VegasJen

o.k. guys. this should be pretty basic but i just can't figure out what is going on with my truck. suspension/brake related... somehow. the truck is a '94 1-ton diesel dually. the problem is i have a nasty vibration when i get on the brakes. what it feels like is a wheel that is really out of balance, but only when i apply the brakes. it's as smooth as you could expect in steady-state cruising.
it started a couple months ago and i thought i just had warped rotors because i knew they were already worn too thin to turn. so i junked them and got new ones. put them on and everything seemed to be fine for the test drive around the neighborhood. i didn't notice until later when i got on, or more correctly, got off the freeway that when slowing down from any speed over about 45, i get this really nasty vibration. it's still there below 45, but just not as noticable. it goes up proportional to speed until about 65 and then it pulses so fast it's not as violent, but just as scary.
checked wheelbearings and they appear to be o.k. new rotors so i don't think they're the problem since it's doing the same thing it did with the old rotors. just had a tire fixed so the tire is not out of balance. pads were replaced just a few months earlier as well. i'm confused!
i thought it might be the back brakes for a while so i made it a point to stop the truck from ~45 with just the e-brake a few times and it's as smooth as when it's cruising. feels like it is primarily on the left side from what i can tell.
what am i missing?
:confused:

kaz1961

If it is a Chevy try asking the guys on the truck forums at chevytalk.com.

GDaina

Sounds like the rotors are out of round...put a dial indicator on them and see.

Tom454

I used to work in an Auto Parts store where they sold Delco and other brands of rotors.
I also turned rotors on a AMMCO machine.

1) New rotors were almost never straight. Our highest volume rotor purchaser was right next door... he bought a lot of rotors from us. He insisted that we turn all new rotors BEFORE we delivered them. When you turn a rotor on a machine, you can see and hear it when the carbide bits hit the warped surface... and with very few exceptions, the NEW rotors were warped. Recently, I purchased several new rotors and I measured them with a dial gage... they were all warped beyond spec.

2) There is a difference between expensive rotors and cheap rotors. I recently purchased new rotors at Advance Auto and I asked them to open both boxes for me. They both had the exact same outside thickness, but the cheap ones were substantially thinner at the inner plate (surface). In other words, the rotor consists of 2 plates welded together with a web in between (or cast). The inner plate was thin, and there was more webbing to make up the difference. The cheap ones had a lot less meat on them to absorb heat.... hence they were more prone to warping. If you purchased the cheap ones, then you have two evil forces working against you... warped from the factory, and warp easily due to poor quality.

My guess is that your new rotors need to be turned. If you can't do it yourself, ask someone to measure the runout with a dial gage.

markdtn

:iagree: Check the Rotors, I think you will find your problem.

Van Steel

:iagree:

VegasJen

i was afraid you guys were going to say that. i was thinking the same thing but i was really hoping someone had an idea i hadn't thought of. DAMN! now it's just a matter of finding the appropriate time to take my truck out of service for a day to have this done. :cuss

Robert N

Don't feel too bad. I have the same issue on my Dodge right now. My brake pads have less than 10k miles on them, new front tires mounted and balance, same problem on the left side too!

For now, I try not to brake. :D

NHvette

It sounds like the rotors may need turning - but maybe you got the pads
greasy or oily during RnR of rotors. THis can make the pads grab more -
and make the problem worse. Go for new pads when they go back on.

:seeya

The_Dude

It happens in my '99 F250 every 15k miles. They just don't make rotors like they used to. :mad

killain

I think you have drum or rotor problems. Most likely warped drums on the back. You really can't cut drums or rotors and have an improvement. Everytime you cut them they are going to get warpped faster. Replace them with new drums. :yesnod:

GUSTO14

Don't know if your truck has one, but the early (up to 82) Corvettes and trucks do and it will cause the problem you've described. It's the Idler arm. It's something we only seemd to notice when we're doing the front suspension, but they do go bad. I've seen them bad in 40K miles, especially the standard ones. The heavy duty (Moog?) ones have a grease fitting and last much longer but the standard ones don't.

It's a quick check to see if you have one and isn't difficult to check to see if it's loose. It's on the passenger side of the car and carries the right side of the steering relay rod. It bolts to the frame and is linked to the steering relay rod.

GSUTO