Float-A-Motor Mount on 28 roadster with fixed front mount

bavArian

bavArian

Senior Member
Hello everyone,


I'm driving a '28 roadster with a fixed front motor mount. As far as I know only the early '28s had that mount.
As I'm having vibration-issues at certain revs I'm thinking about switching the fixed rear mount for a "A-5089-FAM FLOAT A MOTOR KIT". While researching about that kit I found posts here that it's not recommended on the roadster as it reduces chassis stiffness.

Is anyone driving that setup and can confirm that it helps with vibrations? Or is it an unnecessary expense?


Thanks and have a nice day,


Daniel
 
The service bulletins showed cutting off the cross piece parts that bolt to the front of the motor and installing the stock coil spring mounts. People have had problems with after market non Ford mounts in the front. As far as the rear is concerned, the stock mounts are good if the rubber pads are replaced. The Float-a-Motor in the rear is also good if the bolts that go through the rubber pads are just snugged up and not tightened. Although there is some concern of loosing a frame component that the engine is part of with the Float-a-Motor in the back, as you alluded to.

My suggestion is to change to the stock Ford coil spring mount in the front and then replace the rubber pads in the back and go with that. If you have a copy of the service bulletins, it gives information on how to change to the spring mount in front.
 
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My Tudor came with the rear float-a-motor setup and some weird beehive spring with rubber isolators under the springs in the front. The rubber on the rear mounts was shot and the front mount held the engine too high and too stiff.

When I put the original style springs on the front, it took care of a lot of vibrations. Then, I put new rubber on my old rear mounts and it really got rid of a lot of vibrations and resonating noises throughout the cabin.

I don't have anything to compare the rear float-a-motor kit to, but the setup I have seems to work very well IMO
 
Hi guys,

I do have a copy of the service bulletins, will take a look at that. I am really hesitant to cut the front mount though and would rather like a bolt-on solution. However, I'm pretty sure the rear mount rubber needs to be changed, I have yet to find a rubber part that didn't need to be changed on that car...


Is the fixed rear mount working well with the fixed front mount or will that combination always have some vibration? Maybe that's why Ford changed it after only half a year?
 
Ford figured out in a hurry that bolting the engine to the front crossmember was a BAD idea and came up with a better design and a service fix. I am amazed that 90 years later there are still cars with solid front mounts. If you Have to have your car as built for whatever reason you will always have vibration due to harmonics. As crude as it sounds cut the mount off go to the improved factory parts. As far as the floaters new rubber is a good idea. Make sure sure the rear most part of the floaters is installed. Some folks just leave those parts off, big mistake. The magic of the floaters is in the adjustment of the thru bolts. Too tight, too loose is a very fine adjustment. One quarter of a turn can make big difference. This where persistence pays off. OR you could sell that roadster and get one built at a later date!
 
Hello Richard,


that car is quite original with only VERY minor modifications, it doesn't even have external door handles that the later cars had as standard for example. From the condition I'd guess it was stored in a barn or sth. for a long time and then revived on a budget sometime mid-80s.
Being an mechanical engineer I'm aware of the reason that these vibrations are occuring and I have no idea why Ford decided to mount the engine rigid on both ends. For a long time now that's reserved for race cars because of the vibrations and noise coming from the engines being passed on right to frame and body.


Selling the car isn't as easy over here as it is in the USA, these cars are extremely rare over here and a really good one will lighten your bank account a lot. Also I've already done a lot of work to the car and am at the point where, apart from a few engine/carb-related problems, everything works fine. That's why I want to get the rest working properly too. :p

I think I'll test it with fixed front mount and floating rear mount and gearbox. That should remove almost all vibrations. If it still causes problems I can always modify the front mount according to the service bulletin.
 
Using the floater motor mounts on the engine in the rear reduces the rigidity of the frame and you most likely will have more frame sag than you would if you leave it original.
 
I have an early ‘28 Phaeton with the solid front mount and stock rear mounts, and also a ‘29 Fordor with float-a-motor mounts. Both engines are professionally rebuilt. Vibration is about the same in each; what I think is about normal for a Model A.

I suggest you take one step at a time. Before you do something irreversible like cutting off the front mount, try only replacing the rubber pads on the stock rear mounts, and see if that helps. If you still are not happy, you can take the next steps.

Before you order pads, research this forum concerning the correct thickness of the replacement pads. I lot has been written about the new pads from some manufacturers being too thick.

W. Michael
 
For sure that is a conundrum. Original unrestored cars are the ultimate for me and preservation of those cars is very important so I do understand your situation. If the car is that original maybe a different tack would be best. Have you considered disassembling the engine and having ALL reciprocating and rotating balanced. Everything means fan, pulley. Clutch disc, etc. Everything. Have the balancer zero in on 2000rpm plus or minus 200 rpm. You made need to remind we don't care so much about 4k. Most balancing is done at lower rpms with some math that says oh this will be ok at 2k or whatever rpm range they are selling. I knew of one balancer that would spin the crank at 2k. He wanted to be sure. I see that as the only way of dismissing the amplitude of the harmonics. Next on the rear floaters I wish the durometer of the rubber was published so we would be able to find the best number to use. Floaters have no affect on frome sag. If you haven't straightlined your frame and know different at this stage most model A frames have some sag. As for stiffness of the frame, if you are thinking about collisions well from what I have seen the flywheel housing is always busted so as far as strength I am not so sure. I first installed floaters most likely early 80s as best I can remember. I do have an unrestored original sedan with 48k miles. Yes it has floaters. Amazing to drive.
 
