Hello, I'm the new guy here with a new (used) 1999 Chevy blazer 4x4. I had the truck since Sept 2015 and have been fixing things here and there. Some of the things I replace are:

Front end rebuild - Tie rod ends, pitman arm, idler arm, both wheel hubs, new shocks, upper and lower ball joints.

Rear - Shocks only

Just recently replaced a rattling and clogged catalytic converter and felt like I gained 50 hp (back). I think I can go up a hill now. I've already done a tune up, for the most part, and now just need to replace battery and cap/rotor.

On to my question. I've been hearing a slight roaring noise coming from the rear when on the freeway. Usually happens from 40mph on up. Once I replaced the wheel hub assemblies a month ago, the front end felt better, but the noise was still present. Now the noise turns into a louder growl with a bit of ticking noise, more evident at 55 to 65mph. Had trouble going past that due to the clogged cat. I have felt a bit of shaking the last time I drove on the freeway. Can you guys help me diagnose my problem and what my options are? I want to keep the truck stock and as reliable as possible. Thanks for your help.

 

Welcome to the forum. The 4.3's prefer delco caps and rotors. I would plug my nose and pull the cover off the rear diff. Closely inspect the spider gears while rotating the tires. It sounds like they may be chipped. Keep us posted, many of us have been through that problem.

 

Thanks for the response. Lets say the gears are damaged. What would be my best choice? Rebuild the differential? Axle swap? Axle swap and differential rebuild? I'm on a student budget while also working full time and taking care of a family so I can't spend too much.

On the subject of differentials. I know that the swaps should be with like gear ratios, such as 3.42 with 3.42. I have the code GU6 in my RPO so that tells me 3.42 gears. My question is, does it matter if I swap gears from the 4x4 or 2wd with the same gearing or does the only thing that matters is the gear ratios itself and just the correct size?

 

If it does turn out to be the spider gears I just looked at rock auto they are around a 100 bucks for the set

 

For replacement spider gears, or nest kit, the needed info is 10 bolt cover, 7.625 ring gear and 28 spline axles. There's no way to tell whats damaged without removing the cover. The roaring noise could have been caused by simply being low on gear lube resulting in bearing groan. You also mentioned ticking and shaking which makes me think your differential needs to be inspected. The sooner the better. It's cheaper to fix something before it scatters apart.

 

Thanks for the responses. I will definitely have to check everything out and see what kind of damage there may be. Hopefully there is none and just low on oil, but still need to see whats inside. Thanks again.

 

Check your "U" joints

 

Hey guys, I'm back. I finally cracked open the differential and drained out the oil. Raised the blazer onto jackstands so I can rotate the wheels, thus rotating the gears. I don't really see anything that could be a problem. The oil was full before I drained it and was black. Replaced the cover, gasket and added Mobil 75w-90 oil.

Drove it around for a bit and noise is still present. Sounds like it is starting around 30-35 mph then winds down as I slow down. Not sure how to check the U-joint but I did tried to move the drive shaft and seems nice and solid with no give or noise. I am still hunting for the cause of the symptoms. Could it also be related to worn tires? I will try to attach some pics I took of the open differential, along with my rear tires.

 

Have you considered or checked the noise when in 4 wheel or 2 wheel mode?