hi all, i have a fiat 500 which i restored, total stripdown and rebuild, i have one problem whch has been annoying me for a while now, the car vibrates, it can be felt at low speeds and under heavy breaking. This problem was not there before the stripdown. it seems to be in the back wheels, when i spin the wheels the brakes can be felt catching the drums on and off, i fitted new shoes but still no joy. I did rebuld the gearbox with new gears (1st gear was damaged) would this have anything to do with it? what is the effects of the pinion gear not meshing right?

Did you fitted new brake drums at the time ? If so, your vibration may be down to out of round drums. That would be my first thought.
I suspect that a badly rebuilt gearbox would manifest itself in other ways - noise and difficult gear engagement being the most likely.

Anyway, 500's are subject to considerable engine vibration. When the interior rear view mirror stops blurring with your boot to the boards you are just about due to hit valve bounce....

thanks for your response, i did swap drums from another 500 and still the same vibration, i feel the car is 'hopping' when not breaking, new bearing were fitted during the rebuild, could these be faulty?

Try substituting the bearings for know good ones - other radical thought being bent rear stub axles for whatever reason. Are these new as well ?

Just a couple of thoughts -

After a reline/rebuild, drum brakes need to be set so they do not bind.

Drums do get out of round and they should be skimmed or replaced when this is suspected.

Out of round or unbalanced wheels can cause problems with vibration much like you are describing.

Chris

Check the tyres too. Get them spun up on a wheel balance machine to see if there is any undue up/down or side to side movement when rotating

With reference to Bambino's post 500 wheels are relatively easy to distort, especially on modern tyre fitting machines.

Have you considered having a look as to how the wheels and driveshafts rotate with the engine running, in gear at tickover, obviously with the car supported safely on stands ?

Strangely, I seem to recall a similar issue with mine some 30 odd years ago - it turned out to be a failing coupling

now that you mention it i did fit new couplings, hardly the bearings.

also fitted new white wall tyres. I did have it up on stands running, slight wobble on the wheels but nothing to give the vibration i am getting under breaking. I also changed drive shafts just in case it was a bent driveshaft, but no joy.

i think i will swap wheels first, than drums again, followed by couplings. I just delighted that its not the gear box.

i will post the results

thanks for the help all

Bambino said:

Just a couple of thoughts -

After a reline/rebuild, drum brakes need to be set so they do not bind.

Drums do get out of round and they should be skimmed or replaced when this is suspected.

Out of round or unbalanced wheels can cause problems with vibration much like you are describing.

Chris

Click to expand...

Thanks for your help Chris, just a quick question, when you say "drum brakes need to be set" can you explain? just in case i am doing something wrong.

You may not need to do much with these brakes as from memory they are self adjusting. Apart from gently pumping them a couple of times to centre the shoes and making sure that the self adjuster is sitting properly on it's peg mount, they should work well from the outset. All new shoes take a little time to 'bed in' but if they rub or bind excessively, the bonded friction lining may be too thick. In that case you will need to fit shoes with a thinner lining. I think that someone on this list had that problem not long ago. The other problem that may also cause binding is eccentric or warped drums. These should be skimmed or replaced.

Some drum brakes have a snail cam that is used to adjust the shoe/drum distance so it lies within the tolerance dictated by the manufacturer. These drums are not self adjusting and need periodic readjustment to maintain braking efficiency as the lining wears.

And finally, like disc brakes, the friction surface must be kept clean and free of grease/oil for the brakes to work properly.

Whilst drum brakes are not as efficient overall as disc brakes, with simple maintenance they perform more than adequately. Checking the wheel cylinders for hydraulic fluid leaks, linings for wear, drums for eccentricity and regularly changing the brake fluid will go a long way to ensuring a trouble free, safe braking experience.

Chris