Olitho

The SCCA just recently approved Delrin or Poly bushings for use in T1 Corvettes. One of our local race mechanic/crew chief is concerned that the Delrin will be high maintenance. His concern specifically that the Delrin with loosen up or crack under the heavy impacts leveraged against it and the bolts when racing frequently. The rubber will give a bit, but Delrin can't do that so the holes will get pulverized into elongation and then the material will crack.

He admits he does not have personal first hand experience, but that is his concern. Who has first hand experience running Delrin, Poly and other materials?

Please share your experiences.


Thanks,

Oli

RX-Ben

me.
trouble free during over ~12k miles last year.
Including some monster potholes in NYC...and Pocono. I freely used curbs on the track as I was using base model suspension last year.

They are a pretty penny from Phoenix, but they last as they aren't the (weaker) white delrin.

CorvetteZ51Racer

If you're worried about the wear on the Delrin and have access to a machine shop, ream out the inside bore where the bolt runs and insert a metal sleeve inside the Delrin. That will increase the bearing area of the bolt against the material.

I don't have first hand experience with it, but I have a number of friends who ran their C4 BSP cars on Delrin for years with no issues.

fatbillybob

I just completed the task and Oli it is a ****** on a C5. Doing this on Ferraris is easy. The C5 uses about 2 different sizes of delrin stock, 6 kinds of bushing designs. The problems I don't think are wear when I used them on Ferraris but you know I'm gentle (code for "slow!"). The problem is going to be 1- manufacture tolerances 2-the funny off angle rear LCA and the caster problem generated by the front UCA. I have solved those problems but I don't like the answers. We will see how it holds up. Also, you can cannibalize the OEM metal hard parts out of the rubber bushings. They come clean and release from the rubber with heat and electronic parts cleaner eats the residual burnt rubber. The hard parts support the delrin and it does not genade. But the delrin should wear and tolerance open up with time as the control arms articulate. How fast they wear the way the T1 group races is anyone's guess. I don't think the life is anyless than a monoball. Poly is the way to go for guys like pfadt to make and sell because poly is low durameter and then can make it ovesize to stuff in the control arms and it will yield so you get all the qualities of a harder rubber but IMO poly has too much stichion. I did buy phadt's UCA dogbones throw out the poly and milled delrin. I have a theory as to why people have problems with the phadt poly popping the c clips. I think the poly is not high enough tolerance and thus the poly bangs into the clips a weird angles and weird forces and pops the clips. I made delrin with basically zero tolerance and the there is no play of the clip in the land. Any force on the clip will be exactly perpendicular to the clip where the clip can take the maximum force. I bet my clips stay put. We will see. My car is basically done. I want to go out once before our national race at WSIR in Feb. You are welcome to drive my car and see what you think and see if you think delrin has an advantage over the rubber.

fatbillybob

This is the completed UCA in delrin using the pfadt dogbones. You could speed the job if you bought the entire pfadt kit and just used the metal parts and sub in delrin for poly.

travisnd

Nice work... make me a set

I've been racing my car over a year with Pfadt polys in the car. No issues with the C-clips. When installing I took great care to make sure the C-cips were 100% properly seated in the "dog bone". It is very easy to get them to where they snap in place, but aren't 100% seated in the slot. My guess is that this is what's happening when people have them popping out.

John B

I made a set for the front of my C4. I was worried about plastic bushings. The rear lowers are close to headers also. I would check them every time I lifted the car. I had over 80,0000 miles of use on them. I ran 18X12 on front. It got street/autox & tracked hard. They were still tight when I sold it this fall. I want to make everything out of delrin.

John B

Delrin is solid like heims. No give. That is as much or more of an improvement over poly to rubber. If I had a choice of racing an expert sorted rubber/poly car or an unsorted solid bushed car, I would drive the solid car. If you are driving 95% not so much. If you are constantly at the limit solid is the only way to go. If SCCA is allowing delrin or poly in T1 I know what I would be using.

John B

You solved the misalignment issue? What about Delrin lower/ poly upper to deal with caster/alignment.

trackboss

At one point I had the delrin/poly combo. It worked well, but the front uppers (poly) still moved around a lot. I still have delrin rear uppers and poly front uppers.
I think one problem with the front uppers is that the control arm distorts because of the loads. Particularly under hard braking.

jfaphoenix32

We have been using delrin in our Grand Am cars since 2007. We have never broken one.

We are using Delrin on Corvettes for at least two years on track day cars, grand am rolex corvettes and now SCCA T-1 cars with virtually no issues. They take time to make, and we use the expensive delrin and there are always fitment issues, but they are far superior to anything else that is on the market.

Fatbillybob sums it up pretty accurately...

