Broken shift linkage
Melting Slicks
Joined: Mar 1999
Posts: 3,211
Likes: 167
From: Rochester Hills Michigan
Just ran the chemistry of a Dorman replacement yellow/white bushing in the Chem lab - result was surprising not a nylon but a high density Polyethylene. Melting point was found 275F. Very low for a tranny area near the exhaust pipe. This is basically milk jug plastic.🫠 I assume the OEM is same material as reports of black and yellow colors are coming back.
Such a poor material choice by GM Materials Engineers - no wonder issues with these. Cost driven🙄
Bottom line is over heating/cycling is the potential problem, along with ozone degradation potential etc. Worse life in hotter states, racing, or long periods in traffic idling etc.
https://www.polymershapes.com/product/high-density-polyethylene-hdpe/
Such a poor material choice by GM Materials Engineers - no wonder issues with these. Cost driven🙄
Bottom line is over heating/cycling is the potential problem, along with ozone degradation potential etc. Worse life in hotter states, racing, or long periods in traffic idling etc.
https://www.polymershapes.com/product/high-density-polyethylene-hdpe/
Last edited by RedC5; Aug 17, 2023 at 08:52 AM.
Thread Starter
Heel & Toe
Joined: Jul 2023
Posts: 19
Likes: 1
HDPE has very good chem resistance and is non-hygroscopic, but is just a commodity resin. Since the part is probably injection molded (and not machined from an extrusion) and is round, it likely fails at the knit line. COPP may have been a better choice with higher heat resistance, but I think if I was designing this part, my first choice would have been Delrin.
Melting Slicks
Joined: Mar 1999
Posts: 3,211
Likes: 167
From: Rochester Hills Michigan
Most optimal would be a bronze bushing - aluminum not the best since no “self” lubrication riding on the steel tranny lever and always exposed to the elements. It will oxidize to an abrasive aluminum oxide.
If a plastic, he’s saying Delrin offers the higher properties and is a higher quality plastic including melting temperature..,and of course higher cost.
If a plastic, he’s saying Delrin offers the higher properties and is a higher quality plastic including melting temperature..,and of course higher cost.
Thread Starter
Heel & Toe
Joined: Jul 2023
Posts: 19
Likes: 1
The ultimate material would be UHMWPE (Ultra High Molecular Weight PolyEthylene). Great lubricity, extremely tough, but very difficult to injection mold in thin walls. It would have to be made from an extruded rod and machined to spec. Ultra-high-molecular-weight polyethylene - Wikipedia
Race Director
Joined: Oct 2004
Posts: 12,861
Likes: 4,663
The ultimate material would be UHMWPE (Ultra High Molecular Weight PolyEthylene). Great lubricity, extremely tough, but very difficult to injection mold in thin walls. It would have to be made from an extruded rod and machined to spec. Ultra-high-molecular-weight polyethylene - Wikipedia
Last edited by grinder11; Aug 18, 2023 at 04:06 PM.
Thread Starter
Heel & Toe
Joined: Jul 2023
Posts: 19
Likes: 1
The natural color for UHMWPE is white. I live near Cincinnati, and in the winter months the city covers the Fountain Square plaza with plastic sheets for 'ice' skating. I believe the material is UHMWPE due to its abrasion resistance and natural lubricity, as this surface is not refrigerated.
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Burning Brakes
Joined: Sep 2006
Posts: 1,061
Likes: 106
From: The Natures Coast/Caribbean
yep, I shifted mine w/o jacking up the car, if you know what to look for. Quite easy fix, did one from underside under half hour. The one at shifter takes longer to repair.
Melting Slicks
Joined: Mar 1999
Posts: 3,211
Likes: 167
From: Rochester Hills Michigan
Tell us more!!
Last edited by RedC5; Aug 19, 2023 at 05:15 PM.