I purchased an IR thermometer at autozone, it appears the rear rotors have more heat than the front which seems to be a problem to me. Here's how I tested. I jacked up the rear end of the car and tested the following. - Spun the wheels to see if there was any drag....it really didn't feel like much drag at all, even after pressing the pedal down/releasing the pedal. It seems to release properly. - Took off the brakes/calipers/rotors, cleaned everything again, cleaned slides then re-greased everything. - Tested the caliper pistons outside of the rotor...watched as each piston clamped then released when the brake was released, it looked like both sides had good release on the pistons. - I used a dremel to slightly file the brake pad shoes where they make contact with the caliper bracket, they weren't gliding as freely as I wanted them to, now they seem to glide easily. - Put everything back together, torqued everything down. Test drive (not towing): I went down the interstate for about 25 minutes, then turned around and came back for 25 minutes at about 75 mph. I then shot the rotors and got the following temps. - Both front rotors were around 100- 110F after the drive. - Both rear rotors ranged from 135-145F depending on where I took the measurement from on the rotors. - Rear diff/pumpkin was around 110F. It seems to me that the rear brakes should probably be the same or less temperature as the front....correct? I know it's rear wheel drive, but I can't imagine the hubs/driveline in the rear make the rotors heat up that much higher than the front. The test drive is pretty flat too, and I didn't really apply the brakes much other than when I absolutely had to. The only thing I can think of is that I replaced the rear caliper slide bolts with newer bolts...maybe the newer bolts don't slide as well, or are manufactured just slightly larger than the original/oem? Thoughts?
I have E rated tires, and I'm running just about 60psi rather than 80psi. The tires are surprisingly not super hot, but probably warmer than they should be given the wheel temperatures. It's like that Seinfeld episode when they made fun of the hot coffee lawsuit thing. I expect them to be hot...but "not that hot".
Hmm that's a good idea. I'll go buy a thermometer if I can find the IR type locally. I should also probably go drive the car unloaded/loaded for comparisons on heat.
Forgot to mention, ambient temperatures have been between 85-100 degrees depending on the elevation, though a few times it has been in the 60s- 70s and the wheels still seem way too hot.
148K miles I replaced a rear axle seal about 3000 miles ago due to a leak (inner/larger seal). I noticed it had a Timken bearing which I'm guessing is not stock, it looked like it was in great condition/no marks/no heat marks on race etc. The brakes were replaced on all 4 wheels around the same time the axle seal was replaced. New AC Delco Brakes/Rotors and fluid flush was done. New Caliper bolts were installed on rear wheels to replace the dreaded torx head caliper bolts. Brake/Caliper slide area where the pads are installed was clean/free of rust, new slides installed and fresh grease on everything. I didn't notice either of the pistons being stuck, but they could be sticking/not releasing. Parking brakes were are NOT tight at all...in fact the parking brake doesn't work currently because I adjusted them in too far....so they don't touch when the wheel spins nor do they touch when the brake is applied :).
jlrosine posted a topic in 2000-2014 Silverado & Sierra HDI'm hoping to get feedback from others that are towing a lot of weight on steep grades, how hot is too hot for my rear diff/wheels? Here's the problem I'm having with my current setup. Vehicle: 2004 Yukon XL 2500 SLT with 8.1L (weight/axle info here) Trailer: 34' Rockwood 2901SS (dry weight around 5600) Equalizer weight distribution hitch rated at 1200lbs. Fresh differential fluid about 2000 miles ago (Mobil 1 Synthetic Gear Lube LS 75W-90) CAT Scale Weights when loaded (this was with kids/gas/dog and all gear). Steer Weight: 3440 lb Drive Weight: 5240 lb Trailer Weight: 5920 lb Gross Weight: 14600 lb Ambient temperatures have been between 85-100 degrees (very hot this summer). The past few trips we have taken all require that I drive up 6-7% grades here in Colorado (Ike gauntlet) among other passes, then down the same grades. I'm typically towing for 3-4 hours and almost all of it is going up or going down. I know this type of towing is much much harder than the flat land towing, but I still don't think my wheels should be as hot as they are. I'm always using lots of gas going up and stressing the engine/tranny......or I'm going down the other side of a mountain and using the transmission 95% of the time to keep us around 50-60mph using gears....again very hard on the drive system. After towing, my front wheels are hot but I can usually hold my hand on them without yanking it away. To me they seem "normal" for the conditions I'm driving in. The rear wheels however are a different story, If I put my fingers on the wheel near the hub, I typically have to pull my fingers off after 1-2 seconds due to the heat....it would definitely burn your skin. Further out on the rim toward the tires seems to be less hot...but still very hot. Initially I thought it could be due to the brakes dragging, but I have never smelled any bad brake/brakes too hot smell. The vehicle doesn't smell hot at all when walking around it....if you didn't touch the wheels you'd probably think everything was functioning normally. My concern is that I'm going to probably ruin bearings/rotors/axle seals if it continues to run this hot. Wondering what others have for wheel temps when hauling their max GCWR under very stressful situations (not flat land towing). Also, given that I've probably driven 600 to 1000 miles with this sort of heat....have I already done some damage? Any help is appreciated.
Thanks Grumpy. I did some calcs on rpm/gear ratios here > http://www.csgnetwork.com/multirpmcalc.html Looks like my RPMs are where they should be given the ratios, rear axle and tire size. Thanks!
Thanks guys. garagerog: Yes I feel 1 => 2, 2 => 3, 3 => 4 . I've just read some other threads where I thought the 4.10 ratio folks were at about 2000rpm @ 60mph, so then I wondered if I was missing OD or something. I was expecting it to hit 4th gear, and then go in to overdrive at higher speed when letting off the gas or setting cruise. I could have sworn my 2004 yukon denali was like that...but it was a different transmission and drivetrain altogether. Edit: I just re-read what you stated. I think I'll have to go out and drive it again, I'm not sure I feel any dropoff after going in to 4th. 4th just feels like 4th all the time, I'm not sure I feel any dropoff in rpm until I completely let off the throttle. Thanks again, -Jeremy
jlrosine posted a topic in 2000-2014 Silverado & Sierra HDThis might be a stupid question, but I feel like I'm missing overdrive in my 4speed on my yukon. Is it 4 speed + overdrive? Or is 4th the overdrive? 2004 GMC Yukon XL 2500 - 4spd with 8.1L Vortec My axle codes from the glovebox read that I have the 3.73 gearing, however when I'm travelling down the road I notice at about 60mph, I'm around 2000rpm which seems high for 3.73. Here's a video (couldn't accelerate fast due to other traffic): https://photos.app.goo.gl/9hS6brqufCsYdquA2 From a stop, just counting the shift points, I have 4 total shifts, and no overdrive (rpms don't drop after I reach 4th gear). Is this normal? I'm new to the 4L80/4L85
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