Lotus Elan

Brake Caliper bridge bolts - source

PostPost by: jono » Tue Mar 21, 2023 8:58 am

I'm struggling to locate replacement bridge bolts for my front calipers.

They are 7/16 UNF nominal length 2.25" and I believe they need to be grade 10.9.

Any pointers as to source please?

Cheers

Jon
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PostPost by: 2cams70 » Tue Mar 21, 2023 10:11 am

Personally I tend to avoid splitting the caliper halves unless you really have to (i.e the bridge seal is leaking - and this is something I've never encountered)

Why do you want to replace the known good quality and correct specification original bolts? They aren't stretch bolts as far as I'm aware. It's not like a conrod bolt in an engine that can be over-revved. Most normal people do not regularly stomp on the brake pedal with the full force of two legs.

If you do reuse them make sure you don't get them plated. Black oxide or paint is OK but best not to zinc plate due to the risk of hydrogen embrittlement.
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PostPost by: jono » Tue Mar 21, 2023 11:25 am

I split the calipers to blast them and fit new pistons and seals - I can't imagine how impossibly difficult it would be to do that without splitting them.

The received wisdom seems to be to replace the bolts if you do this but I must confess I do not fully understand the rational for this given that the quality of a 1968 bolt will doubtless be better that one of unknown origin in 2023.

So, yes, I will probably just re use them (I managed to source new bolts for the rears).

Classiccar Automotive use cap heads when they do them so there must be an issue obtaining hex head bolts of this type.
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PostPost by: rgh0 » Tue Mar 21, 2023 12:08 pm

ARP sell 7/16 inch UNF 2.25 inch length under head bolts that may be suitable ?

cheers
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PostPost by: Andy8421 » Tue Mar 21, 2023 12:13 pm

jono wrote:Classiccar Automotive use cap heads when they do them so there must be an issue obtaining hex head bolts of this type.

There is indeed.

I searched high and low for suitable hex bolts. I was unable to find any, and ended up using cap headed bolts. I spoke with Classicar Automotive, who said they were unable to source hex head bolts in a suitable material.
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PostPost by: jono » Tue Mar 21, 2023 12:15 pm

Thanks for all the comments guys, I'm going to re use the existing bolts
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PostPost by: 2cams70 » Tue Mar 21, 2023 12:18 pm

jono wrote:I split the calipers to blast them and fit new pistons and seals - I can't imagine how impossibly difficult it would be to do that without splitting them.


The only area in the caliper bores that is a little difficult to clean properly is the area in the bores above the seal groove. This area is typically corroded somewhat due to moisture being trapped under the dust boot. I can normally clean it adequately with some wet and dry. No need to blast into the bores themselves. A little corrosion pitting below the seal groove is of no consequence whatsoever.

If you wish you can grind down the top of an old piston so the top of it only reaches the top of the seal groove. This will expose that critical area above the seal groove to the blast media whilst protecting the area below the groove.

If the area above the groove is not properly cleaned you risk the piston sticking prematurely and causing brake pull
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PostPost by: jono » Tue Mar 21, 2023 12:47 pm

Indeed, it took ages with a hardened steel pick to clean those grooves then as you suggest I used an old piston to protect the bores from the blast media.

The piston gaiters were a bitch to fit as well and would have been much more difficult without the calipers split.

Lots, and lots of work in the handbrake mechs - I now appreciate why Classicar Auto charge so much for the rears.
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PostPost by: jono » Tue Mar 21, 2023 12:49 pm

Andy8421 wrote:
jono wrote:Classiccar Automotive use cap heads when they do them so there must be an issue obtaining hex head bolts of this type.

There is indeed.

I searched high and low for suitable hex bolts. I was unable to find any, and ended up using cap headed bolts. I spoke with Classicar Automotive, who said they were unable to source hex head bolts in a suitable material.


Interestingly Andy, SJ show new hex heads on their refurbished exchange front calipers which may mean they are using grade 8.8
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