Rear Subframe Mounting

[sylvia.fry2]

Hi all, I'm considering mounting my (Ford's) rear sub-frame on the rubber bushes to chassis & diff rubber mount to chassis--so-as to give a smoother less noisey ride & also hopefully avoid the bracket fracture problems as mentioned in the last club mag. I intend to use the Ford Sierra plates & additional metal-work to anchor the inner tube to the chassis plus remove & rebuild the chassis diff mount to accept the rubber diff mount----comments please. Regards Bob & Mo

[Longboarder]

Seems like a good idea. However the hood is a pretty basic drive with lots of noise and vibration regardless. You won't notice the difference. Some owners have removed the rubber mounts and have solid mounted the rear subframe to minimise compliance leading to unwanted suspension movement in the hope of improving the rear suspension.

 

There is also a possible issue at SVA. If the subframe is rubber mounted it is regarded as moving and you can't bridge from chassis to subframe with solid fuel or brake lines. Assumed potential fatigue failures.

 

Nigel

[Guest timswait]

Personally I wouldn't. A fair bit of welding required to fit that big rubber block on the back of the diff to the chassis. A Robin Hood is never going to be a refined ride anyway, and the extra compliance would compromise the handling. Remember everything on the Hood is stiffer than on the Sierra, so the compliance in those rubber mountings will make a greater proportion of the total suspension movement than they did on the Sierra. I'm pleased with my brackets, and reckon they're the way to go

Incidentally, picky SVA examiners have been known to fail cars for having solid brake pipes from the chassis to the subframe even when it is solidly mounted, daft really.

[sylvia.fry2]

Hi all; thanks to timswait & longboarder; my reasoning was to cancel-out the vibration which is probably the main cause of the standard chassis bracket failure --do you consider the failure to be down to a weak bracket that will fail in time even with the removal of vibration? Same rubber carrying half the load should be less compliant -- is this over-simplifying the action? I'm good at bicycle & lawn-mower engineering but your site suggests better !! I intend mounting the diff rubber upside-down--new bracket then very easy & short, if too soft --add stiffening cones -- as per mini engine top mounts which we used to good effect 40+ years ago. Yes I'm that old & silly & a fool & --what was the ? Regards Bob & Mo

[Guest chris brown]

I wouldn’t either in fact if I was to build again I would do away completely with the rubber mounts and there mountings on the tube and weld on steel plates that can be bolted directly to the chassis so as to give that bit more ground clearance and at the same time give a more positive fixing without having to do Richards trick of drilling another hole to bolt it down solid. I do think it does have to be bolted solid after all it is a sports car not a car built with noise (or lack of) in mind and the front end is for steering not the back.

 

As far as I am aware there has only been one mount failure. I have well over 20k not so gentle miles on mine with no problems as yet.

[Dave R]

having followed chris i can vouch that at least some of them have definitly not been gentle

 

i did away with the bushes on mine, and if i did it again i would weld the plates to the rear beam, instead of my original method

[Guest vacinc]

having followed chris i can vouch that at least some of them have definitly not been gentle

 

i did away with the bushes on mine, and if i did it again i would weld the plates to the rear beam, instead of my original method

i did the same solid mount bolted to the rear frame, and then welded, no differance at all in the way it feels are drives

[Guest timswait]

As far as I am aware there has only been one mount failure.

I know of two (three if you count Andy's which failed on both sides at different times!). They were both stainless chassis. The main reason I did the reinforcement wasn't for fear of it cracking, but to reduce the compliance and sharpen up the handling. I noticed an (albeit small) improvement in handling by going from the robin hood method of 'solid' mounting to fitting my reinforcement brackets. I assume it would have been even worse if it was mounted on rubbers.

I doubt that vibration has very much to do with the fatigue, I think it's more due to bump and cornering loads, and the occasional wallop when it grounds out, so I can't see the rubber mounts having too much effect on the cracking either way.

Same rubber carrying half the load should be less compliant

Actually, that is a good point. However the power applied through the wheels is the same (or more), the braking force is the same, stiffer suspension loads them more heavily over bumps, and you're likely to be generating higher cornering g's, so the rubber will be carrying far more than half it's original loads, possibly as much or more than the Sierra, and with shorter travel suspension and everything else that much tighter and sharper, you'll notice it more.

I'd definitely recomend mounting as rigidly as possible. Chassis stiffness is only as good as the softest part, there's no point in having a stiff chassis if the loads are being applied via compliant mountings.

[Grim]

the other guy i know of had a mild steel chassis....

[philshelton]

has any one got any pics of how sub frame can be solid mounted and get rid of the large alloy cones that alway bottom out on speed humps

[Guest elwe]

The stanless plate goes very brittle round the welds. I cut most of the welds round the plate the peddle box should mount on leaving a 40mm length of weld. I then tried to fatigue the weld but the first time I grabbed hold of the plate and pulled it fractured next to the weld and the plate came off. That was with just one hand.

[Guest pmk159]

Sorry if I am high-jacking the thread, I have a 2B DOHC kit and I am just going to start fitting the rear subframe.

 

The video seams to show it only fitted by two bolts holding the trailing arm the the subframe, one either side, and two bolts into the diff.

 

Is this correct ? If so which bolts are failing ? Where are these cones that are mensioned ? Where are the extra holes required ?

 

Thanks,

 

Paul

[Guest timswait]

Paul. Not sure if your chassis is different to mine, but you normally have the four bolts you mention, plus another pair which bolt through the subframe next to the rubber doughnuts, plus the bolts through the rubber doughnuts too, mostly just for luck as they shouldn't really bear much load with the more solid mountings next to them. On the video Tricky shows you using some great big cups from the front suspension to put over the doughnuts (I think the cones Phil talks about). These are very low and grind away quickly. Even if you don't use the cups and use flat washers instead you will still tend to grind the bolt heads off over time. The fatigue cracks (if they happen) tend to appear in the 3mm plate that the rubber doughnuts mount on, next to the weld.

For a more solid mounting you can fit the brackets I wrote about in the last mag. They don't do away with the cones (replace them with flat washers anyway, that gives you an extra inch or two clearance), but do make them pretty much redundant.

[Guest pmk159]

Paul. Not sure if your chassis is different to mine, but you normally have the four bolts you mention, plus another pair which bolt through the subframe next to the rubber doughnuts, plus the bolts through the rubber doughnuts too, mostly just for luck as they shouldn't really bear much load with the more solid mountings next to them. On the video Tricky shows you using some great big cups from the front suspension to put over the doughnuts (I think the cones Phil talks about). These are very low and grind away quickly. Even if you don't use the cups and use flat washers instead you will still tend to grind the bolt heads off over time. The fatigue cracks (if they happen) tend to appear in the 3mm plate that the rubber doughnuts mount on, next to the weld.

For a more solid mounting you can fit the brackets I wrote about in the last mag. They don't do away with the cones (replace them with flat washers anyway, that gives you an extra inch or two clearance), but do make them pretty much redundant.

 

The rubber mountings you talk about are cut off so there is no fixture there. Thats is one of the first things that we are told to do in the video. Hope I do not need to put them back on again!!!

 

So it looks like I now only have three or four bolts holding the whole thing on!! It but worrying.

[Guest timswait]

Can you put up some photos? It does sound quite different to mine (which is a 2001 Pinto 2B).