I just broke the spider gears in my 87 with a 7.5. As understand it has 26 spline axles and a 2.41 gear ratio. What i want to do is change the whole gear set. Id like a 3.73 or 4.10. My problem is im not sure exactly what car to get the gears out of. So id really appreciate someone pointing me in the right direction. Thanks.

 

 

the cheapest thing to do would be get the guts out of a 86 up monte ss. the more expensive move would be to rebuild it. i believe that since you had 240s in it you might have a different series carrier so in order for you to add gearing you want your going to have to swap out the carrier. auburn makes a nice one. if i were to do it i would ditch the 7.5 and get a 9 inch. pricey but well worth it. if you cant afford that and want to throw money into the 7.5. get a auburn 9* carrier but 28 spline. get 28 spline axles and what ever ring and pinion you want for it. itll all work in your housing. then youll have the gearing you want and everything is pretty much new with a posi,beefier axles, and carrier. your only real weak link then will be the c clips and the 7.5 ring gear.

 

Don't use used gears, you won't be happy. Used gears have a wear pattern, and if you don't get it nuts on, it will be noisy. If you are going through the hassle, buy new gears.

Cheapest would be to get a whole rear end from a Monte SS. My 87 is a posi with 3:73 gears, my 86 was a posi with factory 4:10s, and my Grand National with the 8.5 rear is 3:42.

I am currently building a 12 bolt Chevy for my 87, I want it to remain GM. I got the housing from a 70 Chevelle, and plan on cutting the ends off and replacing them with externally retained Ford 9" ends. I'll replace the lower control arm brackets, as well as the spring perchs. The upper mounts have a slightly different offset than the metric cars do, but there are companies that make the control arms with that factored in. The 12 bolt will also get an Eaton, or true trac locker.

I replaced the blown out "gov-lock" in my older Z71 with an Auburn diff and didn't care for it. It didn't always kick in, especially when needed, and is not rebuildable.

 

the auburn unit is rebuildable. ive never had a problem with it kicking in, and its supposedly stronger then the eaton.

 

Everything I have seen and read, say Auburn unit is not rebuildable. As for the kicking in and out, I am only relaying what my experience is, and I have heard the same from others who have installed them.

 

http://auburngear.com/aftermarket/d-rex.aspx

http://www.carcraft.com/techarticles.../photo_05.html

you cant rebuild it but auburn can if it blows up within 4 years you send it to them and they rebuild it for you. so yes and no its rebuildable.

 

imo i would get a ford 9 inch rear end out of a mustang they come with posi trac stock and slide it in you might need to modify the axle. but you will be pleased with it because the spider gears and shims are a little stronger than the stock 87 spider gears but i would also find a 8.5 rear end from gm that you can slide in for your monte and go from there. its imo to go either route but it is up to what is the hp route you are going for because the trans and the rear end are the weak links for some rear end cars. but it is up to you on what you might like to do.

 

Spider gears and center shaft do not constitute a rebuild kit.

How convenient is it to remove the rear diff. and send it out, wait for the return, then go thru all the setup again with a good chance of a noisy rear gear. The cost of shipping, new carrier bearings, and the cost to have someone set it back up.

The Eatons I have dealt with in the past have had almost no problems. The only problem I have run into is worn clutches from higher (500-600) horse cars, and slicks used for drag racing. The fix, a telephone, credit card, and a 3 day wait. The Eaton clutches can be replaced without removing any more than the axles and rear cover.

 

i think that since every part of the diff can be serviced that means its rebuildable, and i highly doubt that hes going to dynamite the auburn. to each his own. i was making a suggestion as per my personal experience. ive had a bad experience with scallops and so have some of my friends thats not to say anyone and everyone else will. nor would i run out and tell everyone to avoid them cause theyre poisonous. personally ive thrown money at the 7.5 and its not worth it. i do have an auburn behind a car making decent power and its not noisy, not non functional, or on the verge of catastrophic failure.as i stated before if he has the money he should upgrade now. at this point were debating what carrier to put into a rear that isnt worth the carrier, ring and pinion and axles that he should put in it to make it worth while. if your going to throw that much money into it save up and get a dana60 or a ford 9".