Light rumble at low speed.

[gerviswaddell]

Hey there, I am leaving tomorrow for a long road trip across the US, and have a problem. At low speed (maybe 5-10 mph) there is a vibration (frictional) somewhere in the front end, it happens regardless of brake use, just seems to happen when the car gets to that 'sweet spot'. I should mention that I recently did the brake upgrade to Corolla brakes, and changed to snow tires. I messed up the alignment on the left front wheel slightly when replacing the power steering boot.
If feels and sounds like something is rubbing in the front end, and the sound and vibration goes away at slower and faster speeds. Im going to re adjust the tie rod and bleed the brakes tonight & check for any rubbing or unusual wear, anyone have any other ideas?

thanks,

GW.

[Petros]

Many types of snow tires with an open and aggressive tread will have a harmonic growl at certain speeds. This sounds like this kind of harmonic. It is annoying but there is no harm, nothing is rubbing, it is just a tire internal vibration due to the spacing of the tread and the speed they contact the ground. I used to have a Pathfinder with some aggressive off road tires that made this kind of noise. You might try changing the tire pressure, go from 24 psi, and than at 36 psi (or more) and see if it changes, and which one is better.

Those snow tires will reduced your fuel economy, and usually reduce your stopping distance on dry pavement. I have abandon them because of that, and now just go with "all season" tires with a good aggressive tread design. If I have really icy conditions I use studded tires, but those light weight cable chains will also work for icy conditions. Even aggressive off road tires will not work on icy roads any better than the all-season tires.

[gerviswaddell]

That is an interesting thought about all seasons, I typically hear the opposite, my thoughts were that the softer rubber was the most important factor (because of the lower winter temperatures) anyways, looks like you are in Washinton, so you certainly know a thing or two about snow! Im headed to northern BC (near the panhandle) and temperatures there certainly get down low. Anyhow I adjusted the alignment and bled the brakes and the rumble is gone...

I used a vacuum jar to do the brakes, and they still aren't that firm, any thoughts on how to improve this? I am now running a new master cylinder and have upgraded to 93 tercel Calipers and rotors, as well as new rear cylinders...where is the problem likely to be? in the lines? could I still have air in there? I would really like to have better brakes for this trip and I have tomorrow to work on the car, any thoughts would be greatly appreciated.

Thanks again masters of the turtle.

GW

[takza]

When I redid my brakes...I ended up needing to use a vacuum pump to get all the air out.

[4wdchico]

I don't consider my brakes fully bled/flushed until I put at least a full quart of fluid thru the system. Do that every year or two and the odds of having a failure in the hydro portion of your brake system goes down massively. Also, I prefer to use DOT 4 brake fluid, it has a slightly higher boiling point, but the real reason I like it is that it has higher anti-corrosion package specs. DOT 3 & 4 fluid are fully compatible.

[Petros]

If you had your whole brake system apart likely you have air in it still. Just keep pumping it out. I bleed the master at the lines of the master so I do not pump the air through the whole system. I bleed it from the lines on the master until there is no more air coming out (I stuff a large rag under it to keep the brake fluid from getting all over everything). Than I go to the furthermost rear wheels (I think that is the driver's side), and than work up to the front wheels. The rears take a long time to get fresh fluid pumped back there. It should firm up real nice once you get the air out.

How thick of a shim did you need to put under the corolla front rotors? The corolla has a larger off-set the the '92 and later Tercel rotors.

[gerviswaddell]

I used an 1/8" shim , but I think that 10 guage steel is perfect (just over 4mm)

[dlb]

Those snow tires will reduced your fuel economy,

why is that? i just put snow tires on a few weeks ago and noticed that right around the same time my km/L went to sh*t so the two are likely related.

[Petros]

The larger open tread has more rolling resistance.