Technical Need advice on how to fix a bounce rear end

Afternoon everyone, I have a 1938 Ford pickup that I’ve been trying to sort out little things little by little but the one thing I’m having issues with is my rear end being very bouncy. Here in Ohio 85% of the roads are crap but on newly paved roads there not that bad. When I’m driving I feel like my rear end is hopping when I drive over raised bumps in the road. What is some things I can do to help smooth out my rear end so it’s a softer ride. I have a Chassis engineering rear end leaf spring kit for the rear end. Have 3 inch lowering blocks, took the bottom leaf spring out so there’s only 3 leafs in the pack. I did have KYB shocks in the rear but made things worse so I switched to Monroe shocks, the angle of my shocks is 30 degrees. I don’t have a lot of money to buy a whole new system but would like to improve on what I have now if I can

 

I have a 54 F100 that rode rough, like you describe. I figure the springs were too stiff. I removed the shocks and went for a short ride. Surprisingly, lots of spring compliance. I changed shocks. Pickups are so light in the back.

 

Do you know what part number your shocks are? Application? Like KevKo said, try removing the shocks and see if the springs are too stiff or not. Unfortunately the lowering blocks will have some effect on that too. If the springs ride OK, try a different part number shock.

 

My initial thought is to try adding some ballast and see if there's any improvement. A few bags of sand or similar works well.

But looking at the springs they appear to be almost over centered and wonder whether the harshness might be from bottoming out. If you bounce on the fender (!!) does it feel solid, wallowy, or somewhere inbetween?

My experience of KYB's is that they are very firm, which seems to mirror yours.

Chris

 

It may just be bottoming out on the bump stops. How much clearance is there?

 

That's what I was thinking. Looks pretty tight up above the axle tube. Maybe a quick n dirty 'C' notch would help? But try it without the shocks first...that's cheap and easy.

 

How does your spring work when it's flat and the shackles are straight up and down?

 

Monroe shock number is 33033

 

There’s about 4 inches before it touches the bump stops, with all the driving I have done it has never touched the bump stops

 

Leaf springs are straight with a slight upward arch , it has the same motion with or without the shocks if I step on the bumper. My shackles has a slight angle to it

 

Just for curiosity sake, how much air do you have in those rear tires?

 

Your springs are overloaded, or sprung the wrong way. Also that is not 4 inches between bump stop and axle, and the other shot shows that it has been hitting the bump stops.

 

I have 25 psi in the rear tires

 

I was thinking it was hitting the stops as well or someone ground the stop to make it shorter? Also looks like the springs are almost straight so there can't be much give to them if they are already bottomed.

 

I took pics after I was stepping on the bumper mounts to check the travel.what would I have to do to get the shocks to be sprung the right way. I don’t think the shocks are overloaded, but I may be wrong, what would I have to do to correct that?

 

Previous owner welded the kit in, I have tried both longer and shorter shackles and they sit the same way. Not sure how to fit that problem

 

The shocks don't seem to be mounted badly. How much can you compress them by hand? They look sort of short? They should provide some sort of rebound control but the springs being as flat as they are won't give much when hitting a bump. The two need to work together to control the impact of the bump and the rebound from it. I'd check both those things.

 

Might there be anything to be gained by removing the clamps on the rear half of the springs? At least it would be free and easy to try. . .

 

Disconnect the bottom mount of the shock while at ride height. Compress the shock all the way up and measure the distance from the bottom mount to the shock eye. Now measure from the top of the axel tube to the bump stop. The shock measurement should be a little more than the axle to bump stop measurement to allow for the rubber compression of the bump stop. If the shock measurement is less, the shocks are bottoming out when you hit a hard bump.

 

...maybe not the "correct" fix, but I'd try some weight in the rear of the truck, you'd be surprised what a difference that can make...don't cost much to try.
...I've heard many complaints about Chassis Eng. parallel rear springs,...installed em on a 38 Chevy coupe, rode like yours, but with some weight near the rear of the trunk, it rode pretty decent.

 

Clamps on springs both in front of axle and behind may be binding spring-also as a caution- the U bolts are below the scrub line it appears. Are you sure its not hitting the bump stops? Stuff something in the hole in the bump stop sticking out some and see if it crushes after a drive over a few bumps

 

Leaf springs are "progressive" due to the taper of the leaves. They can also have a small space between the leaves at the ends, so as the spring pack flexes, the spring ends contact the leaf above, therefore bringing the next leaf down into service. Put simply, as a leaf spring moves towards a flat state (jounce / compression), the stiffness increases.

Your springs appear to be almost flat in the pics. This would mean that they are near their highest rate of stiffness at ride height. This could be your problem.

 

No expert however I'd suggest relocating the rear shackle top pivot to alter the shackle angle as it appears perpendicular to spring eye at ride height as shackle angle definitely changes effective spring rate.


