55.2-59 56 Front Shocks Bottoming

[thumper56]

I believe the fix to be pretty easy, but am wondering if anyone else has run into this...

My truck is a 56 C3100, original front suspension. I believe the leaf springs to be original and while they may be "saggier" than when new, seemed to be in good shape when I took them apart to clean and reassemble. The truck seems to sit properly and rubber bumpers on frame are exactly 2" above the springs.

The old girl rides better than most I have been in, but every once in a great while I hit that dip in the road that bottoms something out with a solid BANG that could wake the dead- quite un-nerving and always happens when least expected!

I see no evidence of scraped paint on suspension parts or frame, and no indication rubber frame bumpers are hitting the springs- though I did just put some gobs of grease on top of the springs under the bumpers to leave a witness mark when it happens again.

My shocks are the listed Monro 31000. These have a compressed length of 12". I measure 14" on center when mounted static in the truck. (Leaving 2" of travel before bottoming)

I've looked for shorter shocks by dimension on the Monro charts, but no joy. A couple are 11.75 at compressed but I would spend $140 to gain 1/4". All others were way too short.

Looks like an "easy" fix would be use longer spring u-bolts and sandwich a 3/4" or 1" shim over the shock mount bracket.

Anyone else had this issue and came up with a different approach??? (Unfortunately putting in a new, modern, front suspension is NOT an option!)

Thanks

[mr48chev]

full specs on the 31000 are:
Product Attributes
Compressed Length 12 IN
Travel Length 7.5 in
Extended Length 19.5 in

After all of that what about a front shock for a 70 C-10?
https://www.oreillyauto.com/detail/c...ckup-rwd?pos=5

Compressed length 10-1/8. Extended length 14-5/8. That may be wrong the other way though as 4-1/2 inches of travel isn't a lot.

I'm not sure that you can knock the sleeve bushing out of some of these that have more interesting lengths.
https://www.shockwarehouse.com/news/...asurements.cfm

[geezer#99]

Is the rest of the truck all stock?
Could very well be something else besides shocks.

Put some grease on the rubber stops. Any contact will show up easier.

[thumper56]

Thanks for your input guys.

All suspension is stock. All new parts except the leaf springs. Drivetrain is different, 350/TH350 and Chevy Van rear end. I had already put a gob of grease on top of the springs, under the rubber bumpers and thus far have not seen any grease "witness marks" on the rubber bumpers.

I found the size chart link easier to read than the Monroe chart, and came up with a shock (32207) that has a compressed length of 3/4" less than the stock #31000, but with a near stock travel. I will give these a shot and see how it goes as I could pick up a pair for $38.

I am thinking that with as random as this "bottom out" is, the additional 3/4" bottom travel may do the trick.

Thanks again

[dsraven]

seems like the easy way to find out if it is really the shocks is to make sure the shock fasteners will be easily removed on the road, then take the required wrenches with you and find that bump that is going to make it do it's thing, drive over it so it does it's thing, check the grease witness spots on the springs and see if it is indeed bottoming. if it is bottoming on the springs then new shocks are not going to help. shocks are there to control spring oscillations, not set the suspension limits. if you find witness marks on the snubbers then look for a split in the rubber which would mean the snubber is shot but also means the snubbers are taking more abuse than they were made for, possibly a spring issue. new springs will likely raise the front end some and mess with the stance for a bit until they get their "set". also check the shackles to ensure they are not bottoming on the frame etc. if you find no grease witness marks on the bumpers then the springs are not bottoming. now find a quiet spot that will be safe for you to work and remove one end of the shocks from their mounts and tie the shock up out of the way. or simply remove the shocks for the test. now go over that bump again and see if the sound is reproduced. if it is then the shocks are not the problem. go back to the safe spot and install the shocks again then take it home for a thorough check over. look for shiny spots or places where paint has been removed from contact between parts. check engine mounts, trans mounts, rad support mounts, cab mounts, steering parts etc. personally I wouldn't spend time looking for new shocks until I know for sure thats the problem. I have seen engine mounts that look just fine until the engine is jacked up a little and then the split in the rubber parts becomes apparent. if you have a helper you could get them to do a "brake stand" while you watch how much the engine moves under hard accelleration, that could point a finger that would be a tell for engine mounts. be safe doing this as you likely know the outcome if you're standing in the wrong place-it is alll mechanical parts holding back the truck under a loaded driveline.
keep us posted with what you find, shocks, springs, something else.

[geezer#99]

How is the 350/turbo 350 mounted?
One piece driveshaft or two piece?

[dsraven]

good call there geezer, maybe the driveshaft is bottoming in the trans or between the 2 peice driveshaft. again, some grease smeared on the slip yoke would be a witness mark as to how close things are getting.
a few pics of the underside from different angles would be good aa well.

[thumper56]

Update...

Thanks for all the thoughtful replies! (And all distinct possibilities)

In searching for the random issue I had placed gobs of grease about everywhere and searched for witness marks, with none found. In my build, the original driveshaft was just a bit short so I ordered one for correct slip yoke dimension (no monkeying around with a longer yoke).

I did as suggested by dsraven and removed the shocks roadside, then plowed over some of Vermont's finest backroad washouts, railroad tracks, potholes, etc. Results: plenty of bouncy bounce but no slam of a bottom out!

Using the chart provided earlier in this post I found some shocks with a somewhat shorter compressed length of the stock Monroe 31000 (12"). Keeping in mind the static, bolted on length in the truck was 14" center to center.

Since my problem was random (often surprising) I felt I did not need but maybe 1/4" to 1/2" less compressed length.

I chose the Monroe 32207 (11.25 compressed and 17.875 extended). This reduces my compressed length by 3/4" yet still leaves 3.875" extended length if I ever launch the truck while giving Daisy Duke a ride.

Knock on wood- bottoming seems to be solved! Even though my leaf springs seem to be in good shape, I guess with the weight of a V8 and age they are just a little more "set" than they were 60 years ago. (But nothing else is bottoming)

I hope this post may help someone else in the future.