I have a 91 GMC Sierra 350TBI 2wd ext cab, long bed and a 91 Chevy Camaro 305TBI, 700R4, that are both open axles :(. I think the Camaro is 2.73 but the truck I have no idea. The Camaro I would like to get more acceleration out of, so I'm thinking 3.73 gears(?), but the truck I want the same or better gas milage(currently 15mpg hwy)
What gear ratios would you recommend and what are ALL the parts I need to do the conversions?
Also, is there more than one type of posi? I read about gear types and clutch types. Are they 2 different things? Which is best?
Well LF, We need to figure out the ratio that is most important. If you give the vin numbers to the dealership I am sure they can let you know the ratio the vehicle was equipped with.
Now for the posi units. there are 3 major types of posi (real industry term is Limited Slip Differential) Posi is a chevy term / nick name for limited slip. Mopar term for limited slip is sure grip etc. every car group had a name for their limited slip diffs.
Ok now the LSD units
- clutch type LSD
- uses a series of clutch discs preloaded by a center mounted spring and cage kit. 200 400 800 pound preload springs.
- examples of clucth type units are (Eaton, Trac lok (gm 1970 -1980))
- Cone type LSD
- these type units use 2 conical pieces off casting that fit a matching degree cut conical case pocket and is also preloaded by springs for pressure into the case to make the metal machined surfaces grip each other. spring pressure very again
- example is a auburn factory and after market
- Helical gear LSD
- These units are one of the newest design in factory cars. They use sets of tubular helical cut gears that slide from side to side upon forces put to it from turns. staight away the helical gear usually a set of 8 are contacting both sides of the side gear makeing the LSD effetive and has very well mannered feel in turns. Very good in rally cars. There are no clutches to wear or get weak. Unit tend to run hot though so good fluid is a must. I have not fully tested these unit as far as power but I have heard good things about them.
- examples are torsen gleasen factory camaro firebird, true trac after market .
- then there is the locker area.
- these unit rachet and mechically lock up and disengage totally
- GM has a eaton governer locker unit which acts like a open when not needed and locks up into a posi when slippage is encountered. Then disengages again when not needed. Saves gas clutches etc. I do not recommend these for all out race performance or cars that like to do burn outs alot.
I hope some of this info has helped you deside what you would like to do. all unit work well. I is just usually a preference on the owners part...what you prefer. I have all of these units in stock new and used. Plus gears for both truck and car.
Recommendations: I really would like to know the ratios you have and what your intentions are with both.
You said you want better gas mileage from the truck. What size tires are you running now diameter or size will help. you might be able to go to 3.08 or 3.23 which might help get your mileage in check. most came with 3.42 if it has overdrive. You really have to watch how low you go with a overdrive because when it gets into high gear you may put such a load from the freeway gear the engine will not work efficiently and get even more gas trying to move the truck at such a low rpm.
Camaro; If you like low end performance 3.73 is a very good choice it will defently wake that car up if you have only 2.73. again we need that ratio to know where to begin.
Were always here if you have more questions or would like pricing on anything.
The dealership says...
The Camaro is 2.73 open axle
The Sierra is 3.42 limited slip
I jacked the camaro up and turned one wheel, the other one turned backwards. They both turned very easy. While I had it up and running in gear, both wheels were turning forward, but I was able to stop one wheel. I did the same thing on my truck, and when I tried to turn them by hand, the left one I had to really force and barely managed to turn maybe 1/16th of a wheel revolution before it hit something and stopped. The right one wouldn't budge at all. when I ran it up in the air, only the left wheel turned. Is that how limited slip is supposed to act when it's up in the air? Driving though, the truck doesn't act like it has posi. When I'm at a stop and turning right to pull out onto a main road, it will spin for days and days. When it's cold or rainy it's about impossible to keep it from spinning. I have to get off and back on the gas 2 or 3 times before I'm going fast enough to where it won't spin, but apparently it does have posi. I wonder if a locker would be any different? It may just be a result of it being light in the rear it being a pickup, and the wheelbase so long... I wonder if lowering it an inch or two in the rear would help?
I'd like to hear prices for the camaro, 3.73 gears new and used, gear or clutch type posi new and used. For the truck, I would probably keep the same gears, so how much for a new or used posi IF it needs to be replaced, and can't be rebuilt? and complete/mega install kits for both.. wheel bearings and seals and everything?
Well definetely sounds like the camaro is a open...the truck however might have a gov lock unit as I described in the last unit in the LSD diff section . will act like a normal open till it is needed. It could be worn out or not working properly too.
Prices:
10 bolt 7.6 camaro with 28 spline unit
- torsen posi is 249.99 used, 359.99 new for a 3 series (3.23 3.42 3.73 4.10 and up)
-eaton posis are more expensive 449.99 (nothing used)
-gears are 159.99 3.73 3 series carrier
- 2 series carrier 3.73 189.99 for 3.08 2.73 2.56 and down carrier
10 bolt chevy truck 8.6 30 spline axle rear
- I have great new Eaton type clutch posis for 8.6 for 389.99
- I have used auburn posi units also for 199.99
- I also have the torsen /true trac units also for you truck at 389.99
You can pretty much get anything you want for the truck rear they make alot for those rears.
Rebuild kits :
10 bolt camaro is 79.99 +30.00 for the axle bearing to make it a mega kit is 109.99 total.
10 bolt truck 8.6 rebuild kit is also 79.99 + 30.00 for the mega axle bearing kit 109.99
These kits will include all your shims marking compound bolts nuts seals bearings races gasket lock tight everyhting to completely redo the differential.
Please do not forget shipping too. If I have your zip I can get you a guesstimate on that too. Jim
:(. I think the Camaro is 2.73 but the truck I have no idea. The Camaro I would like to get more acceleration out of, so I'm thinking 3.73 gears(?), but the truck I want the same or better gas milage(currently 15mpg hwy)