Fixing bolts - upper & lower arms to subframe

[trikey]

Why not weld on an M12 nut? It will be far stronger than the original captive nut.

[Typhoon190]

These should be OK.

https://www.spaldingfasteners.co.uk/...-high-tensile/

[DMGRS]

I'll see if I can get XPart's restocking date for you

[Ducati750cc]

Originally Posted by trikey

Why not weld on an M12 nut? It will be far stronger than the original captive nut.

It all depends if a captive nut replacement needs welding on the lower arm inner mounts, or the upper arm inner mounts.


With the subframe on the bench, the lower arm nuts are relatively easy to deal with due to reasonable access to the captive nut area, see Blinks photo's on post 1 & 30.


In post 30, photo 4 shows the quite good access to both dress off the captive nut mount and mig or tig weld a new nut on.


However the upper mount captive nut is a different kettle of fish.


If you look at Blinks post 30, photo1, you see the lower mount captive nut access hole looking from the top face of the subframe, from the bottom face there is plenty of access, as in photo 4



There are identical access holes for the upper mount captive nuts, but these are on the lower face of the subframe and that is all the access there is to the nut, the opposite side, the upper face of the subframe is a flat surface with no access to the nut, see Blinks post 31 photo 5.


With careful use of an air chisel, time and a die grinder a reasonable job could be done to ensure all was square so that the bolt would enter the nut easily first time with no danger of cross threading, the length of the bolt and it passing though the bush tube doesn't give much wriggle room.


Seeing as I am not too keen on ' reasonable ' I cut two approx. 80mm x 80mm working holes in the top subframe surface, used the old arm and bolt and did a blobby weld through rust on the captive nut to see what was needed, took it apart, dressed everything up, again used the old bolt and upper arm (or more correctly the bit I cut off) to line everything up, but had shortened the bolt slightly so it just protruded through the nut by 1mm to prevent spatter on the thread.


A good squirt of anti spatter spray all round and welded it up, with the bolt still in, gave the inside of the cavity and the underside of the cut plates a coat of weld through primer and welded it all shut, a quick tickle with a flap disc on the welds, a good dose of Waxoil in all the box sections/cavities, primed and painted, with no sign of anything being done to it, the rest is history.


Yes I could have skipped it and sourced another, but I'm from that old, odd, stubborn, don't give up, tribe of tight......( enter your own Anglo Saxon ), how much !!!, I wonder? I bet I can fix that for nowt folk


Oddly enough, time wise, it was all done, dusted and fitted in far less time than it would have taken me to Google, purchase and get one delivered.



As I've mentioned in previous posts on different threads, I was given the car, so all it owes me to keep another 75 breathing for a few more years, is a bit of time, dedication and whatever I spend on it.


Again, as mentioned on other threads, I'll do a thread on what I've been doing with some, but not enough, photo's.

[alanaslan]

The bolts that are required to attach the upper and lower arms on the rear sub frame are the same both for the top and the bottom. The bolts required are what are called Flanged head bolts they are 90mm long and have a diameter of 12mm. PLEASE NOTE THESE BOLTS NEED TO BE HIGH TENSILE. So that is a total of 8 M12 90mm high tensile flanged bolts. I normally would fit flanged nuts and assemble with blue Locktight thread seal. Due to a recent Amendment sent to MOT testing stations I have to suggest that you use a flanged nylock nut I would still however use thread seal when assembling. Don't worry if there is still some thread inside the fully assembled part this is normal.

[Ducati750cc]

Originally Posted by alanaslan

The bolts that are required to attach the upper and lower arms on the rear sub frame are the same both for the top and the bottom. The bolts required are what are called Flanged head bolts they are 90mm long and have a diameter of 12mm. PLEASE NOTE THESE BOLTS NEED TO BE HIGH TENSILE. So that is a total of 8 M12 90mm high tensile flanged bolts. I normally would fit flanged nuts and assemble with blue Locktight thread seal. Due to a recent Amendment sent to MOT testing stations I have to suggest that you use a flanged nylock nut I would still however use thread seal when assembling. Don't worry if there is still some thread inside the fully assembled part this is normal.

If you look at the photo's on post 30 you will see that to get a nut to sit flush, as it should, with the subframe face, the old flange nut cages would have to be dressed off, simple for the lower arms, not so for the upper arms.

[trikey]

Yes the upper arm captive nut can be a beggar to weld in position, it is doable though and better than the captive nut when done.

At least you know the bolts will come out in future.

