Most people who have wanted a firmer rear end have used polyurethane, aluminum, or delrin bushings. Most agree that the cradle needs the firm-up treatment but say to keep the rubber bushings in the a-arms. I would also keep rubber engine and tranny mounts and dog bone bushings.
Solid aluminum cradle bushings do basically the same thing. No welding or fab work necessary.
On a side note, the '88 Fieros have solid-mounted cradles from the factory. And they don't vibrate like Harleys. So I don't think that's really a concern.
Thanks guys for the info. I forgot to mention that this was going to be a 3800 s/c swap with a cam and no balance shaft. I was aware of the 88 solid mounted cradle, and i wanted to replicate that if i could.
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You could get the aluminum bushings from Rodney for the same effect
I guess i never realized i could get aluminum bushings actually. I figured the solid mount setup shown in the link above would be a cheap and good way to accomplish what i wanted. However, It doesn't say what is used for the rear mounts. Rubber would probably work fine in this case, wouldn't it?.. and it would help to diminish vibration, if any. troy
Solid mounted engines are asking for cracks. Why do you think the oem puts in rubber isolators, because of vibration. Talk to any engineer who has done dynamic balancing with rubber. Instead of a high peak load from the oscillation, the rubber spreads it out over time at a lower amplitude. the same energy is absorbed , but over a longer span. this is a fact of design. But i know there are so many fiero owner who know more than the oem's.
If you are a drag man and dont care go for it.
Former vibrations engineer from chrysler, now retired with a cam on a 4.3l v6, lambo feiro.
The OP is not referring to solid mounting the entire drivetrain. The topic is hard-mounting the cradle to the space frame, which has been done many times. In fact, GM realized in 1988 that it made sense to do this also, hence why as mentioned above the 1988 model Fieros eliminated all cradle bushings in the updated cradle design and hard-mounted the cradle to the space frame.
There is no serious disadvantages to hard-mounting the cradle. It will for sure eliminate the "cradle slop" that occurs when cornering. This is when the cradle is actually traveling slightly forward as opposed to turning in an arc with the car. Obviously at some point it "hits" an end, and "grabs" to travel along with the car. The only thing I would see that would occur is that any deficiencies in the drivetrain mounts would be more pronounced with a hard-mount setup. However, if one is going this far then I would assume they would be replacing all the drivetrain mounts anyway.
I solid mounted the cradle AND the engine when I had a V8 in my car. It was so solid you could feel the starter mesh with the ring gear. It was too harsh for me.
------------------ 1986 SE Aero coupe.
3.4 DOHC swap is complete and running, now just have to finish the rest of the car...
Gm saw a way of pulling out a few bucks and did their cost cutting. one more reason the car only lasted four years. Pontiac pushed this car against the choice of higher mgt at gm. When sales began to fall this car was toast. When i started my project and saw the many offerings in the name of improvement like welded tubular steel control arms i stayed away from these guys. Welded arms failed by stress cracks at the joints on proving ground endurance tests.
Going back to my original statement. Rubber isolation of loads prevents cracking of metal joint and cast iron structures. if i had any opportunity to put your stuff on a lab shake rig you would see for yourself..
Gm saw a way of pulling out a few bucks and did their cost cutting. one more reason the car only lasted four years. Pontiac pushed this car against the choice of higher mgt at gm. When sales began to fall this car was toast. When i started my project and saw the many offerings in the name of improvement like welded tubular steel control arms i stayed away from these guys. Welded arms failed by stress cracks at the joints on proving ground endurance tests.
Going back to my original statement. Rubber isolation of loads prevents cracking of metal joint and cast iron structures. if i had any opportunity to put your stuff on a lab shake rig you would see for yourself..
I'm not sure if I'm following you. Are you saying that GM's decision to COMPLETELY change the cradle and suspension on the 88 model was a cost cutting exercise?
