TR5/TR250 TR250/6 Rear Trailing Arm Bush Options

[tdskip]

Good to know somebody gets me Don!

 

[TR3driver]

I have also read all polyurethane is not created equal,

Definitely true. Polyurethane comes in a wide range of hardnesses, from about the same as the original rubber to about like wood. In some applications (don't know about TR6 trailing arms), you can even get different hardnesses from the same manufacturer. 'Prothane' is one of the better known makers of aftermarket poly bushings. They do seem to have a good reputation for quality, but it's still just polyurethane.
https://www.prothane.com

I use Nylatron, so no direct experience with poly. But my opinion, if it is deforming and taking a set like that, you need a stronger/different material.

Harder bushings do transmit somewhat more peak force (under the same conditions), because they don't absorb as much of the shock & vibration. Think of dropping an egg onto foam rubber instead of wood or concrete. Which one is more likely to break? The egg falls at the same speed either way.

 

[swift6]

The harder bushings do transmit more of the force, but the force is not increased unless the cornering speeds, or the size of the potholes, are increased. As Randall says, they absorb less.

The trailing arm bushings don't resist the pivot (up/down) action of the trailing arm, they resist side to side and twist. They allow the trailing arm to pivot without twisting (or less twisting depending on the hardness of the bushing). Since they don't inhibit the pivot they don't greatly affect ride quality. You may feel more vibration of regular road surface because they do absorb less of the regular vibrations, but a bump will feel pretty much the same.

 

[glemon]

I am not an engineer, but I believe that the reason rubber bushings continue to be used even on modern cars is because they do absorb some of the noise vibration and harshness. Think about the TR6 trailing arm suspension, if something were to push the rear wheel up from directly below all the force should be absorbed motion of the trailing arm on the bushings, but in reality you hit a pothole or a rock it is not directly underneath the car, it will hit towards the front half of the wheel, putting some backwards as well as upwards force on the suspension mount. The rubber in the bushing can absorb this somewhat, which would also I would think be a little easier on the mounts as well.

As far as my car, the goal was to upgrade where possible but not at the expense of making it unpleasant to drive on a day to day basis.

Also on the statement I made earlier about "competition use only" I was referring to the TS Imports site which lists nylatron and delrin and the actual wording is "not recommended for street use".

I did talk to one vendor and he said they get the same poly bushes as I got from the other, he said he was surprised to hear that I had this issue, he had not heard of it. Although I read on an internet forum of at least one more person having the same issue of poly bushings collapsing and they had returned them to this same vendor multilple times.

Anyway, I am thinking about prothane polyurethane, the harder rubber TRF offers, or the Richard Goode nylatron, and leaning towards trying the hard rubber. I know it will compress too, but I am thinking that it should last longer before the compression becomes permanent or semi permanent.

 

[Monkeywrench]

As for racers, anyone who is serious is probably using heim joints.

I'm not sure what the quality of the rubber is on the replacement bushings, but it is common for SCCA Showroom Stock and Spec Miata racers to bake brand new OEM units in the oven at a lower temperature for several hours to make them harder :wink: .

 

[tdskip]

Problem with a lot of the rubber provided on our cars is that it deteriorates rapidly, or at least does down here.

For how you are going to use the car I'd go with Richard's stuff.

 

[swift6]

I am not an engineer, but I believe that the reason rubber bushings continue to be used even on modern cars is because they do absorb some of the noise vibration and harshness. Think about the TR6 trailing arm suspension, if something were to push the rear wheel up from directly below all the force should be absorbed motion of the trailing arm on the bushings, but in reality you hit a pothole or a rock it is not directly underneath the car, it will hit towards the front half of the wheel, putting some backwards as well as upwards force on the suspension mount. The rubber in the bushing can absorb this somewhat, which would also I would think be a little easier on the mounts as well.

Not sure if I'm reading you right or not, but the force of the impact would initially be absorbed by the spring and shock absorber. The bushings are a pivot point, not a shock absorption point. Under straight line driving you should feel no difference between a poly or rubber bushing in that pivot point. When you apply cornering, side load, then you get the twist of the pivot point. The rubber allows a lot of twist which allows the rear tires to follow different arcs and upsets the handling. The outside tire will twist more (more force/weight on it) and change its track much more than the inside tire. That is how the handling gets upset, harder bushing resist the twist, not the pivot.

