View Full Version : Gear chance, Gear Vendor or Turbo
My Blazer is a 4X4 and I changed the wheel size to 33X12.5X15 ( do lots off sand driving) and with 3.08 gears I suppose that's the reason for loss off power going up hill in OD.
The only towing I do is a small 1200 lb luggage trailer with scuba diving equipment. Driving on freeway at maximum speed off 75 mph the engine only do 1750 rpm. Most off the driving is at 55 to 60 mph and then the rpm is much lower at
Well, I had an 85 C1500 w/2.73 gears that I swapped a 99 6.5lTD into and that extra power made all the difference - it averaged 22mpg when I drove it normally (most of my driving was on the highway), and when I had to do some hauling the power more than offset the tall gears. It still averaged 14mpg when hauling, too. From least to most expensive for new parts, I'd say your options are gear swap, turbo, Gear Vendors, but if you shop around and do all the work yourself you can probably turbocharge it for the same cost as a gear swap and have a LOT more fun! :)
Phil
I'm more than halfway with building my own manifolds with steam pipe and could get a turbo for a reasonable price R4000 =
DmaxMaverick
06-13-2007, 09:33
A turbo is a good way to get back that power, but consider the rest of the picture. Will the tranny handle the tall gears with extra power? 700R4, correct? Also, a turbo is pretty useless with RPMs as low as you are seeing, and taller gears is longer lag. It will help, but it won't be a night/day difference. 3.08 gears are too high for 33" tires. I changed my 3.73 gears to 4.10 when I upsized my tires to 33", and got back my power and MPG. 28 MPG stock, 21 MPG and a real dog with only the tire change, then 26-28 with the tires/4.10, and it would bark the tires pretty easy off the line. The tires are 33x12.50 Bridgestone M/T (mudders).
A properly sized and wastegated turbo (the turbo can be built to his specs) would help with the lag and low RPM power, although it is still not the best answer in my opinon. I would do a gear change to 3.42 or 3.55 gears. The low gear of the TH700 will give you power off the line and the 33's will offset the gearing nicely to still give decent mileage. Then, add the turbo for good measure! :)
What RPM should be the ideal, when driving in 3rd the motor is doing 2000 rpm at 60 mph and performs much better on up hills but then one already lost a gear.
I could lay my hands on a set of complete 6 stud diff's with 4.1 ratio's. The rear is a 12 bolt but I'm not sure about the front. Is there really a big difference between 10 and 12 bolt rear ends? Could one modify a 14 bolt to take 6 stud rims? My reason for asking is that decent 8 stud rims are hard to find in South Africa. I was told it's possible to modify a 14 bolt to go with disc brakes and 6 stud rims. Could anyone give me more info in this?
DmaxMaverick
06-14-2007, 01:18
I replace the OEM 10 bolt in my 1985 with a 1978 12 bolt with Auburn L/S. Got tired of rebuilding/replacing the 10 bolt. It's held up for over 250K miles. It's a 6 lug axle. Mod'ing a 14 bolt FF for a 1/2 ton would not be at all practical, IMO. Unless you were into rock crawling, or the like. The 12 bolt fit right in, brakes and all. I did have to use a special size U-joint at the rear, but the pinion could be changed to use the original. The special U-joint was common enough, the parts store had one on the shelf.
4.10 may be a bit low for your needs. Anything lower than the 3.08 will be a huge improvement, but 4.10 is a long stretch. It all depends on what you want from it. I've done a lot of towing and off-road, which is probably the reason for the failed 10 bolts. The tranny is a lot happier with the lower gears, too. If you do a lot of towing and/or off-roading, lower gears are more desirable.
What ratio would you suggest?
The reason thinking about a 14 bolt 4.1 ratio is there are lots off them around an are cheaper than any other rear ends. No more than R2000 or
There are 9.5" 14-bolt rears that were produced with 6-lugs, but they are probably harder to find in South Africa than the wheels!!
Personally, I like 3.73's, but anything from 3.42 and numerically higher would work well.
I Would suggest that you do the gear change to 3:73 or 4:10 gears. I'm running 3:73 with 33X12.5X15 with a 700r4 trans and am very happy with it. Check with you local 4x4 clubs for a set of used one and look to spend $300.00 on-up per set. If you wanted to upgrade to 3/4 or 1 ton axle with bigger brakes for stopping them bigger tires!
