Technical Rear subframe (I think) - again!

[Brian Partridge]

Had a loud thumping sound from offside rear when hitting potholes. Took to Kwikfix for diagnosis to be told "Car unusually springy at back", "It could be shock absorbers", "It could be rear springs" or even wheel bearings (even I knew it couldn't be this).
So devised a cunning plan of putting blutack on the bottom bump stops both sides to see if suspension was bottoming out. It wasn't.
Reverting to The Forum I realized that most probable cause was sub-frame bushes (considered trailing arm bushes but wheels vertical).
Now I've considered many options from new bushes, to welly boot rubber cure on Forum to tyre rubber buffer 'cure' on u tube.
On the forum attitudes towards this problem seem to range from it being a mild nuisance to an impending catastrophe.
So my question is this.
The vehicle was planned to do a 1400 mile round trip with three passengers. snowboards and various equipment and provisions.
What is the worst case scenario?

With my thanks in advance to those willing to contribute.

 

[JamesAtthews]

Hi

To help to answer your question, I have replaced the front sub frame bushes with the ones for the Bravo, FirstLine part FSM2026 IIRC, which stopped the knocking from pot holes etc. I replaced these on both sides of the car, which made a massive difference to the ride, however I had to fit these with washers between the bushing and the bolt head, as they are thinner than the originals, but were available when I needed them. To remedy this, I cut 4 rubber donuts, from 6mm rubber sheet that I bought on ebay. I cut them to the shape of the bushing, and clouted a length of 15mm copper pipe through the middle to make the bolt hole. This gives a noticeably quieter ride than the replacement bush alone, but also remove the stack of washers that I originally had to fit. All I do now is check the bolts periodically, to take up any slack as the rubber squashes out through use.(for reference, a 1/8th of a turn every 6 months!)

With hindsight, I would have preferred to fit the bushes that you can now buy for the car, but they weren't an option at the time.

I also had to grind the bush's outer layer to fit the sub frame, but with the bush mounted in the drill on a length of all thread, and the grinder running on a bench, I was soon able to "machine" them to fit. To ensure that they fitted securely, I bedded them in with the metal araldite to be sure. They haven't moved at all since fitting.

At worst case, the clattering would get really loud/ annoying, but the subframe would never drop out through the bolt, as there is a big washer on below the head which is slightly larger than the hole in the subframe. It's a job that needs doing, but I wouldn't bust a gut to resolve it before your trip. Another option is to get a rubber donut, as per Youtube, but use it as a temporary fix rather than permanent fix.

As an aside, my car has since passed 2 MOT's with no advisorys regarding the bush and rubber spacer arrangement.

HTH

James

 

[Brian Partridge]

Thanks James,
I'm attermpting to do a temporary fix as you suggest but having a real problem undoing the 18mm nut that holds the bush!
It's an 03 plate with 106k so I doubt if it has been off before.
Thanks again for your advice.

 

[BikeDoc]

If you jack the car up at the rear, jacking on the chassis, not on the subframe or trailing arms, then look at the four bushes.
You'll see a gap between the subframe and the upper flange of any bush that is loose in the subframe.
Lever lightly with a large screwdriver (between the top of the subframe and underside of each bush's upper flange) to make sure they're all tight in their bores.

Edit; The rubber doughnut/washer fix (between the top of the subframe (and/or bush) and the chassis) won't cure the knocking if a bush is loose in the subframe.

One of the Vauxhall bushes I used at the front of mine came loose a few months ago, and was knocking as described.
Due to the layout/geometry of the rear suspension, there can be a downwards loading on the front of the subframe (and so on the front bushes) at various times (braking, hitting bumps/dips), so if the bushes aren't tight enough in the subframe, they can 'chatter'.

I fixed mine temporarily by making three spacers to fit between the subframe and the large 'cup' washer at the bottom of the bush, so the bush is held down tightly into the subframe.
No more knocking

 

[BikeDoc]

Thanks James,
I'm attermpting to do a temporary fix as you suggest but having a real problem undoing the 18mm nut that holds the bush!
It's an 03 plate with 106k so I doubt if it has been off before.
Thanks again for your advice.

Very likely that the bolt is corroded into the captive nut in the chassis.
You need to get some penetrating oil onto it, either through an existing access hole, or by drilling a small one yourself (<4mm) in the side of the chassis beam.
Drill approx 20mm up from the lower edge (of the beam), and in-line with the bolt.
you can then squirt the oil directly onto the end of the bolt threads and nut.
Give it a good dousing, a day or two beforehand if you have the time, and let it soak.
You really don't want to break the nut away from the chassis, or strip the threads
The small hole can be plugged afterwards with sealant/underseal.

You'll also want a well-fitting hex (six-sided, not bi-hex) socket (1/2" drive) and a long 'breaker' bar.
Put a block of wood on the 'knuckle' of the bar, and put a bit of upwards load onto it with a jack, the socket is less likely to slip off the bolt head, and you can put all your effort into turning it.

Good luck

 

[Brian Partridge]

Hi BikeDoc,
Many thanks for taking the time and trouble to reply.
There is certainly a gap between the flange abutting the chassis and the top of the subframe. I've levered as you suggested and can move the bush downwards somewhat but am not sure how this relates to therm being tight in their bores>
Also you mention your temporary 'three spacers' fix. I take it that having removed the bolt the spacers are placed immediately above the very bottom cup washer so making a tighter fit?
Sorry to be so mechanically thick.
Regards,
Multplicity (I accidentally left an 'i' out of my title!)

 

[BikeDoc]

The gap between the bush's top flange and the subframe, I take it that's only when it's jacked?
If there's a gap even with the car not jacked, then take a short (6" or so) piece of wood (2"x2" is ideal), and jack the subframe up near to the bush, using the wood on top of the jack-pad as a 'pusher'.

Levering down on the bush flange with the bolt still in place, you're just flexing the rubber interior section of the bush, that's normal, as long as it's not really loose, which would indicate the rubber has sheared, or broken down considerably.

I cut a length of thick Steel tube, approx 3" long (basically the same length as the distance between the 'cup' washer and the underside of the subframe), and with a wall thickness of around 3mm, then cut it lengthways into three sections.
I stood these upright on the cup washer, spaced evenly around the bush, with the inside faces against the bush body, held them in position with a cable-tie, then clamped them tight with the bolt/washer.

This should explain more fully...

This may be of interest too...

 

[Brian Partridge]

Wow,
Thanks for the explanation and the graphics.
I'll test as you suggest tomorrow.
I'm not sure I have the mechanical competence to produce your spacer solution but admire the ingenuity.
I'm beginning to believe that, though this must not be ignored indefinitely, it does not pose an immediate safety risk or imminent catastrophic failure?
My regards,
Multplicity

 

[lancia8888]

The sub frame bushes are available from a company in Dewsbury called a2z.
The are not cheap at £90 front and £60 rear the larger ones… I sweated mine in by heating up the subframe with an oxcy torch. And used a press to get them seated down. Its a big job but do-able if you have access to the correct equipment. There's no need to bodge them in anyway,the parts are oem bushes fully stamped with fiat/lancia markings. Widemouthfrog did a great write up with photo's… hope this helps