The rubber does absorb more of the road vibrations, but not really the shock of hitting a bump/hole. Your poly's were deformed by the increased force you were putting on due to the cornering forces they were allowing you to achieve. Too soft for the job proper and not elastic enough to reform after they deformed. Polys are not "fit and forget" type of parts, unless you never push the car, push them hard and they wear out just like any other part would. Ideally not as fast as yours did though.

 

[SkinnedKnuckles]

Your poly's were deformed by the increased force you were putting on due to the cornering forces they were allowing you to achieve.

Or from plastic deformation just from carrying the load of the car over time.

 

[tdskip]

Or from plastic deformation just from carrying the load of the car over time.

I've never seen that happen - anyone else?

 

[SkinnedKnuckles]

Or from plastic deformation just from carrying the load of the car over time.

I've never seen that happen - anyone else?

Umm, that was kind of the start of this thread. In fact, I did the TA bushing change out coincident with putting in a Toyota diff after the original started making noise, so it had been just sitting for a week or so.

In looking at things I was wrong about the "plastic" deformation - that's irreversible. It's elastic deformation, even though the recovery is slow.

 

[glemon]

There are at least a couple different things being discussed here, and I think some may be getting mixed up, ride quality and bushing deformation under load,

I will stand by my statement about the rubber abssorbing some of the loads of, for want of a better term, road vibratio, I don't know how else to state it other than if the tire is pushed up from directly beneath the car the force should be theoretically be taken up by the motion of the suspension (trailing arm up and down) but the fact of the matter is that forces from the side or slightly front and back act on the wheels in real world conditions, and in these cases the rubber bushings could absorb some of the shock for both less load on the mounts and possibly a perceptably smoother/quieter ride.

As far as deforming under load, I don't think they did it over time, I have front annd rear sway bars and 205/65s on the car and was driving in a solo speed event, the bushing deformed fairly suddenly under load, I found reference to others experiencing this on the VTR or Six Pack forum don't remember which.

My goal is to upgrade the car performancewise, but I don't want to compromise ride quality and noise to the point where it is not pleasent to drive around in, hence my questions about the effects fo the nylatron bushes. I did not think the ride quality was bad with the poly, but I never drove it stock, so don't have much to compare it to.

I also contacted the vendor that sold them to me, pointing out a possible safety issue, didn't ask for another set, bought them a couple years ago, but just got the car back on the road a few months ago. They told me they would send me another set, and said that they had had prior sets with hardness issues, but were testing samples from the sets they have now, since they are coming to me at the right price I will try them out. I am sure they will be fine for regular road use and the real test will be the autocross coming up in a couple months...

 

[tdskip]

I also contacted the vendor that sold them to me, pointing out a possible safety issue, didn't ask for another set, bought them a couple years ago, but just got the car back on the road a few months ago. They told me they would send me another set, and said that they had had prior sets with hardness issues, but were testing samples from the sets they have now, since they are coming to me at the right price I will try them out.

That sounds like a pretty good vendor to me.

 

[tdskip]

BTW - I drove my TR6 with Richard Good's TA bushings quite hard and it handled it just fine. No rear bar however.

 

[SkinnedKnuckles]

As far as deforming under load, I don't think they did it over time, I have front annd rear sway bars and 205/65s on the car and was driving in a solo speed event, the bushing deformed fairly suddenly under load, I found reference to others experiencing this on the VTR or Six Pack forum don't remember which.

What I was thinking is that you went into the slalom with a vertical deformation in the bushes and the back & forth horizontal stresses opened it up so there was "wallowing". It don't want to argue the point, but I know what I found on my car. I didn't have handling problems, but I wasn't doing a slalom, either.

 

[glemon]

Hi Brent, I don't know exactly what happended, no, no argument,we are just trying to figure out how some parts behave and why.

Mine seemed to be ok until the second run on the autocross (not actually an autocross, but close enough) then the car went wonky, and I could tell it was the rear end. I jacked up the back and could see the arm had significant motion, up and down on the inner mount. It could have deformed slightly with regular use and noticably with hard use, don't know.

