Gearvendors Overdrive
 

As I begin to drive the '72 Jimmy. I'm definitely looking for a way to add an overdrive unit.

I currently have a new/rebuilt turbo 350 transmission. I have 33" tires with 410 gears.

I would like to place a gear vendors unit behind the transfer case, and I would like to hear from anyone who has used gear vendors in their Jimmy, or Blazer.

Please let me know if you have utilized this setup.

Thanks,

Pat

Re: Gearvendors Overdrive
 

Member cleszkie is running one on his K5 with a double cardan rear shaft, it’s a pretty cool rig, check it out.

Re: Gearvendors Overdrive
 

Thanks!

I sent him a message, so hopefully I'll hear from his soon.

Pat

Re: Gearvendors Overdrive
 

Too expensive, and I would like to know how in the world anyone would be able to adapt one to a 4WD Blazer.
The most economical way to do it is to get rid of that TH350 and build up a 700R for half the cost.

Re: Gearvendors Overdrive
 

As much disdain as I have for the 700, I'd have to agree. If you have any type of lift kit on your K5, driveline issues become apparent really quick---even with a CV. UNLESS you move the engine forward; but that is limited to about 2-3 inches and will only work with about a 4'' lift due to oil pan clearance.

BTW: they do have adapters for bolting one to a 205 t-case, but you have the length of the adapter and the length of the OD unit

Re: Gearvendors Overdrive
 

Pat - fwiw I have 33" tires, th350, and 3.73s and this combo works well for the mostly non-hwy driving I do with the Blazer. I do drive it at 65 mph or so. I also have a 700r4 in my K20 and that works well with the 4.10s. However, there is a minuscule amount of clearance between the tranny pan and the U-joint on the front shaft.

Re: Gearvendors Overdrive
 

Forgot about that---I've actually had to clearance the pan slightly in the past to get a little more room if the joint starts to go bad

Re: Gearvendors Overdrive
 

I have the same combination and find it to be a good balance for highway, city, and off-road (not rock crawling) driving. Would I like an extra gear on the freeway? Sure, but I can buy a lot of gas for the price of an overdrive.

Re: Gearvendors Overdrive
 

Yea, now I wish I would have went with 3.73's. I could possibly have lived with that, but this with 4.10's.…..I'll have to do something.

Pat

Re: Gearvendors Overdrive
 

Thanks for the responses guys. Looks like I change the gear ratio's, or the transmission. Either ones not a lot of fun!

Re: Gearvendors Overdrive
 

4.10 is the perfect gear for 33's and an overdrive. That's what I run, but I have the 5.3 and 4L60E. At highway speeds, my engine runs around 1800-1900 RPM which is perfect for that generation of engine. Older engines like to run slightly higher, around 2500-2600 RPM at highway speeds. I think you will find that 3.73's will be a bit boggy and will actually use more fuel at highway speeds when the OD kicks in. FWIW, I get slightly over 20MPG with my current setup, and have way more power than what I need.
Why not consider replacing the engine as well as the transmission with something late model? You definitely won't regret it.

As far as the 700, it had issues for sure, but the aftermarket industry has fixed most problems. If you get all the good parts, a 700 should last for years if not abused. The same can be said for the 4L60E. The pan clearance mentioned above is not really an issue because it's only a matter of modifying the pan a bit.

Re: Gearvendors Overdrive
 

Here's an example pic of how close the corner of the 700r4 gets to the U-joint: http://67-72chevytrucks.com/vboard/s...5&postcount=11

Re: Gearvendors Overdrive
 

Yep mines the same..w/in .25" for sure. Except someone mentioned above you can't go more than 4" lift...i have 6" :smoke:

Re: Gearvendors Overdrive
 

Yes, I have been running a GV unit for many years in my Blazer. Not a single regret. I run it behind an SM465 and NP205 combo. Bulletproof and allows me to split all forward gears in addition to overdrive. A 700r4 is fine for light duty. But I tow heavy loads up mountain passes (27' boat and car hauler) and the GV allows me to do this without breaking a sweat or generating a huge amount of heat.

