Fitting 3/8" rear hub studs.

[Davenott]

I've just fitted updated rear hub studs, and thought I'd post this in case it helps anyone.
My car was fitted with the original 5/16 UNF studs, and when I checked these the nearside had 2 studs which were firm into the alloy trailing arm, and 4 which wiggled round when held with fingers and these had poor or stripped threads in the alloy. The offside all 6 studs were firm, but this was partly because whoever had powder coated the trailing arm, hadn't removed the studs first!

The up rated studs are 3/8" UNC into the aluminium trailing arm and the original 5/16" into the hub and back plate. The 3/8" part as well as having the coarse thread instead of fine, are also wider and longer; this requires a wider hole drilling in the aluminium arm but also deeper, and as there isn't a huge amount of metal here, be careful not to over drill in depth (I found I could go 2.5mm deeper, but check you don't over drill any holes) I used a 5/16" drill bit and made sure I drilled each hole parallel.
When cutting the threads, I would recommend using high quality taps, as you want the best thread you can make, also make sure you use a 3 piece set, as you need a good thread to the base of the hole. Also I used cutting oil and took my time to cut the threads slowly and carefully removing shavings regularly.

Other options instead of fitting these up rated studs, would be to heliocoil and use original size studs, but this requires a wider hole to be drilled than when fitting up rated studs, or if original aluminium thread good you could consider thread lock.

Dave

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[jleyton]

All good stuff Dave, well done.

It would also seem a good opportunity to remind everyone that the torque fitting for the nuts is VERY LOW at just 16 lb ft. I am convinced that virtually all problems in this area are due to overtightening.

Cheers

Julian

[milothedog]

I've just fitted updated rear hub studs, and thought I'd post this in case it helps anyone.
My car was fitted with the original 5/16 UNF studs, and when I checked these the nearside had 2 studs which were firm into the alloy trailing arm, and 4 which wiggled round when held with fingers and these had poor or stripped threads in the alloy. The offside all 6 studs were firm, but this was partly because whoever had powder coated the trailing arm, hadn't removed the studs first!

The up rated studs are 3/8" UNC into the aluminium trailing arm and the original 5/16" into the hub and back plate. The 3/8" part as well as having the coarse thread instead of fine, are also wider and longer; this requires a wider hole drilling in the aluminium arm but also deeper, and as there isn't a huge amount of metal here, be careful not to over drill in depth (I found I could go 2.5mm deeper, but check you don't over drill any holes) I used a 5/16" drill bit and made sure I drilled each hole parallel.
When cutting the threads, I would recommend using high quality taps, as you want the best thread you can make, also make sure you use a 3 piece set, as you need a good thread to the base of the hole. Also I used cutting oil and took my time to cut the threads slowly and carefully removing shavings regularly.

Other options instead of fitting these up rated studs, would be to heliocoil and use original size studs, but this requires a wider hole to be drilled than when fitting up rated studs, or if original aluminium thread good you could consider thread lock.

Dave

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Been splashing out on posh drive shafts Dave

[Staggard]

Been splashing out on posh drive shafts Dave

There's definitely money in that ole dentistry BTW where did the studs come from?? I hope your gonna wash your hands before the next filling job comes up

[Davenott]

Studs were from same place I bought drive shafts from; Classic Driving Development. They had an offer on the driveshafts/hubs and studs at Stoneleigh last year. They were about £100 a side dearer this year, so glad I bought them in advance.
I was going to do Nissan driveshafts, but the only place that had the donor shafts available seemed to be the Australian scrap yards!

[Motorsport Micky]

Well done Dave, I'm doing exactly the same operation in about 2 weeks with the CCD Driveshafts (CV type) and these 3/8th UNC bigger studs for the trailing arms with the reduced shank 5/16thUNF hub ends to remain standard.
I hope you used a jig to ensure the tapping of the holes were completely square in both planes, the hubs have only a small clearance on the 5/16th studs, I'm just making mine now.

