Brake discs...

[Bud English]

Wish I'd seen this before I did all that masking. I missed it when I blasted the rust off. It goes all the way through to the other side.

Do any of you routinely crack check these or is this fairly uncommon? What's the consensus on changing these? Just replace the one or change them in pairs. The other one looks good and has plenty of thickness left.

[MickG]

I would change the pair.
In fact in the UK most if not all company's will only sell them in pairs.
Mick G

[jkatthehelm]

And they are inexpensive unless you have an early S1 with the larger pcd.
JK

[AHM]

If you can find one with a similar level of ware then just change one. Rear brakes don't do much of the work.

I don't crack detect but do a close visual inspection.

Satisfy yourself that the result will produce even braking and be safe.

[Bud English]

Thanks all.

Here, they are just under $100 each plus shipping for a plain, solid, replacement. Looking at UK eBay prices for pairs, with all the EBC replacements, plain, drilled, slotted or both, makes $100 seem a bit steep for one, "no name", stock one. I do realize that they are in higher demand there and expensive to ship, but....

Okay, having whined about that, I suppose I'll order up a pair and replace them both.

Just for the record, are the rear's originally the same thickness as the fronts? The manual gives only the 10" diameter for the discs, but no thickness spec that I can find.

Are both okay to turn down to 0.335". Nobody local has any information on the minimum thickness for the elan but that's what they show for Triumph 3/8" discs.

[lotocone]

Brian Buckland's book indicates the rear discs are 10 mm new (0.3937") and the minimum thickness should be 8.7 mm (0.3425") for an Elan. They are a Lotus only part according to the book.

[garyeanderson]

I got curious and did some measuring. I have a pair of new rear rotors that I bought 6 or 8 years back, these measured .378 inch

And I also recently removed a pair of NOS rotors off of my original chassis that was never driven installed 20 years ago and they measured up at .376 inch.
These were cleaned of the surface rust and will install in the sows ear chassis.

Then just because I had them I went out in the garage and measured the rusty stack of rear rotors and there are 4 big pdc and 15 later rotors

These are as follows

Big pdc
,346
.342
,357
.298
Small pdc
.357
.337
.293
.372
.374
.342
.330
.373
.348
.366
.380
.368
.345
.346
.348
all measurements are in inches, Looking at the numbers I guess I would think about re-using any of the ones over .350 and maybe even go as low as .345 inch. just looking at the stack, you can see that I haven't re-used any of them, I just don't like tossing out good Lotus only parts, I have tossed out plenty of fronts, in the pile behind the rears are fronts and one pair of used stock Elan front rotors and one pair of used GT6 or Plus2 fronts.

Gary

[Bud English]

Sounds like my best bet is to start fresh with a couple of new discs. There are probably better places to try and save a few bucks than the brake system.

[Jason1]

Here, they are just under $100 each plus shipping for a plain, solid, replacement.

?24.25 +VAT each from SJ Sportscars

[Galwaylotus]

Here, they are just under $100 each plus shipping for a plain, solid, replacement.

?24.25 +VAT each from SJ Sportscars

That sounds more like it!

[Bud English]

The shipping estimates I got from vendors in the UK were 40 - 60? for a pair of discs. I ordered them from Dave Bean in California. I'll have them day after tomorrow.

[CBUEB1771]

Brian Buckland's book indicates the rear discs are 10 mm new (0.3937") and the minimum thickness should be 8.7 mm (0.3425") for an Elan. They are a Lotus only part according to the book.

It is not likely that the discs were originally dimensioned in metric units. The rear discs were probably designed as 0.375 inches thick which is consistent with Gary's measurements. Neither the Elan or Elan +2 work shop manuals provide new or minimum thicknesses, only the maximum allowable run-out of 0.004 inches.

[cal44]

Bud,

you did the right thing. Messing around too find the best deal usually turns out too be, in my case, a fools errand.
I can't tell you how many times in the past I've wasted time looking for "the deal".

Gary, put some oil on those rotors!

Mike

[alan.barker]

hi bud english,
for me after 35+ years of lotus it is o.k. just to replace one rear brake disk. I had a rear cracked disk which caused vibration. I bought just one new one and had the locating lugs on the outboard driveshaft surfaced. After there were no problems.
Alan B

[Bud English]

Hi Alan,

I appreciate your input and that of everyone else.

I replaced them both because my "good" one only measures 0.331" (8.4mm) thick. Didn't want to risk it and didn't want to be tearing into the car again in the near future. Had this one been thicker I would have sought out a used replacement of similar thickness or a new one.