Marina brakes

[stevejgreen]

Re: Marina brakes

With regard to the stress cracking, I have come to believe that some if not all of the bulkheads may have been manufactured badly.

Sheet aluminium has a grain structure usually denoted by the direction of identification printing on the sheet.
If aluminium is folded too sharply along the direction of the grain, it is inherently likely to stress crack. If two or more sharp folds are close, the chance increases.

If sheet stock aluminium was originally cut to get the best use of a whole sheet, to manufacture several bulkheads, without reference to the grain structure, this again might be reflected in the apparent randomness of the cracking occurring.
Without having engineering drawings available, it's unlikely that my conjecture can be proved or disproved.

[andyf]

Re: Marina brakes

Mine cracked diagonally out from one of the corners in the transmission tunnel opening.

[stevejgreen]

Re: Marina brakes

Mine cracked diagonally out from one of the corners in the transmission tunnel opening.

That is unusual, to me.

Could that confirm my theory?
Did someone just put a template up against the largest sheet they had, that was not long enough so the template fell at an odd angle?

It would be curios to do a survey in Pitstop and/or online to see if there is a pattern of failure modes.

But I guess those that were spotted early have the bracket fitted.

[lil_red_roadster]

Re: Marina brakes

Mine cracked diagonally out from one of the corners in the transmission tunnel opening.

So did mine.

[stevejgreen]

Re: Marina brakes

So did mine.

So my theory may not be true.
today you might do a full stress analysis 40 years ago, probably not.

interesting to hear different responses.

[andyf]

Re: Marina brakes

So my theory may not be true.
today you might do a full stress analysis 40 years ago, probably not.

interesting to hear different responses.

You might not be totally wrong, it may explain those cases where the cracks run along the folds.

[b_caswell]

Re: Marina brakes

May also depend on the grade of alloy sheet that was used back then as Spec 1050A-H14 seems to be a better bet!

http://www.leengatemetals.co.uk/index.php/products-and-services/aluminium/aluminium-sheet

[FranklinLeicester]

Re: Marina brakes

This is all very interesting but why not use steel like mine? But more important (to me), going back to my original question - by disconnecting the servo, to what extent is the extra pressure required to push the pedal due to the redundant servo workings?

[stevejgreen]

Re: Marina brakes

You might not be totally wrong, it may explain those cases where the cracks run along the folds.

I only raised a technical discussion. Without technical drawings, that I doubt exist, the discussion comes to an end.

I dare say that the materials used, were more than likely what was readily available, without special order, in and around Plymouth.

Today with better material knowledge and computer simulation of stress analysis, a Roadster would look a very different car.

It is what it is, I offer a theory, no more, no less.

[cameronfurnival]

Re: Marina brakes

the force multiplier of the servo will depend on things like its diameter etc but in general terms servos are designed to give about 3 times more force. Depending on where you look you will find servos giving double or quadruple the force, it all depends on the sizes of the components etc
A car as light as a roadster will certainly be able to cope without a servo but why would you want to push harder on the brakes than you need to - the servo makes it easy! I guess trouble arises with over braking if the servo is too powerful? Also, iirc the braking effort is around 70% front and 30% rear. I hope this helps.

[b_caswell]

Re: Marina brakes

Franklin's original Q was does the redundant servo cause any additional pedal effort over a straight non servo system.

A I wouldn't think it would ! Another way to get a better pedal feel would be to find a smaller bore master cylinder. My sons car albeit with a four cylinder as apposed to my six has the same basic brakes except a smaller bore M/C and the feel is much improved compared to my car.

[stevejgreen]

Re: Marina brakes

This is all very interesting but why not use steel like mine? But more important (to me), going back to my original question - by disconnecting the servo, to what extent is the extra pressure required to push the pedal due to the redundant servo workings?

If I understand your question, you ask what the load the internal workings of a servo alone, no hydraulics, might be.

I don't know, but assuming the vacuum port is open, so that the internal diaphram does not attempt to pressurise the servo body, I would suggest that the abscence or presence of the diaphram makes very little difference as it would be the lever mechanism and the master cylinder itself that is the larger resistance, and then of course the hydraulics.

A point to note is that all master cylinders are 0.75" bore and of course the front disc brake pistons are the same across the range. There are two different servos, apart from none, a slightly larger one fitted on a TC.

But Camerons question stands, why would you want to push harder on the brakes. It's your right foot, used to delicate modulation of the accelerator so you should have better control. Try braking with your left foot, normally just on the clutch, you have little sense of modulation it's just on or off!

If you are continually locking your front brakes I would suggest there is a problem between the seat and the pedals, or as I suggested before a problem with the width, pressure or quality of your tyres, the only contact with the road.

I commonly drive one of five different vehicles. Each has its own characteristics, but the assimilation time between each is about 20 seconds.

[FranklinLeicester]

Re: Marina brakes

OK, thanks once again for all this helpful info. The brakes only lock up in serious emergency situations, specially in the wet. Steve's earlier point about tyre pressures is one I can do something about because I probably tend to over inflate them at 18-20 psi with 165/80/14" tyres. I think I may try 16 psi. I have never hit anything but have come bloody close once or twice! As regards the servo, yes, the port is open so as suggested there should be no pressure exerted on the system. Also, I think the shorter Marlin brake pedal robs us of some feel. I think that about covers it. Regards, Franklin.

[stevejgreen]

Re: Marina brakes

OK, thanks once again for all this helpful info. The brakes only lock up in serious emergency situations, specially in the wet. Steve's earlier point about tyre pressures is one I can do something about because I probably tend to over inflate them at 18-20 psi with 165/80/14" tyres. I think I may try 16 psi. I have never hit anything but have come bloody close once or twice! As regards the servo, yes, the port is open so as suggested there should be no pressure exerted on the system. Also, I think the shorter Marlin brake pedal robs us of some feel. I think that about covers it. Regards, Franklin.

Feel varies from vehicle to vehicle. Modern vehicles have ABS, even my Trike, with only a footbrake, has traction control, power steering and ABS. I manage between 5 very different vehicles.

I would have said that 165/80/14 on your MGF space saver steel alloys is narrow, not as much rubber on the road as 185/70/13 that could be considered as the standard Marina/Marlin Roadster setup. 20 Psi is the 'Standard' pressure on 185/70/13 tyres, where sidewall deflection accounts for a comfortable ride. 165/80/14 sounds a very narrow tyre with a small contact area.

There is a compromise between appearance, and safety. have you found it?