I got my driveshafts direct from CCD at Stoneleigh and a set of their uprated studs also, did the swap go as straightforward as the instruction sheet from CCD suggest ?

Micky

[Davenott]

Well done Dave, I'm doing exactly the same operation in about 2 weeks with the CCD Driveshafts (CV type) and these 3/8th UNC bigger studs for the trailing arms with the reduced shank 5/16thUNF hub ends to remain standard.
I hope you used a jig to ensure the tapping of the holes were completely square in both planes, the hubs have only a small clearance on the 5/16th studs, I'm just making mine now.

I got my driveshafts direct from CCD at Stoneleigh and a set of their uprated studs also, did the swap go as straightforward as the instruction sheet from CCD suggest ?

Micky

Thanks Micky.
I agree on the recommendation for a jig, but must admit that I did it freehand, but I am used to precision drilling. My studs lined up nicely with the new hubs, but there isn't much room for error!
The hubs and driveshafts went in fine, which is just as we'll as I had mislaid my instructions!
I wasn't too impressed to find my existing hubs to be held on by 2 nuts each side rather than 6! I was redoing the rear suspension anyway as my rear steel trailing arms had been put on upside down.
Dave.

[Motorsport Micky]

"I wasn't too impressed to find my existing hubs to be held on by 2 nuts each side rather than 6!"

Ooppps...good one to find in the garage rather than at the side of the road when you're searching for your lost wheel and hub !

Uuuhhh "rear steel trailing arms " is that right ?

Micky

[jleyton]

I think he's referring to the box section arms - not sure of their proper name !

[Davenott]

It was the studs (the ones I replaced) that had 4 missing nuts each side. I guess the car was put together as a rolling shell in a hurry, but how long does it take to put another 8 nuts on!
Dave.

[new to this]

looks a good mod,when you look at pictures 3 - 4 did you have to have ali welded in, corners are bigger,can you buy just the studs

dave

[Motorsport Micky]

The trailing arms have had small blocks of ali added onto the forging of the hub diameters when forged to ensure when the hub studs were drilled there was sufficient wall thickness. Unfortunately it was done by a drunk 1st year apprentice ! and the results are variable to say the least with some of the studs entering the blocks way off centre.

I have seen a few trailing arms which have been reconditioned by helicoil where because of the haphazard supporting block placement the thread breaks through the wall ! Counter intuitively a 5/16th UNC helicoil needs a .328 thou tapping drill (because you have an inner and an outer thread to accommodate) and a BIGGER 3/8th UNC parent thread stud without helicoil only needs a .312 thou tapping drill, some 16 thou on dia smaller. Helpfully a stripped 5/16th UNF stud hole is .312 thou and so only needs the merest application of a drill to clear the hole out.
If you observe the hybrid 3/8th UNC x 5/16th UNF studs in Daves grubby paw against the original studs alongside it it's quite clear the superior grip afforded by the 3/8th UNC thread against the wussey 5/16th UNF standard thread. Julian is correct that mistorqing these studs higher than the required 16 lb ft helps strip them. But the main reason for the stud stripping is because the wrong thread was chosen for the aluminium by the design engineers (you know, the same ones that designed the engine cooling system by watching tea leaves circulate around it ...ha) the UNF profile is fine in steel but doesn't have enough thread form to prevent the clamping motion down the shank eventually stressing and shearing the softer alloy casting.
These studs are also available from CCD

http://classicdrivingdevelopment.co.uk/gallery.asp

and as long as you make sure the holes are drilled (easy) square in two planes, but more importantly and with more difficulty tapped with a 3/8th UNC taps square in both planes the hubs will be affixed never again to part from the trailing arm. The 16 lbs ft torqueing is wussey but because it's on 6 points and also because the stress on the studs is a shear force directly across them it's ample and they don't offer to pull out.

Micky