Hot Rods 32 rad vibration

I just finished up my model a and took its maiden voyage down the highway. The car itself runs super smooth, no vibrations, and tracks awesome down the highway.

I noticed when I get above 60 mph the grill shell seems to vibrate a little. I have the rad mounted with a rubber pad and light to medium spring. I also have triangulated 3/8” rods to the firewall.

It’s super smooth at 60mph but seems like the extra wind resistance at 65-70 it shakes, I notice nothing through the steering wheel or in the cab, floor or seat as far as vibration.

I’m not sure if this is normal and I should expect some vibration or if there something I should try, it seems like if I left it this way wouldn’t be good.

Any suggestions? It’s a custom built rad. I only did a couple of runs at that speed so I couldn’t investigate if anything else would be making the vibration. I’m running bias plies and haven’t balanced them, but really can’t feel anything in the cab like you would a new car if you have unbalanced rim or something along those lines.

Also it’s a new 32 frame that’s fully boxed.

Thanks.

 

Bump, any insights?

 

I used 4 drilled patchs 2x3in. cut from a old tire tread as pads,one under an one above each base mount,rod at top are stock set up. I did two that way with out prob. My 28 "A" hot rod, I long ago base is same,but I used two small braces coming up about 8in. back from rad too 1/2way up rad shell.

 

If the radiator is built like an original (copper with steel side straps), and you have stock style springs above the radiator mounts, I wouldn't worry. My 32 with a stock unboxed frame has a little shake of the radiator every now and then. The Walker is just fine.

If you have an aluminum radiator, well there's nothing I can do for you.

 

My first thoughts is the radiator springs are too weak, but if that was the main cause, you should also see the radiator wobble on bad/rough roads even at low speeds?

If wheel balance is off, you should feel it in the steering wheel at the same speeds you see the radiator moving.

I used a spare set of repro Model A radiator mounting pads, springs & bolts. Those springs are pretty stiff. I don't see much movement that I can recall, and the radiator is very visible when driving with no hood. I'm running I-beam buggy sprung front end, with bias, too. (at 20PSI)

The car has a very smooth ride, so that must also help.

 

Thanks for the replies , it is a copper rad, much like a walker but has heavier gauge top and sides.
I’ll probably order a set of factory style springs and see what that is like. Just in case my springs are too light.
I don’t notice any movement at any speed up to 60, either rough or smooth roads.
It’s just a bit of shaking side to side. It would be nice if I had a go pro to strap on the front to get a better idea.
I’m only at 2000 rpm at 60, so I’d like to be able to stretch her legs out a bit without shaking my rad apart.

 

I would tape a square of bright colored tape to the grill edge and the. The rad tank and go for a drive and really see which one is moving. Way easier with a focal spot to focus on.

That’s about all the help I am right now.

Other thoughts are to post some photos here of your set up, maybe someone will see something.

Use your iPhone set on the time lapse setting and maybe it’ll catch what’s moving.

Last thought is to take that bright tape and tape it tight between your stay rods in a place you can see it while driving. Maybe they are flexing and a simple. Rod between the two of them solves everything?

Just throwing shit out maybe something sticks

 

Fix what's causing the vibration.

 

Thanks, good ideas.
I will give it a try. We have a couple of weeks of cold weather right now, when it clears I will be able to investigate further.
I can’t find any photos of just the rad.
I appreciate the help. Being my first hot rod and my first build, you never know if you are over complicating things or not.

 

I thought I would have felt a vibration? But it’s smoother than any new car I’ve ever drove.
Thought it was maybe a wind thing?
Like I said I’ll do some more checking when it warms up.

 

I also have made a fan shroud, so unless I can't get enough air through so something. Like I mentioned I'm only 2k at 60 mph so its not like the fan is screaming. Just thought I'd throw that in there. I'll research into balancing the tires, do people normally get their bias plies balanced? Like I said it runs super smooth, I expected wandering and some vibration but it does none of that, its actually a pleasure to drive down the highway at 60. And at 60 like I said there isn't an ounce of rad shaking or vibration. Just when I start getting to 65. I never tried any higher of speeds to see if it smoothed out, or tried it in 3rd gear wound out to get the fan speed up.

 

I have 50k miles on my 18 year old aluminum radiator ,were doing fine , thank you !

 

That shroud has a lot of flat surface ...I am wondering if the 65mph wind is buffeting that? If you can, try removing it for a test.

Yes, Bias should be balanced no matter what, just like any tire.

