Rear wheel bearing ...
 
Notifications
Clear all

Rear wheel bearing advice?


Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  

Anyone have an idea on the permissible runout for a genuine Cobra rear wheel bearing?

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


Quote
David Beck
(@webmaster)
Estimable Member Admin
Joined: 7 years ago
Posts: 102
 

I dearly wish I could tell you Roger, it would make my year!

😀

The Cobra Register - Founder Member


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  
Posted by: @webmaster

I dearly wish I could tell you Roger, it would make my year!

😀

...and it's only July!

As it's a double ball race I think I can assume the answer is nil, or nil detectable.  I suspect I'm going to need another N/S/R stub axle, which I suspect is not an inteference fit in the bearing inner race(s).  Further investigation required in the form of rear hub dismantling, but I need to sort the electrical issues first or it won't be at Sliversnot.

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  

...and when did I become a 'reputable' member?  Surely that's a subjective assessment?  Deeply flawed, anyway...

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
David Beck
(@webmaster)
Estimable Member Admin
Joined: 7 years ago
Posts: 102
 
Posted by: @roger-king

...and when did I become a 'reputable' member?  Surely that's a subjective assessment?  Deeply flawed, anyway...

The system is set to polite mode, it rarely says what is actually thinking, more along the lines of HAL than anything else, in which case you may want to reconsider your comment...

The Cobra Register - Founder Member


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  
Posted by: @webmaster
Posted by: @roger-king

...and when did I become a 'reputable' member?  Surely that's a subjective assessment?  Deeply flawed, anyway...

The system is set to polite mode, it rarely says what is actually thinking, more along the lines of HAL than anything else, in which case you may want to reconsider your comment...

Maybe there should be 'system friendly' days, when it can say what it really thinks?  If 'thinks' is the right word...

I think that could be very revealing, although I admit I haven't seen 2001 for a very long time

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  

There should, of course, be no detectable movement in a double ball-race wheel bearing, if the bearings are of good quality.

I finally got this job done using a spare axle shaft and hub carrier, pending the arrival of the materials needed to build a dedicated press to separate the old parts.  Need to get to Silverstone, if I can...

I thought I'd just commit this to record, as the Cobra chassis manual reprint helpfully gives four sentences on rear hub removal, and even less on rear upright removal.  Replacement, the tricky bit, doesn't even get a mention.  Thanks, AC.

The job took a while, due to issues with minor problems with parts and operator error.  Given the issues around separating the old components I followed Peter's valuable advice and took my spare LH rear stub axle to a local precision engineering shop, along with a new RHP LJ1-½ bearing (made in England) to have the axle polished to the recommended tolerance for an interference fit.  The workshop manager at Jencol Engineering looked up the figures and said he would get the shaft to 0.0005-0.00075" oversize to the bearing bore, which he did beautifully within a couple of hours.  He also faced the fit surface of the stub axle and mounted a new brake disc, which he machined to 0.0005" runout to both sides.

Whilst being fairly easy to remove, the leafspring rear hub assembly is more of a challenge to reassemble into position due to the weight of the parts and the fact that you can't (easily) compress a leafspring to align the pivot mounts.

IMG 6623

Removal gave an opportunity for clean-up.  Whilst in here, it's worth replacing the small oil seals that press into each side of the lower wishbone outer pivots as they can get chewed up during removal.  They're easy to do, and very cheap, so it only makes sense.  I have turned up a brass press tool to tap them in square with.

After careful reassembly of the bearings, spacers and oil seals in the hub, these were pressed into place in the 12T press.  Careful with the large inner oil seal, they're £35 a pop...  The assembly is held together with a large set screw on the rear of the stub axle that holds the driveshaft flange on, located by a loctab washer and done up FT with a 1-⅛ BSW socket.  Unless you are a contortionist and/or juggler, assemble the lower pivot to the wishbone first, with new thrust washers (coated surface facing inwards, to the upright).  At only 4,000 miles I opted not to change the pivot bearings as I was refitting the original pin and there was no discernible wear.  Alignment of these components is... interesting, but not impossible.

Then it's on to special tool no.2, which is a brass proctoscope guide pin that threads onto the front of the upper pivot pin to help hold all the components in place and align them without damage during installation into the spring eye.  This was also turned out of brass and threaded to match the retaining thread on the pivot pin (thanks to Dan Case for the drawings).  It's also a good idea to fit a pair of new Vandervell thrust washers either side of the spring as again these are cheap but wear quickly to shape, so are best renewed.  The ones supplied were of too large a radius to fit neatly in the trunnion, so a spindle was made up to enable me to turn them down 0.25" in the lathe.  For assembly, the weight of the hub assembly helps to hold the lower wishbone down, hopefully just enough to engage the guide pin - but a little levering downwards can help with this if necessary.

Guide pin in action:

IMG 6624

Once everything's aligned, tighten up to appropriate torque figures (needless to say, there are no such figures published anywhere for this car) as far as can be judged.  Refit driveshaft, caliper and handbrake cable - sounds easy when you say it quickly enough, but casting variations on the replacement upright meant that refitting the caliper took a couple of hours.  It's a very fiddly job, involving balancing the caliper on the disc with one hand with the mounting bolts inserted and the spacer shims held delicately on the bolt threads whilst trying to assemble the whole lot blind and not losing any shims.  So not funny when the bolt won't align and you have zero visibility and shims dropping on the floor.  Hmm - after all these years, you'd think I might have run a dummy caliper mount to the upright first just to check.  Never assume anything...

IMG 6627

Here's the finished item.

Just one further bit of advice.  The rear uprights are not handed castings, with ears cast in for caliper mounting in either direction.  So it doesn't matter which one you pick up to use, right?  Not right.  The casting may not be handed, but the machining work is.  If you're not careful, you could find that the handbrake cable extension arm and the rear wheel bearing grease nipple holes are swapped around because you've picked up the upright that was machined for the RHS, not the LHS, and you'll have to press the whole lot apart again and reset the bearings etc. 

Ask me how I know.

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
Paul Blore
(@paul-blore)
Reputable Member Admin
Joined: 7 years ago
Posts: 398
 

Great write up Roger and very useful information for those with original and accurate replica cars.

Thank you for taking the time to do it.

Paul

The Cobra Register - CEO


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  

No problem, Paul.  That's the short version.... I realise I'm writing for a very small target audience!

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
Roger King
(@roger-king)
Reputable Member Member
Joined: 7 years ago
Posts: 372
Topic starter  

A little bit of further advice, secondhand from Peter Adams:

If the old stub axle steadfastly refuses to press out of the wheel bearings, you may be able to get things apart by dismantling the outer wheel bearing housing.  Shine a torch through the peg-drive holes in the stub axle/disc.  The bolts holding the outer wheel bearing split casing together will be visible - these may be hex-head bolts, or they may be socket cap screws.  If the latter, you will be able to get a hex-wrench through the hole to undo the split casing, one at a time.  It's fiddly but it works.  With these loosened (you won't be able to undo them completely until the casing has moved a little), you can press the outer bearing out with the stub axle, thus freeing the outer assembly from the upright.  It should then be relatively simple to press the outer bearing off the stub axle on its own.

If they are hex-head bolts, you're on your own...  given the price of uprights and stub axles, I'd cut a window in the disc setback and access the bolt heads that way.  I got up to 8 tons on the press before doing the above, which might risk damage to the upright elements you're using as pickup points for the puller/press.

 

The Cobra Register - Historian
Several old bangers, which used to include a 289
fbhvc.co.uk
thesahb.com


ReplyQuote
Share: