Jump to content
Click here if you are having website access problems ×

Runout on new discs???

Myles

By Myles
in TechTalk

 Share

Recommended Posts

Myles

Myles

Posted
Posted

I'm upgrading to HiSpec 4-pots at the front this w/e - and taking the opportunity to install flexi lines at the rear to make bleeding and maintenance easier - and (some say) get more even brake wear on the rear pads.

 

Anyway, I've been at it for the last two evenings and have some issues/questions:

 

i) The front discs are new and were sourced from HiSpec - I noticed (by chance - I had the old calipers still dangling from their hoses) that the LH one has some run-out (I think the term is). The caliper was lightly touching the surface of the disc - and as I checked the bearings for stiffness, I noticed that the caliper left the surface of the disc in one area (noticed by dint of the scraping sound coming in and out...). I took the disc off, removed it from the hub, checked that the hub-face was clean and reassembled - same result.

 

It looks like the variation is something like 2-thou (I think -I'd need to check my feeler gauges again) - it's certainly not visible to the naked eye (unless you've got a soon-to-be-redundant) caliper hanging against it.

 

Should I carry on with the installation, or cry fowl (). To be honest, I can't tell if the problem is with the disc or hub or whatever.

 

Vinnie (on Cam7) has suggested that if I noticed it with a dangly caliper, the runout is probably worse than I measured - and I really ought to get it measured properly and then source another disc. I've not really got time for that though... 😳 ☹️ ☹️

 

Project Scope-Creep is live...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

Link to comment
Share on other sites
stevefoster

stevefoster

Posted
Posted

Hmm,

Well, max disc run out quoted on my Passat is 0.05mm (vented disc) = 0.001968504 inch.

On our Citroen ZX it's 0.2mm (solid disc) = 0.007874016 inch (seems too high).

On a Ford Capri 1969 to 1974 it's quoted as 0.0035 inch (Solid disc).

 

So from that I conclude vented discs seem to have less allowable run out.

 

I'd call Hi-spec and query it. Are you sure the disks were bolted up with the mating faces nice and clean?

 

Also do you have a dial gauge to measure it with. If not a good opportunity to invest...

 

 

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

Link to comment
Share on other sites
Myles

Myles

Posted
  • Author
Posted

Right, well, I spent a fair bit of time investigating today - no dial-gauge though...

 

To cut a long-story short, I put the old disc back on and checked that...

 

...it exhibited worse runout than the new one *AND* the runout was in exactly the same place...

 

So, I'm reasonably confident that;

i) The new discs will be no worse than the old and

ii) (part of) The problem lies somewhere in the hub or bearings (unlikely**)

 

I'd say bearings are unlikely - because they went back in randomly - and so it would have to be a hell of a coincidence for it all to line up again.

 

The hubs are alloy - I'm assuming this is standard and is *not* the lightweight option - I'm guessing it's quite expensive to replace for little gain???

 

Project Scope-Creep is live...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

Link to comment
Share on other sites
stevefoster

stevefoster

Posted
Posted

It sounds like machine tolerance in the face of the hub or bearing surfaces. If both are near max tolerance you are unlucky and they add up. his happened to me with De dion tube end and ear = too much -ve camber.

 

The alloy hubs are the lightweight versions. The SLR/R400 racers went to all steel = very heavy, as they crash the curbs so hard the alloy ones were at risk of failing.

They get pad knock off on most fast curbs *eek*

 

You could split the disc and put just the hub on and measure the run out of the mating face with that dial gauge you have promised yourself *smile*

That way you would know it was the hub.

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

Link to comment
Share on other sites
Myles

Myles

Posted
  • Author
Posted

I always seem to end up doing most jobs three or more times - it does give me the advantage that I end up working about as quickly as a WRC mechanic...

 

I can't be ar7ed to split them again. I'm not about to replace the hubs - and I haven't got time before I need the car on the road anyway.

 

If I do end up with problems (and I'll be doing 1000-1500 miles within the week), I'll get that gauge... *smile*

 

Project Scope-Creep is live...

 

Alcester Racing 7's Equipe - 🙆🏻™

 

Alcester-Racing-Sevens.com

Link to comment
Share on other sites
oldbutnotslow

oldbutnotslow

Posted
Posted

Hi Myles,

I had run out problems on a new set of standard discs that I fitted prior to my upgrade. I found that there were a couple of contributory factors,

1, the large mounting holes in the discs were slightly smaller than the original set and therefore sat slightly tighter to the hub bearing.

2. one of the 4 mounting flanges on the hub was slightly proud ( I established this using engineers blue and a DTI)

 

Cure: -

I increased the chamfer on the large mounting hole to allow greater clearance

I used a fine oilstone and very thin oil (wd40) and honed the offending mounting flange.

 

They are fine now.

 

Regards

 

Grant

 

Black and stone chip.

*smile*

here

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing
×
×
  • Create New...