47-55.1 Cab mounts

[hopalong]

1951 1/2 ton cab mounts. Although my year truck has the later hinged type mounts I see a lot resto 3100 cabs are being mounted on "block" type mounts which may give a firmer ride. Most cars and trucks now days have fixed isolater rubber or neopreme dough nut rings mounted to the chassis similar to the pre 50's solid mounts. The hing type seems to add to the cab moving and rocking alot. Any posigive or negative thoughts on this...thanks

[nvrdone]

I used some poly mounts under my '49. The cab doesnt move around as much as it did with the stock mounts. There is some noise from the harder poly mounts but with a small block, 2.5" exhaust etc I dont hear the noise too often

[fauXGT]

I saw someone somewhere that instead of the shackle style rear mounts he made a rigid 90 deg mount to bolt onto the frame vertically and a more modern body mount horizontally. He left the stock front body mounts.
I am still in the build stage, so i can't determine if I want to replace the stock shackles in the rear if I don't like the ride or leave them.

[hopalong]

I kinda think the shackle mount is like a stage coach or a horse and buggy type ride.

[mr48chev]

I plan to build some brackets that either bolt or weld to the frame rails that use the same holes that the shackles use with a biscuit or rubber block style insulator.This not even to scale doodle shows how it should work.

This style needs a rubber or Poly block between the cab bottom and the bracket and a block under the metal of the bracket working very much the same as the 55/57 Chevy car mounts or the TF truck front mounts work.

[dsraven]

instead of the polyurerhane mounts why not use a stock insulator from a more modern truck. they last forever and seem to work well, how many times do you hear guys saying they have to change the body mounts on their 2000+ vehicle? just remember the whole thing needs to have the same kinda mounts so it all flexes, or doesn't flex, the same. cab and rad support mounts should be the same material no matter what type you use as that ensures the body parts that are bolted together will all flex at the same rate and less stress is put on the sheet metal fastener points, so less apt to start stress cracking etc and less chance fenders and door gaps get close enough to rub paint off. the speed bumps installed at a slight angle (man, I would like to find that engineer) are a good example od something that will cause body gaps to open or close as the frame and body flex.

[leegreen]

Are the shackle style mounts so bad?
If you have a stock frame you may want to keep them.
Read this old thread http://67-72chevytrucks.com/vboard/s...d.php?t=624325

[mr48chev]

Originally Posted by leegreen

Are the shackle style mounts so bad?
If you have a stock frame you may want to keep them.
Read this old thread http://67-72chevytrucks.com/vboard/s...d.php?t=624325

Not bad in most respects except that they were designed to be able to go over pretty rough ground with an AD truck with the frame twisting in the process.

The majority of us just don't need that flex anymore and if the frame is boxed with an independent front end it shouldn't flex like a stock frame anyhow.

As for me, I am moving the rear cab mounts back 9-1/4 inches when I stretch the cab and will probably end up welding the brackets to the frame rather than bolting.

[whitedog76]

I don't think it's a big deal just leaving the rear cab shackles as is. If the bushings are in good shape, they at least provide some isolation from the frame. Now, the front cab mounts could use some improvement, they're just a 1/4" piece of rubber between the cab and frame. A modern style cab mount and bushing would do wonders.

[dsraven]

I am more familiar with the task force trucks, but I think you need to consider the whole front end as a single part. cab-fenders-rad support-hood. if the rear mounts are easily felxible, te center mount is fairly non flexibe, and the front mount is flexible, then what you really have is a see-saw effect. I will be using the stock mounts from a newer style truck under all contact points of the cab and rad support. that way they all have the same ability to flex as a unit. the box is solidly bolted and seperate from the cab so that part is straight forward. my frame, however, is not a stock frame and is fully boxed and cross membered fairly stiffly along the ladder as it goes along. my floor is also not a stock floor so I will just say consider how one body part needs to interact with the other body parts. the old stock mounts will likely be fine as long as the rest of the system isn't modified for strength and flexibility (or non flexibility).

[hopalong]

Originally Posted by dsraven

I am more familiar with the task force trucks, but I think you need to consider the whole front end as a single part. cab-fenders-rad support-hood. if the rear mounts are easily felxible, te center mount is fairly non flexibe, and the front mount is flexible, then what you really have is a see-saw effect. I will be using the stock mounts from a newer style truck under all contact points of the cab and rad support. that way they all have the same ability to flex as a unit. the box is solidly bolted and seperate from the cab so that part is straight forward. my frame, however, is not a stock frame and is fully boxed and cross membered fairly stiffly along the ladder as it goes along. my floor is also not a stock floor so I will just say consider how one body part needs to interact with the other body parts. the old stock mounts will likely be fine as long as the rest of the system isn't modified for strength and flexibility (or non flexibility).

my 51 frame has the MII independent suspension and going to box it in as I already have all the boxing plates cut and about ready to weld them in. So yes the truck is modified with other mods up coming. I rebuilt a sbc 327 I had with forged pistons rods etc. with the old green stripe Duntov cam and a 700 r4 trans. Broke-in the 327 on my engine run stand a while back. Now working off/on cab and chassis. This is why I was concerned about the cab mounts as the non box chassis flexes byitself quite a bit and that shackle mount kinda looks like it will increse swaying with shake roll of the stock chassis. Probably gonna add steel support bracket for the rear cab mount and do the latter truck/car type mounts. The rear chassis will remain leaf spring suspension for now. I have a 67 Nova street muscle car to finish up while starting on the 51. And a 57 chevy belair post after that. All mine to keep in the family. Thanks to all for the great replies

