I recently acquired an 84 Jimmy. It has a crate 350 4bolt, manual tranny, and an almost perfect body. I have a couple of questions if anyone has any input........I also have an 85 Blazer that has a rebuilt 350 4 bolt, a 350 tranny, and a rebuilt transfer case. I am not going to be off roading any more than I have to, but I will be pulling a 20' camping trailer, mostly highway driving.

I am thinking of swapping out the transfer case, because I had it rebuilt a while back and it has seen lettle use since. But would I be better off (milage wise) to swap out the tranny? What transmission would be best? It has stock differentials, would it be good to change them out (to achieve the optimum mileage)?

Also, the drives side door has a gap almost 3/8ths of an inch at the top front hinge side. Is this a hinge problem or a door problem? Can it be fixed with just new door gaskets or do I need to replace hinges.......or is the door just sprung and needs to be replaced or bent?

Thanks, in advance, for the help.

 

Alright, to begin with, are you talking about both full size blazer and jimmy?

Either way, I don't think removing the transfer case is going to do too much for you..maybe reduce the value of the truck. Fuel mileage isn't a strong point of these trucks. As far as your rear ratio, figure out what you've got because there can be variances. If you want possibly better mileage you could look into reducing the rear ratio with a different gearset, but it would hurt your towing capabilities.

I'm not sure which truck you'd be swapping the trans out of, but going to an overdrive transmission may be best, since you can retain the rear ratio but still have that final drive reduction.

Again, fuel mileage isn't going to really come with a 350/350 setup especially if its a full size. Even with overdrive and a perfect tune I wouldn't expect much more than 15 mpg...they are big rolling boxes.

 

It's a full sized. I don't think swapping transfer cases will make a difference in mileage. But it might in reliability. There is no question about removing the transfer case.

I have always believed that properly driven a manual would get better mileage, but I am hearing the automatic will. This seems like a bit of a disconnect, but am willing to consider it. What would be the best tranny out there for a combination of power and mileage?

Also, has anyone converted to CNG? Either as a full time CNG or optional?

 

I'm not too sure going without a T-case would make your vehicle more reliable, but if it gives you extra piece of mind then go for it. The only time i've really heard of T-cases going bad is mostly from wheeling or lack of maintenance. If they spend most of their time in 2wd under light load they should be ok.

Either way, for me, rule of thumb is to keep an automatic car automatic, and manual car manual. Its just easier that way. So, if your going to swap out your TH350, I would be looking for a 700r4. No matter what you do, your going to have to change driveshaft length. I know in a 2wd application the 700r4 is about 3 1/2 inches longer than the TH350. It would be best to measure everything before removing the trans and after installing the new one to determine the correct driveshaft length.

Fuel mileage wise, a manual usually does a bit better than an auto, because there is less rotating mass, and lighter over transmission weight. Also power wise, there will be a slight improvement over an auto. But, an automatic can perform pretty well fuel mileage wise especially if you take advantage of the lockup torque converter. In my opinion, the added work of making provisions for a clutch, and removing the column shifter and shift selector, and cutting an additional hole in the floor, is not worth it


I'd also like to add, that I was driving a '91 full size for a while, and the best fuel mileage I could get was about 17 mpg with mostly highway driving, 65-70 mph. That was a TBI 350 with a 700r4, 3.73 rear, and 31" All terrain tires.

 

Where did you get the idea that I was going to go without a transfer case?

I have TWO transfer cases. One is on the 84. One is on the 85. The one on the 85 was recently rebuilt.

 

Sorry I assumed you wanted to run without 4x4

 

I wonder if you could find a 5 or six speed manual tranny to put in there? Probably would need more adapters and such than it's worth though.

 

i would say that mileage wise won't be to much different between the auto and manual trans but if you are going to be towing alot i would say the manual would hold up a lot better