High mileage Fluid Change?

[Sdp1234]

Working first to determine everything I have in the Truck
4L60-E/4L65 4 speed heavy duty A/trans (M32)
NR3 - Transfer Case
Stabilitrac?

What are the differentials?

3.73R(GT4) (from the build sheet)
Can't find the front one on the build sheet.​

How do I tell if they are limited slip (want to use the right gear lube)

Should I use RTV or a gasket on the differentials? (I use RTV on my 2004 wrangler)

 

[Sdp1234]

Don't forget fluid in the diffs. With no real service history, I wouldn't do a trans flush. Better just to do a fluid swap--dropping trans pan and replace the filter.

I'll do the other fluids but I'd rather not mess with the Trans. What would I tell a transmission shop to do. Just tell them to "drop the pan and replace the filter"?

Should I go to my local garage mechanic or a Trans Shop? What is a reasonable charge to do this?

 

[wjburken]

I'll do the other fluids but I'd rather not mess with the Trans. What would I tell a transmission shop to do. Just tell them to "drop the pan and replace the filter"?

Should I go to my local garage mechanic or a Trans Shop? What is a reasonable charge to do this?

I’d call around and talk to a few shops, mechanic and tranny shops, and see what prices are and which ones try and talk you into doing more that just dropping the pan and replacing the fluid.

 

[Wylie_Tahoe]

I'll do the other fluids but I'd rather not mess with the Trans. What would I tell a transmission shop to do. Just tell them to "drop the pan and replace the filter"?

Should I go to my local garage mechanic or a Trans Shop? What is a reasonable charge to do this?

Id have the filter changed since its new to you with little known, then ive a trans flush performed. The flush will cycle all the fluid out. Just dropping the pan leaves 6+ qts of old fluid in there.

 

[treehan77]

I would not do a flush on an unknown high mileage transmission unless you want a new transmission

 

[OR VietVet]

I would not do a flush on an unknown high mileage transmission unless you want a new transmission

That has been said many many times here. It's true every time I hear it. Unless of course you just have money burning a hole in your pocket and you want a new trans. If so, drive it close to home.

 

[Sdp1234]

I get it, no flush. Not questioning, just curious what the benefit is of droping the pan and changing the filter?

Thanks for all the responses.

 

[treehan77]

You get a new filter that you know isn’t clogged, and some fresh fluid. And don’t immediately wreck the transmission

 

[Wylie_Tahoe]

I would not do a flush on an unknown high mileage transmission unless you want a new transmission

Please explain your theory. There is absolutely ZERO harm in the transmission pumping out its old fluid, as fresh fluid is pumped in as the same rate and pressure. In under 2 minutes, you have 12 qrts of fresh fluid in the transmission.

@Sdp1234

As stated earlier, dropping the pan only changes out about HALF the transmission fluid and a new filter. So upon startup, you mix the 6 qrts of fresh fluid with 6 qrts of who knows long long its been in there fluid.

 

[OR VietVet]

Please explain your theory. There is absolutely ZERO harm in the transmission pumping out its old fluid, as fresh fluid is pumped in as the same rate and pressure. In under 2 minutes, you have 12 qrts of fresh fluid in the transmission.

@Sdp1234

As stated earlier, dropping the pan only changes out about HALF the transmission fluid and a new filter. So upon startup, you mix the 6 qrts of fresh fluid with 6 qrts of who knows long long its been in there fluid.

I believe what I have heard many times before is that trans fluid is high with detergents and to replace all fluid could shock the system and help damage the plates. then all that gets clogged in the recent fresh filter and the problems get worse from there. I see no problem with a fluid flush if it is done every 50k miles or so but if is high mileage and don't know if flush has ever been done it is best to skip the flush and just do the filter and add back what is lost when drop pan. I also saw a couple times on here that the 4L60 trans is good for about 160k before likely having to plan on replacement.