TR2/3/3A TR3 A-Arm Bushings

[martx-5]

I'm progressing pretty well with my TR3 resto, but realistically, this won't be done 'til next summer. I've redone the front end with new bushings etc., but still haven't installed the shocks and springs. I've read that if upper A-Arm bushings are left with spring pressure on them while the frame is jacked up, it will permanently distort them out of shape. So, everytime I look for something to do on the car, I keep looking at the front suspension that needs to be completed. Should I just wait awhile, or is all of this "permanent distortion" stuff just a bunch of BS. By the way, I have the original rubber type bushings installed, but at this point in time, I would have no problem going to the urethane type if it's better, and I can put the whole suspension back together.

 

[TR4nut]

For what its worth, I went with polyurethane bushings on my TR4 and I'm happy with the ride. The rubber bushings were completely shot on the old setup and from all the stories it sounds like polyurethane is an excellent upgrade. I really don't drive that much to discern performance/handling differences between the two so I guess for me it would hinge on future maintenance - I think the poly bushings would last longer for you if that matters.

I put everything together including springs, but left the upper bushings loose until the car was back on the ground and tightened everything up with full weight on the suspension.

 

[Alan_Myers]

Hi,

Randy is right. Urethane bushings are definitely the way to go. The original rubber ones might have lasted a few years. The replacement rubber ones I suspect won't be much good after a year or so. Urethane will last much, much longer and will distort far less. It can really help transform the way the car feels on the road.

Here in the U.S., each vendor seems to offer a "choice" of exactly one type of urethane bushing. They seem inclined to just use the term very generically, like all urethane bushings are the same. But, they're not.

There are different hardnesses ("durometer" in the U.S., "shore" in the U.K.) of urethane available. Many of the U.K. vendors seem to know this and often offer a choice. Choices might be stated as "street", "rally" and "race".(In the U.S., Land Rover vendors have figured it out, and offer stiffer "highway" and softer "off-road" versions of urethane bushings, which there are a lot of on these cars!)

Some urethane bushings approach the original rubber in softness, others are almost as hard as the white nylon bushings used elsewhere on TR suspensions. Some increase in hardness gives for more precise feeling steering and handling. Too much makes for a harsh ride and more noise, but all this comes down to personal preferences. Also, really hard urethane can be a bugger to install in some applications, however installation in the front TR suspension isn't usually a problem.

One "brand" that seems to have a nice balance of bushing hardness is Superflex, if you can find them and don't mind having bright yellow bushings peeking out at you.

Personally, I don't like to let a suspension hang at "full droop" for too long. But there's not much you can do about it and there are spring pressures on those bushings no matter what the position or weight on the car/chassis. So I wouldn't worry about it. Not much you can do other than use good bushings that are less likely to distort.

Randy is also right, the bushing fasteneris suspension shouldn't be fully tightened up until the car is off the jacks and sitting back on the ground, "normally laden". (You might need to put a stack of 2x10's flat under the tires to raise the car a bit, so you can get to the nuts to tighten them.)

/ubbthreads/images/graemlins/cheers.gif

 

[martx-5]

OK, Alan and Randy, thank you for all of your input. I've decided to replace the rubber bushings that I put in there with the urethane type. Since I don't have the springs and shocks in there, this would be the time to do it. I certainly don't want to be doing any front end work on this car a year or so after it's all back together again. /ubbthreads/images/graemlins/hammer.gif

 

[4aNot4]

A search of Land Rover forums will turn up a lot of interesting opinions on urethane bushes. Many of the off roaders have reverted to rubber bushes due to the poor performance of urethane in that application.

 

[Alan_Myers]

[ QUOTE ]
A search of Land Rover forums will turn up a lot of interesting opinions on urethane bushes. Many of the off roaders have reverted to rubber bushes due to the poor performance of urethane in that application.

[/ QUOTE ]

Hi,

Agreed. But, the key word there is "off road". Many off-roaders are looking for the softest possible ride and maximuum suspension flex, and even the softest version of urethane is still harder than rubber.

I have a full set of "soft/offroad" urethane bushings ready to go on my Disco, as soon as I get inspired to do the job. There are *a lot* of bushings in that suspension system! I don't expect the urethane to be as cushy as the rubber bushings, even if they are the softer durometer urethane, but they will hopefully last longer. The car has 55K miles on it now, really needs the rubber bushings replaced! (Got new OME heavy duty springs at 30K mi. and Bilstien shocks at 21K). I'd like to modify as many bushing joints as possible with zerks, so that they can be greased. Still scratching my head about that, though.