Ps
My blazer came with 31X10.5X15 and 3:42 gears but when I went with the 33" tires the performance went down!
Ebrown
I agree with you and the other guys that gear change is the first step to go for an a turbo would be a bonus. The options I would go for is to keep the 10 bolts and change gears.
Could you recommend gear brand names to go for and also the ones not to buy.
Another thing to think about is, from what I understand, the gear vendors will not work in a short wheel base 4x4 due to the extended length of the driveline the driveshaft has to be shortened and it would create too much angle for the u joints to be able to turn properly. I was told this by a GV distributor when I was looking at buying one for a short box Chevy 4x4 that I used to own.
hotrodelko
07-11-2007, 00:21
OK, sorry to barge in on someone else's thread, but I have a related question... How can I find out what gears I have in my 'Burb? There's no tag on the the rear end any more. I know that my mileage and power are suffering most likely from the taller tires/wheels (running 265/75/16 instead on the stock 235/75/15). Can I run my VIN somewhere to get the original build sheet? Any help would be appreciated!
DmaxMaverick
07-11-2007, 01:44
OK, sorry to barge in on someone else's thread, but I have a related question... How can I find out what gears I have in my 'Burb? There's no tag on the the rear end any more. I know that my mileage and power are suffering most likely from the taller tires/wheels (running 265/75/16 instead on the stock 235/75/15). Can I run my VIN somewhere to get the original build sheet? Any help would be appreciated!
It will be on the RPO code list in the glove box, that can be decoded HERE (http://www.thedieselpage.com/members/rpocodes.htm).
Or, you can jack one wheel, rotate it 2 times and count the rotations of the driveshaft. If you have limited slip or a Detroit type locker (one wheel won't turn with the other on the ground), you will have to jack both wheels, rotate it once (with both wheels turning the same), and count the rotations of the driveshaft. Each gear ratio will increment by about 1/4 turn of the shaft. ~4 turns will be a 4.10, ~3-3/4 turns will be a 3.73, ~3-1/2 turns will be a 3.42, ~3 turns will be a 3.08.
hotrodelko
07-11-2007, 11:47
OK, from the rpo code I found it's got 3.73 gears..... should be plenty low I'd think. I guess I may have to bite the bullet and get my IP and injectors checked.. This thing is WAY too low on power. Towing my 17' boat is an adventure in pissed off drivers following me!(45mph up a gentle hill with it out of OD and on the floor????):confused: Nevermind the fact that just going down the road empty I can have a hard time getting out of my own way.
It will be on the RPO code list in the glove box, that can be decoded HERE (http://www.thedieselpage.com/members/rpocodes.htm).
Or, you can jack one wheel, rotate it 2 times and count the rotations of the driveshaft. If you have limited slip or a Detroit type locker (one wheel won't turn with the other on the ground), you will have to jack both wheels, rotate it once (with both wheels turning the same), and count the rotations of the driveshaft. Each gear ratio will increment by about 1/4 turn of the shaft. ~4 turns will be a 4.10, ~3-3/4 turns will be a 3.73, ~3-1/2 turns will be a 3.42, ~3 turns will be a 3.08.
If, as I suspect, you have a 6.2 with 3.73 axles and oversize tires, don't expect too much.
My suggestion is to turbo charge it. Or, check out Dr. Lee's quest for normally aspirated 6.2 power on the dieselpage.com
Ratau,
To answer you question of the 10 bolt to 12 bolt rear axle
12 bolt rear:
1977-1981 8.875-inch ring-gear, Pinion diameter 1.438 (Truck) & 1.625 (Car), C -clip retainer axles, 1.31 Axle shaft Dia and 30 Spline, The most common types of yokes are the 1310,1330, units, but the 12-bolt generally uses the smallest, 1310-style U-joint, and there are the thin or thick ring gear,
Corp 10 bolt:
old style 1981 - 1988 : 8.50-inch ring gear, 1.28 Axle shaft Dia, 28 Spline, C -clip retainer axles
new style 1989- 1991 :8.50-inch ring gear, 1.28 Axle shaft Dia, 30 Spline, C -clip retainer axles
Corp 14 bolt (Semi-Float)(SF)
1981-1996 heavy 1/2 ton and Light Duty 3/4 ton chevy trucks, They come in 6 or 8 lug, 9.50-inch ring gear, 1.876 Axle shaft Dia, 30 Spline axle shaft, C -clip retainer axles, and it's quite heavy, and the use of a conversion U-joint might be needed.
