Jimmy/K5/CUCV family

[dirtyfingernails]

I bought this Jimmy over the weekend. I'm not much of a Chevy guy. Really never owned one, but I like the look of the K5 and CUCV blazers. Unfortunately, my eyes took over my brain. I figured out (after the purchase) that this vehicle has the corporate 10 axles and an NP-241 transfer case, which are very weak components. Is this true? Good news is that the engine is a rebuilt 350 with TBI. Runs great and rebuilt tranny too. Can I make this more stout relatively easily? Thanks and sorry it's not OD.
Steve

 

[mangus580]

Unless you do heavy off-roading, i wouldnt worry too much about the 'weak points' Chevy to this day still uses the 241 transfer case, even in the 1 tons (I believe).

The 10 bolt axles work decent for on-road... when you have bigger tires and play in 4x4 is when they really show signs of weakness.

BTW.... Sharp truck! I have always liked that front clip on this body style.

 

[dirtyfingernails]

Mangus,
Thanks man. The truck currently has 35 inch tires on it. Should I upgrade the "automatic" hubs to lockouts? Or is that a waste of money? Will the 10 bolt axles hold up to this tire size with a little 4x4 action? Thanks again.
Steve

 

[OLDCHEV4X4]

35" Tire's are the MAX for those axles. Tread lightly when off roading. If you want to really off road put some M1008 axles under it.
The 241 is a decent TC.
I would put some manual lock-outs on it if it were mine.
Nice Blazer!

 

[colomil]

Upgrading the axles is fairly cheap. Put a 14 bolt from a 3/4 ton (not a 1-ton) in the rear as the spring pads will line up correctly. You will need a different rear driveshaft U-joint, these hybrid u-joints can be found on ebay for around $40. Swap out the front hubs/rotors/backing plates for the 8-lug style and you now have a true 3/4 ton blazer. This upgrade can be done pretty cheap (I did mine for $250).

 

[OLDCHEV4X4]

Upgrading the axles is fairly cheap. Put a 14 bolt from a 3/4 ton (not a 1-ton) in the rear as the spring pads will line up correctly. You will need a different rear driveshaft U-joint, these hybrid u-joints can be found on ebay for around $40. Swap out the front hubs/rotors/backing plates for the 8-lug style and you now have a true 3/4 ton blazer. This upgrade can be done pretty cheap (I did mine for $250).

You will still have the 10 bolt front axle and u joint in the front. The limit is still 35" tires with this set-up.

 

[K45]

The 241 is a good case overall and there is some debate on the best. If you feel you need to you can swap a 208 tcase it is an easier swap but not a better overall Tcase swap.

You can get an adapter and drop in a 203 or 205 which is very beefy. Any of these mods besides the 208 will require changes to the drvieshafts

As for the axles. People have done 3/4ton 1 ton and rockwells and others. It just depedns on your pockets and desire. a 3/4 ton or a 1 ton set up are realitively easy. Change some spring mounts and your drive shaft mods and you should be good. You will not be able to use your old rims. You will be 8 lug. The cool thing is those 35's are not going to cause these axles any problems. The best would to get a matching set from a wrecked vehicle that way the gears are matched up and you do not worry about gear ratios. Good luck

O yeah if you wanted it to look more like a cucv you can bolt on the front and rear bumpers with shackles.

 

[corelokt]

I'd like your auto hubs.

 

[mangus580]

I wouldnt bother swapping out the auto hubs unless they give you trouble. I used to have them, and loved them. I didnt run into problems with them until I started plowing.... They dont like all the forward/reverse action. They unlock/relock every time you change direction.

 

[colomil]

The 3/4 ton axle swap does still leave you with the original 10 bolt front axle and hot rodding a 35 inch tire may eat a u-joint. However, I have found that most of the weakness is in the rear 10 bolt since it is on duty 100% of the time. Just look up "snapped axle" on youtube and you will see a bunch of 10 bolt rears snapping and in some cases, sending a wheel down the road. The best solution is of course a dana 60 front, but since these are obviously made of gold, it is a cost/benefit decision that should be taken into account.

The 3/4 ton setup will also give you bigger brakes so theoretically you can tow more. Rear disks are cheap to put on as well and the beloved detriot locker is cheapest for the 14 bolt.

In any case, do take it easy on the 35's with the stock axles.

 

[AJMBLAZER]

Nice K5! What year? Gotta be 89-91. The pinnacle of these trucks with that great TBI engine. Nice power, good mileage, and simple fuel injection.

Yes, manual hubs are better aside from requiring you to get out and lock them in. Just lock them in before you plan on wheeling and call it good until you're done. Up here we do that for 6 months at a time.