Being a mechanical engineer, you know that a conventional inline engine cannot be completely balanced because the small end of the con rod is moving in a linear motion and the big end of the con rod is moving in a circular motion. However, using a completely counter balanced crank will help with the vibrations. Machine collars to go around the rod journals that weigh 100% of the weight at the big end and maybe 67% of the weight at the little end (including pin, pistons, and rings). Have the crank balanced with the collars on the journals.

If you want to keep the solid mounts in front, you could come up with some sort of rubber isolation system, like grommets and necked down bolts. You could keep the original bolts in case someone in the future wanted to change it back to stock. To add rubber between the engine and the mount, you could machine off some material from the cam gear cover that the mount bolts to. I don't expect this to be as good as the spring system that Ford came up with.
 
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bavArian said:
Hi guys,

I do have a copy of the service bulletins, will take a look at that. I am really hesitant to cut the front mount though and would rather like a bolt-on solution. However, I'm pretty sure the rear mount rubber needs to be changed, I have yet to find a rubber part that didn't need to be changed on that car...


Is the fixed rear mount working well with the fixed front mount or will that combination always have some vibration? Maybe that's why Ford changed it after only half a year?
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The issue with the chassis mounted front is that it is solid. Any twist forces in the chassis will be transfered into the engine and will give problems in the long term. A three point engine mounting system is needed as all manufactures have had for a long time.
 
The issue with the chassis mounted front is that it is solid. Any twist forces in the chassis will be transfered into the engine and will give problems in the long term. A three point engine mounting system is needed as all manufactures have had for a long time.
 
The rear axle pushes on the back of the transmission through the torque tube when moving forward and the pulls on it when braking. Add that to the twisting movements of the frame and road vibration and the original AR type fixed mountings started to have cracking issues. Ford came up with the semi-rigid mountings to give enough flex as to slow the cracking problem a good bit. They redesigned the rear engine to frame mounts and used the rubber pads with bushings. They put out service bulletins for this stuff that included the modification to the front cross member and addition of the coil & leaf spring set up for the front. Eventually, the front cross member was changed again to open up the yoke stud hole for the front mount since they were having problems with cracks in the smaller hole they punched in those that came equipped with the more flexible front mount.

The front cross members went through a LOT of changes in the first year of production alone. After they finally got it the way that they wanted it for the 1930 model year, very few changes happened till the end of production in 1931.

I feel fortunate to have the later 1929 model that is fully equipped with the semi-flexible mounting since it functions about as well as Ford ever made it to. This set up was used through the end of production for the most part. Those that have the early cars and want them to be factory original are pretty much stuck with the rigid mount. Apply all engine balance procedures and add a counter balanced crankshaft and that will smooth that part out without showing much to the Judges at model A show events.
 
rotorwrench said:
The rear axle pushes on the back of the transmission through the torque tube when moving forward and the pulls on it when braking. Add that to the twisting movements of the frame and road vibration and the original AR type fixed mountings started to have cracking issues. Ford came up with the semi-rigid mountings to give enough flex as to slow the cracking problem a good bit. They redesigned the rear engine to frame mounts and used the rubber pads with bushings. They put out service bulletins for this stuff that included the modification to the front cross member and addition of the coil & leaf spring set up for the front. Eventually, the front cross member was changed again to open up the yoke stud hole for the front mount since they were having problems with cracks in the smaller hole they punched in those that came equipped with the more flexible front mount.

The front cross members went through a LOT of changes in the first year of production alone. After they finally got it the way that they wanted it for the 1930 model year, very few changes happened till the end of production in 1931.

I feel fortunate to have the later 1929 model that is fully equipped with the semi-flexible mounting since it functions about as well as Ford ever made it to. This set up was used through the end of production for the most part. Those that have the early cars and want them to be factory original are pretty much stuck with the rigid mount. Apply all engine balance procedures and add a counter balanced crankshaft and that will smooth that part out without showing much to the Judges at model A show events.
Click to expand...
I agree with rotorwrench and would like to add the following. All of these changes to the crossmember are due to the stresses that were induced into the engine by the continious torsional twisting of the chassis. The cracks were caused by the resistance of the engine to "torsionaly twist". Having said that, we only need to distort the tunnel bore by 0.001 to 0.002 to create a problem of interference in the main bearings. It seems unreasonable that judges would take points away from what was a Ford production rectification. Just remember that a three legged chair will always sit even on an uneven floor. The engine should not be subject to any external torsional forces if you want it to last.
 
With a roadster body, I don't think chassis sag would be an issue as they are the lightest body. If you use the rear support that comes with the FAM's that bolts onto the rear of the gearbox and rests on the cross member, I think this would also help with preventing chassis sag. I have FAM's on my 29 Tudor, with the gearbox support, and haven't noticed any sag yet. Alos, I think modern roads are a lot smoother in general, which would also help in preventing sag and vibrations. I use the standard front mount as the FAM front mount doesn't fit a 28 chassis that has had the solid mounts removed as per the bulletins, as there are two pressed ribs that interfere where the pads sit and prevent them from sitting evenly.
 
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