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#1
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Torque, Rubber Bushings and the F-Body Subframe
I kind of want to give you guys a graphical illustration of the problem with running rubber body bushings in first and second gen F-Bodies when power and traction is significantly increased over stock.
I'm currently in the process of replacing bushings and adding subframe connectors. Here's a look at the driver side mid-body mount Looking at this you can see that the bushing itself while not in the greatest of condition, isn't completely mangled and deteriorated. These are wear parts and were never designed to last the age these vehicles are. I don't know if these bushings are what the car was delivered with, but I'm assuming they are. What you will notice however is how the washer that holds the bushing together is folding like a taco. What is occurring here is that due to increased torque and levels of traction, the body of the car is trying to rip away from the subframe mount. This is in part due to the car's unitized rear chassis. As the axle takes torque it wants to twist. That twist translates to the front eye bushings of the leaf spring and physically wants to pickup the body of the car. The subframe, with all the weight of the engine, transmission and front suspension is along for the ride. Keep in mind, my combination isn't even crazy. At my altitude, my trap speed vs weight indicates about 330hp to the tires. While much larger than factory, my 245/45/17 and 275/40/17 summer performance tires aren't crazy either. The ultimate solution is a full frame of course, like The Heidts frame or a Roadstershop SPEC or FastTrack. But 15-30K for a full frame isn't realistic for a lot of people, me included. The next best option is to physically weld the subframe to the body and connect the two ends of the car with a set of subframe connectors. The DSE through floor connectors are a popular choice here. Until full frames became available, this is pretty much what you saw in every serious build. Not only does it provide a large increase in strength, it also has the benefit of lowering the front of the car without losing any bump travel. With small LS engines, there's typically no big issue, but with a big, tall Pontiac you can run into hood clearance issues doing this. For cars that are complete or don't want to have the floors cut, the next best option is solid body mounts with an incorporated set of under the floor subframe connectors. This is the solution I'm working on currently. Any time you say the word "solid" concerning the front end of these cars, you always get a lot of naysayers talking about noise, vibration and harshness. There are "some" trade-offs here, but mostly the people that complain about such haven't actually riden in, driven or own a car with solid bushings. Almost all modern cars have unitized chassis that are literally part of the body. This exercise is achieving that same thing. What to look out for in the bushing department is the early aluminum offerings that were little more than round pucks. Because of their design they would spin and chatter against the body and the frame, not transmitting, but instead creating some of that noise. What you want is a set of bushings that interlock with each other and physically sandwich the frame between the interlocking junctions. I opted for the RideTech subframe bushings because not only do they interlock, but the frame to body portion of the bushing is Delrin which provides 95% of the stiffness of aluminum, but also acts a diffuser for noise and vibration. The last piece is tying the front subframe to the rear unitized frame. I again opted for the RideTech connectors because of one main reason. That being the integral front eye mount for the leaf springs or aftermarket 4 link systems. This ties them directly to the frame rail and bolsters an area of the chassis that takes much of the forward drive forces. The front of the connector is also captured by the rear body bushings, which lets these work better as a bolt in option instead of a weld-in option. FWIW I do think that the Chassis Works g-connector system is probably the best option for a car that can't have a welded in subframe, or a full chassis under it. But that system is much more expensive and the installation requirements are much more in-depth. One thing I wish the RideTech subframe connectors had, is a relocation of the front eye mounts. Raising the front leaf spring perch would really help anti-dive in these cars and would also likely help out with wheel hop as well. This got a bit long, but I hope it illustrates the importance here of ditching the rubber (or poly) bushings on cars that are anything other than stock, or near stock. In my eyes the poly options should never even be considered. They do nothing but gain you the compromises of a solid body bushing with only a very small portion of the benefit. Cheers!
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-Jason 1969 Pontiac Firebird |
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#2
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Mine is now mostly poly with subframe connectors. I haven’t had a noise issue with them. Just grease them. Honestly I’ve felt it’s easier to find quality poly stuff than it is rubber. I don’t claim to be an expert so I won’t be trying to change anyone’s mind. I will say that I’ve had poly bushings in pretty much everything I’ve replaced save the leaf spring shackles and have no complaints.
With the solid bushings would cracking not become a problem due to work hardening?
