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Old 12-11-2010, 12:03 PM   #1
SCOTT9X33
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Default front and rear diff questions

i just picked up a 76 chevy 3/4 ton 4x , with a 400 and and t-400 tranny full time 4 wheel drive , i am not a truck guy but i was wondering if anyone could tell my what the running gear is ? or tell me how to find out ? thank you
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Old 12-11-2010, 12:37 PM   #2
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Default Re: front and rear diff questions

6 or 8 lug?
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Old 12-11-2010, 12:41 PM   #3
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Default Re: front and rear diff questions

3/4 should be 8 lug, full floater 14bolt rear axle (good), and either a 10bolt front (bad), or a dana 44 front (better).
Oh yeah, I think the tcase is a np203, it's. A chain driven case and not the best.
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Old 12-11-2010, 01:00 PM   #4
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Default Re: front and rear diff questions

76-77 was the split for the 44 to 10 bolt, so it could go both ways
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Old 12-11-2010, 02:25 PM   #5
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Default Re: front and rear diff questions

I think 76 was d44, but it could be either one after 35 years.
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Old 12-11-2010, 07:47 PM   #6
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Default Re: front and rear diff questions

sorry make that a 79 chevy .... still the same stuff ? how can i tell the front diffs apart from a 10 bolt or a d44 and the transfer case ?
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Old 12-11-2010, 09:04 PM   #7
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Default Re: front and rear diff questions

79 should be a 10 bolt unless someone changed it out. Rear is 14b as long as it's 8 lug. Easiest way to identify the diffs is by the shape of the cover. If it's a full time t-case I think the only one they made was the 203.
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Old 12-11-2010, 09:26 PM   #8
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Default Re: front and rear diff questions

yes it is 8 lug
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Old 12-12-2010, 01:58 PM   #9
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Default Re: front and rear diff questions

http://coloradok5.com/axleguide.shtml

match your pumpkin. 8 lug would be a 10-bolt, dana 44, or if you are lucky somebody swapped in a dana 60.
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Old 12-13-2010, 05:37 PM   #10
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Default Re: front and rear diff questions

Might a 9.5 semi-floater 14 bolt too. Behind the 400 though it should be the full-floater though. Chevy did alot of strange things those years so matching your diffs will be the best way.

Quote:
Originally Posted by kbeefy View Post
it's a full time t-case I think the only one they made was the 203.
Ken is right. The 203 was the only full time case. Its huge and heavy. There is a part time kit which allows a 2-lo as an option too. If you find a 205 with the 400 adapter, snag it.
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Old 12-13-2010, 05:49 PM   #11
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Default Re: front and rear diff questions

not to be a rude, but this should be moved to 4x4 tech....
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Old 12-14-2010, 05:20 AM   #12
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Default Re: front and rear diff questions

I didn't think they used semi floaters until after 87.
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Old 12-14-2010, 10:11 AM   #13
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Default Re: front and rear diff questions

Quote:
Originally Posted by kbeefy View Post
I didn't think they used semi floaters until after 87.
my '82 was a semi-floater.
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Old 12-22-2010, 06:52 PM   #14
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Default Re: front and rear diff questions

I would contend that 9.5" were more prevalent before the IFS trucks started. There were lots of LD 3/4 tons that came with 8 lug semi-float rears. They are a very common rear-end in 3/4 ton Suburbans too.

Both the 9.5" and 10.5" 14 bolts are good rear-ends. The smaller of the two will hold up fine up to around 37"s. It's just that the ease of swapping, availability, and cheap-to-free-cost of the 10.5" steals the thunder from any other GM rearend (hell, a lot of jeeps, fords, dodges, buggies, everyone runs 14 bolt rears).

10 bolt and Dana 44 fronts are almost completely identical in both strength and parts (even the knuckles are interchangeable...the splines are one of the only differences, and strength-wise is not really relevant). They will hold up just fine even with 35"s-37"s if you wheel with a brain and running a full-time locker wouldn't be the best idea for one if you're pushing the limits on tire size. Both axles hold up pretty well (a guy on CK5 jumps his, even has a shot in the calendar), but the shafts use 297 ujoints, which are the same as Dana 30s...Most Dana 44/10 bolt front failures are due to high torque/shock loading and the ujoint or shaft ears fail. The rest of the axle in my opinion is durable enough to have a reasonable service life even under pretty abusive conditions. I wheeled my Dana 44 for about two years on my truck with zero maintenance until I swapped in a Dana 60. And that was rock crawling with me knowing full-well that it was worth $0 and was going to be replaced when it broke (I beat the hell out of it with 35"s rock crawling, but I also left it open because I didn't want to put any money in to it). My final reasoning for putting in a 60 was because crossover steering was much cheaper for a Dana 60 and I did not have to buy as many parts to do it, not because the Dana 44 wasn't strong enough (I would have probably ran 37"s and built the 44 and enjoyed the same ground clearance but used much cheaper tires).

If it is full-time 4 wheel drive, it has an np203. Leave it part-time unless you don't care about it. There is only one part-time kit I have ever seen for that case that is manufactured acceptably (I think it was the expensive mile-marker one, I think they make two). Most kits are machined poorly and add lots of slop. The only benefit I feel to running part-time is gas mileage, but I can't for the life of me understand why someone would buy a truck of that vintage and be concerned about gas mileage. Besides, for the cost of the kit, you could swap in a 205, 208, or 241 (my preference) and have a case that is designed to run 2 wheel drive. The 203 is difficult to get parts for, and putting money into it is just polishing a turd. The part time kit is one of the big reasons why they are known for having bad chains. With a part time kit, the chain does not spin, and therefore the lubricating system of the case no longer functions. It wears out everything. Also, that case should have non-detergent 30 weight oil in there. Lots of people run gear oil in them and ruin the case that way. The shifters are problematic with them, but there's simple things you can do to fix it if it becomes an issue and cleaning it up doesn't work.

