1999 F-250 used 50/50 pleasure, towing. anybody using synthetics in there transmissions and rears? if so whos and changing at what intervals...

im getting ready to buy another truck and was wondering the same thing.

I use synthetic in everything- including the premix for my weedwhacker. Try to stick close to the mfg. recommended intervals or at least no more than 50% over. I know they'll go longer- I use them as "I forgot" insurance rather than money savers.

I have one GM 5.7 with 425K on it- never been opened up. Put injectors in it (again) this summer. Did the compression- 185 psi +/- 5. Not bad.

that egine doesn't owe you a thing dayum dude thats the most ive ever seen on a sbc

I use synthetics on all my stuff as well....oil changes on the engine i do every 10k miles....the filters i change every 3k and top off with frsh oil.....the trans on my last truck was changed at 45k and i got rid of it at 134k and the oil was like the day i put it in....and thats with 3 trips down to Tampa pulling a 30' boat.....my current truck i bought at 150k miles.....changes to all synthetic the first weekend.....it now has 170k and runs like new still....It all comes down to maintenece....change your oils like the mnf suggests and regular oils will be just fine......i'm lazy and prefer just doing a 30sec oil filter change every so often

I use synthetic in the motor.
What about the trani ? I got my truck with 107K on it, Now it has 127K can I just drain the trani pan and refill with synthetic trani fluid ?
99 F250 S/D 4x4 Diesel

I build transmissions as a business,ANY synthetic atf is a great improvement over oem fluid for most transmissions,don't be afraid to change it out. As far as rear ends if you live where it is extremely hot and tow extreme loads use 75/140 or any version that has second number of 140 (the viscosity index hot) in a full synthetic.If you drive empty the majority of the time or have cold seasons a 75 or 80/90 full synthetic is your best bet as the thicker oil will hurt your mileage and doesn't flow as well when real cold. A few things to keep in mind is the duramaxes 05 and older came with dexron 3 and should be converted to castrol transynd which was specifically designed for them. The dodge and ford trucks with limited slip rear ends should always have a posi addittive added to them when changeing rear end oil to prevent chattering when making wide turns,it about 5 dollars a bottle,the gm's use a gov lock posi so its uneccessary on them,Smitty

I run 75/90 Mobil Synth in both axles.
OEM stuff for the trans, with a Lucas additive.

Standard warranty on Peterbilts is 3yr/300,000 mi...trans and rears

When you run Synth in rear ends you get a 5yr/750,000 mi warranty
Synth in trans goes to 5yr/500,000 mi

Unfortunately, I can't say the same for the transmission. The truck is on its 5th one. The 4L60 is a POS.

have tci build you a 700r4