Also my rule of thumb for shock angle is 20 degrees form the vertical for optimum rate. Also the rebound rate needs to match the spring and car weight. Also the shock needs to be compressed 1/3 at ride height so check the length of it as well.

 

I don't think I have ever seen a leaf spring with the "eyes" down as yours are. Are these springs made to support the load with the eyes down? Or were they just put in that way to make it fit??? I am not a expert and I don't know, but that seems to be a question you need to know.

 

Here is a link to monroe shock specs, 33033 has a compressed length of 10.13" extended length of 14.63" for 4.5" of travel. You can find a replacement shock on the chart if your current shocks aren't in the correct range. http://www.monroe.com/downloads/install-instructions-guides/MonroeMountingLengthSpecifications.pdf

 

take out the bumpstops
fabricator john
miss you dad

 

Your leafs are either too short or the mounting locations are not correct, or the leafs are not strong enough to support the weight that is on them. With the negative arch your springs have, the rear shackle would need to come forward, past center, to allow the spring to bend any more, and that is not possible.

Leaf springs are designed with an arch that has both ends above the center point. Then the rear shackle is mounted with the top that is anchored to the frame being farther forward more then the bottom end being bolted to the spring. When a bump is encountered, the leaf spring flattens out and the rear shackle leans more backwards. The spring is at its longest length when it is flat. That is what smooths out the bumps. The shocks need to be able to compress, and expand as the spring moves, before it reaches the end of its travel. If it bottoms out on either end of its travel, it limits how much the spring cam travel.

Your leaf spring is already past being flat, it is arched the wrong direction. Any movement from this point will bind up the spring. When you hit a bump now, the spring center moves up and shortens the spring even more, and then it would need to extend itself to get back to its original condition, which would require lifting the back end of the truck up. With the current position of your spring shackle, the top connection at the frame point being forward of the bottom connection at the leaf spring, For the shackle to allow the spring to bend up more, the bottom end of the shackle would need to move forward, which means the lower shackle end would have to move down towards the ground to allow the spring to bend. The spring and the shackle are both moving in the wrong direction. You will never get a softer ride because the rear shackle will not allow the spring can't bend anymore.

One thing that I thought of, if you jack up the truck from the frame high enough to lift the tires off the ground (several inches if possible) does the spring flip the other way (arched down instead of arched up) or can it be forced to flip past center the other way? If the springs are somewhat weak, and they were installed with the arch facing up (sometimes installing one spring at a time will cause this), forcing the arch down past center may solve your issues. You will probably have to disconnect the shocks from the rear end to be able to force the springs past center, then you will probably be able to reinstall the shocks. A bottle jack between the frame and the spring with the weight off the rear end might work to force the springs past center. This may be a no cost solution.

If that didn't work, I see two options.
1) Add leafs, or get a stronger spring, or get a longer spring. For this to work as laid out, your rear spring needs to have both ends farther from the ground then the center is, with the truck weight on it. Flipping the top leaf on the spring, and adding that leaf you took out may do the job, but at this point I suspect that won't be enough to do the job. Unfortunately, this would probably raise your ride height a couple inches. Do you want the look, or the good ride?

2) By far the worst option. Leave the spring alone, but move the frame mounting position of the shackle towards the rear of the truck enough so that the top shackle mount is towards the rear more then the lower eye on the spring. That may require moving the mounting point on the frame a couple inches rearward. With the way your springs are bent, that rear shackle needs to move forward to allow the spring to bend more, and with the shackle leaning this way, the spring will be able to bend more. This may shorten the life span of your springs a bunch. This will not effect your ride height immediately, but I suspect the rear will drop more and more as time goes by (might be a very short time) until the springs break. When you replace the springs with the proper springs, you may have to move the frame end of the shackles back where they were. Gene

 

I've had the same issue and it was my shocks being too short. They were fully extended at ride height, kinda putting preload or tension on the springs.

 

This. You may as well have a flat bars not springs.

You need springs to be able to flex and appropriate shocks to dampen that action.
You need springs with some arch.
You need weight on springs to make them work.
You need shackles orientated like in the illustrations above.
You need nuts and bolts and anything else ABOVE the scrubline.
You need shocks with travel and don't bottom out.

Easy first steps:

• Put leaves back to reinstate some arch.
• Check shocks for travel.
• Put some decent weight like sandbags as suggested to help the springs 'work.'
• Road test.
• Remove shocks, road test.
• Report back.

If the leaves are too short or the installer installed the springs incorrectly (eye locations too far apart for the spring length, hence the vertical shackle with fully extended leaves) that in more problematic.

 

Not about your ride but I cringe every time I see a car that some part of the car will drag if a tire goes flat. Like your U bolts