rear hub/disc warp

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rear hub/disc warp

Postby chrism » Mon 08.12.2025, 13:11

In July'24 I did Jamie's excellent type-R rear caliper upgrade. At the time I noticed a bit of n/s/r scuffing as the wheel turned.

Fast-forward to today's MoT advisory :- "Service brake fluctuating, but not excessively Nearside Rear" and I'm thinking how to cure it?

The discs/hubs were renewed in Feb'22 and still look 'as new' having done ~6000mls. I've just checked and there is a very slight low spot on that n/s/r. I'm wondering if that wayward disc can be machined to stop the fluttering (that's actually not felt on braking) OR can I get away with replacing just that disc at today's prices :(?

I know that yet another option is RonR's excellent Astra hub + separate disc replacement/upgrade but methinks that'd be a hammer to crack a walnut fix atm for me - even tho' it makes ultimate sense. But I really don't want to trash the newish o/s/r disc...

Hmm...any offers of advice please? I realise that new discs ought to be replaced in axle pairs...but... :?:

(ps I'm wondering if this may have been 'one of that bad batch' :shock:?)
Last edited by chrism on Sat 20.12.2025, 14:41, edited 1 time in total.
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Re: rear hub/disc warp

Postby dapinky » Mon 08.12.2025, 14:13

chrism wrote:(ps I'm wondering if this may have been 'one of that bad batch' :shock:?)


This was my first thought when I was reading the post - and then you put it in writing yourself.....

Mine were so bad that they were immediately obvious, and the measurement of 'run out' with a dial gauge confirmed just how bad they were. In fairness, one was so bad that it caused an issue straight away, whilst the other would have been okay in use, but was a long way out of true. So, if yours were 'bad-but-not-quite-very-bad' it may have taken until now to realise. Do you have access to a dial gauge to check them? It is a quick and simple procedure.

However, if found to be 'wrong' then I'm not sure how much material would need removing to get it 'right' again - and if it would reduce the thickness too much.

I'd get them checked, and if wrong, contact the seller to see what they will do about it as although it has been a while, they are aware of the issue, and they clearly are not "fit for purpose"....

.... after that, it is a case of seeing what is best to do.
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Re: rear hub/disc warp

Postby chrism » Mon 08.12.2025, 14:53

Thanks dapinky for the prompt reply. I made my own 'dial gauge' with a screwdriver-in-a-vice-on-a-block (of wood).

No real measurement but sufficient to reliably detect a warp. It's not a major problem atm but I suspect it won't get any better over time. (I'm a bit suspicious that it was 'duff' when new, tho'.)

I don't know where these hub/discs came from; they were fitted to 'make the sale', I suppose. And I'm not minded to arm-wrestle.

My gut-feeling is to replace it with new whilst the other side shows no sign of wear in order to maximize use on the other side, but woe betide this vendor if the the new one's anything other than true...

I'm hoping LEC-ers might agree that'd be an acceptable resolution. (I used to be decisive but I'm not so sure now... :wink: )
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Re: rear hub/disc warp

Postby Tuga2112 » Tue 09.12.2025, 09:14

i understand the reluctance to changing a side that is working fine.

the astra conversion is one of those things that you are likely to save money (and time) on getting both uprights machined at the same time.

by all means put the old good disc back (my yellow car is proof thats safe). but i do advise getting both uprights sorted at the same time. so you need to wait for the machining to be done only once.

as far as skimming the bad disc. that would depend on circunstances and the result of your measurements. i personally would do it.. but thats because i have access to a lathe for free and i can take 5 hours to get it setup and nobody would bother me (and probably would get help from a retired machinist anyway) your circunsances are not likely to be similar.
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Re: rear hub/disc warp

Postby chrism » Tue 09.12.2025, 10:51

Wise words Tuga that have crystallized my thoughts.

If the other side was less than new I'd be climbing up the wall to be no.4 in the Astra G list; I think that conversion is definitely the way to go...

Atm it's only an 'advisory' of 'service brake fluctuation' that's so slight it's not felt through the foot brake - but (you know what it's like :? ) I'll probably ultimately bite the bullet and go for one new n/s hub/disc and bearing 'cos (unfortunately) that's 'what we do' with these little gems 'innit'? Like most it's a fair weather car and the current weather gives me a bit of breathing space I suppose.

Again, any thoughts/advice are most welcome.
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Re: rear hub/disc warp

Postby RonR » Tue 09.12.2025, 11:10

Here's a thought:

When I did the first conversion I bought a set of second hand uprights to modify in case things didn't work out, so my old ones are sitting on a shelf.
If I donate them to LEC we could have a spare set to pass on to the next person to do the mod. That way the Upright/Hub/Disk can be built up off the car so there's minimum 'downtime' involved.
The removed uprights can then be used for the next person, etc. Assuming the ones removed are cleaned up & serviceable?
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Re: rear hub/disc warp

Postby chrism » Tue 09.12.2025, 11:34

You know, that's a brilliant idea...

We ought to do more of this as well as, perhaps, sharing amongst ourselves things like O2 sensors,rear discs, windscreens, hoods, rear uprights :) etc that are sometimes in such short supply (or have to come from RA) that we feel the need to store 'just in case'...
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Re: rear hub/disc warp

Postby Tuga2112 » Tue 09.12.2025, 12:41

i commend the thought but advise against it in the format your suggesting.

the issue we have is the same old recurring issue that things shared are often "lost" and then nobody takes advantage of them.

a more centralised approach with some degree of monetary remoneration is what i would advise, i suggest you contact Dave, i know in the past he was intending on doing something on this basis, and given the implicit level of trust, i think you may find some means to help offset your costs while helping the next person.

i have ideas on how i think it would be fair to offer this to new adopters, but i believe it would be best you discuss that with Dave directly.
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Re: rear hub/disc warp

Postby chrism » Tue 09.12.2025, 14:06

Again, sensible thoughts Tuga: There are often too many individuals who want to make use of a system rather than nourish and cherish it.
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Re: rear hub/disc warp

Postby dapinky » Tue 09.12.2025, 14:38

In the interests of transparency, I will post my thoughts openly....

