bulkhead flex under braking

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Rob Bell
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bulkhead flex under braking

Postby Rob Bell » Sun Oct 08, 2017 7:14 pm

I've been doing some research for Project Shed - I am determined to try and rid the car of the slightly spongy and feel-free brake pedal that all MGF and TF suffer from - the original pictures here: http://mgf.ultimatemg.com/group2/common ... _servo.htm

On the above page you'll see some of the things I've been going through trying to get a decent pedal feel. What the page doesn't show is that I have, on my other MGF, relocated the brake master cylinder to the driver's side such that there is a slightly more direct operation between the brake pedal and the master cylinder.

Even that hasn't resolved the problem completely... :roll:

I haven't done this on Project Shed, but I have fitted the "Jaylad" bracket to the servo master cylinder support bracket. It gives a useful improvement by triangulating the master cylinder to the top of the bulkhead.

However, this - like all the other solutions I've tried - has not elicited a complete 100% cure.

A couple of animated gifs - anyone like to spot the problems?

OS_bulkhead_flex_GIF.gif
OS_bulkhead_flex_GIF.gif (135.05 KiB) Viewed 519 times

NS_bulkhead_flex_GIF3.gif
NS_bulkhead_flex_GIF3.gif (132.74 KiB) Viewed 519 times

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Re: bulkhead flex under braking

Postby talkingcars » Sun Oct 08, 2017 10:07 pm

Rob Bell wrote:....A couple of animated gifs - anyone like to spot the problems


It looks like the whole bulkhead is twisting!
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Re: bulkhead flex under braking

Postby Rob Bell » Sun Oct 08, 2017 10:17 pm

Exactly. Both sides and the whole scuttle panel.

Unfortunately it appears that the whole structure is underengineered. :(

It needs some bacing adding...

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Re: bulkhead flex under braking

Postby daz » Sun Oct 08, 2017 11:05 pm

just a thought, have you tried bracing where the heater inlet is?

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Re: bulkhead flex under braking

Postby Rob Bell » Mon Oct 09, 2017 1:32 pm

I do have a cunning plan! ;)

To provide some context, I took these pictures in the same way as I did with the previous series of images: no brake pedal pressure versus a full heft on the pedal - mimicking what you or I might do for an emergency stop. The bulkhead (hopefully) doesn't move that much under normal road conditions.

I took the pictures to try and visualize and confirm what I thought was going on in respect to the force and reactions.

The brake operation is a little more complicated than perhaps it needs to be. The brake pedal has a link that goes to the transfer torque tube across the bulkhead. The vector of movement is upward and forward. The top of drivers bulkhead therefore moves backward and upward, seemingly rotating on a pivot that appears to the front edge of the bulkhead/scuttle, as the torque tube mount on the lower part of the driver's bulkhead is moving outward and upward.

Image

The rotating torque tube then actuates the master cylinder in the same vector movement - upward and outward. Consequently, the master cylinder/servo assembly downward and forwards, tugging the bulkhead behind with it.

Bracing the servo bracket down to the subframe below did improve the situation:

Image

But still not a complete win.

Daz, you're right, the bulkhead behind the heater does need some kind of support/bracing. Easy on my race car, as I have removed the heater. Harder to do on a road car: the heater is in the way.

My cunning plan?

I want to take out weight anyway, so the plan is to do away with the cross tube completely, and get the master cylinder operated from the brake pedal directly. If my measurements are correct, this may be a little easier than you might think... ;)

Also, relocating to the drivers side is beneficial, because:
1. you can keep the force couple contained within one structure
2. the heater aperture is actually also the pedal box aperture, and this is also triangulated to the pivot of the brake pedal itself - and a major reason why this part of the bulk head doesn't move anything like as much as the other side.

But even this won't completely cure the movement. My idea at the moment is to try and contain the forward movement by tying the brake assembly to the cross bar behind the dash, and any upward movement to the "transmission" tunnel (more of a longitudinal strengthener on the MGF, in which the brake cables and heater pipes run).

