Worn splines on shaft

[Darren CooperParticipant @darrencooper24986]

[Darren CooperParticipant @darrencooper24986]

I have a ’51 MG TD shock absorber that needs attention – the damper arm needs fixing back onto the splined shaft.

Originally, the arm would have slid onto the splined shaft and then the end of the shaft would have been flared to fix the arm in place.

The splines in the cast damper arm on mine are badly worn.

Sometime in the past, the shaft has been ground down, punched and welded and is now in a sorry state.

Would it be appropriate to fix it by pinning ? The shaft is 3/4" diameter.

Last photo shows the general arrangement, The arm is just in place loosely and will go further onto the shaft, probably until it is flush.

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[Clive FosterParticipant @clivefoster55965]

Pinning may well not be appropriate. Well fitted splines are very effective at transmitting loads from arm to shaft with minimal stress on the components. This was why the original parts got away with relatively soft material. Hence vulnerability to mechanic abuse. In comparison pins put quite high stresses on small areas. Taper would probably be better than parallel.

Trouble is you have no idea what the ral loadings onthis component look like. Given the failure I'd suspect they can be surprisingly high. Making new shaft and arm would be best or at least re-making the shaft end. Next best would probably be several small dowel pins e.g. ex needle roler bearin needles in a ring of drilled holes dutch key fashinon as course splines. Done nice and tight with loctite its very effective. Pig to do though. Sounds easy but a gremlin magnet.

Clive

[Michael GilliganParticipant @michaelgilligan61133]

I wonder if anyone does a repair device ?

I have not seen, but could imagine, a thin "corrugated" bush in spring steel.

… like a linear version of a HeliCoil, if you see what I mean.

MichaelG.

[Gordon WParticipant @gordonw]

I've done a few bodges of this sort. First try to get a new or s/hand one. Welding is next, grind a big chamfer on shaft and a big c/sink in the arm. Would say about half thickness of arm. Two holes in arm,about 10mm dia. for plug welds,these will act a bit like a pin. The problem is that any oil seal etc. will get hot, try with the damper under water, or a very wet rag wrapped round. Second problem is that the shaft will have to be cut to dismantle. Another way that may work, depending how bad the splines are, Weld a piece of steel the same thickness as the arm to the end of arm Drill thru' this for as big a bolt as possible. Then slit with a hacksaw right thru' and clamp with a suitable bolt and nut.

[Ian PParticipant @ianp]

Even though parts must be hard to find for your car I think the only way to go is replacement!

The shaft is normally hardened or at least pretty tough steel (Rockwell 60?). In normal use no movement between the two parts takes place so that joint would last forever.

Both parts could be refurbished by welding on more metal and then recutting the splines but I think you would have to be both well equipped and pretty desperate to go down that route. The loads on that suspension joint are very high if the damper is working effectively (especially if you drive over a pothole!)

Clive's method of multiple small pins and Loctite would work but the shaft and bore would have to be a very close fit, and if the shaft is hardened then its not going to be easy to drill.

Ian P

[V8EngParticipant @v8eng]

It might be worth searching online to see if there is a club for your marque, they usually have specialist knowledge and repairers available.

Sometimes there are replacement parts available via such sources for this type of item as well.

It is many years since I had any involvement with cars so hope this situation still exists.

Edited By V8Eng on 03/06/2014 11:08:13

[Clive FosterParticipant @clivefoster55965]

Posted by Michael Gilligan on 03/06/2014 10:46:01:

I have not seen, but could imagine, a thin "corrugated" bush in spring steel.

MichaelG.

You are thinking of tolerance rings **LINK** .

Correctly used the grip is good, as I recall it the guy on an exhibition booth where I first encountered them said one of the mass market applications was to join a two or three part steering column together. My reaction was Eeek!

Unlikely to be up for this sort of job tho'. Clearances and finish need to ge right for max strength.

Clive

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Foster on 03/06/2014 11:58:09:

Posted by Michael Gilligan on 03/06/2014 10:46:01:

I have not seen, but could imagine, a thin "corrugated" bush in spring steel.

MichaelG.

You are thinking of tolerance rings **LINK** .

.

Clive,

Yes and No

I was postulating something roughly that shape, but with the corrugations running the full length, and [obviously] profiled to be somewhat "splinier"

MichaelG.

[Darren CooperParticipant @darrencooper24986]

Many thanks for these ideas.

Obviously a replacement would be best, though you must provide an exchange unit when purchasing and my unit was not acceptable.

To follow Clive's suggestion of 'mini' dutch pinning, I think I could use a 1/8" peripheral end mill and working on the inside of the hole, put some 1/16" (nominal) deep internal grooves into the circumference. Then I would put corresponding external groves in the shaft again 1/16" (nominal) deep so I end up with 1/8" diameter holes on re-assembly. A bit of trial and error on the depth, but hopefully this avoids a lot of snapped drill bits.

Plan is to have nine grooves/holes; this gives a space between the grooves/holes of about 1/8".

If I'm lucky there may be some deflection of the cutter at the lower end as I mill the grooves out, which would give a slight taper to the groove.

 

 

Thinking aloud, I could start by cutting just 3 grooves/holes to test the principle; if it's not going to work I can revert to the welding route and use the grooves for the plug welds suggested by Gordon.

Any further thoughts will be very welcome.

 

Edited By Darren Cooper on 03/06/2014 20:51:23

[Roy MParticipant @roym]

Darren, have you considered using a taper cotter pin? This requires a reamed hole through the cast damper arm, and a flat machined on the splined shaft. The pin has a taper flat machined along the length and is tightened up with the use of a thread and nut. (As used on bicycle pedal cranks). Perhaps you could buy one on fleabay?

hope this is a help, Roy.

