DavidLG45

3 May 2015 at 09:43 #51233

Some of my brake rods have kinks in them where they shouldn’t have kinks.

I would like to replace them as I don’t want to try and straighten them and possibly weaken them. Possibly replace them all.

They are 5/16 inch rods. They would need to be tensile steel I imagine. Engineering advice needed. What grade of steel should I use?

David

Alec Rivers-Bowerman

3 May 2015 at 19:09 #51234

Hi David;
I’m working on that same area on my 16/80. I’ll probably use 1144 stressproof rod – here is a North American link. http://www.mcmaster.com/#grade-1144-steel-rods/=x0ubtt
I’ve been checking various bits with a hardness tester at work – I’ll take a brake rod in tomorrow and see what hardness it is – this gives me the steel’s tensile strength and it should confirm the above suggestion.

Alec

DavidLG45

4 May 2015 at 10:44 #51235

Hi Alec,

Thanks that’d be very helpful. I’m in the UK so would need to find the UK equivalent grade. Imperial sizes are not used a lot these days but can try and find 5/16. Could possibly use 8mm – at least it’s slightly bigger and not smaller.

David

Bill LG45

4 May 2015 at 20:11 #51236

If you want to source suitable brake rod material in the UK quickly it might be an idea to canabalise Model A Ford brake rods, which I managed to get off the shelf from Belcher Engineering in the past for my Model A Ford.
NB: Any threads on these would be “American” UNF rather than the BSF threads on the Lagonda but they are 5/16 inch dia and the main Model A brake rods are about 4 ft long.
There are a number of other UK suppliers for Model A parts such as Oneillvintageford.co.uk who list two available ( made in the USA) on their web site at ?20 each
If you decide to use metric rod remember you will need to cut 5/16 BSF thread on the end to match the Lagonda fittings
Hope that helps
Bill

Alec Rivers-Bowerman

4 May 2015 at 23:29 #51237

HI David;
I did check out a brake rod today – it was 90,000 psi (600N/mm2) tensile strength on the outer surface and somewhat higher internally, about 100.000psi (660N/mm2). This is stronger than a low carbon cold drawn rod. Something with 0.5% carbon, cold drawn, maybe? I don’t know the European nomenclature but a 44SMn28 looked interesting and similar to 1144.
Alec

Alec Rivers-Bowerman

5 May 2015 at 05:00 #51238

I measured up my front brake levers as they were usually set up and assuming a gargantuan 300lb pedal force acting only on the front brakes, worked out the tensile stresses in the brake rods. The short rod connecting the brake pedal lever to the cross-shaft carries the highest load, some 56kpsi in this scenario, while the others carry less than half this. So you do need a good grade of steel for that one short rod, but the other rods could be a standard cold rolled low carbon steel. Sketch attached, I hope.
Alec

Attached files

DavidLG45

5 May 2015 at 09:23 #51239

Hi Alec and Bill,

Many thanks for your help. I will see what I can find. I am not in a particular hurry but cutting down off the shelf rods is an option that hadn’t occurred to me. The longest I need is 1s 44 7/8th inch. But I would need that amount without a thread.

David

DavidLG45

5 May 2015 at 16:24 #51240

Apparently EN8 steel would be a suitable equivalent in the UK.
So that’s what I will get.

Thanks once again for the assistance.

David