Garage star derlin door bushings - NB

[Mr Morlock]

PLA may not be suitable for bushings on a car i.e. its soft. Replacing a worn bush with a new one is likely to bring an improvement. Are the OEM bushes too expensive? Rubber bushes are often chosen because there is a degree of flexibility, excellent durability and long life.

[StillIC]

PLA may not be suitable for bushings on a car i.e. its soft.

Compared to steel, yes.
Compared to rubber, no.
Compared to Delrin....
Delrin has a Tensile Modulus of 1.9 to 3.5 GPa, depending on the blend.
*Extrusion grade* PLA has a Tensile Modulus of 3.45 GPa. That is, it is as hard or harder than Delrin.

[Mr Morlock]

PLA is regarded as soft even compared to ABS> Delrin is bloody hard- it is used often for runners in cabinets however in taking another look at the door bush I am not really quite clear on what is required. My doors don't rattle or shake and I cannot feel wear on the hinges. Mazda make the bush out of rubber and they could have just as easily moulded it from delrin / acetal or pp etc just like many other components in the car. In truth you can mould faster in an injection moulding die than an equivalent rubber part which has a longer cycle time etc. I have not taken the bush off the car but maybe it has metal in it as well ? In any event Mazda never intended for a hard bush in that location- even the rubber is not hard. So is the shake caused by worn hinges or just age in the body and does that mean the hard bush is a fix for that wear which the designers did not foresee.? If people reckon it works good oh.

[taminga16]

Is it possible that the door bush 'captures' are mounted on the ends of the side intrusion system? and if they are, then it would explain the effectiveness of solid bushes over the OEM parts. Having said that, I took great care in ensuring that they fitted correctly, and adjusted them by carefully filing the mounting holes more than once. If they are sloppy, I do not believe that they will work and if the door 'fires' open then they may be too far outboard. The OEM part is such, to ensure that the door closes neatly and without fuss or too much noise, harshness or vibration.
Greg.
P.S. Look closely at how well the Derlin bushes fit into the capture plates and ask yourself why you would even consider changing their shape?

[StillIC]

PLA is regarded as soft even compared to ABS> Delrin is bloody hard- it is used often for runners in cabinets .....

Just like Delrin, there are lots of different PLA plastics, some relatively soft, some just as hard as Delrin, as per the *extrusion grade* hardness that I gave previously. The reason Delrin is used in runners and sliders and door bushes, is because it is usually infused with Teflon and therefore has a low coefficient of friction, not because it is particularly hard when compared to other plastics. It's about the same range of hardness as ABS, extrusion grade PLA and a whole host of other plastics.

To get a feel for how many varations on any given plastic there are, just go to http://www.matweb.com/ and search on whatever plastic you are interested in. Hardness is expressed as "tensile modulus", the larger the number the harder the substance.

[StillIC]

Mazda make the bush out of rubber and they could have just as easily moulded it from delrin / acetal or pp etc just like many other components in the car. In truth you can mould faster in an injection moulding die than an equivalent rubber part which has a longer cycle time etc.

The problem with injection moulding the bush, for Mazda, is that they only have ~53 seconds to install the bush on each car. And knowing that every door cup is slightly different, and that they are not all in the same position, it takes a good half hour of mucking around to get a hard moulded plastic bush to fit perfectly. The rubber bush can be bolted into the approximately correct position, and the softness of the rubber can then elastically deflect to the shape and position of the cup. When new, this is an adequate solution. But after some period of time, the elastic deflection becomes plastic (permanent) deflection. And the more rattle that is allowed, the more permanent deflection occurs, causing more rattling etc.; positive feedback loop.

This may well also occur with the Delrin or PLA bushes over time, as I imagine they are both susceptible to creep, but hell, for $2 worth of PLA I don't give a rat's.

[Mr Morlock]

StiiIC explanation seems feasible i.e. a rubber part is easy to fit on line but is functional . Maybe it follows that a worn rubber bush when replaced will perform like new - no rattles. The plastic part evidently calls for fine tuning and clearly if not fitted correctly then doors will not close without slamming etc.

[trader]

The OEM bush fits loosely in the retaining cup. It has a metal plate embedded in it. The local Delrin one is bout 1 mm larger and fits snug in the cup. Dead easy to align using method in this post. I think my doors rattled mainly because I have stiff suspension.

[RJ45]

My doors rattle and this thread got me thinking, so I had a look at the current rubber door bushings and I noticed wear on the top edge, but no wear on the bottom edge.
On a hunch, I decided to swap them over, driver side to passenger side and vice versa to see if that did anything.
It does close with a much more solid thud than before

I did the bolts finger tight, opened and closed the doors a few times, then pushed them up a few mm higher in the door jam before tightening them properly.
I'll see how long this lasts

[BlackLeaf]

I got a very similar product from an Australian manufacturer... section of elevated freeway not far from home that provokes a lot of vertical movement... the little fella was considerably more pleasant to be in through there.

Ditto that. Yesterday I installed delrin bushes purchased from AT Performance and took the NA out for the obligatory NVH test along Ham Road in Mansfield. It's a sh!tty piece of road but it has just been made a little more bearable with the new bushes. The install was straight forward and no issues encountered.

Interestingly, taking my daughter to school this morning and she commented on the car feeling different. She wasn't sure how except it "was in a good way". More empirical than scientific, but I'm okay with that for $50.

Drawbacks... yep, the rattle under the dash and the squeaky hardtop are more noticeable. I will be transplanting the dash from my mariner blue NA soon so that will sort that out, but not sure what to do about the squeaky hardtop.

Edit: I notice the bushes are now $60 on the AT Performance website.

[Lokiel]

... but not sure what to do about the squeaky hardtop.

Take it off, your car is supposed to be a convertible.

Right, fixed that problem, what's next?