Sierra trailing arm mounting bolts catching on the road

[James Agg]

Hello everyone. Apologies, I’m sure this subject has been posted about hundreds of times before, but I can’t seem to find a thread and so I’m asking the question again…

 

My RH S7 Mk2 is running the standard Sierra rear subframe/suspension where the springs are sandwiched between the lower wishbones and the underside of the stainless tub. The shocks are then independent of the springs and mount to the sidewalls of the tub. The issue I’m getting is constant scraping of the bolts that mount the trailing arm of the subframe to the tub right behind/underneath where driver and passenger sit on each side. Me being heavier than my wife it’s my side that seems to catch the most. On the front I have protech inboard coilovers at 120lbs and am thinking that it might be a plan to try lifting the front end to get around this scraping problem - it might help a little in the short term, but in the long term, I’m very much wanting to go down the route of converting to adjustable coilovers on the rear in place of where the current shocks are and ditching the roped springs that are there currently. Does anyone have some detailed photos of how they reinforced the top mounting points on the bathtub? Mine are only just good enough in my view for the shocks alone (although I can see where the tub has slightly distorted on one side presumably because the mounting point isn’t strong enough…) With coilovers it will definitely need reinforcement. Also, what were the dimensions of any reinforcement plates/angle irons used? I will see if I can post a picture of what my mounting points are like currently.

 

Also, poundage and dimensions of coilovers on the Mk2? I have a feeling I’ve seen 180lbs for the rear suggested somewhere? Or maybe I’m misremembering that as what the front used to be? Is Dave at Dampertech likely to go back as far as the Mk2 in his knowledge?

Edited June 14, 2023 by James Agg

[James Agg]

Ok, a couple of interesting finds having gone out to snap these pics…

 

1) Driver’s side wheel arch clearance is about a finger width’s worth tighter… Having examined my photos, I just noticed that the shock on the driver’s side doesn’t have some sort of spacer at the mounting point that the passenger side does have… odd! That may have something to do with it all…

 

2) I’ve noticed having looked around the car properly at ground level, it is looking a touch nose down at the moment. I did the front coilovers about 3 years ago now and I wonder if they’ve generally compacted slightly and need a slight lift to get the car back to a more level position. Will play with this tomorrow… 

 

I’m still interested in a coilover conversion for the rear though!

Edited June 15, 2023 by James Agg

[IanS]

If  you are still running the sierra springs then a lot of builders had this problem and simply inserted a square of inch thick ply between the top of the spring and the bottom of the tub.

Otherwise spring assisters might help. https://www.ebay.co.uk/itm/353620461910?chn=ps&var=622939135134&_trkparms=ispr%3D1&amdata=enc%3A160PHCej5T7WuyFHTDh_tDA34&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=622939135134_353620461910&targetid=1816181028179&device=c&mktype=pla&googleloc=9046508&poi=&campaignid=19090194174&mkgroupid=147009364227&rlsatarget=pla-1816181028179&abcId=9303860&merchantid=7216794&gclid=Cj0KCQjw7aqkBhDPARIsAKGa0oJgIvBcJyxFI9WqVflgTK7RQ-vKOcBzeSvbJ-KXtHVtpMXIAXTijIIaAlyrEALw_wcB

This could make the suspension too firm at the back.

[James Agg]

Thanks Ian, good thoughts. The Ply sounds a bit ominous but I can see how that would help. I am also slightly puzzled by the spacer hat on the top of one shock but not on the other. It explains why one wheel arch has less clearance than the other given that the hat side is the one with more clearance. Makes me want to go to coilovers even more… The spring assisters look interesting - I knew not of the existence of such a thing. It is possible that the springs on there are knocking on and have compacted somewhat too.

 

Today I raised the ride height at the front and re-tracked accordingly and not only is the steering feeling generally better, it would also appear on an initial test drive that the car isn’t scraping now in places on my test route  where I’d normally expect it to. That’s not to say that it won’t ever scrape again on a particularly big pit in the road or errant speed hump as that trailing arm mount is a real nuisance of an appendage and is bound to find something again at some point. I ought really to replace the bolts/nuts given the amount of road grinding they’ve done

 

 

[Sparepart]

You have fixed it, and I am still puzzling about what was scraping what ?, was something coming into contact with the road ? I am just curious.

[James Agg]

1 hour ago, Sparepart said:

You have fixed it, and I am still puzzling about what was scraping what ?, was something coming into contact with the road ? I am just curious.

The nut on the underside of where the Sierra rear subframe mounts to the underside of the bathtub right behind where driver sits and same on passenger side. I think I’ve fixed it. Ride height was too low at the front, but I reckon I will still find the odd speed hump with that nut even with the front ride height lifted

[Foz]

I don't know if this helps or confuses but ..................

On the 2B you could remove the rubber "donut" from the front mount, turn the cup thing the other way up and gain 20-30mm more ground clearance on the bolt head. 

I used to replace the bolts 2 or 3 times a year before I did this mod. afterwards it never grounded again.

Like a say, that was on my 2B so I'm not sure if it's possible on yours.

Steve

[James Agg]

Good thought! That might work. I saw a picture of how the mounting is done on the 2B the other day and I think with the reinforcement plate on my bathtub, it’s much the same principle. I will investigate…

[Sparepart]

Just FYI, the Exmo build instructions used the same mounting hole and bush as used on the Sierra, the one that has a the bolt head that is scraping, as on your car. This means that the subframe is not rigidly fixed to the bodyshell, there can be some movement via the rubber in the bush, probably good for absorbing vibrations etc. Not long after I had mounted the subframe as per these instructions I received a build update from RHE telling me that some cars had failed SVA due to this small possible movement and safety concerns about bush failure leading to the subframe coming adrift. The new instruction was to bolt the subframe directly to the big steel plates using M12 high tensile bolts, on on each side. This involved opening a hole in the lower part of the subframe large enough to get a socket wrench head to the underside of the subframe plate through which the bolt protruded. The message to use a really tight nylock nut here and check it pre MOT every year was repeated several times. Consequently the bolt through the original Sierra bush became redundant.