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MG TD TF 1500 - TF stub axle thread

Ive just completed reaming the swivel links and once I clean up the threads with a tap & die will be ready for assembly.

I will purchase a BSF tap & die set as the DPO used all sorts of nuts and bolts with about 30% missing or needing replacement. There are tap & die sets available on eBay but Im having trouble determining the thread of the front stub axles (I need to tidy up the LHF, which is a LH thread).

The thread is 20mm in diameter with a 11g 5/8" thread, which does not appear on my thread chart, and after 2-days of searching I'm non the wiser.

Any suggestions on what it is - perhaps UNF?

Chris
Chris Cullin

Hi Chris,
5/8" 11 tpi is Whitworth. I believe later cars had a 3/4" UNF thread,over the years many TD's and TF's were scrapyard maintained and the parts all mixed up.
Just realised 5/8 x 11 is also UNC and I have seen damaged threads cut back to a smaller size.
If both are the same size then probably Whit.
Try just using a thread file to clean up the threads, left hand dies are hard to come by.
Ray TF 2884
Ray Lee

"Just realised 5/8 x 11 is also UNC"
While the Whitworth and UNC share a common thread count, the thread profiles are different and shouldn't be mixed and matched. UNC threads have a 60° included angle, whereas BSW threads have a 55° included angle. The two thread systems have a different roots. See a comparison at: http://www.britishfasteners.com/threads/unc.html Cheers - Dave
David DuBois

First I must admit a doh! moment. I called the message "Stub axle thread" where I meant the "kingpin thread".

I'm using is 55degree Whitworth thread gauge and 11G 5/8 fits very well (see photo).

However the diameter is 20mm (.787in) and my thread chart does not have any imperial threads that diameter. The only BSF 11g-5/8 thread is 22.225mm (0.875in) diameter. There are BSW and UNC 11g threads but these are both smaller diameters.

I must be missing something or the table I am using is wrong.

It may also be possible that I have a mismatched kingpin and stub axle combination as the kingpins rotate 1-2 degrees within the stub axle with steering arm bolted tight.

Chris Cullin

Can you show a photo of the damaged area? I have not had a damaged thread there, and would be interested. It's a coarse enough thread that I would probably just use a triangular file, depending, of course, on what is wrong and where.

Tom Lange
MGT Repair
t lange

The thread form is a modified Whitworth.The flat top diameter is much less than the nomimal bolt size. It was used until the 60's in high load moving threads ie large Steam valves.As Tom says just use a triangular file to clean up.
As for the play in the king pin, assemble it tight without the Woodruff key.If this takes out the play then trim the top of the key until everything fits.
Ray TF 2884
Ray Lee

Tom - I will post a picture of the thread shortly.

Ray - good suggestion. I will work on removing the key and then try the fit.

I also found that the concave grove in the pingpin is not aligned with the stub axle - To guess I would say the grooves as the same radius but on a different inclination. The photo is not super clear but you make out that the grooves are align on the right but left they are not.

There is no visible wear in either the Stub Axle or the Kinpin.

A tighter steering arm may stop the rotation but there seems to be something more amiss.

Chris.

Chris Cullin

Tom - the thread damage is barely visible, but the links screw on the top of the kingpin but not the bottom. To the touch it appears the first thread may be damaged as its sharp whereas the other end is quite rounded.

in the collection of parts I have there is a bent kingpin and a Link that has been ground down about 1/2in (10mm), suggestion it has lost a wheel at some point. This also tells me the Kingpin is not original, which may be cause of the problem I'm having.

Chris Cullin

I have cleaned up those threads with a thread file from Snap-On.
They get damaged by people trying to unscrew them without removing the steel link pin. It does round the top of the threads.
Sandy
ss sanders

Well I have more information. I have the old original kingpins (or swivel pins as some call them) and after cleaning these up and installing them they have the same problem.

So I think this is a kingpin problem. Its also possible that the gap, or difference in the grooves between the kingpin and stub axle where the steering arm locks them together, is meant to be a different between the two parts (sorry - hard to describe - the earlier photo shows it).

The stub axle has part number 8640 stamped on the rear - does anyone know what this identified the axle as?

Chris.
Chris Cullin

Chris - this problem is usually caused by the bushings not being pressed in quite at the right angle, and catching on the threads. The oval of the bushing has to be perfectly aligned. If this is the case, remove the bushing and press it in straight.

Tom Lange
MGT Repair
t lange

all - Thanks for the suggestions on the thread damage on the kingpin (swivel) pin, I will use a triangle file.

Tom - the problem I have the kingpin is able to turn 1-2degress in the stub axle.

I tried Ray's suggestion of removing the woodruff key from the steering arm and assembling it tight. You can see in the photo that the steering arm is seating tight - but the kingpin still turns 1-2 degrees.

The photo is 7th post shows the how the groove in the kingpin is a different shape to the groove in the stub-axle and this allows the kingpin to rotate even though the steering arm is tight.

I'm starting to think either this is normal or that I have the wrong stub axles.

Chris.

Chris Cullin

Tom - I think you may be right with the thread problem. I have other kingpins that the links screw onto OK. I will have to see if the bushings are protruding into the thread area.

Thanks all for you help.

With the loose Kingpin I will start up a separate thread.

Chris.
Chris Cullin

This thread was discussed between 30/04/2014 and 04/05/2014

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