Any questions, don't hesitate to call..

mgarfias

The stock uppers always looked iffy to me. Do you have any evidence that they're distorting, or assuming that based on how the bushings wear?

Pfadt Racing

This is absolutely the case in our experience. The front uppers are definitely the pickup point that has the lowest margin for error on install because of the loads the front uppers see in hard braking.

This is definitely the #1 most common issue we've seen with the poly kit. We recently updated the instructions and being more explicit about how to make sure that the snap ring is properly in the groove.

The problem actually lies in the tolerances within the ID of the control arm bores as well. As a manufacturer we need to produce a piece of Poly that not only works in the tightest of control arm bores, but the largest as well. Depending on the condition of the tooling when your control arm bores were cut the ID of the control arm bores can vary from control arm to control arm. From the factory this tolerance doesn't need to be incredibly precise because they're stuffing a piece of rubber in there anyway. The poly provided in our kits measures out very consistently from kit to kit, but if the ID of the control arms varies we have to size the poly appropriately to work for everyone. We have stuck with Poly as a control arm bushing material because it's more aggressive durometer than the factory rubber, as well as it's tendency to be relatively forgiving which makes it easier for a Garage mechanic to install without special tools or machining skills. We've got full spherical bearing kits which require no machining at all for those looking for an all out race solution, so long as you can run a spherical bearing in your class.

What we typically see happening on cars that are having problems with the clips popping out are either the clips not quite seated properly, or users with control arm bores on the tighter side. Upon installation into tighter bores this can compress the poly and elongate it slightly. This generally only becomes an issue on the front uppers since they see so much of the braking forces they will continue to compress and elongate the poly potentially pop the clip out of the groove machined into the pin. In our previous instructions we mentioned that if it requires a lot of force to squeeze the entire assembly together to get the pin in the groove to remove some material from the inside face of the two sides of the 2 piece bushing to give the poly a small void to compress into when it sees those braking loads. Our current instructions go into detail of this process.

You can see the updated poly kit instructions, including photos of how to properly fit your front upper's here: Pfadt Race Engineering Control Arm Bushing Kit Instructions

fatbillybob

Yes! this is a huge issue which I eludded to in my earlier post. The tolerances for the control arms are so all over the place that I had to make each bushing manually and sneek up on final fit by shaving a couple thousands on the lathe and trial fitting. It took forever. I have since completed this job got requests to make bushings for others and I have said "no way" you can't pay me enough to do this job. It is a real PITA! It sounds like pheonix either has a kit or will do the job for you. I did not know that before I started all this. Anyway if people want Delrin bushings Pheonix sounds like the source. Whatever they are charging its not enough.

If you must do this job yourself do yourself a favor and by the Pfadt poly kit and swap in your own delrin using all the Pfadt hard parts. I was not smart enough and out of project fatigue was finally too lazy to turn down the OEM dogbones and modify so I just bought the Pfadt UCA parts. They are very well engineered and of high quality in fit and finish. Amazingly, the UCA's were then the fastest part of the fabrication. I wish I had thought of using the Pfadt parts earlier.

froggy47

To Pfadt,

Those new instructions are much better, especially the pics.


To All,

Given that the poly is quite a bit easier to custom fit (and it may not even need any fitting) does it make any sense to bother with delrin at all, or should the choice be either poly or spherical?

Sure if you have a lathe in you garage or have the budget to pay someone to do it, then maybe there is a small incremental gain with delrin, but for most of us, would we be dropping seconds per lap by going from poly to delrin?

Nothing against delrin, just whether the additional cost/labor/etc is "worth it"?

For myself I would just go to spherical.

el es tu

I agree completely

pfadt poly is in under 300 from some vendors (check RPI) while 400 at others

the spherical kit from pfadt is 1900

considering the price for the delrin, Id go with the spherical kit if I had the cash


that said, 1900 + labor is a lot to spend for an all metal setup, while 300 for the poly is much easier to deal with.
The difference can buy brake parts or even tires...

drivinhard

I'd say there is way more gain going from stock to Pfadt's poly than from poly to delrin. Having pressed in a bunch of kits for various C5's, the durometer of the poly material is quite rigid. While I'm sure there is still some compliance under load, it's fractional compared to the OEM rubber. The price point is good and install is easy, delrin is a good choice for those with patience, and those stuck with non metallic bushings rules chasing every last half a tenth and a bit more accurate set-up (I plan to try at some point).

95jersey

Looks like with the ability to use long tubes, open exhuast, aftermarket brake calipers, and now poly or delrin bushings, the cost of racing T1 is going up an up.

travisnd

Don't forget the $$$$ custom shocks too.

trackboss

does anyone know what the taper is for the upper balljoint? I have been thinking about building a steel upper control arm and have actually found some made for muscle car applications, but they will not sell the ball joint cups (or any individual components for that matter).