49 cab rear shackles - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jackson · 12-22-2014, 10:02 PM

do I have to use them. reason I asked , several months ago I rebuilt them with new bushings and shimed one side to get them within specs. now the one I shimed has sagged . why cant I replace them with a later model solid mount with rubber bushing pros / cons thanks

**mr48chev** · 12-23-2014, 01:20 AM

I don't see why not if you have stiffened up the frame by boxing or adding crossmembers. I've been thinking seriously about doing it on mine when I put it together. These trucks don't need the flex cruising around on the streets as a custom truck as they did back when they were the farm or construction truck hauling loads over rough ground every day.

One thing that kills AD truck frames and causes the cab to sag big time is removing the crossmember that normally runs under the bellhousing and holds the back of the engine up along with and maybe more importantly keeps the frame rails from twisting under the weight of the cab pushing down on the outrigger style cab support brackets.

I had it happen on my truck even after I had subframed it and have seen it on dozens of other trucks. The weight of the cab pushes down on the mounts and twists the rails out until the bottom of the cab is laying on the top of the frame rail. One reason that a lot of V8 AD trucks have that bent in the middle at the cowl/hood joint if they have been on the road for a while.

jackson · 12-23-2014, 09:38 AM

[

One thing that kills AD truck frames and causes the cab to sag big time is removing the crossmember that normally runs under the bellhousing and holds the back of the engine up along with and maybe more importantly keeps the frame rails from twisting under the weight of the cab pushing down on the outrigger style cab support brackets.

I have removed the front crossmember. so if I box the frame under the cab will that be enough

**mr48chev** · 12-23-2014, 12:48 PM

I would box the frame to help stiffen it. I wish someone made a bolt in tube crossmember that would run under the same area to support the frame rails that guys could use.

dwcsr · 12-23-2014, 04:24 PM

Quote:

Originally Posted by jackson

[

One thing that kills AD truck frames and causes the cab to sag big time is removing the crossmember that normally runs under the bellhousing and holds the back of the engine up along with and maybe more importantly keeps the frame rails from twisting under the weight of the cab pushing down on the outrigger style cab support brackets.

I have removed the front cross member. so if I box the frame under the cab will that be enough

If you have done a clip or MII cross member then you should be ok but having cross member in that area is better

dwcsr · 12-23-2014, 01:28 AM

It has to do with the way the cab, front clip and radiator are mounted

The front cab mount is pretty much bolted solid. The rear is where it flexes with the frame. The fender struts are bolted to the cab and the fender and the front clip is mounted on rubber so it moves as the cab does. The rear hangers absorb that flex. If you lock down the rear mount something has to flex and the sheet metal will start to flex with the frame and start popping spot welds, buckling panels and can pull the radiator into the fan. If you have ever seen a radiator on a 47 to 54 with a half moon at the top of the core that's the front clip pulling back into the fan from all the flex

If you box the frame then you could do it

12-22-2014, 10:02 PM	#1
jackson Registered User Join Date: Jan 2012 Location: el campo texas Posts: 322	49 cab rear shackles do I have to use them. reason I asked , several months ago I rebuilt them with new bushings and shimed one side to get them within specs. now the one I shimed has sagged . why cant I replace them with a later model solid mount with rubber bushing pros / cons thanks

12-23-2014, 01:20 AM	#2
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,705	Re: 49 cab rear shackles I don't see why not if you have stiffened up the frame by boxing or adding crossmembers. I've been thinking seriously about doing it on mine when I put it together. These trucks don't need the flex cruising around on the streets as a custom truck as they did back when they were the farm or construction truck hauling loads over rough ground every day. One thing that kills AD truck frames and causes the cab to sag big time is removing the crossmember that normally runs under the bellhousing and holds the back of the engine up along with and maybe more importantly keeps the frame rails from twisting under the weight of the cab pushing down on the outrigger style cab support brackets. I had it happen on my truck even after I had subframed it and have seen it on dozens of other trucks. The weight of the cab pushes down on the mounts and twists the rails out until the bottom of the cab is laying on the top of the frame rail. One reason that a lot of V8 AD trucks have that bent in the middle at the cowl/hood joint if they have been on the road for a while. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

12-23-2014, 09:38 AM	#3
jackson Registered User Join Date: Jan 2012 Location: el campo texas Posts: 322	Re: 49 cab rear shackles [ One thing that kills AD truck frames and causes the cab to sag big time is removing the crossmember that normally runs under the bellhousing and holds the back of the engine up along with and maybe more importantly keeps the frame rails from twisting under the weight of the cab pushing down on the outrigger style cab support brackets. I have removed the front crossmember. so if I box the frame under the cab will that be enough

12-23-2014, 12:48 PM	#4
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,705	Re: 49 cab rear shackles I would box the frame to help stiffen it. I wish someone made a bolt in tube crossmember that would run under the same area to support the frame rails that guys could use. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.

12-23-2014, 01:28 AM	#6
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,131	Re: 49 cab rear shackles It has to do with the way the cab, front clip and radiator are mounted The front cab mount is pretty much bolted solid. The rear is where it flexes with the frame. The fender struts are bolted to the cab and the fender and the front clip is mounted on rubber so it moves as the cab does. The rear hangers absorb that flex. If you lock down the rear mount something has to flex and the sheet metal will start to flex with the frame and start popping spot welds, buckling panels and can pull the radiator into the fan. If you have ever seen a radiator on a 47 to 54 with a half moon at the top of the core that's the front clip pulling back into the fan from all the flex If you box the frame then you could do it



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