I will go ahead an point out that the th-400/np203 combo is VERY desirable. The np203 is very common used in a dual transfer case setup because the gear reduction (hi/lo) portion of the case is actually a seperate housing that is bolted to the center differential (very easy to separate). An adapter plate is used bolted to the back of the gear-reduction section of the 203, and then an np205 is bolted to the back of the adapter. This enables you to have to hi/lo sections and the center-diff of an np205 (the strongest conventional transfer case). The chain-driven portion of the 203 is thrown in the trash, and you end up with an all-gear-driven system with 1:1, 2:1 (standard low range for most vehicles), and 4:1 ratios, and the whole system is the same length as the original np203 (you don't have to get new driveshafts).

The big reason your setup is so desirable is because your th400 uses a 32 spline output shaft. This is the strongest transmission output that GM used. The 32 spline np203s are somewhat more challenging to find than the more common 27 spline (th350). Both are very strong, but a lot of people choose to run a th400 because they are very strong transmissions and I believe you can even change the first gear ratio in them.
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Last edited by owenst7; 12-22-2010 at 07:00 PM.
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Old 12-22-2010, 11:35 PM   #15
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Default Re: front and rear diff questions

Quote:
Originally Posted by owenst7 View Post
I would contend that 9.5" were more prevalent before the IFS trucks started. There were lots of LD 3/4 tons that came with 8 lug semi-float rears. They are a very common rear-end in 3/4 ton Suburbans too.

Both the 9.5" and 10.5" 14 bolts are good rear-ends. The smaller of the two will hold up fine up to around 37"s. It's just that the ease of swapping, availability, and cheap-to-free-cost of the 10.5" steals the thunder from any other GM rearend (hell, a lot of jeeps, fords, dodges, buggies, everyone runs 14 bolt rears).

10 bolt and Dana 44 fronts are almost completely identical in both strength and parts (even the knuckles are interchangeable...the splines are one of the only differences, and strength-wise is not really relevant). They will hold up just fine even with 35"s-37"s if you wheel with a brain and running a full-time locker wouldn't be the best idea for one if you're pushing the limits on tire size. Both axles hold up pretty well (a guy on CK5 jumps his, even has a shot in the calendar), but the shafts use 297 ujoints, which are the same as Dana 30s...Most Dana 44/10 bolt front failures are due to high torque/shock loading and the ujoint or shaft ears fail. The rest of the axle in my opinion is durable enough to have a reasonable service life even under pretty abusive conditions. I wheeled my Dana 44 for about two years on my truck with zero maintenance until I swapped in a Dana 60. And that was rock crawling with me knowing full-well that it was worth $0 and was going to be replaced when it broke (I beat the hell out of it with 35"s rock crawling, but I also left it open because I didn't want to put any money in to it). My final reasoning for putting in a 60 was because crossover steering was much cheaper for a Dana 60 and I did not have to buy as many parts to do it, not because the Dana 44 wasn't strong enough (I would have probably ran 37"s and built the 44 and enjoyed the same ground clearance but used much cheaper tires).

If it is full-time 4 wheel drive, it has an np203. Leave it part-time unless you don't care about it. There is only one part-time kit I have ever seen for that case that is manufactured acceptably (I think it was the expensive mile-marker one, I think they make two). Most kits are machined poorly and add lots of slop. The only benefit I feel to running part-time is gas mileage, but I can't for the life of me understand why someone would buy a truck of that vintage and be concerned about gas mileage. Besides, for the cost of the kit, you could swap in a 205, 208, or 241 (my preference) and have a case that is designed to run 2 wheel drive. The 203 is difficult to get parts for, and putting money into it is just polishing a turd. The part time kit is one of the big reasons why they are known for having bad chains. With a part time kit, the chain does not spin, and therefore the lubricating system of the case no longer functions. It wears out everything. Also, that case should have non-detergent 30 weight oil in there. Lots of people run gear oil in them and ruin the case that way. The shifters are problematic with them, but there's simple things you can do to fix it if it becomes an issue and cleaning it up doesn't work.

I will go ahead an point out that the th-400/np203 combo is VERY desirable. The np203 is very common used in a dual transfer case setup because the gear reduction (hi/lo) portion of the case is actually a seperate housing that is bolted to the center differential (very easy to separate). An adapter plate is used bolted to the back of the gear-reduction section of the 203, and then an np205 is bolted to the back of the adapter. This enables you to have to hi/lo sections and the center-diff of an np205 (the strongest conventional transfer case). The chain-driven portion of the 203 is thrown in the trash, and you end up with an all-gear-driven system with 1:1, 2:1 (standard low range for most vehicles), and 4:1 ratios, and the whole system is the same length as the original np203 (you don't have to get new driveshafts).

The big reason your setup is so desirable is because your th400 uses a 32 spline output shaft. This is the strongest transmission output that GM used. The 32 spline np203s are somewhat more challenging to find than the more common 27 spline (th350). Both are very strong, but a lot of people choose to run a th400 because they are very strong transmissions and I believe you can even change the first gear ratio in them.
wow ... thanks for the info ... now .. we are parting out the truck so let me know what you guys need !!!!!
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