Marlin Front disc options.

[stevejgreen]

The original thread has been deleted at my request as I have found a possible problem with the conversion.

I beleive that this is a Roadster specific issue and will not effect cars with standard Marina suspension.

Until such time as I have investigated and taken further advice, I ask that any Marina based Roadster owners planning or in process with this conversion should put the project on hold until my investigations are complete.
I am sorry for any inconvenience caused but I must err on the side of caution and safety.

When I have had time to dismantle and examine my disc conversion/Roadster suspension, I will publish my findings and if appropriate re-publish the thread on the MOC forum.

Meanwhile, because I believe this to be specifically a Marina based Marlin issue, my original thread is still available on the Morris Marina Owners forum. Please treat this as information only.

[stevejgreen]

Re: Marlin Front disc options.

A cautionary note and a plea for info.

First checks have revealed the source of the noise from the front of my car that concerned me so much.
When I first grabbed hold of the top of the suspension upright I noticed some movement from the top of the upright. There was significant movement fore and aft, with an unsatisfying clunk as it reached the end of its travel. This movement is from the Mini wishbone used to locate the top of the suspension upright back to the chassis.

I have also checked my brake and hub assembly, location and fixings and can find no other faults. So the noise that concerned me so much was Marlin specific, as I surmised, and not a direct result of the custom brake installation, though it may have contributed to the issue.

I perhaps over reacted in having the original thread deleted but I was compelled to act promptly, in the interests of safety, not knowing the cause of the loud noise. If you had heard it, I am sure you would have reacted in a similar way. Leaving the thread in place at that time I felt was irresponsible.

A Bit of History:-

Some time ago I had a problem on the nearside of my car. I posted a thread on the forum.
http://www.marlinownersclub.com/forum.php?read=9972&cat=0#n9972

I have now posted some pictures on the Marina Owners Forum in order to demonstrate my belief that the problem is Marlin Roadster specific.
http://www.fastmarinamagazine.com/viewtopic.php?f=13&t=2907&start=30
This time the movement of the offside wishbone is five times larger, and clearly visible, though I can find no reason why this should be. You can perhaps imagine the noise with the top of the suspension leg having 1.3mm free movement, being amplified by the chassis.

There are several mysteries to resolve and would welcome comments.

• There were no untoward noises from the front offside, either before or for several days immediately after the brake conversion despite deliberate heavy braking to test the system.
• This appears to be a sudden failure, how can that be?
• This is the second wishbone I will be shimming. Has anyone else come across a similar circumstance? Even with a new shaft the gap is the same.
• Is this problem exasperated by the new brake installation, perhaps increasing the forces transmitted through the wishbone to the chassis?
• Marlins have been fitted with 4 Pot Princess calipers. Have any of these conversions had similar problems?

I believe that, apart from this issue, this conversion is simple, effective and worthwhile. If others of a mechanical inclination and Marlin Roadster/Mini experts would like to boost confidence in this conversion I would be happy to restore the original thread on this forum and release an article for publication in Pitstop.

[stevejgreen]

Re: Marlin Front disc options.

If what I have in this attached picture, what does it say about BL manufacturing tolerances?

Of all the Wishbone shafts I have, all are in good condition. There is no obvious wear on any of the parts.

I tried shrinking this pic but I could not get a good image that showed the extremes clearly.

http://farm3.static.flickr.com/2753/4080688398_26a6ceea0f_b.jpg

Hopefully that will get you there.

On the left the parts look OK, on the right the shaft appears to have a lead in taper to the parralel section, also the washer has a large countersink, and you can see a trace of contact wear on in the countersink itself.
Obviously in combination the errors compound and the final length between the washers on the assy will be somewhat less than the parts on the left.

The problem is, that most of the parts seem to have different degrees of taper and countersink, and I now have to swap parts around to get a good fit. But being an engineering perfectionist, I might select the two longest shafts and machine them to match a pair of wishbones, with sharp shoulders and then fit un-countersunk washers at either end.

I will have 4 wishbones and 6 shafts and 12 washers to choose from.

So if you have an unidentified rattle from the front of your Marina Roadster this might just be it.

Has anyone got any more thoughts, even the Mini boys are mystified!

[h_m_cumming]

Re: Marlin Front disc options.

Hi Steve,
I can remember way back when I was assembling my front susp. that I turned back the shoulder on the shaft to suit the wishbone so that there was about a couple of thou. end float.
What you need to keep an eye on is that the nut doesn't become threadbound on the unthreaded portion of the shaft before it tightens up on the mounting plates.
The chamfers on the bore of the washers are to clear any radius at the root of the threaded portion as a sharp corner here creates a stress point.
When everything is bolted up tight the only part that should move is the wishbone so that's why I wondered if the nuts were becoming threadbound before nipping the washers against the shoulders of the shaft.

[stevejgreen]

Re: Marlin Front disc options.

Thanks Hugh. I was concerned that higher braking forces were perhaps to blame. If you have seen the same problem then perhaps it's more common than we both realise.
I don't know if you looked at the picture but the countersink in one washer is way beyond any clearance for a corner.
I did notice early that the threads were not long enough without a mounting plate either side. Also if I finger tightened with the standard spring washer, the main masher sometimes sat at a slight angle, making accurate measurements impossible.
I think I will be creating a matched pair over the next few days.

[h_m_cumming]

Re: Marlin Front disc options.

Yes I did think one csk. was a bit excessive, but as long as some flat sits against the shoulder of the spindle it should be OK. from memory , I think I added some washers to the outside of the mounting plate under the nuts to clear the unthreaded portion. I tend to use Locktite a lot instead of spring washers, a habit from work use.

[dogoncrazy]

Re: Marlin Front disc options.

Steve
fail to see how you can generate a 'higher braking force' regardless of type of caliper installation.The point at which you lock that particular wheel and prevent it rotating remains the same does it not? The only advantage that I can see with four pot or whatever calipers would be a possible reduction in effort at the pedal.
that doesn't however answer the question of the apparent increase in the for and aft movement of the wishbone does it!

[donsayers]

Re: Marlin Front disc options.

A more modern ventilated disk brake might have advantages in terms of fade resistance and ease of obtaining pads. On the back it would give you handbrake that always worked, no more seized marina adjusters.

On the other hand with Ferodo greenstuff pads I have never faded mine yet.

[stevejgreen]

Re: Marlin Front disc options.

Alan, my thoughts went that if the mod apparently helped the car to stop better, then the rate of conversion from rotational energy to heat and its subsequent dissapation must be happening more efficiently. I also have larger brakes on the rear from my Sprint axle install that should contribute to the effect. I have not yet been to my MOT tester to see if his measurements have changed. That will be the real decider.

My current state of play is that I have machined some new shafts to give 0.005" clearance that are yet to be fitted. Meanwhile the existing wishbones are shimmed to the same gap. Shimming is not the prefered solution as it effecively closes off a lubrication route (thanks Don from postings on the Marina forum). The alarming noises have gone, though I am still none the wiser why it reared its head so suddenly.

I will be rewriting my original instructions including an advisery statement about the wishbones and the need for a critical inspection of all parts of the steering/suspension system before carrying out the conversion.