Restoring a Top Hat

[David Cochrane]

Looking very smart! A similar double brake cable system was used for LHD Ruby-type front brakes. If you e-mail me I can send you some photos which may be of interest (or I might be able to post them here).

[Parazine]

Hello David,

 I'd be really interested to see the pictures if you can post them......

Thanks

Tim R

[Parazine]

So, here's this weeks work. A subframe that is attached to the chassis extensions to support the rear end of the body. I've seen too many vintage Sevens with broken backs over the years to risk using one without some support at the rear, especially when you have to load the back with "stuff", passengers (not over 10st please!), dogs, children etc etc. It's actually quite an involved piece of fabrication from 25mm square x 3mm  (1" square x 1/8") and 25mm angle iron (1" angle) and it's arc welded together with my trusty stick welder. Just waiting for a coat of black paint before final fitting this weekend.

   


   


I've fitted one to the same design to the Chummy and it's much more rigid. I feel that I can now, in an emergency, put a light person in the back....

[David Cochrane]

Tim,

The files are rather large so I don't want to place them on the forum (I know there's a way to put up thumbnails, but life's too short). To access the photos, go to www.a7c.co.uk/public/ and look at LHD Ruby brakes?.jpg
Hope they are of interest.

David

[Howard Wright]

Hi Parazine

Good job.  I must think about doing something similar on my RK.

Just one thought.  It may be worth jacking up the body slightly before fitting the frame.  The frame itself (despite being very robust) will deflect under load and that deflection may be enough to cause cracks and door misalignment. When you release the jack the frame stresses and deflects back to where you want the body to be.

In a former life I was a structural engineer and remember a builder fitting a huge overdesigned beam into an newly formed opening.  The beam deflected, ever so slightly and all the brickwork above cracked!  He should have inserted slate wedges above the beam to prestressed it and take the load.

Hope I’m not “teaching grandmother to suck eggs”?


Cheers 

Howard

[Parazine]

Hi Howard,

Yep, did that on the Chummy implementation! I made everything to fit, then packed the body up on the extension, under the back floor, just slightly to make sure it was tight.

I really ought to do the RK that I have as well as the door apertures are quite lozenged and the doors catch the openings at the back. However, the RK subframe will have to be a different design because on the 1929/30 style chassis, the factory chassis extensions come off the chassis in line with the main rails and are part of the rear spring seat. I've got enough material but......

[Nick Lettington]

The problem here is you are trying to support additional load from people/ luggage,  not the self weight of the rear of the car. If you put a steel beam into a brick wall,  you can preload the beam so it doesn't deflect when the weight is taken up, but in this case the "live" load is much greater than the "dead" load of the rear bodywork.

If you jack up the rear before supporting it, you still have the same problem with cracks if it deflects under load. 

The solution is stiffness in the supporting structure. This is best done with triangulated shapes and members that have more depth than width... but on reflection,  you're not going racing with this, so a bit of extra weight probably doesn't matter!

[Howard Wright]

Hi Nick

You are right of course. However introducing some upwards stress in the frame may also help with live loads by introducing negative stresses in the body (a sort of prestressing).  You are also right about triangulated frames and deep stiff sections.

The problem with the rear support in early cars is the necessity to avoid the rear axle and find good connection with the chassis which means that a good triangulated framework is not possible. Parazine’s solution seems as strong and as stiff as you are likely to get without increasing the weight too much. 

Cheers

Howard

[Parazine]

Tim,

The files are rather large so I don't want to place them on the forum (I know there's a way to put up thumbnails, but life's too short). To access the photos, go to www.a7c.co.uk/public/ and look at LHD Ruby brakes?.jpg
Hope they are of interest.

David

Thanks David, really interesting. So basically, for the LHD Ruby, Austin put the uncoupled handbrake back into production?

It's really not that dissimilar to the Bodelo (or whatever) attachment on the Top Hat. I'm more intrigued than ever to find out what the brakes are like when I'm finally driving it!

Tim R

[Ruairidh Dunford]

Another LHD car...