need help from the suspension experts
 

I just drove my newly almost finished 48 GMC. I am experiencing bump steer
In the rear(I think).

I using Chrysler 5th ave station wagon springs. They are 60" long
& they are mounted so that the rear of the spring is 5' higher than the
front. I am assuming that this is causing the spring to move forward
when hiting a bump, thus moving the rear of the truck sideways.

What would you recommend doing.....1.) moving the rear chackles down
2-3" or so, thus raising the rear of the truck 1 1/2"......don't really want
to do that.
2). buy shorten springs from a vender that have are flatter.
3.) buy a coil over kit- 4 bar
4.) other

Thanks Don

Re: need help from the suspension experts
 

I vote 4-link! DeWayne
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Re: need help from the suspension experts
 

Rob......would you please advise, Do you have a rear suspension kit for a 1947-54 truck? I do not want to drive the truch as-is.

"THE TRUCK HAS A 3' extended cab w/a late model narrowed bed, thus the reason for a lengthened frame in the rear.
.

Thanks Don

Re: need help from the suspension experts
 

Bump steer is usualy in the front suspension. What fron end do you have? I would think those rear springs may be a little long also.

Re: need help from the suspension experts
 

I'm not an expert but these questions might help you pinpiont whats going on. sounds like something is almost binding.
what pinion angle did you set the rear diff at?
I will just assume that there is room for the slip shaft at the trans to move in and out slightly?
the springs may be a little long but when you drove it did you have any weight in the rear like the box or something to simulate the weight of the box?
not sure if the box was removed to show the set up but if you drove it as in the photo it just might be a very light rear end (front heavy) getting minimal traction over a bump.
one other observation which probably has little effect on your problem with the rear, in the pic the rear extension by the rear shackles looks like it's 3or4 1" welds holding the piece on. might just be an illusion in the pic but I would weld that area solid..just me, I over weld.

Re: need help from the suspension experts
 

What you are describing, sounds to me like a too stiff condition. I have experienced it myself in an old 4X4 on washboard gravel roads around here.
Have you done the bounce test? Bounce the back of the truck and see how fast the truck comes back to rest. This will let you know how stiff the shocks are. In one picture your shocks appear to be upsidedown, in another fine.
Or take the shocks off and go for a ride.

Re: need help from the suspension experts
 

Your basic set up looks OK> And while I do make a nice 4-bar kit for the 47-54 (and others), I think you can sort this out. T Hilde may be right. Was the bed on when you drove it? Your p/u, even with the extended cab and late bed, will only wiegh about 1250 lbs on the rear axle. - without the bed, 950. My guess is that the rear of the wagon was around 1700 lbs. Now, does it turn the steering wheel, or does it 'hop' to one side when it hits a bump? If it turns the wheel, its in the front. Find a set of RR tracks and drive across them at about 30 mph, with you hands just off the wheel. Watch what it does when you go over. At a lower speed 25 - 30, its easier to pick out the front/rear action. Next try to soften up the rear, maybe pull the shortest 2 leafs out and try the same route. - The same effect can be created by adding wieght to the rear to match the spring wieght. If the bed is on, put 300 - 400 lbs in it and drive it. We use sand bags (well, garnet, from our FlowJet) This will give you a quick idea where the trouble is. What is the IFS? Any shots of the stretched cab?

Re: need help from the suspension experts
 

Hey Guys....thanks for the replies. The truck was driven w/the bed on. It's a 94 full sixe Chevy bed narrowed 12".

It's raining here to day so I can not test drive the trk.
The IFS is a TCI unit w/a t_bird R&P. The flow rate has been reduced & the pressure also reduced in the pump.

It appreared that the bump steer was coming from the rear.i think the axel is moving forward when I HIT A BUMP.

Here are a few pics.........thaks Don

Re: need help from the suspension experts
 

One more comment.......I just had the front end aligned & I did not notice this on my first drive in to the alignment shop, however
it might of been due to the excitement of the first drive.

Don

Re: need help from the suspension experts
 

Shot of stretched cab.

Re: need help from the suspension experts
 

Don, if everything is tight in the rear (U-bolts shackle bolts front spring perches) I would say it's unlikely the bump steer is coming from there. More likely from the front, sometimes the way the tie rod mounts to the spindle can cause bumpsteer. Do you have any pics of the front suspension/steering ? Are the tie rods mounted on the top or bottom of the spindle?

