum if the correct shocks had been provided by the supplier…havent had a S2 & S3 shock sitting side by side…so maybee the top mount is different
Thanks Philip, know that’s food for thought. It’s always the shock on the driver’s side that breaks, I rarely have a passenger so there’s more weight on that side so if there is any interference it would be greater on that side. it will be easy enough to check for wear on that side once the cage is dropped. I’ll let you know what I find,
The bush looked good and it did have the metal sleeve. The car had done VERY little mileage since they were fitted. I had to bring that sleeve over to the new Bilsteins. On my car the interference was marginal when standing without passengers.
On the car of which I posted the IRS pic, the interference was so bad that it tore the cage. In this case it was not Boge shocks but ones clearly locally made. Problem was the same though.
No need to wait. Simply remove those covers below the rear seats through which the rear brake pads can be changed. (10 minute job) Problem should stare you right in the face. My close up pic was taken through that opening.
Also, whilst you should see evidence by way of marks on both shocks and cage, you most likely won’t see the actual interference because the suspension will be fully dropped and hence shocks rotated inwards max.
Furthermore, the ride height of the car would also affect the degree of interference. If a car stands higher than standard, the interference will also be less. Likewise heavier persons in the car will also increase the amount of interference.
The Boge shock on my car broke during a long trip that started with 3 adults in the car (only for the first 30km) with as much luggage as it could take. I believe it was those first heavily laden 30km’s that weakened the shock to eventually break 2000km later.
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Hi Peter…i fitted a set of Boge to a S3…the top definatly did not touch the cage…are you saying that they should…?.
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Not at all, Steve. I agree with your experience but there is clearly an issue in South Africa!
Yep. This car was immaculately restored in the finest detail.
but there is clearly an issue in South Africa!
Could be. Many of our roads (that we do travel on with this car) are 3rd world compared to 1st world. Our suspensions therefore has to flex much more than a typical 1st world car. Still, there is no excuse for a correctly manufactured shock to break in this way.
Still, once I have my garage back (re-commissioning a friend’s E at present) I do intend doing a suspension LIFT on my car. Even our speed bumps now require an SUV for town driving!
I’ll just patiently wait for Jeff’s feedback to hear what his findings were.
