[Sirrotica]

Originally Posted by Tom Vaught

I have seen the rubber isolators on most 64-67 GTOs and always on Convertibles which is all I have owned and actually worked on. Convertibles are pretty filmsy on the frame structure as is without the steel roof and if you put a Bolt On solid frame crossmember in place on the car vs the isolator mount system, you could very well break the transmission crossmember ear off the solid part.

Nope, I am not jerry rigging anything on a convertible chassis.

Tom V.

Some of the other GM divisions A bodies had no isolators on the ends of the transmission crossmembers. There aren't any problems when the crossmember is mounted solidly to the frame. The 78-87 G body crossmembers are bolted solidly and they are essentially a downsized early A body chassis.

I've had Pontiac crossmembers that the ends inside of the isolators rusted off and I welded a piece of steel across where the ends that had rusted off, and drilled holes and bolted them solidly to the inner frame channels, no problems.

GM F bodies have no isolators on the transmission crossmember ends, they're bolted solidly to the top of the subframe rails. And finally ford and chrysler have transmission crossmembers bolted solidly without any isolators between the frame and transmission crossmember.

Many GM cars/trucks have been built without rubber bushings on transmission crossmembers. I've studied the design that Pontiac used and have never come up with a definitive reason they built some of their cars this way.

I've eliminated the rubber isolators without any adverse effects years ago on my own cars, due to rust from dirt and salt being packed into the rubber isolator. In the end it's your car, and your choice, but in my own experience eliminating the rubber works without any adverse effects.

Actually making a solid bolted connection from frame side rail to side rail using the transmission crossmember is going to stiffen the chassis by adding a solid connection, not make it weaker. If it were triangulated instead of just being a 90 degree connection it would be even stronger/stiffer.

[Tom Vaught]

Originally Posted by Sirrotica

Some of the other GM divisions A bodies had no isolators on the ends of the transmission crossmembers. There aren't any problems when the crossmember is mounted solidly to the frame. The 78-87 G body crossmembers are bolted solidly and they are essentially a downsized early A body chassis.

XXXX not shouting (with the caps) Last time I looked I don't remember any 78-87 G body CONVERTIBLES

I've had Pontiac crossmembers that the ends inside of the isolators rusted off and I welded a piece of steel across where the ends that had rusted off, and drilled holes and bolted them solidly to the inner frame channels, no problems.

XXXX Again, Were they CONVERTIBLES?

GM F bodies have no isolators on the transmission crossmember ends, they're bolted solidly to the top of the subframe rails. And finally ford and chrysler have transmission crossmembers bolted solidly without any isolators between the frame and transmission crossmember.

XXXX And GM F-Bodies with T-Tops, not quite as bad as CONVERTIBLES, move all over the place with any real load on the chassis.

Many GM cars/trucks have been built without rubber bushings on transmission crossmembers. I've studied the design that Pontiac used and have never come up with a definitive reason they built some of their cars this way.

XXXX Again, you seem to be stuck on the point I was making. Solid mounts on a CONVERTIBLE is probably not a good idea.

I've eliminated the rubber isolators without any adverse effects years ago on my own cars, due to rust from dirt and salt being packed into the rubber isolator. In the end it's your car, and your choice, but in my own experience eliminating the rubber works without any adverse effects.

XXXX How many were CONVERTIBLES

Actually making a solid bolted connection from frame side rail to side rail using the transmission crossmember is going to stiffen the chassis by adding a solid connection, not make it weaker. If it were triangulated instead of just being a 90 degree connection it would be even stronger/stiffer.

XXXX It doesn't make it stiffer if the frame flexes and breaks the solid mounted cross-member due to high loads at that point.
FROM CHASSIS TWIST.

Tom V.

[Sirrotica]

Originally Posted by Tom Vaught

XXXX It doesn't make it stiffer if the frame flexes and breaks the solid mounted cross-member due to high loads at that point.
FROM CHASSIS TWIST.

Tom V.

Tom, would you care to explain how other chassis built similarly without rubber isolators don't break anything in hundreds of thousands of miles, be they convertibles or hardtops?

I've made A bodies Pontiacs solid in street, and race cars.

If memory serves me, chevy malibus were solid mounts. Malibus and Tempest chassis are for all purposes are the same. The chevy sister car used many of the same drivetrain parts as Pontiac did and I don't know of any parts that broke on them due to chassis/body flex, do you?

If I was theorizing, and hadn't converted some Pontiac A bodies to solid mounts it would be purely theory. However I actually have made the conversion without any problems, not a theory when it has no downside and works without problems.

[Sirrotica]

To further prove that other A body GM cars bolted the transmission crossmembers solid, here's a picture of a chevelle crossmember that fits 1964-72 chassis:



As anyone can plainly see the crossmember bolts directly to the side frame rails, no rubber isolators are needed. If someone drilled the proper holes in the Pontiac frame, the chevelle crossmember would bolt in and function just fine, as the chevelle and Tempest frame are essentially the same part.

Why did Pontiac decided to use isolators? I'm not sure, they may make the car a bit quieter. They are however not going to break any driveline parts or damage the frame when it is in a twisted situation, say during hard cornering, etc. I've already eliminated the isolators in enough Pontiac A body cars and driven them myself to know that it won't harm any parts or cause undue stress that will cause some breakage down the line.

I just remembered an incident long ago during a burnout contest where a friend of mine dumped the clutch on his GTO and the left side of the transmission crosmember came out of the rubber isolator and we had to jack up the crossmember and put it back together so he could drive it home.

Hopefully this puts the notion to rest that they are needed to make the car function properly, whether it's a convertible or a hardtop because chevelle made a bunch more A bodies than Pontiac did and both body configurations were solid mounted crossmembers.

I can't recall if other GM divisions bolted the transmission crossmember solid, it's been too long since they were common for service work. I do remember chevelles in both body styles had no isolators.

Back to F bodies, yes they were convertibles in 67-69, yes solid bolted crossmembers.

[topfuel67]

I've had that drive shaft issue too. It is due to the body bushings being worn out. You can try all these other fixes, but you'll still have worn out body bushings. I replaced my body bushings by myself in a couple of hours. You have to get an extra set of radiator bushings and modify it for the third one.

[TPM]

I had the same problem and my 65 GTO has brand new body bushings....I plan to remove the trans crossmember insulators

[NEW64OWNER]

Originally Posted by topfuel67

I've had that drive shaft issue too. It is due to the body bushings being worn out. You can try all these other fixes, but you'll still have worn out body bushings. I replaced my body bushings by myself in a couple of hours. You have to get an extra set of radiator bushings and modify it for the third one.

Nope, body bushings are like new. 1/4" short mount= problem solved.

[highrisk]

When I got my 65, before the restoration, the driveshaft rubbed all the time. I finally realized the frame was bent up where the transmission crossmember attaches to the frame. I used a large adjustable wrench to bend the frame back down and that stopped the issue. When I had the frame out during the restoration I was able to properly straighten the frame. I would imagine this happens when people use that area to jack up the entire side of the car and it bends/collapses the frame.
Dale