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Not very happy - wife even less so!


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Hello all.

 

As I've mentioned before, my TR was restored by the PO to a very high standard in general by farming out most of the work to 'professional tradesmen'. There were some issues however which I was made well aware of prior to purchasing the car, but the latest revelation is a bit scary.

 

I'd decided some time back to upgrade the brakes by fitting new discs and Mintex 1144 pads to the front, larger Morgan wheel cylinders to the rear, braided stainless hoses all round and DOT 5 silicon fluid. The latter may not be considered an 'úpgrade' by many, but after having repaired th extensively damaged paintwork below the master cylinder I came to the conclusion that the DOT 5 is the lesser issue for me. At that time I converted the clutch to DOT 5, with parts procurred for the brakes after that with conversion to follow in the winter.

 

I'm now in the process of stripping everything to clean out the old fluid and change components. One of the other of the upgrades I planned to do (if required) was to repair the handbrake lever pivot damage in the rear backing plates (as recommended by Stan and Stuart). As you can see from the photos this does need doing and I'll probably build it up with weld and grind back in place.

 

However, shock, horror, I've noticed that the LH hub housing is secured with only four of the six nuts and two of the studs are missing altogether - Aaaaahhhhh

 

The RH side has the six fasteners. Some advice on how to proceed from here would be much appreciated.....

 

post-14246-0-22781400-1522629071_thumb.jpgpost-14246-0-84054800-1522629083_thumb.jpgpost-14246-0-61913700-1522629094_thumb.jpg

 

Regards

Gavin

Edited by KiwiTR6
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The studs are totally missing - not sheared off below the flange?

 

Gone completely. Suspect the threads in the trailing arm are stripped and someone has taken a shortcut...

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I recently upgraded the studs from the standard 5/16unf to 3/8unc with a kit from CDD

 

The kit price includes rental of kigs and taps that makes the job a doddle.

 

Highly recommended.

 

Steve

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As posted above the hub retaining holes in the trailing arm are prone to stripping after 40+ years.

 

Be careful drilling or tapping these holes in the trailing arm, these need to be at 90 deg in both axis, the clearance in the hub for the studs is tight (only some thou clearance on each stud). Because of their parallel axis with the other studs any "lean" on the stud swill prevent the hub fitting over the studs, which then tempts owners into drilling the hub holes out larger (not recommended).

 

Using the search box will give many threads, this is just one of them.

 

http://www.tr-register.co.uk/forums/index.php?/topic/49527-trailing-arm-stud-alignment-jig/?hl=%2Bhubs+%2Bstuds&do=findComment&comment=400104

 

Mick Richards

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Hi Gavin,

not the end of the world :o

 

Firstly remove the hub

Then screw in a 5/16"UNC (course UNF fine thread) bolt to see if it can hold reasonably tight - it is only 16 lb.ft of torque.

If it does then simply replace with decent studs.

 

If the thread has gone then consider 5/16"UNC UNF helicoil - this is the simplest first step - as if you cock up you have another chance later on. (3/8"UNC)

As Mick states it MUST be square to the plane of the hub face. Ideally a jig that holds the drill/tap.

I made one from 1/4" ali alloy plate that 6 x 5/16" holes on the PDC with one hole bigger to take the drill/tap guides. see my pics.

 

 

Roger

 

post-4113-0-48159700-1522657922_thumb.jpg

Edited by RogerH
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Get the Classic Driving developments (CDD) as mentioned above, comes with the loan of a jig, drill and two reamers (starting and full depth)

 

Probably takes 15 to 20 minutes per side to replace all studs with larger ones. Just be aware of the low torque setting on the bolts. Perhaps you might wish to seal the studs in with purple Loctite to reduce corrosion.

 

No connection just a happy customer.

 

Alan

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Hi Gavin,

not the end of the world :o

 

Firstly remove the hub

Then screw in a 5/16"UNC (course thread) bolt to see if it can hold reasonably tight - it is only 16 lb.Inches of torque.

If it does then simply replace with decent studs.

 

If the thread has gone then consider 5/16"UNC helicoil - this is the simplest first step - as if you cock up you have another chance later on. (3/8"UNC)

As Mick states it MUST be square to the plane of the hub face. Ideally a jig that holds the drill/tap.

I made one from 1/4" ali alloy plate that 6 x 5/16" holes on the PDC with one hole bigger to take the drill/tap guides. see my pics.

 

 

Roger

 

attachicon.gifP1030513aa.jpg

Hi Roger.

 

If the thread in the trailing arms are ok he'd be unable to screw in a 5/16th UNC cos it's 5/16th UNF the fine thread, that's partly why the threads strip, they are too feeble in the alloy at the thread root.

 

Mick Richards

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Hi Roger.

 

If the thread in the trailing arms are ok he'd be unable to screw in a 5/16th UNC cos it's 5/16th UNF the fine thread, that's partly why the threads strip, they are too feeble in the alloy at the thread root.

 

Mick Richards

Hi Mick,

quite so - I was having one of my moments :o

 

I have been thinking about this odd engineering conundrum.

If using UNF is so much of a no no why did ST do it. Not just the 4A but the 5, 6, Stag 2500 .........

 

And I think I have the answer B):blink:

 

Clearly the material spec and the forces applied through normal driving are happy with each other - they have ;asted a very ong time.

The torque loading is very low and nyloc nuts are in there to stay put - but only the nut. The nut doesn't necessarily hold the stud in place.

 

So why not UNC?

