Rear lever arms working loose

[thirdangle]

Hi.

 

Over the past 2 months of so, both of the lever arm shocks have worked losse from their mounting bolts on my TR4. - what a ridiculous design, using only 2 bolts.

 

I noticed that they each had a split spring washer & plain nut - I have now replaced them with nyloc nuts. Due again to the poor design it is hard to get a decent grip on the front side when tightening up (i.e looking at the shock face on), this makes it hard to do the other side up super tight - if you see what I mean.

 

All seems fine now but I suspect they may work loose again - anyone had any better ideas - I am considering using longer bolts with a second lock nut

[RogerH]

Longer bolts with a lock nut is a good idea. Or you could put some 'stud lock' on the plain nut/spring washer.

 

Roger

[bob-menhennett]

Nyloc nut is a good solution, ditto the longer bolts.

Some thread lock liquid might help next time.

Speed humps and the general state of repair of the roads

leaves a lot to be desired.

I put a socket or spanner on everything I can see when

doing the servicing on my car to to check nothing will fall off!!

 

Bob

[Don Elliott]

I had this problem with my 1958 TR3A about twice a summer for about 10 to 12 years and I was forever tightening them. So I got 4 longer bolts (about an inch longer) and my friendly neighbour who has a lathe turned 4 spacer washers for me about an inch long. Then I assembled the new longer bolts with the spacers which put the nut about an inch away from the body of the rear lever shocks where I can get a 1/2" drive and socket onto the nut to really tighten the nut properly.

 

It would be as if you got 4 longer bolts and stacked up about 15 to 20 flat round washers before putting on the nut. I supose a nyloc nut might help but I hace a split lock washer under the nuts. I hasn't come loose in 10 years.

 

BTW, two bolts are sufficient to hold a lever shock in place. Just look at the front lever shocks on an MGA. On the MGA, two bolts always stay secured because the lever shock is bolted (as bolts were intended) by securing parts together in tension. That's where good design starts.

 

But the TRs with rear lever shocks are secured to a flat support bracket plate and the bolts were designed to hold it all togeter in shear (not in tension). When your tyre hits a hole or a bump the lever arm moves but the whole body moves as well. I'll bet you a Bob that the holes in your support bracket are oval from the rotation of the shock body.

[88V8]

I think two bolts is standard on lever arms, also on the vane-type dampers that preceded them. The first car I had with vane dampers, I recall from the owner's handbook that rear dampers were an optional extra.

 

Anyway, yes they do come loose. Always used to be the bottom bolt on my car, then the top one came a bit loose in sympathy.

 

The top one will probably be OK with just a new lock washer - proper UNF size, not the metric approximation. If the bolt has been more than slightly loose then the thread may be hammered in the captive nut, in which case a longer bolt and another lock washer and a new nyloc on the back end, as has been said.

At the bottom, definitely a longer bolt and extra lock washer and nyloc.

 

The bolt needs to be a bolt with a shank, not a set bolt.

The top bolt is indeed a bit of a pig to get at, depends what extensions you have for your ratchet.

 

While you have the opportunity, disconnect the drop link from the trailing arm and make sure there's no play in it. One can't tell when it's under load. A worn drop link can make much the same clonking noise as loose dampers.

 

Ivor

[RogerH]

Hi Ivor,

your comment about the bolt with a plain shank is a good point.

But, have you tried to but (from the usual suspects) a bolt with a certain shank length.

 

In the aviation world all bolts are designated by their shank length (and diameter, head shape etc) plus enough thread to fit a washer(s) and a nut plus a couple pf threads for safety.

It would appear that for our cars a 2" bolt may have a 1" shank and 1" of thread.

If the shank fits well you have yards of thread sticking out.

If the thread/nut looks good then you have too much thread down the hole.

 

Why can't they designate them by their shank length (so much easier).

 

Roger

[Nick Webster]

I used allen headed bolts to secure my shock absorbers. With the appropriate key it is easier to get a good grip on the shock absorber side of things.

 

Nick

Edited July 16, 2010 by Nick Webster

[Nigel 628]

I agree with Nick.

 

I also replaced the mounting bolts with cap head (allen) bolts, and use a proper allen key 'socket' bit on a wrench handle to tighten them. You probably couldn't get them tight enough with an ordinary hand-held allen key. Spacer washers are not needed of course as there is no clearance problem. Imperial cap head bolts are rare nowadays, but a metric equivalent will do: if tightened properly they won't work loose. Good quality cap heads are always high tensile, often higher than normal, so no shear problems. I use a plain washer with a nyloc nut and have never needed to use thread lock - it's not good practice to use it to compensate for not tightening the fastener correctly in the first place.

 

If they survive my TR4 hammering over rally stages without coming loose that's good enough for me! I spanner check the whole suspension after every rally as a matter of course but have never had a problem with the lever arms - apart from the fact that they are not telescopics, of course......

 

Nigel

[Nick Webster]

Hi Ivor,

your comment about the bolt with a plain shank is a good point.

But, have you tried to but (from the usual suspects) a bolt with a certain shank length.

 

In the aviation world all bolts are designated by their shank length (and diameter, head shape etc) plus enough thread to fit a washer(s) and a nut plus a couple pf threads for safety.

