front brake disc/hub

[Colin McA]

My front discs are well over due for a change so today I got my finger out.






They came apart a lot easier than I thought.

One thing I did note is that the rear hubseal is cracked? what do you guys reckon?

[Phil Nottingham]

Classic overheating hub - probably by a binding caliper but also hub bearing worn/slack and rarely just old age!

[baconsdozen]

I had a similar thing the other day although it was the outer race that was cracked and had damaged the hub.The hub got a bit hot but turned freely with no noise.David Green provided a new hub and a new bearing and seal fitted OK.

[Colin McA]

Inner race looks a bit dis-coloured, and a tad rough, found a few metal flakes.

new set to be ordered from the club.

The brakes are free having been rebuilt a few years back, I suspect a combination of the pre rebuild calipers and the thin discs added to 40 years have caused this problem.



Colin

[baconsdozen]

This is what I dug out of my hub.The inner race was cracked before being knocked out.The inner race is a different make and size to the damaged outer.It doesn't show well in the pic but the outer race had broken up badly,the rollers were running on the outer ring so the bearing was relatively quiet.

Uploaded with ImageShack.us

[enigmas]

Given the example you've shown...I don't know how you drove the car any distance, at any relative speed at all. That original front disc is dangerous. (Don't ask me how I know). Variations in thickness from one side to the other cause all sorts of braking anomalies including: erratic braking, smoking discs, veering to one side and overall substantially reduced braking ability. Bearings and seals are cheap so replace these if they'll at questionable...and it also gives peace of mind.

[Colin McA]

I always drive to a safe stopping distance.

Surprisingly the car did pull up very well even recently passed an MOT with good results on the brakes.


Good lesson in actually looking at parts up close. Not sure why but why does the pitts not clean out with normal use, they seem to dig deeper.

Hopefully new club supplied bearings on will arrive soon and I can get the new disc and pads fitted.

[enigmas]

Interesting Colin about your MOT. It's unusual that whoever checked your car was obviously unaware that the disc was way under tolerance which is easily evidenced in the initial picture you posted comparing the old disc against the new. Off-hand I believe a new disc is about .500" or half an inch thick. It is an enormous variation when your old disc seems to be around the .350" mark using my precision eyeball caliper.

Note: A disc with .003 runout will cause the brake pedal to pulse especially with fixed head calipers as fitted to P5s

[p5tgc]

Regarding disc wear, I was recently told that these days MoT testers will not fail a vehicle on discs worn below manufacturers limits, their only check is for cracking and /or severe corrosion. As I had just replaced discs worn below Ford spec (by 2mm) on a Focus I was somewhat suprised! Anyone know if this info is correct?

Pulsing from the discs can be due to many factors, disc run out and variation in disc thickness around the wearing surface being the most obvious. Some new disc pads come with a top surface coating which is abrasive, in order to attempt to "true up" the disc surface.

[Colin McA]

during the test the tester is not permitted to remove the road wheel. This and the dust cover prevent a good look at the disc and pads.

The old disc may just be a different manufacturer or been previously skimmed as you would see the huge ridge where the pad doesn't sweep.

How is a tester supposed to know the spec of all cars made especially older ones. I have heard of garages changing discs and pads but not been able to provided the measurements to show how they are under.

Out of interest does anyone know the original min/max thickness of the discs?

Colin
Colin

[enigmas]

I always 'imagined' that a tester would have a spec book for a particular model car and with items such as brakes being critical safety factors would measure these with a set of calipers/verniers...but I'm on the other side of the world and practices are different on this side of the pond.

[p5tgc]

Nominal thickness of a new disc is quoted as 14.4mm (0.568inches); Minimum thickness of worn disc is 13.16mm (0.518inches); according to Service News Letter dated December 1970 (Vol 3, item 246).

[Colin McA]

Yikes chaps!!!

I measured the thickness of the disc yesterday and found that the new ones are as Trevor posted however the old ones were .421 or 10.7mm. That is a serious difference from the 13mm quoted.

I would say that the orginals had been skimmed at somepoint, dangerously so it appears.

just waiting on my new bearings and then I am back in action.

Colin

[enigmas]

When you swap the discs and check the front hubs for bearing play & condition ensure that you eliminate all lateral play in the hub bearings but without bind...you'll find that the car will track better under hard braking and pedal feel is also improved.

Any play will lead to pedal kickback and erratic braking as the disc will want to push the caliper pistons back into their housing.

[Colin McA]

Got round to this today, What I couldnt find was the torque for the discs to the hub.

Can some one tell me what it is supposed to be.

Thanks
Colin

[johnwp5bcoupe]

I don't think there is one Colin only for the two bolts holding the calliper on.
It's a case of taking up the play and not over tightening which would be the death of the bearing.

Reading it again taking foot out of mouth

There is still nothing in the WS manual so the link below from P5tgc is a good starting point if it were me it would be one grunt tight with studlock

[p5tgc]

Colin,

If you know the size and spec of the bolt you could use a standard torque setting as per the table on this link:


www.yetmans.mb.ca/kohler/page3/page3.html

regards TC

[Colin McA]

It was the 5 bolts to that hold the disc to the hub.

I wonder is the P4 WSM has anything. Anyone got a P4 WSM? Phil?

colin

[Phil Nottingham]

Yes - 30lbs/ft - diagonal

[Colin McA]

Thanks Phil,

I am going to go and finish them off now.

What I seem to have misplaced is 2 anti squel shims for the brake pads. Don't suppose anyone has a couple lying around? might drop an email to David Green.

[Phil Nottingham]

They are only needed if you ger brake squeel so try them without - they turn up on Ebay from time to time NOS. Also needed sometimes as well as or instead of are the bent spring clips that go over the pins

[johnwp5bcoupe]

Aug 17, 2011 16:13:38 GMT Colin McA said:

Thanks Phil,

I am going to go and finish them off now.

What I seem to have misplaced is 2 anti squel shims for the brake pads. Don't suppose anyone has a couple lying around? might drop an email to David Green.

For sure David has I took them off yesterday

[Colin McA]

I didn't have the springs but did notice them in the WSM.

colin

[johnwp5bcoupe]

Mine are just the flat variety as were the ones at David's

[Phil Nottingham]

Ho Colin

Nice to meet you today and put a face to quite a lot of posts thanks for taking the trouble to look me out

I hope you get your carbs sorted - you came along way to Elsecar I did not realised where you lived - pity you did not come in your Coupe!

I looked at pour pics too - good work - have you got a Mini Cooper Classic too?

PS

I did notice the genuine Scottish plate 3500S P6 - I assume it was your mate's from West Lothian?

PPS
We do not normally go to P6 do's but this was only 55 miles away and we had never been there. Hoped you both enjoyed it too?