Trans. Seems OK otherwise, but here's the problem........from a standstill after I've put it in 4Lo and slowly start to move on a level surface, it sounds like it revs too high (for maybe 3 to 5 seconds), then "clunks" into gear. Not super hard, but more than just noticable. So does jolt the truck forward. All other gears/settings seem OK. Except when starting to drive away after I start it up from cold, in 2Hi.....there seems to be a "rushing" noise, like air almost. And seems it's GOING to clunk into gear, but never does, and finally goes away after several minutes of driving. But the 4Low thing has me worried. And I recently had a fluid flush at a Trans. shop. Also had a cooler installed. The fluid was properly checked by me and is at least 1/4" above the top full mark. Was 1/2" after they did the flush......but I brought it back for them to drain some..........all the while with the manager insisting that having a 2002 Blazer that much over the full mark is not a problem at all (ummm, yeah). And it does shift into reverse normally .........................so, thoughts on the 4Low overrev-then-clunk? And also my fluid level......is it OK at 1/4" over? And that manager is correct?? Thanks (sorry if this needs to be moved).

 

4LO is exactly that: a very low gear ratio. It's meant for power/torque, not speed. If you accelerate normally from a stop, the transmission shift points will be quick and harsh, and the transmission will be in 4th gear before 20mph. Best to keep engine rpm below 3K when in 4LO.

The "rushing " noise might be low on coolant.

Trans fluid level should be at the "full" mark after driving for ~20 minutes, 30 minutes in colder ambient temps. The transmission needs to be at operating temp when checking the fluid level. It takes longer to bring the trans fluid to its normal operating temp, than it does to bring engine coolant to its operating temp.

 

Thanks. Hope you're right and that the overrev-jolt is entirely normal. Just seems so harsh for only moving so slowly.

And never thought of the coolant. Just had that flushed few months back.

 

In 4LO the engine and transmission are doing the same thing they always do, just doing it a lot faster due to the low gear ratio in the transfer case, that's what is causing the harsh shifting. Basically the same as flooring it off a stop sign, engine revs up higher and harsh shifting.

 

That rushing air noise is still there, for the first few minutes after starting to drive away, in normal gear, cold engine. The coolant level is fine.

 

Rushing noise when cold may just be your fan

 

The rushing noise is classic jet plane noise very common on the fan clutch, not to worry.

 

i always thought it was fun to put it in 4low with my manual trans and try to fly through the gears as quick as i could while getting to 20mph in 5th gear. i would be scared to let them fly through the gears on a auto that quick in fear of breaking something. 4low should only be used in 1st gear while climbing, offroading, or pulling out tree stumps never for normal or winter driving

 

My mech told me my clutch fan is messed. Not turning fast enough at times. Found this out after getting him to diagnose why my AC isn't cold enough. Said my coolant is fine..........and that it was just because there was not enough air passing through. Said one of his guys put a large fan in front of the grill.........and THEN my AC was cold enough. But now, several months later, that makes no sense, as I can go on the HWY right after starting the truck, at 20 deg. C. outside...........and it feels even LESS cool than it did before, hardly any better than the heater set to cold position. I will have to start a thread on this now......in the right section. If a search turns up no answers. But anyways, I guess my fan is just acting weird?