Front:
1981-1991: corp10 8.50-inch ring gear, 1.28 Axle shaft Dia, 30 Spline axle
1977-1988: corp10 8.50-inch ring gear, 1.28 Axle shaft Dia, 28 Spline axle
196?-1978: Dana44 8.50-inch ring gear, 1.31 Axle shaft Dia, 30 Spline axle
xxxx-xxxx : Dana60,1977-87 K30 1 ton, 1984-88 CUCV, 35 outer 30 inner spline ( Knuckle side), Axle tube dia. 3.125", wall thickness 0.5, fully dressed axle Weight 460-480lbs, ring gear dia=9.750, U-joint size 1310,1330,1350,1410,1480,7290, 1.50 dia axle shafts
IF you were looking for the perfect combo would be a Dana 44 front and 12 bolt Truck rear. There are alot of limited Slip to full locker these axle. Make sure when you looking at a axle to open the diff and check the ring and pinion for even where, Rust line on inside of diff, water in oil, metal shavings in oil, and if you looking at a pair of axle make sure they are the same gearing. Check the edge of the ring gear the gear ratio should be stamped on it or you can check it this way dividing the ring gear tooth count by the pinion gear tooth count. So say the ring gear has 41 teeth and the pinion has 10 teeth so you would have the ratio of 4.10.1 (41/10 = 4.10).
I'm running 10 bolt 30 spline in front and 12 bolt rear with 3:73 gears. If you swapping out a 10 bolt rear for a 12 bolt you will have to use a conversion U-joint at the rear drive shaft, at the axle end.... Conversion Ujoint for 12b to old 10b shaft(S44 to 1310)- Neapco 3-3130, Checkers part number is 215-0356 10.99
As for the gearing I would suggest 3:73 for a DD and If you tow quite often then go with 4:10.
Military K-5: came with the j-code 6.2, 350 or 400 trans, Np208 and 205 transfer case and 3.08 gear ratio and 10 and 12 bolt axle's and were call 3/4 ton's
Military Pickups: came with j-code 6.2, 400 trans, np205 transfer case and Dana 60 front and Corp 14 bolt FF and had 4:56 gearing in the axles and were called 1 1/4 ton
I hope this info will help.
Axle Id
http://coloradok5.com/axleguide.shtml
Wish I'd noticed this thread before posting a question about 10 and 12bolt axles a short time after this one.
Military K-5: came with the j-code 6.2, 350 or 400 trans, Np208 and 205 transfer case and 3.08 gear ratio and 10 and 12 bolt axle's and were call 3/4 ton's
Military Pickups: came with j-code 6.2, 400 trans, np205 transfer case and Dana 60 front and Corp 14 bolt FF and had 4:56 gearing in the axles and were called 1 1/4 ton
I hope this info will help.
just as a matter of interest I have a Military K-5 with a c-code 6.2, 700r4 trans Np208 transfer case and 3.73 gears. dual front dampers. coil over rear dampers and a 2.5 inch solid stock drawbar. It was used as an aircraft tug.
N.E. TMRPR
07-18-2007, 16:44
I have a 84' m1009 body and rolling chassis that I am getting ready to repower. I was going to use a 91' 6.2 with a 700r w/208 set-up. Will the stock 3.08 gear ratio make it too much of a dog for a daily driver. The previous owner of the trans had it rebuilt HD so I'm not afraid of burning it up in 1st. Will the mileage be bad or decent. I do have the axles from the 87' Jimmy that also donated the trans. They have also been redone with a Detroit locker in the rear but the 84' chassis is very low mileage and all springs, shackles, brake lines are like new and I don't want to mess with them if I don't have to. I believe the jimmy axles are 3.43's or 3.73's. I will check. I see here that most recommend the 3.73's but most my driving will be at around 75mph. All comment are appreciated.