When I discussed this with Joao, it was my intention to acquire a pair of rear uprights (one side was available new, the other would be used - not sure of the current situation though), and get them machined to accept the Astra hubs.

I thought that I could purchase a pair of hubs and discs and fit them up so they would be 'plug-and-play' - but that brought into question the postage costs, so maybe leave the discs for the next person to source themselves as they are heavy and pointless to have to go via me (or anyone else) when they are a bolt-on item freely available (and some people may want different discs to those I had sourced anyway).

If I were to do a set as a 'one off' then machining may be an issue, more so than if i were to do a few sets over a period of time. For a single pair, it is easier to out-source the job - but if a few sets were needed, then I would buy a suitable cutter for my bench drill and set it up on the X/Y table and do it myself.

I never really got as far a costing it up, as I don't want to make a huge profit, but equally, I don't want to lose actual money (time isn't an issue in this respect). As such, I would be seeking to 'break even with whatever number of sets I were to produce, dividing the initial purchase price of parts, cutter and even the uprights amongst the first 6 or so sets. After that, it would be unfair to reduce the price for later applicants, so my thoughts were to keep the price the same (assuming parts remain the same cost), and put any excess money into the LEC kitty (which may keep Geoff happy!).

I have no actual numbers in mind, but it would need to be financially viable to do the conversion for the buyer, otherwise there would be less takers.

Realistically, whilst "we" tend to know each other on this forum, not everyone does - so there will always be an element of trust (which could be mitigated with a 'core deposit' system, as long as it doesn't get more complex than it needs to be.

Inevitably, there will come a time when the returned uprights are in a condition that cannot be processed (things happen during their life!), so other units would then need to be sourced - and who would fund that?

In an ideal world, I'd be able to source 4 or 5 pairs of uprights, machine them, assemble them with bearings, and have them ready to send out - but finding the initial supply of parts makes that unlikely.

Timescale becomes an issue if someone 'needs' a pair now, and the returns are not inbound due to issues with the last person - again, not impossible to sort out - but may cause agro somewhere along the line.

These are all just wild thoughts, and I may well have missed something out during this post.
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Re: rear hub/disc warp

Postby chrism » Tue 09.12.2025, 16:26

Yep I like those wild thoughts and I'd be happy that there was a 'unity' of upright conversion from a known consistent operator (such as da pink)

The properly-machined uprights could be supplied as a 'recon' article (tho' the inevitable refund process might include complexity - but would be necessary to shorten the postage overlap) with the buyer paying the price of upright return and absorbing the postage cost within the final price. To morally 'police', If the uprights weren't serviceable deposit would be lost, offered uprights could be pic'd and the culprit might be admonished on LEC and asked for a return, perhaps?

I think 5 or 6 units is a sensible 'first draft' especially with the cost of tooling and I reckon the correct hub/lifelong bearing ought to be supplied as part of the process, since the discs can more easily be a more-personal correct individual choice. Could sand-blasting be part of the refurb process, too, I wonder?

I reckon that facilitating m100 rear hub upgrades (over the expensive dinosaur GM originals) in this way will encourage those of us who can't engineer but would rather 'plug and play' (than risk our own engineering 'adventures' with various degrees of success, I bet) and 5 or 6 units might well be a significant underestimate wrt final numbers. If costs went down I wouldn't feel 'cheated' - it'd just be an honourary part of being 'there at the coalface'...

I'd certainly be confident to be a customer under these circumstances! It's a no-brain ugrade, tried-and-tested and please can I be no.1 on the list if costs are viable and brave LEC-ers decide to go ahead?

(ps I have few engineering skills but I'd be happy to play a part to initiate this process if I could help in any way...
We have the skills to 'do' these sensible upgrades, Jamie, Ken, Ron, Matts, yourself and others have shown this to be the case; we shouldn't expect individuals like them/you to take all the risks and financial worries should we?)
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Re: rear hub/disc warp

Postby chrism » Fri 12.12.2025, 14:13

Image

Update: I thought long and hard and, whereras I'm an absolute supporter of the Astra conversion, I couldn't come to terms with 'trashing' the hub/disc/bearing on the other side

On Mon I spoke to Mike of SWLCPerformance who had a rear hub/disc etc in stock. I was a bit worried about the bearing so I asked him to see if the w/shop could press it in. The outset was that they could so I 'pulled the trigger' on Weds am and by Thurs am I had a shiny new disc c/w bearing, fully lubed-up and ready to roll, that SWLC fitted w/out making any charge :D

So, a big 'high five' to Mike Hopes and SWLC...and grateful thanks for going the extra mile :D
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Re: rear hub/disc warp

Postby Tuga2112 » Mon 15.12.2025, 09:46

its no fun if you just take the comertial approach.

your supposed to make your life harder in order to keep the car on the road :lol:
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Re: rear hub/disc warp

Postby chrism » Mon 15.12.2025, 12:05

I'm fairly certain that's an option with our cars :( :D

update 20/12/25;- the n/s/r now feels so solid that I've just 'had to' renew the bearing in the o/s/r. Never done an m100 before - but now attending emergency counselling for project creep... :D :D
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