[dsraven]

are you talking about a fully boxed frame then?
I think GM relied on the box bed as partial strength possibly, although they did sell the cab and chassis only, not sure if they sold them as a 1/2 ton truck.
I think bolting the box onto the chassis helps make it more rigid in the rear half. I have also seen some boxed frames that have cut outs around the area of the front of the box. this, to me, could cause problems, especially with high horsepower units, because the rest of the frame is pretty solid and the section left unboxed (sometimes because there is a crossmember in that location and the cross members were not replaced and attached to the boxed section) becomes the soft area that will do the flexing, and therefore possibly become the area that stress cracks or stays in the flexed position.
just my 2 cents worth, and I am a long way from an engineer. haha.
with the MII cross member the front area would have had short boxing plates, correct? there is a whole school of thought around the different ways to weld in the boxing plates to make them look like they are part of the original frame without grinding away a lot of the weld. I suggest to have the frame on stands, cleaned down to bare metal in the welding areas, (as well as the boxing plates), check it straight and square BEFORE welding in any boxing plates. also consider how you will work around the existing cross members etc. you don't want to cause other problems by adding stiffness. also, do short welds in different areas so you don't heat up the frame and end up twisting it.

[hopalong]

Yes the chassis will be fully boxed and yes I know about setting the chassis on stands, leveling, and welding up. Plus cross braced at stress points etc. Thanks for the info and I take it with appreciation

[dsraven]

good enough. sounds like you have a good handle on it. have fun, and don't forget to post up some pics so we can all be jealous.

[schovil69]

Originally Posted by mr48chev

I plan to build some brackets that either bolt or weld to the frame rails that use the same holes that the shackles use with a biscuit or rubber block style insulator.This not even to scale doodle shows how it should work.

This style needs a rubber or Poly block between the cab bottom and the bracket and a block under the metal of the bracket working very much the same as the 55/57 Chevy car mounts or the TF truck front mounts work.

You said exactly what I was thinking when I saw your doodle, "That's a trifive mount." I like it and will have to do some thinking when I get to that point on my '53 3100. First things first, though, I need to finish the '56 Bel Air.

[whitedog76]

If you google, "Ford flathead mounts," you'll get dozens of options which are exactly what we're speaking of.

[leegreen]

or look at the body mounts for a silverado/sierra. Upper and lower rubber biscuit with a steel sleeve through the middle and a bolt

[Chopped53]

I have an aftermarket chassis under my truck. Here's how they did the cab mounts front and back. Nice solid mounts. You could probably do something similar on a stock frame.

[hopalong]

Exactly what I was refering to doing

[fauXGT]

Originally Posted by Chopped53

I have an aftermarket chassis under my truck. Here's how they did the cab mounts front and back. Nice solid mounts. You could probably do something similar on a stock frame.

Looks like the rear cab bracket mounts are a bit high, like the shackle spacing has....and the front brackets taper down to accommodate for a thicker than .25" rubber bushing.

Sorry. Druelling a bit from that pick(Hi-po frame porn).

[leegreen]

That is a nice frame. I'm also curious what was provided for cab mounts? It appears they intended a much like stock chunk of rubber through bolted for all 5 mount points.

it is way better than stock AD, but that does not appear to be a terribly stiff frame. I'm no pro chassis builder but I'd rate it as not quite a stiffly built as a Silverado pickup and significantly less so than a Trailblazer. For handling it would benefit from another structural cross member and some diagonal bracing. Maybe an X frame if you can fit planned exhaust, tanks and spare around one

[Chopped53]

Originally Posted by leegreen

That is a nice frame. I'm also curious what was provided for cab mounts? It appears they intended a much like stock chunk of rubber through bolted for all 5 mount points.

I was really happy with the chassis. When I placed the cab on the frame, the bolts just dropped right into the new mounts and the brake pedal slid straight through the factory hole in the cab. It's a really well engineered piece of work! I used stock rubber bushings for the mounts.

The frame rails are 2" x 6" and the steel is .180" thick. It seems super stiff.

[jweb]

I have the stock style mounts and the bottom cab corners have gotten dented in from the splash apron. I have adjusted the cab twice and this happened both times.

[fauXGT]

On that aftermarket frame I count at least 6 crossover points from the pic, and 99% boxed in.
Alot more than a stock, or even modified stock... unless it's 18ga steel.

[leegreen]

Don't get me wrong, it is a nice frame, I'd trade for it in an instant and will probably never own one as nice.

To my eye and based on that single photo there is a long stretch of tubing mid chassis without much to give it torsional rigidity. I discount the trans cross member as a structural unit based on appearance. I also think these welds will be highly stressed if the chassis is worked hard:


No question it is stronger than stock and probably perfectly fine for a moderate build. Is it stiff enough to live up to the potential of the suspension? Or the horsepower an enthusiast may want twisting against some sticky tires?

A well braced structural cross member near back of cab.... would give something to hang the exhaust on at very least and make the frame appear more rigid. An automotive engineer might run the numbers of those box sections and tell me to take a hike.