Interesting, I checked today and the things have almost gone back to normal. The play is (was) not from an enlarged diameter hole, but from an elongated hole on vertically elongated so it could go up and down, I bet if I pulled the bush right after the autocross the compression would have been greater, the car was behaving better on the way home and I am thinking the bush was slowly going back into shape even as I drove very gingerly home on the thing.

 

[swift6]

If you put all poly bushings in a car with stock springs, shocks, tire size, sway bar etc... then you may notice some increase in vibration making its way through the steering wheel and possibly your seat (if your backside is overly sensitive). Most poly bushes out there are only stiff enough to sharpen the responsiveness of the suspension slightly but greatly outlast the short lived rubber bushings out there now. Harder compounds of poly will last longer under duress and will transfer some more vibration. if your upgrading the performance characteristics of the suspension then you would also need to go to a stiffer spring and shock, those will have a far greater effect on ride quality than stiffer bushings, so much so that the only difference you might feel is in the responsive ness of the car, not in ride difference. The increase in vibration is more like a light buzz, in a roughly 40 year old car full of other noises and chassis flex issues, not bone jarring ride quality.

Before I sold my TR6 I had spent a long time selectively increasing the performance aspects of it. When owners of stock TR6's drove mine, they never commented on the ride quality being overly harsh or tiresome. They would comment on how immediate the response was on turn in and tracking, and how predictable and controllable it was when pushed. Compared to my TR6, a stock TR6 felt like a Buick, the ride was firm but well controlled, never teeth rattling or bone jarring.

 

[glemon]

Thanks Shawn, That is where I am trying to go as well, firm well controlled, good handling, but not bone jarring.

 

[tdskip]

Before I sold my TR6 I had spent a long time selectively increasing the performance aspects of it. When owners of stock TR6's drove mine, they never commented on the ride quality being overly harsh or tiresome. They would comment on how immediate the response was on turn in and tracking, and how predictable and controllable it was when pushed. Compared to my TR6, a stock TR6 felt like a Buick, the ride was firm but well controlled, never teeth rattling or bone jarring.

+1 - same experience with my TR6. She is firm but not uncomfortably so and you can throw her around and she remains fluid and predictable. All depends on what you are going for....

 

[swift6]

The chap that bought my TR6 had driven a few others before he came to mine. He couldn't believe how smooth the car rode, even though it was firm, even when he hit a few bumps. Had him drive briskly through a few s-turns and he was amazed at how responsive the steering was and how flat the car cornered.

I did get pulled over by a Sheriff Deputy one day in one of our local canyons. I had been driving right at and occasionally about 5mph above the posted speed limit through a sucession of very tight turns. I didn't get pulled over for speeding. He pulled me over for nonoperational brake lights, only my brake lights worked just fine, I just hadn't been using the brakes.

The posted speed limits ranged from 40mph-45mph but the "suggested speed" signs preceding the curves (the yellow and black signs that show a number followed by M.P.H.) were posted at 25 M.P.H. He had been following me at the same speeds, but not right behind me, and was experiencing some pretty good body roll/lean in his Charger at those speeds and was having to slow down to reduce the roll. He noticed that my car was staying totally flat through the turns and surmised that I must have been braking too but my brake lights were not working. When he sped up to catch me and lit his lights, I tapped my brake lights so he would know I saw him and pulled over at the next safe spot which was just past another short series of corners.

When he got out and walked up to my car he was shaking his head, explained why he initially pulled me over, apologized and told me I was free to go. We chatted for about five minutes, he had some other questions about how old the car was and what all had been done to it etc... He asked if I had been accelerating out of the corners as he had to keep accelerting to maintain a steady distance between us. I told him that I had just been maintaining the same speed (which I had been), practically coasting down through the canyon and barely on the gas. Then he said; "You can go through these corners quite a bit faster than you were can't you." I smiled, reached under the steering wheel and twisted the ignition key. As the engine barked to life I raised my eyebrows and gave the triple Strombergs a quick kick. He smiled, nodded his head and asked me to enjoy the rest of my drive, as I pulled back out onto the road, he turned around and headed back up the canyon.

I always like to use that as an example of just how much fun we can still have in our old British cars, at the speed limit (or only slightly above), you just need to find the right roads.

 

[tdskip]

Great story Shawn.