Lotus Elan

Girling AR Calipers - help required

PostPost by: nmauduit » Wed Aug 18, 2021 1:31 pm

Regarding the flex of period AR calipers (causing wedged shape wear of the pads and premature change requirements), I was sorting through the parts of my GTS project and realized they were marked with the alloy type : LM4

20210818_115825.jpg and
Girling AR 68049920 LM4 alloy


I checked around a bit e.g. http://www.nortal.co.uk/LM4/

" Heat Treatment

This alloy's response to heat treatment is dependent on the presence of Magnesium; therefore for such treatment, the Magnesium content should be near the maximum.
A very considerable increase in mechanical properties is obtained by Solution heat treatment and artificial ageing.
LM4-TF (fully heat treated) -Heat for 6-16 hours at 505-520°C, quench in hot water and heat for 6-18 hours at 150-170°C and air cool.
If bending or straightening of castings is necessary, this should be carried out after the solution heat treatment, since in this state the castings exhibit greatly increased ductility.
"

so wondered if there is a way to find out whether the period calipers were originally heat tempered or still held that temper, then if re-tempering could be attempted (esp. after being machined into a finished part: would that likely alter the specs and tolerances rendering it useless ? )
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PostPost by: Davidb » Wed Aug 18, 2021 3:28 pm

Hopefully this won't derail the discussion:

Wilwood make a caliper that looks similar to the AR and weighs only 2.3lbs. The downside is a 1.75 piston. A couple of years ago I phoned and talked to a Wilwood engineer and asked if he thought they could be bored out to fit standard Elan caliper pistons. He said "Absolutely, we made these things oversize" or words to that effect. I should have asked if they could go to 2.00" shouldn't I?

https://www.wilwood.com/Calipers/Calipe ... ame=WLD-20
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PostPost by: Elan45 » Thu Aug 19, 2021 3:40 am

Talk about caliper flex!. And on top of the caliper body flexing, you also get a good dose of piston flex in these.

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PostPost by: Davidb » Thu Aug 19, 2021 3:51 am

Elan45 Are you referring to the Wilwood caliper? If so please provide more information/experience/proof.
I have no experience with Wilwood calipers and no axe to grind.
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PostPost by: patrics » Tue Aug 24, 2021 9:51 pm

Hi,
Old aluminium racing calipers with unknown history do not seem like a good idea to me, much better and safer to buy new period calipers from the likes “Performance Braking” in Monmouth who have them manufactured from modern alloys.

These racing calipers were made funnily enough for racing cars – ie very light weight cars requiring very low hydraulic pressures by comparison to a robust production caliper with 3 or 4 steel bolts holding it all together. Applying a high static load to a very weak aluminium caliper would be disastrous for its fatigue life and I’m sure it would not be difficult to bend or break it in half.
Companies tend to like internal routing of the fluid because of the potential failure modes of external pipes.
So the original calipers had external pipes probably for a few reasons:
The fluid is removed from the caliper bridge area and so from the radiated heat – this is where opposed piston calipers have problems with fluid vaporisation.
The original calipers were probably not strong enough for internal routing and I’m guessing that the calipers made later probably had more material in the bridge as well has a better material.
Because the caliper is a one piece design then the cross drillings would also need to be plugged.

Regarding the uneven pad wear.
If it is caused by ballooning of the actual caliper then it is probably working outside of its designed pressure range or the pads were originally only expected to last one race anyway – different times different expectations?
Pad taper could also be down to the design of the caliper regarding centre of pressure or simply disc coning.

Regarding old racing parts in general I’m pretty sure the manufactures never calculated for aluminium parts to last more than a few seasons never mind 50 years!

Cheers
Steve
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PostPost by: nmauduit » Wed Aug 25, 2021 9:21 am

patrics wrote:Hi,
Old aluminium racing calipers with unknown history do not seem like a good idea to me, much better and safer to buy new period calipers from the likes “Performance Braking” in Monmouth who have them manufactured from modern alloys.