I may see whether I can contain the movement of the existing arrangement as a proof of principle - more soon! :)

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Re: bulkhead flex under braking

Postby Rob Bell » Mon Oct 09, 2017 4:03 pm

Here's a picture of the pedal box. Interestingly, there is a captive nut on the left side pedal support bracket. This could prove serendipitous for bracing the pedal box and master cylinder on the driver's side :)

IMG_4368.JPG

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Re: bulkhead flex under braking

Postby Rob Bell » Mon Oct 09, 2017 4:12 pm

Not the best picture to show you what I'm on about: will take more pictures to illustrate!

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Re: bulkhead flex under braking

Postby flyingbanana » Mon Oct 09, 2017 4:16 pm

What are you using to cover the hole where the air intake for the heater used to be, it looks like a fabric?

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Re: bulkhead flex under braking

Postby Rob Bell » Mon Oct 09, 2017 5:52 pm

:oops:

Well, I have some sheet alloy to cover that up, but so far it has been covered up with a different lightweight material.

Gaffer tape.

Will be sorted properly over the winter ;)

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Re: bulkhead flex under braking

Postby flyingbanana » Tue Oct 10, 2017 9:54 am

Rob Bell wrote::oops:

Well, I have some sheet alloy to cover that up, but so far it has been covered up with a different lightweight material.

Gaffer tape.

Will be sorted properly over the winter ;)


That might be the cause of the flex, ally sheet bonded and riveted is the way forward.

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Re: bulkhead flex under braking

Postby ZSx » Tue Oct 10, 2017 10:41 am

flyingbanana wrote:
Rob Bell wrote::oops:

Well, I have some sheet alloy to cover that up, but so far it has been covered up with a different lightweight material.

Gaffer tape.

Will be sorted properly over the winter ;)


That might be the cause of the flex, ally sheet bonded and riveted is the way forward.


The hole is there in all cars though? So shouldn't flex like that.

Although, maybe a couple of Bracing bars corner to corner on the hole would help?

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Re: bulkhead flex under braking

Postby Rob Bell » Tue Oct 10, 2017 5:18 pm

ZSx wrote:
flyingbanana wrote:
Rob Bell wrote::oops:

Well, I have some sheet alloy to cover that up, but so far it has been covered up with a different lightweight material.

Gaffer tape.

Will be sorted properly over the winter ;)


That might be the cause of the flex, ally sheet bonded and riveted is the way forward.


The hole is there in all cars though? So shouldn't flex like that.

Although, maybe a couple of Bracing bars corner to corner on the hole would help?

That's correct - all cars with a heater fitted will have that hole. And even with an alloy plate, the whole structure will move... It is not supported in the correct planes to prevent flex.

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Re: bulkhead flex under braking

Postby talkingcars » Tue Oct 10, 2017 9:40 pm

It would be interested to see the same pictures/gifs for a TF with the improved under dash brace and strengthened screen surround.
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Re: bulkhead flex under braking

Postby Rob Bell » Thu Oct 12, 2017 2:03 pm

I agree, that would be interesting! My hunch would be that the fundamental problems probably still remain, but the TFs I've driven generally have had a better pedal action. There again, the TFs I've driven have generally been pretty new!

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Re: bulkhead flex under braking

Postby bigmac » Thu Oct 12, 2017 5:29 pm

by coincidence--ive just ordered a servo brace this afternoon.

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Re: bulkhead flex under braking

Postby Rob Bell » Thu Oct 12, 2017 6:54 pm

The B&G side one? It helps - but actually the "Jaylad" style upper support is superior. Oddly I have yet to try the combination...

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Re: bulkhead flex under braking

Postby Larry Nicoll » Fri Oct 13, 2017 3:56 pm

I was unable to obtain the jaylad brace a year or so back so I bought a similar bracket from MG Mania.
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Re: bulkhead flex under braking

Postby Rob Bell » Fri Oct 13, 2017 6:38 pm

It's the same - very simple to fabricate yourself and will give you a worth while improvement. Better still it is designed for the snorkel style air inlet that your TF is hopefully already fitted with? :)

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Re: bulkhead flex under braking

Postby John SS » Sat Oct 14, 2017 12:05 am

This was my solution which has worked well
viewtopic.php?f=8&t=17459

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Re: bulkhead flex under braking

Postby Larry Nicoll » Sat Oct 14, 2017 8:57 pm

Rob, yes it is that type of air inlet, a very easy fit.

That together with 280mm discs all round provides much improved braking.
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