[John McNamaraParticipant @johnmcnamara74883]

Gee

The Cats I worry about are the nine lives and if they have been used up? Particularly if driving down the highway at 110K or more? OK its only a damper and a car can do without one maybe…. I would not like one to let go on a wet road curve while passing a B double or some other situation where the physics are pushed a bit hard. would I be able to maintain control?

There must be a more serviceable replacement even second hand that does not have to be hacked to keep it going.

Regards
John

[Keith LongParticipant @keithlong89920]

I have to say I agree wholeheartedly with John McNamara – if the part isn't serviceable CHANGE IT. You're not only potentially putting your own wellbeing at risk but also that of the poor unfortunate that you happen to run into when the part fails and you loose control.

I've only recently become aware of the exemption from MOT testing for pre 1960 cars and bikes. I cannot see the logic behind this as by current standards vehicles built then had pretty rotten brakes, steering etc. and at the latter end of that period we're coming into the "rot-box" era where cars rusted away before your eyes. To allow those on the road without an annual "professional" inspection seems madness with the UK roads of today and the traffic volume.

Keith

Edited By Keith Long on 04/06/2014 14:05:19

[Gordon WParticipant @gordonw]

I can see where you are coming from Keith and John, but a damper only has to push oil about, there is not a lot of stress compared to most other suspension parts. It might surprise you to see the low levels required by the mot brake test, I would not drive one at the minimum pass figures, and that might be on a big heavy 120mph 4×4. I think that non-coded welding on steering and suspension is not allowed, but may be wrong. Surprisingly you can weld up your own chassis on a special with no checks. I just think it will be a shame to take a good old car off the road just for the sake of of a small difficult to source part.The biggest I had with the lever dampers was keeping oil in them, once resorted to hot grease. That did put a load on the lever, until it got hot.

[Keith LongParticipant @keithlong89920]

Depends on the design of the car Gordon – Morris Minors and others using the same suspension type, Riley 1.5 etc – the shock absorber arm doubled up as the top suspension link as well.

Keith

[Ian PParticipant @ianp]

Darren

From memory, I thought the TD front suspension damper had an arm at each side so that it created a basically triangular wishbone? The one in your picture only seems to be single sided to presumably its off the rear suspension. Whilst is important from a handling point of view, the loss of a damper if the splined joint fails is not likely to be catastrophic.

I still think that you should find a serviceable replacement, or, if you are not into originality, install new adjustable, gas filled, telescopic dampers!

Ian P

[Tim StevensParticipant @timstevens64731]

The reason that HMG decided to reduce the requirement for MoTs for old cars was the evidence. Not the guesses, chaps, the evidence. This shows that such cars have few accidents and very few of those are down to mechanical failures of the types that an MoT would catch.

In addition there is the way such cars are driven. If you drive at 110K plus and corner at a rate that having a good damper makes the difference between control and out-of-control, your old car (ie your investment) will not last long for lots of other reasons. And remember, too that the oil damper only provides some of the damping. There is a lot of resistance provided by the leaf springs.

I am sure that the MG Car Club will have members who have faced this before and found solutions. The MG Owners Club might seem a tempting alternative but they are not a Club in the true sense, they are a commercial spares company which also offers some services of a club-type nature.

Cheers, Tim

[Gordon WParticipant @gordonw]

Ah yes Morris Minor front suspension, totally off topic of course, but the best trick they had was the bottom trunnion falling off. But it only happened at low speeds ,so that was alright.

[Involute CurveParticipant @involutecurve]

Personally if absolutely one was not available, I would remove the shaft build it up with weld, and re cut the splines, then Id either make a matching broach to cut the inner splines, or use the dividing head to broach them individually, I have a couple of spline cutters I've made over the years to reclaim bike kickstart shafts etc. So it can be done it just takes time, and really its the only proper way to do this, I know its only shifting oil about but at speed hitting a pothole the oil must move quickly, this will induce more stress than you perhaps think, if it was such low stress it would never have striped the splines, in most cases the shaft twists before the splines strip.

HTH

Shaun

[V8EngParticipant @v8eng]

A car with even one missing shock absorber can be unstable even at fairly low speeds, the effect of road surface changes or bumps etc can have unexpected effects on directional stability.

 

 

Gordon W.

Triumph Heralds could do the trunnion trick as well, mine did!

Edited By V8Eng on 04/06/2014 19:35:23

[Michael GilliganParticipant @michaelgilligan61133]

Posted by V8Eng on 04/06/2014 19:34:11:

Triumph Heralds could do the trunnion trick as well, mine did!

.

Likewise Reliant Scimitar, which [along with many Kit-Cars] used the Herald trunnion.

MichaelG.

[Neil WyattModerator @neilwyatt]

> Ah yes Morris Minor front suspension, totally off topic of course, but the best trick they had was the bottom trunnion falling off. But it only happened at low speeds ,so that was alright.

Yes, a screw in a threaded hole wasn't it? But they got it sorted for the Marina, didn't they…oh, no they didn't…

Neil

[Ian PParticipant @ianp]

Posted by V8Eng on 04/06/2014 19:34:11:

Gordon W.

Triumph Heralds could do the trunnion trick as well, mine did!

Edited By V8Eng on 04/06/2014 19:35:23

Gordon

Its not fair blaming the fault on the Triumph Herald, its purely and simply lack of maintenance!

Ian

[V8EngParticipant @v8eng]

Or using the wrong lubricant !

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