shimming arm bearings.

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really?
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shimming arm bearings.

Post by really? »

anyone able to tell me how to work out which shim, or wedge, i need to use when i'm putting the bearings back in on the rear arms? have got the set of 9 shims (part no 514327) and the skf bearings, but dont know, and cant find, any measurements. the haynes book of lies isn't very helpful either. help much appreciated.
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Re: shimming arm bearings.

Post by tim »

What I did...... depends on you having kept the original 'top hats' as the pattern ones are so tight you can't move them easily. At least in the kit I bought. Assemble up the spindle assembly on the bench, then push the bearing onto the end of the spindle and then down as far as it will go. Then find a shim which, when placed on top of the bearing, will sit just above the edge of the tube. Logically, you have then taken up the relevant slack. I did this on both of ours last year and everything seems fine.
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Re: shimming arm bearings.

Post by sdelasal »

tim - Quote "Then find a shim which, when placed on top of the bearing, will sit just above the edge of the tube" - I'd of thought that there was a nut to tighten up to take up all the slack - then either a clearance to measure or a force to measure to move the arm (using a fishing spring weight device for example)
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Re: shimming arm bearings.

Post by rutter123 »

I used feeler gauges between the top hat and chassis mounting, you may have to fit the long bolt first then slowly remove it whilst sliding in the gauges. Helps if u have a cut down bolt to hold the shim in place whilst fitting the new one.
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Re: shimming arm bearings.

Post by MULLEY »

I thought the other technique was to replace like for like shim if one was already fitted to the old set, if not then don't bother?
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Re: shimming arm bearings.

Post by citronut »

MULLEY wrote:I thought the other technique was to replace like for like shim if one was already fitted to the old set, if not then don't bother?
exactly what i do,
rutter123 wrote:I used feeler gauges between the top hat and chassis mounting, you may have to fit the long bolt first then slowly remove it whilst sliding in the gauges. Helps if u have a cut down bolt to hold the shim in place whilst fitting the new one.
i cant see this method working, as the play you need to take up is between the top hat and the outter face of the bearing inner race, which should give the correct bearing pre/load or not as the case may be,

the OE method is done on the bench with all the new parts assembled and placed under load,

my rule of thumb is if the pivot tube is flush with the outer face of both top hat bush's, once you have squeezed/taped the top hat bush's and sals in as far as you can ( with quality parts that is ), his shoudl be as close as you can be,

if the pivot tube is below or protruding from the top hat bush's this will give the wrong re/load

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Re: shimming arm bearings.

Post by tim »

By 'protruding' I mean a millitad, not a huge amount! Taper rollers are quite picky and I reckon that allowing just enough to catch a short fingernail on will mean that once tightened up in the car, the bearings will be neither overloaded or suffer from any side play.
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Re: shimming arm bearings.

Post by Defender110 »

"Millitad" ....Like it, now in my vocabulary. :wink:
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Re: shimming arm bearings.

Post by mat_fenwick »

MULLEY wrote:I thought the other technique was to replace like for like shim if one was already fitted to the old set, if not then don't bother?
This is what I do too, and haven't suffered with premature failures. And I have done the miles on the same car afterwards to prove it!

Some years back I spoke to a bearings engineer about a similar design in a motorbike wheel bearing, where the manual stated to measure the resistance to turning in order to select the correct shim. He said that whilst there were tolerances to the grinding of the bearings, they would likely be significantly less than the tolerances in the machining of the housing. So by keeping the same size shim upon reassembly, the bearing load would probably be acceptable.

So not strictly correct by the book, but it seems unlikely to cause much of a reduction in life. Especially as the main failure mode seems to be water ingress causing rust, rather than actually wearing out.
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really?
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Re: shimming arm bearings.

Post by really? »

right, i cant measure the lump of rust that may contain 1 part shim, 1 part bearing race and 1 part spacer/top hat. what i propose to do is assemble the inner end, put it in place, caress the bearing into the outer side of the arm, measure the depth of the hole then the length of the spacer, whatever the difference is, fill it with shim. does that sound about right? i've got some verniers to aid accuracy of the measurement.
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Re: shimming arm bearings.

Post by Tinkley »

Like Malcolm and Mat, I too reused the old shims when replacing the arm bearings. On m/cycle taper needle head races the normal practice to set them up, other than torque measurement is to tighten up a bit too hard initially to make sure the bearings are bedded. Then back right off, and re tighten so the front forks still swing freely and drop to each side. As soon as it is stiff to do so you back it off a tad and clamp it up there. M/cycle head races do wear out in a front/rear direction or from corrossion, the main cure for which is better grease and a bit of tape to keep the salt spray out!.

On front wheel bearings on my old Sunbeam it was similar. Remove split pin, tighten bearing and back off one flat of the hex nut and refit the pin. However this application is slightly different in that it has to allow for heat expansion of the bearing. I do the same on the boat (6-7 meter RIB trailers) bearings which are taper needle and no problems so far. Worst thing thing with those is they are lowered into the water including the sea to launch the boat. Now warm/hot bearings lowered into sea water....mmm. I tend to have to replace one set a year because people do not grease them properly. Plus the grease path to the needles is very poor and the so called seals don't!. The bearing buddies do improve the situation but are not perfect.
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Re: shimming arm bearings.

Post by Jaba »

I usually leave the shim, if present out, but first I fit the through bolt and tighten it all up on the bench. Then as long as the arm can still pivot and/or there is not excessive play then that is good enough IMO.
Make sure you fill the plastic tube with thin grease to keep it all well lubed and you will be right for another 10 years.
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