Resurfacing Rear Discs

[Cinbearcat83]

I am the new owner of a 1972 Lotus +2 S130. This is a project car. As this car is new to me, some of the restoration tasks are not as straightforward as my other cars! The current task is to resurface the rear brake discs. I have removed them and verified that they have enough thickness to resurface. I took the discs to my local shop to have them turned (and since I live in the US, the machinist had never seen a disc such as this). He called and said that he needs the hub attached to the disc to turn it. I don't see how this would be possible. What is the proper method for resurfacing the disc? Thank you for any insights you can provide.

[NTG999]

You will be advised that they shouldn't be turned they should only be surface ground, having said that many years ago my brother easily cleaned mine up on his lathe, he just made something to bolt them to. Different machine shop? Buy new discs - I don't think they are that expensive

[pharriso]

Elan discs are small (thin) compared to most cars & especially to American cars from the same period. Looking at the Rear disc:

26j0001as.jpeg (30.31 KiB) Viewed 1517 times

I can't see how the disc could be held in a lath without some kind of hub/adapter being made. Perhaps if you have an old rear driveshaft you could use that?

Buy new discs - I don't think they are that expensive

That may be true in the UK, but parts in the US are usually 2-3x more than UK prices & shipping from the UK is high these days, especially for heavy objects which these are.

[Lotus54]

Bolting it to a faceplate and truing would likely be pretty easy to hold.
My lathe claims a 10” swing (diameter of discs) - but they won’t quite fit. (I suspect the 10” is really about 9.8”).

I was going to just use the 3-jaw, expand out to hold and see if it was true. But since it would not quite fit…
Mine were in good condition, so I didn’t worry about it much.

[berni29]

Hi

You need to have them resurfaced on the car. But if you are restoring the car then thats not going to be easy. Just clean them up a bit and let the brake pads do the rest. If they are warped then throw them.

Use a dial gauge when fitting.

All the best

Berni

[Cinbearcat83]

Thanks for everyone's responses. I may need to buy a new pair. The current discs have quite a bit of rust that needs to be removed - more than can be removed by hand (pitting, etc). I have two new part sources in the US thus far, RD Enterprises and Perfectbrakes.com (EBC rotors). I am visiting the UK in September, but 1. I don't to wait that long and 2. I don't think my luggage could handle the weight!

[pharriso]

I am visiting the UK in September, but 1. I don't to wait that long and 2. I don't think my luggage could handle the weight!

That's what I did

[661]

If they are straight and true I'd just clean them as best you can and let the pads do the rest. The front brakes do most of the work and I'd spend more time/money on getting them right and caliper refurbs front and back.

[MACCA.GLM]

Hi

I have done this job a few times. If you have the outboard drive shaft out of the hub you can bolt the disc to the shaft and put it in the lathe to Mc check or put it between centres or on vee blocks . They will all give you a good idea of the accuracy of the shaft. You can also check bearing journals for size as well

If I were you I would put the shaft in the lathe and check the 3 ears for runout. If they are
More than 2 thou true them up once you have done this bolt the disc to the shaft and then check the runout again if the disc is 10 thou out you will have to take 20 thou off to get it rt
10 thou a side. This also depends on how much wear or thickness the disc is . Should be in the tech data of the workshop manualThe disc wants to be as accurate as possible no more than 4 thou 0 is better
There is no point in truing or fitting a new disc if the outboard shaft is distorted,as when you bolt the disc to it the disc will be distorted also

One of my outboard shafts was out 15 thou that I did not know about so when I fitted the new disc I was puzzled as to why I had 20 thou runout on the disc . It was obvious that the flanges or ears were distorted

Hope this helps

Regards

G

[Quart Meg Miles]

There are at least two other Lotus owners in Michigan. Perhaps one has a spare axle he could lend you if you are not dismantled so can't use your own.

You can measure axle ears' run-out on the car and if not too great you can probably find a position for the brake disc which leaves it with minimal run out and, if necessary, you can add a shim where it bolts on. Beer cans are handy for shim material (when empty).

[h20hamelan]

Has anyone ever taken a disk of similar dimensions, and milled out the pattern
I suspect they are from a common vehicle, and modified.

[Quart Meg Miles]

I'm pretty sure they are uniquely Elan and +2, they are a very tight fit and few cars had rear disc brakes in the early 1960s. The S1 and transitional (early) S2 had different hole spacings to later models and those discs are rare now.

[Cinbearcat83]

I went ahead and ordered new ones. They are arriving today. Any suggestions on purchasing a magnetic dial gauge? I haven't needed to use one in the past. Thanks for all the responses.

[NTG999]

I'm not sure where you would put the magnetic base, when I've done mine in the past I made a small bracket that used one of the caliper lugs and secured like that

[StressCraxx]

I went ahead and ordered new ones. They are arriving today. Any suggestions on purchasing a magnetic dial gauge? I haven't needed to use one in the past. Thanks for all the responses.

The Fowlers are made in Taiwan with parts sourced from China (like many things) for a reasonble cost. I have several precision tools from them. They are very versatile for other tasks too. The other one is the "mighty mag" which is very compact and might work well.

mag base dial indicator sets

https://www.amazon.com/s?k=mag+base+dia ... doa-p_1_23