I do think most sports car drivers are looking for and expecting something different than rock-crawlers, though. So, for TRs, in my opinion, moderate rated urethane is about the best compromise for more precise handling as opposed to road noise/ride harshness. Two possible issues are that urehtane bushings will make more obvious any other faults in the steering and suspension, such as a bent control arm. And, dry urethane can "squeek", so ideally should get a little grease from time to time. (Special grease is necessary, along with a dedicated grease gun.)

/ubbthreads/images/graemlins/cheers.gif

 

[4aNot4]

Alan,

If you fit those zerks, make sure you drill a passage all the way through the urethane down to the inner sleeve boundary. That's where the rotation occurs.

Regarding urethane bushes. The way these work is that the inner opening of the urethane bush rotates against an inner surface to which it is concentric. Often the urethane bush comes with an inner metal sleeve, and the rotation occurs at the boundary of the urethane bush and inner metal sleeve. The better urethane bushes are supposedly precision machined so that the urethane bush is perfectly concentric with the inner sleeve. It is also pretty tight so that there is no slop. When installed, the inner sleeve is held fast by the mounting bracket and thus suspension movement is allowed by the urethane bush rotating around the sleeve. Because it is a tight fit, the interface is lubricated to drop the coefficient of friction and allow free movement without sticking. If the lube dries out or gets pushed out of the way so that the urethane is rotating directly against the sleeve, you get the infamous squeak and stiction. At that point, the urethane is probably wearing against the metal sleeve. A rubber bush works differently in that instead of rotating against an inner surface, the bush itself "distorts" radially. It is a neat characteristic of rubber that it can do that. This is why rubber bushes are bonded to the inner sleeve -- no rotation there is needed or even desirable.

One of the reasons that a urethane bush has to be harder than its rubber counterpart is that it is essential that the inner diameter of the urethane bush remain concentric with the inner metal sleeve. If it doesn't, that means that urethane bush in effect "pinches" the inner sleeve and motion is impeded. Consider that the suspension bushes essentially hold the weight of the car, and then throw in the stresses when the car is in motion. If the urethane bushes are too soft, they will distort and pinch the inner sleeve, impeding rotation. I think this distortion cycling creates a pumping effect that shunts the lubrication to the sides. This may explain why so many folks lubricate the urethane bushes as directed, only to have squeaking and stiction issues return after a few months. While rubber bushes can be rightly criticized for adverse reaction when exposed to oil, water is the enemy of urethane bushes. It is not that the urethane material is affected, but rather that water can and will work itself into that urethane/inner sleeve boundary, displacing lubrication and one again inducing squeaking and stiction.

It is a well-known side effect of urethane bushes that more NVH (noise, vibration, harshness) is transmitted to the car and perceived by the occupants. Rubber bushes do a pretty good job of absorbing vibration, but urethane bushes pass it right on through to the chassis. On an IRS car, that means through the bolt/bolt hole interface on the trailing arm mounting brackets. I've heard of owners noticing that the holes in those brackets have elongated after running urethane bushes for a while. Consider also how the toe-in is set on the IRS TR rear wheels; the trailing arm is shimmed at the bracket/chassis interface. That shimming changes the rear geometry such that one or the other bush gets compressed. That compression doesn't matter to a rubber bush, but it may to a urethane bush, since that compression may propagate down to distortion of the inner diameter and thus pinching of the inner sleeve. Stiction, etc.

I consider bushes to be wearable parts. I far prefer the bush to get beat up than the chassis parts. My opinion is no doubt biased by my being a "daily driver" TR owner. I've depended on my TRs for daily transport since 1980. Being a Bay Area person just as you are, you will probably agree with me that the roads here are pretty rutted up. Daily driving is probably more severe than on a race track! I don't care as much about eeking out a little more handling as I do about having my TR get me around in TR style. I can fully appreciate those like yourself who are fully rebuilding their TR to be a street-legal racer and want the best handling possible. But for me, the TRs handle nicely as is, and a comfortable ride is part of my driving equation. For those reasons, I run all rubber bushes, no urethane. I am very happy with the performance.

 

[mrv8q]

Well, I sure hate a well-reasoned argument against my firmly-held beliefs! /ubbthreads/images/graemlins/rolleyes.gif Hmm, will now have to reconsider rubber bushes... thanks 4A for the dilemma!