88 Monte Carlo LS differential

[Clutch_Grabwell]

the 7.5 is a 26 spline, the 7.625 (available on the monte SS) is a 28 spline.

I thought the 7.625 had 26 splines? What years of Monte SS had the 28 splines?

I've never heard of a Monte with 28 spline axles. The F-body changover to 28 spline didn't happen until after the G-body went out of production. Monte owners upgrading to a later carrier would end up looking for GN or 442 axles (from an 8.5" rearend) to fit the newer carrier.

 

[megaladon6]

it may only be the last 2 years, but my 87 has the 7.625 and the 28 splines.

 

[85GPLef41]

I will be doing a posi swap soon on my 87 SS rear soon i will double check it. Guess i should have waited before buying some 28 spline ones out of a GN :? From what i understood the only G-body 28 splines were on 8.5in rears.

 

[LT1 Monte]

I will be doing a posi swap soon on my 87 SS rear soon i will double check it. Guess i should have waited before buying some 28 spline ones out of a GN :? From what i understood the only G-body 28 splines were on 8.5in rears.

As an additional data point how much did you pay for the GN axles? Is 28 spline the largest that will fit in the tube? IF I used 31 spline it would seem the stock differential would be quite stout...

I am sure they won't fit or it seems that would be part of the discussion but have to ask to be sure.

Thanks

 

[85GPLef41]

I bought mine used for 120 but you could buy them new from Summit for 250 plus shipping if i remember correctly. I don't know about 31 splines axles being compatible with the 7.5in. But i think most upgrades thats everybody has discussed here should be more than enough for a street car.

 

[LT1 Monte]

Thanks for the information. $250 plus shipping is up there but I am sure a good trade off...I would guess 28 spline should hold ~550 flywheel considering that is what is in the LS Camaro's and I know many who go in 6's with the stock 28 spline.

 

[megaladon6]

just make sure of what size axle it is. spline count only helps so much, the real issue is the ring and pinion gears.
personally i doubt you can go 6in the 1/4mi with a fully stock 8.5, definitely not the 7.5/7.625(even an fully upgraded 7.5 would have serious problems). an upgraded 8.5 would hold 500 easily though.

 

[LT1 Monte]

Yes I agree the count is one parameter I do trust Moser material though.

I started driving the Monte with 305 andI have mixed feelings. It has some pluses and minuses the car doen't feel big in fact to me it feels small. I am doubting my plan to go 7/11 in this car. I went 115 in a Buick Roadmaster and it seemed like nothing, The Monte doesn't have the same feel even with the same wheel base. Alot is the stock shocks etc

 

[turbo78]

just make sure of what size axle it is. spline count only helps so much, the real issue is the ring and pinion gears.
personally i doubt you can go 6in the 1/4mi with a fully stock 8.5, definitely not the 7.5/7.625(even an fully upgraded 7.5 would have serious problems). an upgraded 8.5 would hold 500 easily though.

i run a completely stock 8.5 and i went 6.80 in the 1/8 at 106, but i run a turbo car and it launches fairly soft, about a 1.7 60 foot.

 

[LT1 Monte]

just make sure of what size axle it is. spline count only helps so much, the real issue is the ring and pinion gears.
personally i doubt you can go 6in the 1/4mi with a fully stock 8.5, definitely not the 7.5/7.625(even an fully upgraded 7.5 would have serious problems). an upgraded 8.5 would hold 500 easily though.

i run a completely stock 8.5 and i went 6.80 in the 1/8 at 106, but i run a turbo car and it launches fairly soft, about a 1.7 60 foot.

If I had an 8.5 I wouldn't worry, but since I have the 7.5 I am going to modify so I will probably overkill it and go 9" because of the relative cost is not alot at my starting point.

I see you use a GT42 how did you plumb the hotside? I originally was going to use a Turbonetics T7X but changed after seeing problems friend had on a single using an LT1 ECM.

Obvioulsy I am in the lust phase of my project having just put the stock LS Monte on the road yesterday. I saw that your car is a 1978 malibu classic with a GT-42 turbo with a glide with a nice sized stall and stock GN 8.5 3.42 gear posi but wondered if you had a site for your car and setup?

I plan to be close to what you have accomplished. My goal is 7/11 using probably a 98 or 99 Vortec computer via HPTuners. I have LT1's but I worry the 4L60E won't last. I prefer to design the car to be stout IF I can afford it, rather than have to repair or replace parts later. I have made that mistake and I hope to minimize those problems in the car.



Appreciate all the help.

Jack