Re: need help from the suspension experts
 

Thanks Bob.....I will check the tightness of the rear suspension bolts tomorrow.

Don:metal:

Re: need help from the suspension experts
 

To answer Robs question.....The truck moves sideways when I hit a bump. I do not notice anything in the steering wheel.

I have cadiac rehab today, but tomorrow I'll drive it again & try to be more observant.

Don

Re: need help from the suspension experts
 

Your condition seems to be that your rear suspension is too stiff. The picture looks OK, and I don't see anything out of the ordinary. I think it's a combination of a stiff leaf and a stiff gas shock that when combined, are making for a super stiff ride. A quick check would be to pull the shocks off and go for a short ride. You'll notice a huge difference. Some gas shocks (like KYB...Kill Your Butt) have some serious pressures and will exhibit the exact same symptoms you are seeing, when combined with a leaf spring of decent rate.

If you load 1000lbs in the bed, it'll ride like a dream. But, looking at your ride, that bed isn't going to see that kind of action. Go with a low pressure gas shock, and pull a leaf or two out. Problem solved.

Re: need help from the suspension experts
 

Thanks Chevy restoguy, I'll try removing the shocks & see what happens.
I'll get back w/a answer in a day or two.

Thanks Don:gmc2:

Re: need help from the suspension experts
 

BTW.. VERY NICE truck, I'm a little envious

Re: need help from the suspension experts
 

removing the shocks could make it worse. Are they new shocks? If you push down in the center of the bed does the truck react evenly on each side?

Re: need help from the suspension experts
 

I copied and blew the photos up and can't see anything that obviously looks out of kilter but I do have a couple of questons.

1. do the rear shackles have enough room to move to let the spring flex right when you hit a bump or are they at the limit of their travel when the box is on the truck?

The spring may be binding when you hit a bump because it can't flatten out right.
In the second photo you can see that the angle of the shackle is towards the rear of the truck rather than towards the front a bit as it should be without a real load on it.

2. Are the spring bushings new or in top rate shape and do the bolts in front fit the bushings correctly and tightly? The bolts may be correct for the brackets but a little loose in the springs if they aren't the bolts the bolts that came with the springs. A 1/2 inch bolt where a 13MM bolt was originally would have just a bit of slop between it and the bushing. Also does the spring fit right in the bracket?

Re: need help from the suspension experts
 

Not an expert, but have built more than a handfull of custom suspensions:

How about going to the local car parts place and buying a set of OEM style Monroe shocks for your truck.

Take care removing them from the packaging. Install the shocks and drive the truck. If they help, keep them. If not, take them off and return them.

Another thing to try, as was eluded to above, put some sand bags in the back for weight and drive it. If that helps get some springs that aren't so stiff. A Chrysler Fifth Avenue Station Wagon is a heavy vehicle. Your truck without anything in the bed is not comparable.

Hope this helps.

John

Re: need help from the suspension experts
 

I used some Jeep Wagoner springs and they work great.

Re: need help from the suspension experts
 

I found the problem. The T-bird R&P is moving left/rt where it is bolted to the TCI crossmember.
I do not know if the bolts just need to be tightened or if the rubber bushings have failed(110 miles). I just had a stent put in my heart & I tire easily, thus I had to stop & rest for a while.

thanks Don:metal:

Re: need help from the suspension experts
 

I am sure it is the inferior quality of the "rubber" bushings in the kit.
Look for some aftermarket urathane bushings, I had the same problem with a R&P I had on my 55 the new bushings took care of it 7 years ago, still going strong today.

Re: need help from the suspension experts
 

Good on finding the sloppy bushings on the steering. That's one I'll have to stick in the memory bank for later.

Re: need help from the suspension experts
 

Thanks for all the help...........Don

Re: need help from the suspension experts
 

Don, I am looking at your pics and I think the rear shackle is suspect, with the angle you have on it, as the suspension goes into jounce the shackle is going to start to go horizontal quickly, expecially with the weight of the bed over it.

If your shackle is going horizontal it can do all kinds of funny things to the rear axle, expecially if it happens on one side of the truck and not the other, including not allowing the axle to go into rebound because it holds the spring temporarily in the flattened position, thus causing a misalignment side to side.

I bet if you move your shackle hanger 1.5-2" back it will help signifigantly.