Suspension spring or hard bar on dozer?

[nutwood]

I have an old Fiat 70CI dozer. As built by Fiat, the rear of the body of the machine is attached to the tracks via a couple of bushes and the front of the body is supported by a leaf spring that rests on either track frame and is bolted to the sump.
The old bloke I bought the dozer from replaced this front spring with a solid bar. He's dead now so I can't ask him why, but presumably he had some reason for doing this, as he'd been working with dozers all his life. It could just have been cheaper than replacing the spring but he generally didn't seem to stint on doing things properly.
I'm wondering if anyone has had any experience of this situation? I am considering getting a spring made and re-installing, as per original specs. To me I can't see a good reason not to have a spring. It's a tough machine but it's working in rough country and every time it comes down hard, I wonder why the spring was removed. It seems to me that a lot of unnecessary shock loading is being inflicted on everything; including me!
My only experience is with this dozer but I'm assuming that the basic principles of dozer suspension are similar so am also interested in feedback regarding machines other than Fiat.

 

[DMiller]

Most of the older machines had spring cross truck suspensions, Allis had similar that they did away with for a cross beam support. Articulation of the trucks may have been the best thing they could understand when the machines were first being developed but that soon waned to solid suspensions and I have no idea why.

Have been to shows where the old spring loaded machines nose dipped when the buckets or blades were raised also popped back up as those were dropped so could have been bad as to maintaining grade level.

 

[nutwood]

Thanks for that DMiller. What I'm understanding is that solid suspension is how modern machines do it? If I'm working uphill, or trying to push down a recalcitrant tree, the machine has a habit to rear up. If I touch the clutch, or even back off the throttle, she'll come down with a bang that shakes the fillings from my teeth. Hence my interest in the spring; dentists are expensive!

 

[epirbalex]

Blade lift rams mounted on the nose cone make springs work hard and a bar is better . I have owned two D47U's one was down in the nose with a bent spring . Old fella new what he was doing fitting a bar to yours .

 

[Queenslander]

As you would know Nutwood, the thing that distinguishes the 70ci from almost every other dozer is that the lift rams are mounted on the track frames.
You would also know that this weird (to some) setup works surprisingly well.
Back when we owned an AT7C, I wasn't sufficiently interested to find out but I suspect they have some clever valving to allow the track frames to oscillate independently.
If I recall correctly, our tractor had two spring packs, one much smaller than the other, and broken leaves were pretty common, which is probably why old mate opted for a hard bar.
As you say, it would make for a rough ride though.

 

[nutwood]

Understand the logic re the blade but the Fiat has the blade directly mounted to the track frame. The body (operator, engine, gearbox etc) moves separately to the tracks and blade. I can see that a drooping spring would be an issue but I'm looking at re-installing a brand new spring. Back to original specs.

 

[nutwood]

As you would know Nutwood, the thing that distinguishes the 70ci from almost every other dozer is that the lift rams are mounted on the track frames.
You would also know that this weird (to some) setup works surprisingly well.
Back when we owned an AT7C, I wasn't sufficiently interested to find out but I suspect they have some clever valving to allow the track frames to oscillate independently.
If I recall correctly, our tractor had two spring packs, one much smaller than the other, and broken leaves were pretty common, which is probably why old mate opted for a hard bar.
As you say, it would make for a rough ride though.

Ah-ha. No, I didn't know that (apart from that it works well!). You're right, the original specs show two spring packs. You're also right about the rough ride!! If breakage was the issue, it seems to me that my plan of getting our local spring works to make a couple of packs to original specifications is going to save me some dentist bills for a few years at least

 

[John C.]

If it is that rough of use you will likely spend more time fixing broken spring leafs than running the machine.

I had a 13A with a spring and just hated the machine. Picking up the cable blade made the nose drop 6 inches and getting slapped in the back with the seat cushion. Every time someone tried to work a stump out of the ground a leaf would snap.

 

[Queenslander]

Just thinking, the motor and radiator on these Fiat dozers aren't supported by a frame or rails, they are just bolted to the transmission, like a lot of farm tractors, hence the need for track mounted blade rams.
So all those uncushioned blows that are rattling your fillings are probably adding stress to those bolted joints.

 

[epirbalex]

Understand the logic re the blade but the Fiat has the blade directly mounted to the track frame. The body (operator, engine, gearbox etc) moves separately to the tracks and blade. I can see that a drooping spring would be an issue but I'm looking at re-installing a brand new spring. Back to original specs.

For a collector restore project , yeah . If the spring is going to be soft enough to offer a smooth ride it will be soft enough to break and if the bar allows your tractor track frames to oscillate its about as good as it gets . Komatsu D31-16 I did a 100 or more hours was fixed solid and was tricky on uneven ground , a D37 dash unknown , solid track setup to , I had to recover twice as the operator went too far on the outside of his track he cut and it overbalanced , both modern gear . Have you considered a better seat ? Another thing , has the bar that's there now been attached properly as the motor, transmission seat and you could wind yourself backwards out of your track frames climbing steep ground .

 

[nutwood]

Just thinking, the motor and radiator on these Fiat dozers aren't supported by a frame or rails, they are just bolted to the transmission, like a lot of farm tractors, hence the need for track mounted blade rams.
So all those uncushioned blows that are rattling your fillings are probably adding stress to those bolted joints.

That is very true. The cast iron side straps on the radiator have been brazed up previously but are both broken again. I'm the process of replacing the radiator as the broken side straps have stressed the core and it's just too far gone to be solderable.
The solid bar does allow the tracks to oscillate. It's been installed in the same manner as the spring so performs in the same way.

 

[old-iron-habit]

Thanks for that DMiller. What I'm understanding is that solid suspension is how modern machines do it? If I'm working uphill, or trying to push down a recalcitrant tree, the machine has a habit to rear up. If I touch the clutch, or even back off the throttle, she'll come down with a bang that shakes the fillings from my teeth. Hence my interest in the spring; dentists are expensive!

Wither you have a spring or hard bar make sure they are in good condition and connected to both the tracks and the machine. Over the years many operators have been killed running a machine with a broken spring. The machine torque tipped the machine over backwards on a hard push with good traction as the machine pivoted on the sprocket. The broken springs simply pulled out of the side support. A correct good spring or hard bar would have held them down.

 

[nutwood]

Wither you have a spring or hard bar make sure they are in good condition and connected to both the tracks and the machine. Over the years many operators have been killed running a machine with a broken spring. The machine torque tipped the machine over backwards on a hard push with good traction as the machine pivoted on the sprocket. The broken springs simply pulled out of the side support. A correct good spring or hard bar would have held them down.

That's a very valid point. Thinking about it, I can see exactly how that could happen and I'm going to have a good hard look at how the current bar is installed!

 

[Billyboy]

Hello fellas just found this issue and thought i might comment about our 70ci. She has the 2 opposing springs on the front . I believe the big spring is to support the weight of the machine as the sump of the engine sits directly on the spring.and the other spring is adjustable to prevent the engine sump from from coming off the big spring when the blade is pushed down hard and banging down when the blade is lifted up. We had that problem when i first put the engine in but there is an adjustment on the starter side to tension up the small spring to prevent this. Ours is very worn and i had to build up the holes in the brackets that hold the spring but i think that the spring has collapsed a little so cant get enough adjustment .With a little experience operating the machine this banging down doesnt seem to be a problem anymore. Have heard of the solid bar and have been advised to fit one but, not being an operator i dont really see a reason for it. Hope this has helped.