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1967 Firebird 462 580hp/590ftlbs 1962 Pontiac Catalina Safari Swapped in Turd of an Olds 455 Owner/Creator Catfish Motorsports https://www.youtube.com/@CatfishMotorsports Last edited by RocktimusPryme; 02-11-2022 at 08:40 PM. |
#3
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x2 on the poly body bushings, while solid are better for serious racing/power, the poly are considered to be mostly solid as they dont compress but do offer a little more "cushion" than solid metal. looks like the ride tech set up will work fine too.
for connectors i have alway heard you dont want the type that mount under the spring eye or subframe bushings like the cheaper comp engineering kind, its best to mount to the rear & front frame or go with the DSE full weld in that become part of the floor as mentioned but not everyone wants or needs to do that & cut up the floor. what i used & really like are the PTFB connectors that extend all the way to the rear frame & can be welded or bolted in & do the same at the front subframe. any style connector with be an improvement over not having them even for lower power engines & especially on T top cars, ive seen mostly stock engine cars buckle the roof at the back area with t tops. |
#4
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I still believe that most people that run a poly set probably would have been good running a solid setup in the first place. The biggest reason there's a lot of poly in suspension components isn't because it's ostensibly better, but because in large enough quantities, the stuff is damn near free to produce.
And yes any subframe connector will be an improvement, and it's true that you want that connector to integrate directly with the rear frame. There are many versions that don't really do that.
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-Jason 1969 Pontiac Firebird |
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#5
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FWIW you will never notice any difference in road feel using solid bushings. Personally I think the interlocking Global West are the best. My 78 TA has had Herb Adams lowering solids(shoved the Shaker to tight no interlocking portion), Guldstand 1/2 lower-still tight Shaker and no interlocking, and full thickness Globals. They even made me a custom larger OD rear to capture more of the Moroso subframe connector that goes under it. Used the same on the 81 when I freshened the suspension and the Camaro/IA.
Yes those old Moroso that are under the spring eye mount and under the subframe bushing are a little more of a pain. The 81 and Camaro have I think Chris Alstons, PTFB sold those (round tube) before he made his own.https://www.summitracing.com/parts/a...t/model/camaro. All subframe connectors make it a little difficult using a lift.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#6
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Timely discussion, I'm considering discarding my old Comp Engineering subframe connectors with the Chassisworks G-connector system.
While pulling out my rear a few weeks ago, I had cause to drop the sub-frame connectors and noted quite a little bit of distortion in the forward bolt holes the original body mounts. I have solid aluminum mounts...just need to find the time to install them. The subframe connectors will get welded in this time go round.
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1968 Firebird IAIIa 522 340 E-heads Northwind with XFlow TBI 4L80E 3.50:1 Rear |
#7
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I received my car back from the shop today with the newly installed solid body mounts and subframe connectors. They found significant rot in the subframe on the driver's side rear mount as well as the passenger side firewall mount. In both cases new plates were fabricated and installed to correct the mounting points.
As far as initial driving impressions, the difference is pretty significant. The easiest way I can describe the driving quality is that it now feels like the suspension is doing all of the work. The front end is far more direct and settled. As far as NVH concerns, the little I've been able to drive it so far, I would actually say it's quieter. Of course I must take into account the incredibly poor state of the factory rubber bushings. I would need to compare directly to brand new stock type bushings to really get a sense of any increase or decrease in NVH. Ground clearance is not an issue with the new sub-frame connectors. My X-pipe is still the lowest point of the car at it's breakover point and I experience no other ground clearance issues so far than I normally did prior to their installation. They suck up to the floorboards really well. The lighting in my garage sucks right now, once it warms up a bit more and I can open the whole garage up, I'll try and get some good pictures.
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-Jason 1969 Pontiac Firebird |
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#8
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cant wait. thanks
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1968 Firebird IAIIa 522 340 E-heads Northwind with XFlow TBI 4L80E 3.50:1 Rear |
#9
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Took a few photos this weekend. You can see here the fitment on the car. My 69 has the original floors that do show a bit of sag to them. Cars with new floors in them will likely have a bit more space between the connector and the floor itself.
The rear subframe bushings capture about 3/4's of the subframe connector top flange, so while these are bolt-in, they should perform on par with most of the weld in options as far as torsional loads are concerned. I would like to see these fully boxed at the frame mount, but that's somewhat impractical with the design of the factory subframe. The Chris Alston system does address this completely and why again I think it's probably the best on the market when a full frame is not being utilized. You pay for it of course. I do love that they've reinforced the spring mount and tied it directly to the frame with these.
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-Jason 1969 Pontiac Firebird |
#10
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Congrats! They look to fit nice and tight under the floors. Did you notice any increase in under hood clearance with the bushing replacement?
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1968 Firebird IAIIa 522 340 E-heads Northwind with XFlow TBI 4L80E 3.50:1 Rear Last edited by punkin; 03-19-2022 at 02:53 PM. |
#11
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None that I could see or notice. When I did the front end rebuild about 15 years ago, it included a set of poly graphite bushings for the core support. Those were still in excellent shape. I believe those likely kept everything aligned, without as much sag as you'd expect.
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-Jason 1969 Pontiac Firebird |
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