It would appear that for our cars a 2" bolt may have a 1" shank and 1" of thread.

If the shank fits well you have yards of thread sticking out.

If the thread/nut looks good then you have too much thread down the hole.

 

Why can't they designate them by their shank length (so much easier).

 

Roger

 

 

I had a bit of a run in with well known fastener suppliers, Namrick when I ordered some 1/2" BSF bolts together with a number of 1/2" UNF bolts. I bought the UNF because they were cheaper and given "isolated" intended use, I was not too fussy about them being a strange thread on a basically imperial threaded vehicle. I wanted them for the propeller shaft UJs hence the un-threaded shank was important. The BSF bolts for use elsewhere on the chassis had nice shanks but the UNF was little more than about 1/8" and were certainly undesirable for my intended use. I phoned and complained saying the UNF was by my reckoning a "screw" (i.e. no shank) and this was unreasonable since they actually charge more for bolts than screws of the same size. I was told that they were within manufacturing tolerance. I cannot quite remember what this was; something like twice the diameter plus 6mm or something like that. I pointed out that the BSF bolts were the same diameter but a much better bolt but faced with "within tolerance" it was to no avail. I was using mail order, but it would appear that if you physically hunt around you may well turn up a bolt that is a better bolt. Shank length IS a fixed value related to other dimensions but the tolerance is intolerable!

 

Nick

Edited July 16, 2010 by Nick Webster

[TR 2100]

I bought the UNF because they were cheaper and given "isolated" intended use,

I was not too fussy about them being a strange thread on a basically imperial

threaded vehicle.

 

TRs use UNF and UNC threads.

 

I don't know if that qualifies as "imperial"

but BSF they are not.

 

AlanR

[thirdangle]

Thanks for all the good replies. I quite like the idea of the allen head bolts because it overcome the clearances problems. I'll do some net searching for a suitable fastener supplier. Can anyone recall the size of the bolt needed?

[Nick Webster]

TRs use UNF and UNC threads.

 

I don't know if that qualifies as "imperial"

but BSF they are not.

 

AlanR

 

 

Sorry, perhaps I should have made it clear that the BSF purchase was not for a TR in case anyone gets confused. Like many others on the forum I have more than one classic and in my mind can slip seamlessly between them. My post was intended to illustrate difficulties with manufacturing tolerances in general. The fact that two same diameter bolts with different thread conventions had different shank lengths is not due to the type of thread, but the people who made them.

 

Nick

[Nick Webster]

Thanks for all the good replies. I quite like the idea of the allen head bolts because it overcome the clearances problems. I'll do some net searching for a suitable fastener supplier. Can anyone recall the size of the bolt needed?

 

 

Make sure you measure the "flange" on the shock absorber. I have known them to be different thicknesses. Your ideal bolt shank length will go through this, plus the metal of the chassis which may or may not have been reinforced, but obviously not beyond a compressed spring washer. A plain washer and then a spring washer is not recommended best practice. In the real world, addition of a plain washer is sometimes necessary to get everything right. I'm afraid I've forgotten the diameter of the bolt but could nip out and measure some old shocks if you like or someone does not beat me to it. Good grief, does nobody on the TR Register forum actually work during the day?

 

Nick

Edited July 16, 2010 by Nick Webster

[RogerH]

Blimey - how many posts can a loose damper cause.

 

Nigel - don't get 'tensile' and 'shear' mixed up.

A good tensile bolt may be a poor bolt in shear and the other way round. However on the dampers it probaby doesn't matter.

 

If anybody wants quality aerospace fixings (BSF, UNF & Metric) try googling LAS. They operate out of Exeter airport.

ALL the bolts are measured at their shank - you know exactly what you are getting.

They also specify tensile or shear bolts etc.

 

However not cheap

 

Roger

[Nigel 628]

Agreed, Roger, but in practice in this application it allows you to tighten them up really well. If they are tightened properly and don't come loose then shear strength is not an issue.

 

Don't forget to use nuts of the same specification of course.

 

Yes, it's a lot of fuss for a loose shocker, but all this is of general use for many other purposes on the car.

 

Nigel

[thirdangle]

Make sure you measure the "flange" on the shock absorber. I have known them to be different thicknesses. Your ideal bolt shank length will go through this, plus the metal of the chassis which may or may not have been reinforced, but obviously not beyond a compressed spring washer. A plain washer and then a spring washer is not recommended best practice. In the real world, addition of a plain washer is sometimes necessary to get everything right. I'm afraid I've forgotten the diameter of the bolt but could nip out and measure some old shocks if you like or someone does not beat me to it. Good grief, does nobody on the TR Register forum actually work during the day?

 

Nick

 

 

If I recall it is 3/8" UNC, or was it UNF!!!! Don't go to the bother of measuring it Nick, I just wondered if anyone happened to know for sure

 

Thanks

 

Ian

[TR 2100]

If I recall it is 3/8" UNC, or was it UNF!!!!

 

UNF for sure. Not many UNC threads and invariably

into the block.

Wasn't sure if they were 5/16" or 3/8".

 

AlanR

[stuart]

3/8" UNF.

Stuart.