Question about Transmisson and Rear End in 75 GMC Camper

[campingman]

Got a 75 GMC G35 Rally Camper Special dually with a TH400 and 4:10 rear. 69K Miles. Wondering if I should change the tranny filter and fluid or just leave it alone. It has a brown redish tint to the fluid. Works good and shifts fine. Just don't know if the last owner maintained it. Kinda scared to change the filter due to some trannys going out faster. I have the ability to suck out the fluid from pan to just do a fluid exhange. DEX III for this tranny right? The rear end is a 4:10 and was wondering which fluid I should put in it. Thanks guy for all your help on here. Great Forum!

[77 350 Shorty Wide]

Good Morning, With the amount of miles if they are correct I would recommend not doing a complete flush. Just drop the pan and change the filter, discard the fluid out of the pan only then ad the proper amount of new fluid back in. If it's really brown and smells bad you're likely going to need a rebuild. Let others weigh in on this before doing anything.

As for the differential is it limited slip? If it is... make sure you use the additive for limited slip differentials, 90 weight gear I believe is the normal lube to use with or without posi.

God Bless, Terry

[campingman]

I doubt it needs a rebuild with it only having 69.000 miles on it. Doesn't smell burnt. Just looks like its never been maintained. With it being 40 years old, who knows when it was serviced last. Just want to make sure its up to power to climb these ky hills. only will be taking it out 5 or 6 times a year since its only our motorhome.

[slotard]

I doubt the rear end is limited slip. I'm not sure that was available with the 14ff (which I suspect it has).

[campingman]

sticker says GT8 Rear Axle 4.10 Ratio

[68post]

I prefer to get all of the old fluid out every time possible. Trans fluid is only good for aprx. 30,000 miles. Use Valvoline Maxlife , it's proven to be better than all but the most expensive and has conditioners to help maintain an older trans.

Valvoline makes excellent rear gear oil also, if you tow very heavy use 85w-140 weight - otherwise just use 75w-90. ( 90 weight gear oil = 30 weight motor oil, 140 weight = 40 weight motor oil. It's a different grading scale than engine oils)

I'd pull the pan and change the filter this time and you'll probably never need to replace it again ( they're a very coarse filter designed to catch large particles), but I'd also install a drain plug for future use or an aftermarket pan so equipped.

If you're towing any - install a cooler also, the fluid and trans will both last longer.

[campingman]

Thanks for your response. It does have a trans cooler on it. I have no clue how long its been on there for. Just bought it few months ago. Its a 23 foot camper. Pretty heavy. I think ill just change the trans filter and put in what came out. . Rear end aswell. The previous owner did take care of it very well it seems. The drive train part of it. the frame is virtually rust free. it looks like its been kept in a barn 40 years of its life. The motor is clean and quiet, the trans shifts perfect and there is no noise what so ever coming from anywhere but the exhaust, which sounds very nice after I welded up the new Walkers. Thanks again for your all's responses. Very helpful info.