Do you know what the gear ratio is in the axles? If you're lucky someone regeared it to 4.56 which would be perfect for the OD trans and those 35's. If not...start looking for some 3/4 ton axles with at least 4.10 gears. No sense in regearing 10 bolts.
The 10 bolts are okay and hold up decently well to big tires it's just that it's easy to stress them out with big tires and too high of gears. The G80 "Grenade Lock" pseudo locker doesn't help any either. Best fix for one of those is the dumpster. Not known for longevity or durability. Again though, if you need to regear for those tires it's time to start looking for a 14SF or 14FF rear axle.

The 241 is an excellent transmission. Dunno what was being said above but the 241 is a product improved 208 and superior in every way. It is still used by GM and Dodge and Dodge runs an upgraded version in their 1 tons behind the Cummins diesel. It will serve you fine. Just make sure you have a skid plate over it.

 

[dirtyfingernails]

Wow, thank you all very much for the information. I will review these posts a number of times. Sounds to me like the corporate 10 bolts will do okay if I stay off the accelerator. AJM, unfortunately, the gearing in the diffs is three point something to one. Funny thing, all the axles I've worked with have had a tag on them indicating the ratio. Neither of these do. PO told me about the ratio (I've forgotten). Does chevy put a tag somewhere else?

 

[AJMBLAZER]

Well, you're on borrowed time with the axles and 700R4 if the axles aren't geared properly for the tires. 4.56:1 would be ideal.

No, GM never put a tag on their axles except when they used Dana axles. However if you look in your glove box the RPO codes should be in there on a big sticker and one will indicate which gears it came from the factory (and I'm betting are still in the axles). Gears from the factory would likely be 3.42 or 3.73's in that time period but 3.08's were still possible.

Oh yeah, in case you haven't noticed, many of us recommend www.ColoradoK5.com for this era GM. It's the mecca of 73-87(91) GM fullsize trucks. Sorta like Steel Soldiers for civy trucks.

 

[dirtyfingernails]

I signed up over there at CK5, but I can't post or see pictures. I think they want you to pay $25 a year for that. Too rich for my blood. I'm a cheapskate though. 3.73:1 sounds right. Maybe I'll change out the ratios. Thanks for the info amjblazer. If you don't mind, I may pick you brain in PMs. Steve

 

[Recovry4x4]

I have a 91 burb with 10 bolts and 3.42 cogs. I just fried a rear wheel bearing so I'm ding the 3/4t swap. I have a 10B front with 4.10s and a 14 bolt semi float but I'll probably hold out for a full floater.

 

[kennyw]

The 241 is a good case overall and there is some debate on the best. If you feel you need to you can swap a 208 tcase and that a bit beffer set up

The NP208 is a weaker tcase than the NP241. Smaller chain and higher low range gear set. 2.61:1 in the NP208 vs 2.71:1 in the NP241. There are slip yoke eliminator kits available for the NP241 as well.

 

[kennyw]

You have three options in the 3.something to 1 ratio 10 bolts. 3.07, 3.42, or 3.73. None of them will be all that great with 35" tires and an automatic transmission. Without OD 4.56 gears and 35" tires would be ok up to 65 mph. You can go faster than that, but it just gets louder and sucks down the gas faster.

The G80 "Grenade Lock" pseudo locker doesn't help any either. Best fix for one of those is the dumpster. Not known for longevity or durability.

In the 10 bolt rear the G80 gov-lock is a break down waiting to happen. But the G80 option in a 14SF/14FF will hold up fine with anything under 37" tires.

Again though, if you need to regear for those tires it's time to start looking for a 14SF or 14FF rear axle.

If you go looking for a 3/4 ton rear, it would be cheaper in the long run to buy a matching pair of front and rear axles than to buy the rear and regear/convert to 8 lugs up front to match. The 3/4 ton 10 bolt or Dana 44 front is good up to 37" tires if you don't have a lead foot. But carry spare front axle shafts for wheeling as it is the most likely failure point.

 

[kennyw]

I signed up over there at CK5, but I can't post or see pictures. I think they want you to pay $25 a year for that.

The "garage" is the only free forum on ck5 and you can't post pics/links until you reach 15 posts due to spammers. Plenty of useful info and good help in that forum. Another site is www.krazyk5.com, much smaller and a group of guys that mostly know each other well. Sometimes the name calling between friends can be thick, but it's not anything serious. Usually friends giving each other a hard time.

 

[K45]

I used the wrong words there. i was meaning as far as the easy swap the 208 is better as far as easiablity but not a better in overall case. Sorry for the confusion. I will fix my post

I know I had the 241 in my Tahoe and it was nice and I was running 35's with upgrade axle compoents no problem.