[COLVERT]

Originally Posted by alanaslan

The bolts that are required to attach the upper and lower arms on the rear sub frame are the same both for the top and the bottom. The bolts required are what are called Flanged head bolts they are 90mm long and have a diameter of 12mm. PLEASE NOTE THESE BOLTS NEED TO BE HIGH TENSILE. So that is a total of 8 M12 90mm high tensile flanged bolts. I normally would fit flanged nuts and assemble with blue Locktight thread seal. Due to a recent Amendment sent to MOT testing stations I have to suggest that you use a flanged nylock nut I would still however use thread seal when assembling. Don't worry if there is still some thread inside the fully assembled part this is normal.

You say HIGH TENSILE but you don't say what grade.

1/ 8 in number.

2/ M12.

3/ 90mm long.

4/ High tensile grade--?????

[alanaslan]

Originally Posted by Ducati750cc

If you look at the photo's on post 30 you will see that to get a nut to sit flush, as it should, with the subframe face, the old flange nut cages would have to be dressed off, simple for the lower arms, not so for the upper arms.

Totally agree, from my experience I have had three jobs of doing this job twice for my self in the last 14 months and once helping a friend with his. My wife’s failed an upper arm after close inspection, I chose to replace the rear subframe. David’s car though the arms had not failed the rust was very thin and there did not seem to be any metal left. My car is the Monogram Spice Tourer and was scheduled from my original inspection in October 2019 I had noted that the Rear subframe top and bottom arms would need done within the first couple of years. So at the end of March beginning of April this year it got its new subframe, upper and lower arms done along with brake back plates, callipers, pipes, hoses, cables, the only unexpected problem I hit on the spice was wear on the three bushes on the trailing arms. Pressing them out was not fun but my 10 tonne press did the job. That threw up a whole new set of problems with castor, camber, and rake angles. But that is a whole other story.
The thing I found that it was three New subframes from different sources bought over a four year period. None of the subframes appeared to have been made by the same manufacturer. Yet all three had the most difficult nuts already welded in place.
Perhaps it is me just being an oldie but on all bolts that I feel may have angle locating problems and have a probability of locating cross threaded. I always make them chamfered whither on the lathe or with an external cone cutter. Then redress the threads on the bolt and the nut with a suitable tap and die nut.
So from the last three units I have fitted there has been no need to weld nuts.
Welding of nuts can cause changes to the properties of hardness and tempering of the nut caused by the temperature change the nut goes through whilst welding it. If the nut gets very hot and then cools down it will become soft, the result of this is the nut will strip before the bolt reaches the required torque.
Just a thought to remember.
I have to say that due to health and age this is not a job I will be doing again in my lifetime. I will check the bushes on my wife’s saloon, though as it just turned 100k last month, I am hoping that this job will not be needing done to it.
My Thanks to Scott at DGMRS despite me foolishly starting the job on the days before a long holiday weekend, he managed to get me all the bits that I was not expecting delivered in a timely manor.
Each trailing arm has three bushes in it. I have always had bother locating one of them. Scott did a wonderful job supplying all three for each side, the ones I usually have difficulty with he had sourced from America, the quality of these bushes far exceeded the quality of the bushes I have bought in the past. I can’t thank Scott enough for his help in sourcing and supplying parts for me with this one.
A word of warning to everyone. Tackling big jobs like this no matter how well prepared you think you are there is always something you forget or don’t expect. I pride myself in making a list of every part I might need and making sure that I have it in stock before starting the job. In the case of the spice tourers rear refurb I even had the brake hose clips. But confess to not having expected to having to do the trailing arms or the rear drop links and the rear anti roll bar bush carriers. I have now learned for the next time and will make sure all of these parts are on the shelf, just in case. As I have said it won’t be me doing the work but I will put the items on my stock sheets, that way I will be able to help out the next poor bloke who asks for help. Always better to have and not need than to need and be unable to get.
Alan



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[alanaslan]

Brian I would love to talk at length about the Fasteners used on the rear subframe top and bottom arms. I am an old mechanical engineer long retired and in my previous life I used to be an aero engineer on both fixed wing and rotary wing aircraft. at Aero level I was educated to Bsc level and at mechanical to PHD level.
I am trying to get my head around the statements here on Yield strength ( the point at which an item starts to deform) Tensile strength ( the point at which the material will fracture) the above definitions are the Best way to describe in lay terms what each is.
With regard to the top and bottom rear suspension arms surely the weak point in the structure would be the subframe itself and not the securing bolt.

Structural steel has a yield strength of 250MPa with a tensile strength of 400MPa . where an 8.8 stamped bolt with a diameter of less than 16mm has a yield strength of 640MPa and a tensile strength of 800MPa ( assuming that it is a medium carbon steel and has been Quenched and tempered ) from these figures I would have said the weak point is the steel frame and not the bolts that would be the weak point.
Alan