These racing calipers were made funnily enough for racing cars – ie very light weight cars requiring very low hydraulic pressures by comparison to a robust production caliper with 3 or 4 steel bolts holding it all together. Applying a high static load to a very weak aluminium caliper would be disastrous for its fatigue life and I’m sure it would not be difficult to bend or break it in half.
Companies tend to like internal routing of the fluid because of the potential failure modes of external pipes.
So the original calipers had external pipes probably for a few reasons:
The fluid is removed from the caliper bridge area and so from the radiated heat – this is where opposed piston calipers have problems with fluid vaporisation.
The original calipers were probably not strong enough for internal routing and I’m guessing that the calipers made later probably had more material in the bridge as well has a better material.
Because the caliper is a one piece design then the cross drillings would also need to be plugged.

Regarding the uneven pad wear.
If it is caused by ballooning of the actual caliper then it is probably working outside of its designed pressure range or the pads were originally only expected to last one race anyway – different times different expectations?
Pad taper could also be down to the design of the caliper regarding centre of pressure or simply disc coning.

Regarding old racing parts in general I’m pretty sure the manufactures never calculated for aluminium parts to last more than a few seasons never mind 50 years!

Cheers
Steve


thank you for taking the time to reply.

Yet I respectfully disagree with most points ;)

I precisely intend to relive, ever so briefly, the period experience of racing a GTS elan, and with as many period part as I can : racing a brand new car (even a nice replica) is not my intention and I have little interest for this.
Yet I'm open to reconsider if I read testimonies of AR calipers breaking opened or otherwise failing dramatically during track use... which I have not so far.

I've had hydraulic fluid vaporise on occasion, with internally connected heavy Girling calipers (including PB16, on my S4se during track days, which is easily 100kg heavier than a GTS ) : I believe the heat was actually transferred by conduction to the pistons rather than radiated (dust seal also molten). I hope to be able to improve my driving so that this does not happen too often... and will also attempt to thermally isolate in conduction the pistons from the pads (Ti plate, possibly castellated piston...).

My main question regarding heat treatment of LM4 alloy calipers remains, though ...

keep it on the road...
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PostPost by: patrics » Sun Aug 29, 2021 10:30 pm

Hi
I don't think the parts will survive heat treatment in regards to geometry or see much benefit regarding physical properties.
I'm sure you already know that the heat treatment is carried out on the casting not the finished part.

Expensive process to get done and not many companies will do it. The last company I used was Wallwork in Birmingham
You can do your research by googling T6 heat treatment or check the link below which was easy to find.

https://www.sciencedirect.com/topics/en ... -treatment

Regards
Steve
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PostPost by: Mike Ostrov » Mon Aug 30, 2021 1:21 am

I used the original Girling externally piped AR calipers for 20+ years and 8700+ track miles in my Super 95 Lotus Elite without any issues. I have the later internally piped AR calipers on my two Elite/Elans. These are Elite bodies on stretched and re enforced Elan S2 frames (7 degrees of castor, same as my Climax Elites) with fully adjustable suspension on our 15 inch wire wheels. The MK I has a FWB (1460 cc) Coventry Climax in front of a Datsun 280 zx 5 speed and the Mk II has a1725 cc Twin Cam I matted to an automatic gearbox. All gained a bit of weight at 1875 and 1945 pounds (the automatic is a monster). These are street cars and the Girling AR calipers have performed without issue. I do not baby my cars. Yes, they will flex and I have measured this and mentioned it in a previous post. Hope my experiences are useful. Cheers. Mike, in the San Francisco Bay Area.
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PostPost by: nmauduit » Wed Sep 08, 2021 9:53 am

nmauduit wrote:Regarding the flex of period AR calipers (causing wedged shape wear of the pads and premature change requirements), I was sorting through the parts of my GTS project and realized they were marked with the alloy type : LM4
...
so wondered if there is a way to find out whether the period calipers were originally heat tempered or still held that temper, then if re-tempering could be attempted (esp. after being machined into a finished part: would that likely alter the specs and tolerances rendering it useless ? )


upon reconsidering this query, I realized it is most likely moot for my purpose since these calipers are beefy enough to operate within their elastic domain, and the elastic modulus of LM4 won't change when subjected to full heat treatment to make it LM4-TF...

so I'll do what everyone else has been doing for decades : change pads often.

As the saying goes here "yet an other problem that an absence of solution solved wieh elegance"
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