Are you saying that welded structures cannot hold up to proving ground tests? Do you realize that the spaceframe of the Fiero is not a single solid cast piece of metal but in fact many pieces of metal WELDED together? To say that a particular tubular steel control arm failed is not proof that all tubular steel control arms WILL fail. Perhaps it was the choice of steel, the design of the control arm, or a low quality weld that caused the problem. Perhaps the steel used was too stiff. Even though modern high-tech motorcycle frames are aluminum, the off-road motorcycles still have tube steel frames. Why? Because of the reason you cited. Vibration etc would cause a stiff frame to crack where a mild steel frame can flex and survive.
The electrodes I weld with are rated at 70,000 pounds. I think that will hold a car up.
Most agree that the cradle needs the firm-up treatment but say to keep the rubber bushings in the a-arms. I would also keep rubber engine and tranny mounts and dog bone bushings.
I would love to keep the rubber engine/tranny mounts, but from what i hear the rubber won't stand up to the 3800s/c. If i could gear up a set of rubber mounts that were made from control arm bushings like Darth's, I would do that. I think they would last well. He is not making them to sell, and I don't want to have the hassle of making my own rubber ones and doing the work of positioning the engine/trans on the cradle when i can buy a set of brackets for my app fairly cheap from Dan and just use rodneys poly mounts with the guess work all done. Not sure what route to go yet. troy
That's the old bushing outer shell. It is removable, but you'll be leaving it in for this mod. I welded mine to the cradle when I did this.
I used 2 washers on each side of the shell with the tube (salvaged from the worn out stock rubber bushing) running through them. You can use a long piece of threaded rod to line everything up or put it in the car and tack weld everything (as darkhorizon said), then remove and weld it all up.
So, to update, i have gone with rubber mounts for the engine and trans and plan on using two dogbones. I am thinking i will go this route instead of the aluminum bushings since it is cheaper, and one less thing i need to order and wait for. Thing is, what do you do for the rear of the cradle? Still uncleart on this part of it. I still have the collars for the rear, but how to i incorporate them into the whole thing? Does anyone have a pic of something they have done? troy
that was what i was thinking of doing. Do you know a height measurement from the cradle up to the top of the collar (in stock form with the rubber installed)
as mentioned in several other posts, the 88's have a solid mount cradle, and my LS3 is solid mounted to the cradle. No poly, no rubber and it does not vibrate at all. I also have hiem joints on the rear trailing arms so I have no poly or rubber in the rear of the car at all. Feels solid, no vibration and it drives like its on rails.
I have been using the aluminum cradle bushings for years and they work great although when I swapped Rodney poly trans mounts under my 3800 s/c it was a bit vibratey at low rpms. I am now in the middle of replacing the 3800 with an 06 N* that will be solid mounted, steel to steel. I have some experience with this when my son had a N* solid mounted and it felt smooth as silk.
I think most people who say that solid mounts vibrate too much have never used them. I've had them on two cars (one V6 and one V8) and I've never had issues with rattling or any other vibration. They make the car feel more solid and connected. On my Fiero I added solid mounts because I kept breaking rubber AND poly mounts.
With a 4-cylinder engine solid mounts might cause more vibration because 4 cylinders naturally vibrate more than other engine configurations. With balance shafts it might not be much of an issue. A 90* V6 without a balance shaft may also cause vibrations.
A 90* V6 without a balance shaft may also cause vibrations.
Yes this is what i am thinking. My balance shaft is removed and i am expecting some vibration at or a little above idle. As i understand these engines smooth out as the revs come up slightly. I am using the rubber mounts to try and counteract this cuz i am not sure how bad the vibration will be. But, I am using 2 dogbones to help the rubber mounts out as well. Being that it is my fiero and not one of our family cars, i can put up with a little vibration to make the car "better". For me, it will be driven back and forth to work and to tear up the back roads now and then. I can't wait to drive this thing! This car is the first fiero i have ever even sat in, and i have never driven it at all yet. lol troy
Sorry.