 

The radiator is going to have some vibration, as long as you have the springs you will be ok.



With the fan mounted in the original location the car might run hotter in traffic, I used a zips riser and it moves the fan higher on the radiator, just a suggestion. HRP

 

Your fan shroud looks to be dead flat except for the opening for the fan.
Almost every shroud whether factory or home built has some taper to it.
I agree with F&J that your shroud is causing turbulence and causing the grill and radiator to vibrate.
Unless you have a killer small block with high compression, I would think that the shroud should not be needed.
KK

 

I thought about a riser as well when building, but my fan is the full width of rad core and only slightly goes below the core at the bottom so the fan virtually is as effective as can be.
A riser would have made it too high, I needed like a 2-3” rise to hit the sweet spot.

I have always been a believer in fan shrouds, figured one I could build at home would be better than none, but maybe that isn’t so. I had built it with low speed and stop and go in mind, not highway speed. Hence why I’m a mechanic not and engineer. Haha. I didn’t expect everything I did to turn out as planned.

Thanks for the ideas to ponder guys.

 

Another thing that I just noticed. If your overflow hose is a relatively tight fit at the top of the bottle, when it needs to work, it will probably push itself out of the bottle. You need some space for the air in the bottle to go.
KK

 

Yup, it can breath around there, It’s fills and drains the bottle as it should. But it is tighter than I’d like and I plan on a smaller diameter clear hose, give a bit more room and be more aesthetically pleasing. This was one I had around the garage at the time. Good eye, thanks for reminding me.

 

Just voicing my own take on this issue (same outlook for 40 years). A little shake or movement is what the springs are designed to let happen. If it don't have any movement at all it won't be long till you have an issue. In a early chassis you can't solid mount it due to chassis shift. Latter cars with Rad mounted solid in front clip (core support style) the chassis movement is absorbed in how the sheet metal is mounted. I say your worrying about nothing at all.

 

I’d cut a couple holes in the upper part of the shroud,attach a rubber flap over them. When sitting the fan would pull from the shroud, but at speed it would allow air through the flaps.


Sent from my iPhone using The H.A.M.B. mobile app

 

Thanks guy for the info and ideas. Yeah just make a mail slot in the shroud, good idea. Negative pressure will pull it closed when idling and positive would blow it open at speed. I was thinking holes and a magnet to cover of need be, but a hinged plate would work well. Thanks for the idea.

Here’s a short video I took on my first trip at 60 mph, as you can see it’s smooth as can be. And maybe I am worrying about nothing, like I said first rod and first build. Haven’t even sat in a hot rod before I took this around the block for the first time.

 

Were it mine specially without any hood at all I'd pitch it till it proved to be necessary.

 

Nice Job on your First Hotrod Build, Justin ....Enjoy !!

 

Thanks!

 

What did you end up doing? Been a few months figure you’ve got to be out there driving it...

 

I have been out driving, almost 700 miles so far.

Haven’t figured much out, drilled extra holes in shroud which didn’t do anything.
Balanced rims & tires and it is still the same.
I think it’s maybe just bias ply tire shake.
I can see the tires hopping a bit but it’s hard to tell, maybe the Monroe shocks can’t keep up, I don’t know. I wonder if good shocks would help keep tire planted.
I adjusted the speedo and it’s right around 70 mph, so live able. Just would be nice to cruise at 80 at times as it drives so well on the highway.
I think I’m going to play with tire pressures and see if more or less smoothes it out. That’s about all I have left to try at this point.

 

My first thought was try less tire pressure,
My second was to check how round the tires are

 

Also, that’s awesome! 700 miles in your first hotrod!

 

Thanks, it’s been great. We are taking it on a 2000 mile trip in a couple months so want to break anything that’s suspect now haha. But it’s honestly been a pleasure to drive, it’s everything I hoped for and wouldn’t change anything.

There isn't anyone around who will shave or true tires so that’s not an option.
The only thing I’m worried about with less pressure is I’ve heard of tube failures if not rock hard. Just don’t want to run into any of that on our trip.
I believe I’m around 25 or 28 psi right now.
But I’m still planning on messing with it to see if I can find a sweet spot.

 

A lot of people over inflate tires on hot rods to begin with. I'd recheck toe in, put 24 lbs in the front tires, maybe '26 in the back. and check wheel and tire run out and roundness. Make sure that whatever pressure you have in your tires leaves about a 5" to 8" patch on pavement. 80 mph if you want it make it a real car not just an old one. Good luck, nice build.