The UNF (24tpi) stud has 33% more thread in the hole than the UNC (18tpi) So the slope of the thread is much shallower in the UNF

Any vibration would have more effect on the UNC thread than the UNF

 

So, as the torque loading is low and the nyloc nut is only keeping it self in place on the stud it may be the shallow thread angle that keeps it in place.

 

Indeed the UNC may have a deeper thread that will have more thread in contact with its neighbour but the thread angle srea the important part

Roger

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"The UNF (24tpi) stud has 33% more thread in the hole than the UNC (18tpi)"

 

Yeah...I regard this as an analogy of chips...or French Fries !

 

Just as a thicker French Fry (UNC) has less surface area and carries less fat than the smaller French Fries (UNF) with larger surface area and more fat carried, the larger surface area of the UNF French Fry imposes larger loads upon the lessor material content inside the hole (more surface area = more space between threads) and smaller thread root material to withstand it...or maybe I'm just hungry ?

 

Mick Richards

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:lol: (I'm reaching the Mosquito' book end)

Edited by Chris59
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Hi Mick,

quite so - I was having one of my moments :o

 

I have been thinking about this odd engineering conundrum.

If using UNF is so much of a no no why did ST do it. Not just the 4A but the 5, 6, Stag 2500 .........

 

And I think I have the answer B):blink:

 

Clearly the material spec and the forces applied through normal driving are happy with each other - they have ;asted a very ong time.

The torque loading is very low and nyloc nuts are in there to stay put - but only the nut. The nut doesn't necessarily hold the stud in place.

 

So why not UNC?

The UNF (24tpi) stud has 33% more thread in the hole than the UNC (18tpi) So the slope of the thread is much shallower in the UNF

Any vibration would have more effect on the UNC thread than the UNF

 

So, as the torque loading is low and the nyloc nut is only keeping it self in place on the stud it may be the shallow thread angle that keeps it in place.

 

Indeed the UNC may have a deeper thread that will have more thread in contact with its neighbour but the thread angle srea the important part

Roger

Hi Roger! The normal engineering practice here in the UK is to have course threads in soft materials. A UNC thread will be thicker in section at its root than UNF, this increases the shear strength of the flank considerably and has a slower helix angle. When the UK went over to ISO metric threads this was the downer on them as many people said that they were too fine for soft materials! For this application I would always use UNC. Lastly they should always be Loctited.

 

Bruce.

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Hi Roger! The normal engineering practice here in the UK is to have course threads in soft materials. A UNC thread will be thicker in section at its root than UNF, this increases the shear strength of the flank considerably and has a slower helix angle. When the UK went over to ISO metric threads this was the downer on them as many people said that they were too fine for soft materials! For this application I would always use UNC. Lastly they should always be Loctited.

 

Bruce.

That's what my "chip analogy was about"

 

the UNF French Fry imposes larger loads upon the lessor material content inside the hole (more surface area = more space between threads) and smaller thread root material to withstand it

 

"A UNC thread will be thicker in section at its root than UNF, this increases the shear strength of the flank"

 

To have more surface area means you must have more space around the surface, in a confined space that means less stud material in the hole, that means less strength along the stud parallel axis. "the shear strength of the flank" eventually as the material (alloy trailing arm) corrodes the strength in the root reduces and the thread strips.

 

Mick Richards (salt and vinegar please)

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Hi Bruce/Mick,

there is no doubting that the UNC thread will have greater tensile strength (pulling out of the hole) due to an increase in cross sectional area of the

thread form. But that is not the problem - is it!

 

These studs have lasted 40/50 years - far far more than the ST designers envisaged.

As has been shown time and again - the hubs will stay put with one or two studs missing.

 

I still maintain that they went unorthodox to allow the UNF thread on the stud to stay put.

Locking of the stud in position was limited so they used a mechanical means.

 

Roger

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Not sure if it’s wise to throw my two penneth in with all the chips etc. ..... but, does it really matter if it’s unf or unc? Surely the main force the stud see’s is shear perpendicular to its axis - like a dowel - which is why the holes in the hub are close tolerance to the studs. If the stud is seeing significant tension in a working situation then I’d agree unc would be better than unf.

 

It seems that the studs only strip their threads when people apply too much tightening torque ie applying a significant tension load - and this isn’t the design situation. I’m with Roger here, if Triumphs design was wrong, why would they keep with it for all those years and over several models?

 

Cheers

 

Dave.

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"I still maintain that they went unorthodox"

 

Not arf pop pickers ! I reckon they were on the "wacky baccy" why use an UNF with attendant root material compromises when a similar sized UNC would do the job better ? I reckon the studs wouldn't "unwind" when you've got 16 lb ft dragging the threads into contact with one another.

But bear in mind these were the same genius's who developed the Stag engine with NO holes in the centre of head and block relying on thermos expansion to help the coolant flow from the back to the front. Then developed a head retention system with 11" ANGLED studs with 2 threads and one nut and 5" set bolts at 90 deg running alongside them and then 3" set bolts at 90 deg along the cylinder head edge which compresses a thinnish 1" thick head section and ALL of these fastenings are supposed to have the same torque and clamp the head equally, not a chance in hell.

 

Mick Richards

Edited by Motorsport Mickey
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"It seems that the studs only strip their threads when people apply too much tightening torque ie applying a significant tension load"

 

Not convinced, I've often seen the studs just unwind along with a portion of grey powder which used to be alloy 50 years ago, doesn't appear to have had excess torque to me , just corrosion and insufficient thread root strength to retain the studs and hub.

 

Mick Richards

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