When I first bought my car about a year ago i took it into the shop for an inspection...they said that a gasget was stripped on my rear diff. How much HP am i losing from that? I have a 85 2.8 5spd. I havnt gotten it fixed but now i have nothing else to do so should i get that fixed? It hasnt gotten worse but its leaking a little i do believe. And I also have one other question. I have a flowmaster with dual 2.5 in outlets on it and now my car has started back firing. Is it because the muffler is breaking in or could it be my cat converter going bad? I'm getting a new cat soon so that will probably fix it. and it only back fires when i shift. any input will help

 

You aren't really losing horse power with the leaking gasket. You are however reducing the life of your rear end. I'd get that fixed asap. The backfiring is from the reduced amount of pressure pushing out the exhaust. It doesn't have enough backpressure so it could be a combination of both or your exhuast is just too open.

 

The backfire may also be a leak in your exhaust somewhere. I had flex pipes on my Fiat with tips out the side and the flex pipe leaked bad. When I let off the throttle after a couple of seconds BOOM! It would light up a dark night.

 

You're probably losing some power to the wheels in the form of friction if you're low on gear oil. The gaskets are cheap, anyway. Spend the $25 for gasket and some good 75w90 gear oil. If you've got a posi, you'll need some friction modifier in there, too. It isn't too expensive, but it smells worse than gear oil does. If you've got a 10 bolt (which you probably do, the fill plug on the rear is towards the front of the car, and uses a 3/8" square drive, and an extension bar helps, but isn't needed. To drain it, just loosen the top four bolts a little, and take the rest out a bit more, and pry the cover plate off a bit.

Have fun with it, and don't get too much gear oil on you. You'll smell like **** for a week if you aren't carefull.

 

Or what's cheaper than the gasket is Black RTV. As long as you don't use synthetic fluid, it'll be fine. Synthetic eats away at silicone gaskets.

 

The cost difference is negligable. I picked up a gasket for mine for $5 when I changed my fluid last. Fel-Pro, too, not some cheap **** off brand.

The biggest cost is gear oil, and I expect that would cost about $17 or $18.