When I bought my blazer it had 3.42 gear and 31X10.50.15, I then went to 32X10.50x15 and the performance went down alittle but would still do 70+ mph then I went to 33x12.50.15 and driving on the highway sucked it would take 1/2 mile to get up to 70. So I started looking around for axles. I found a large supply on the net ranging for 100,000mile to fresh rebuilds. My next plans is a going to be a Lunch box locker or the Auburn Ected locker for the front diff. You need to think what your use of the truck is going to be on how hard and what you future plans for the truck like towing, DD, offroading, tire size.
I've allways been a big fan of 3.73 gear for gas and diesel for DD. Swapping axles isn't a big deal.
There are a few freeks M1009 out there. I work of a company in Detroit Mi that did the conversion for GM to the Military and converted some m1009 to Sm420 trans, Locker F/R. It depends what there mission were. By far I'm not a pro at diesel or gas truck. I just tell what I know from build my trucks.You got CUCV here the link to Steel Soldiers
SimonUK,
Check your fram rail for hole be you transmission cross member. I could have come that way or someone could have done the swap.My some time trans swap is going to be a 4l80E trans.
M1008
http://www.steelsoldiers.com/index.php?module=pagesetter&func=viewpub&tid=2&pid=1
M1009
http://www.steelsoldiers.com/index.php?module=pagesetter&func=viewpub&tid=2&pid=0
M1028
http://www.steelsoldiers.com/index.php?module=pagesetter&func=viewpub&tid=2&pid=5
M1028A1 This is the Big Daddy
http://www.steelsoldiers.com/index.php?module=pagesetter&func=viewpub&tid=2&pid=27
I have a 84' m1009 body and rolling chassis that I am getting ready to repower. I was going to use a 91' 6.2 with a 700r w/208 set-up. Will the stock 3.08 gear ratio make it too much of a dog for a daily driver. The previous owner of the trans had it rebuilt HD so I'm not afraid of burning it up in 1st. Will the mileage be bad or decent. I do have the axles from the 87' Jimmy that also donated the trans. They have also been redone with a Detroit locker in the rear but the 84' chassis is very low mileage and all springs, shackles, brake lines are like new and I don't want to mess with them if I don't have to. I believe the jimmy axles are 3.43's or 3.73's. I will check. I see here that most recommend the 3.73's but most my driving will be at around 75mph. All comment are appreciated.
I have 3.31's with a 700R4 and 235/75/15 tires. I would not want a higher gear than that. It bogs slightly if I lock the torque converter below 50-55mph in high gear.
sparkylisle
08-24-2007, 07:53
It will be on the RPO code list in the glove box, that can be decoded HERE (http://www.thedieselpage.com/members/rpocodes.htm).
Or, you can jack one wheel, rotate it 2 times and count the rotations of the driveshaft. If you have limited slip or a Detroit type locker (one wheel won't turn with the other on the ground), you will have to jack both wheels, rotate it once (with both wheels turning the same), and count the rotations of the driveshaft. Each gear ratio will increment by about 1/4 turn of the shaft. ~4 turns will be a 4.10, ~3-3/4 turns will be a 3.73, ~3-1/2 turns will be a 3.42, ~3 turns will be a 3.08.
GQ1 is standard gears, is that 3.54????
DmaxMaverick
08-24-2007, 13:09
GQ1 is standard gears, is that 3.54????
3.54 is not a standard gear for GM light trucks. The gears would have to be 2.73, 3.08, 3.42, 3.73, 4.10 or 4.56. Anything else was not a factory option, and many of those were not available, depending on the base vehicle and options.
There should be, or was, a tag on the diff indicating the ratio. I haven't typically seen the tags survive beyond a few years (probably for assembly line convenience or confirmation, with no future intention). There should also be a RPO indicating the ratio, even if it has GQ1, but I've seen some w/o. If you have any doubts, it is easy to count the turns, or count the gear teeth when you do a service (cover will be off). Some of the gears have the tooth count stamped onto the gear, but not all, and sometimes it can't be seen w/o removing the gear. If you are not the orginal owner and are not familiar with the history of the truck, RPO codes and tags are not certain in any case. Gear changes are not uncommon, especially if the vehicle was used a lot for towing.
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