T case and Differential Lubricant recommendations Lubricant recommendations

[Blazer Chalet]

The service manual I referenced calls for Motor oil For the transfer case if it is full time 4 wheel drive and Gear oil if not. I believe my 1977 blazer was born with full time And was modified by a previous owner. I bought it with manual locking hubs. Does anyone know what I should be using?

I also would like to change the differential oil . I have read that if you have positraction you should put in an additive. How do I determine if this rig has positraction ?
I do not know how stock The truck is. I believe there have been modifications.Can anyone help identify what I have here by these photographs? Thanks in advance for your help!

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[Curt]

I would still run motor oil in the np203 because that’s what GM called for.

The only true way to know if you have a limited slip is to pull the cover off,which you’d do anyway when changing oil.

 

[Blazer Chalet]

Thanks Curt.
Do these look like original axles and springs?

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[bucket]

Thanks Curt.
Do these look like original axles and springs?

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@Curt is spot on. If the rear axle has a gov-loc in it, regular dino oil should work well. Definitely run motor oil in the t-case since that's what it was designed to use. The part-time 205 is what takes gear lube.

Those axles are stock, but leaves have most certainly been added in.

 

[Dooley]

Read here in regards to a 205 case.
I would not run gear lube in any 205 case as it does not lube as efficiently as the newer requirements.

Motor oil in full time units even if "part timed".


Help identifying | GM Square Body - 1973 - 1987 GM Truck Forum

 

[idahovette]

@Dooley , his pics show he's got a 203,...Always motor oil in the 203 case, Always have put gear oil usually 80-90 in a 205 and I'm with @bucket on all of it. That's what GM said in the early-mid 70s, when all this stuff came out.

 

[Blazer Chalet]

Bucket, I suspect GM may have installed more leaves to support the factory installed camper and the 31 gallon fuel tank. A previous owner added a
40 gallon water tank at the very back of the camper so it is possible he beefed up the springs too. I will ask an owner of a stock Chalet if they came with 8 leaves.

What do I look for inside the Differential? I am not familiar with locs

Thanks to all for the help and guidance!!!

 

[Dooley]

@Dooley , his pics show he's got a 203,...Always motor oil in the 203 case, Always have put gear oil usually 80-90 in a 205 and I'm with @bucket on all of it. That's what GM said in the early-mid 70s, when all this stuff came out.

My reply was meant for bucket, not the original poster.
I always have run motor oil in the "full time" cases even if part timed.
Same bearings in my 1988 V30 205 as with the 1972/80 205's.
The 205's that have run motor oil and Dexron II always were much cleaner inside and parts moving slick with little wear, not gummed up from years of non maintained gear lube.
Pic shows what I did for many 203's over the last 40+ years.

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[idahovette]

Yes and I see you have the elbow on the filler, that all the part timers are supposed to have to raise the oil level.

 

[bucket]

Bucket, I suspect GM may have installed more leaves to support the factory installed camper and the 31 gallon fuel tank. A previous owner added a
40 gallon water tank at the very back of the camper so it is possible he beefed up the springs too. I will ask an owner of a stock Chalet if they came with 8 leaves.

What do I look for inside the Differential? I am not familiar with locs

Thanks to all for the help and guidance!!!

Some of those leaves were definitely added in at a spring shop. The different style ends are the giveaway.

When you remove the diff cover, just look at the middle of the carrier assembly. If you just see 4 spider gears, it's an open diff. If you see some plates and springs, it is a limited slip. If you can see some goofy looking parts including a little flyweight thingy on a pin, it is GM's GovLoc.

My reply was meant for bucket, not the original poster.
I always have run motor oil in the "full time" cases even if part timed.
Same bearings in my 1988 V30 205 as with the 1972/80 205's.
The 205's that have run motor oil and Dexron II always were much cleaner inside and parts moving slick with little wear, not gummed up from years of non maintained gear lube.
Pic shows what I did for many 203's over the last 40+ years.

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Thanks, I always forget that the later ones called for thinner fluid. But I always thought that original switch to 30w was for fuel economy and then the switch to ATF was due to the later style syncro front output.

So you have been running the thinner fluid in all of yours and have not noticed any long-term durability effects?

 

[bucket]

Looking back at the pictures again, the front springs have had the 2nd from bottom leaf added in. On the rear packs, I count 9 leaves. 3 of which have been added in.


BTW, I'd like to see pictures of the whole rig. It looks good from the underside!

 

[Blazer Chalet]

@bucket,
Thanks again for your help.
I'm traveling this week and will post photos when I can.
Anything in particular you'd like to see?

 

[bucket]

Any pictures of a Chalet will do!

 

[Dooley]

Some of those leaves were definitely added in at a spring shop. The different style ends are the giveaway.

When you remove the diff cover, just look at the middle of the carrier assembly. If you just see 4 spider gears, it's an open diff. If you see some plates and springs, it is a limited slip. If you can see some goofy looking parts including a little flyweight thingy on a pin, it is GM's GovLoc.



Thanks, I always forget that the later ones called for thinner fluid. But I always thought that original switch to 30w was for fuel economy and then the switch to ATF was due to the later style syncro front output.

So you have been running the thinner fluid in all of yours and have not noticed any long-term durability effects?

Pics from my 1980 owner manual.

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[Blazer Chalet]

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