By the way, the GV mounts behind the NP 205. So, you only get the benefit of it in two-wheel drive. But I have never needed gear splitting or overdrive in four-wheel drive.

Driveshaft angle is not a problem. I sourced a series 300 CV/slip yoke combo from an old Cadillac that is much shorter than a standard CV joint. The slip yoke goes into the GV unit instead of running a standard fixed CV yoke. I run 2.5 inch lift springs combined with a Dana 60 and 14 Bolt FF axles with 3" tubes which gives me something like a 4"-6" lift over stock. I run 35" tires with no issues and no trimming (see my avitar).

Re: Gearvendors Overdrive
 

Thanks for the information!

Unfortunately, I spoke with Gear Vendors yesterday.

They discouraged the use in the Jimmy/Blazer, but I told them about yours with the CV joint. They replied that it would possibly work but they couldn't guarantee no vibration.

Then I told him that you were running a manual, and mine was a turbo 350.

He said that could be why you were able to run it, as the manual is about 3" shorter than the automatic.

He strongly discouraged the use as the 3" loss is vital in this case.

Now....thinking about switching over the manual and installing an NV4500.

Thanks, Pat

Re: Gearvendors Overdrive
 

Correct me if I'm wrong, but the location of the transfer case makes no difference on the type of transmission. The transfer case is located in a set position, and everything locates to it. That's why the LS swap requires the engine to be move forward.

Re: Gearvendors Overdrive
 

Ummm, yeah, about that..... Location of the drive train in the K series trucks in these years was dependent upon the front diff not hitting the oil pan with stock suspension. There were different variables regarding engine and trans combos. The t-case was always relatively close to the same spot but not fixed

Re: Gearvendors Overdrive
 

Yea....honestly, I just don't know. Hopefully somebody else will be able to provide additional information.

Pat

I really can’t see GM putting the T-case in different positions. If they did, they would need different front and rear driveshafts, plus the shifter would be in different positions. I think there’s only one spot for the T-case, but I might be wrong.
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Re: Gearvendors Overdrive
 

I don't know this for sure, but I'm guessing that's why you couldn't get a big block from the factory, because the transmission and transfer case would have to be moved forward for the engine to clear the firewall.

Re: Gearvendors Overdrive
 

SM465 is shorter than a TH350 - but there is an adapter behind the 465 which is cast iron IIRC and that makes up the different I presume.

Re: Gearvendors Overdrive
 

Just a suggestion if looking at an NV4500 5speed. Consider a 1995 unit from a big block or diesel. Certain features of this model to consider, if not doing rock crawling. Easier install, improved shifting, gear ratios. Can order from trans rebuilder with warranty. Purchased mine a few years ago 1300.

Les

Re: Gearvendors Overdrive
 

FYI - When I swapped my TH350 for the SM465 I found that the length of the TH350 is EXACTLY the same length as the SM 465 with adapter. No change in position of the NP205. Those dudes at GM were no dummies.

Re: Gearvendors Overdrive
 

I like reading this!!

Thanks for the time to post on here.

I do have just a few questions:

I read where you utilized a 300 CV joint out of an early Cadillac. Can one still purchase one of these?

Did you tilt the rear carrier up a bit?

How long is your rear driveshaft?

Any vibration?

Thanks a bunch!

Pat

Re: Gearvendors Overdrive
 

I couldn't tell you where to find another Series 300 slip yoke/CV combo. I got mine (used) from my local drive shaft shop. I think it came out of an 80's Eldorado.

I did rotate my rear housing. Cut off the spring perches, rotated the axle and burned the perches back in. When using a CV joint, the pinion yoke on the rear axle must point straight at the transfer case output. You don't want any angle in the driveshaft on the axle end (maybe 2 degrees off to take into account slight axle wrap under load). You don't split the angle between both ends of the driveshaft like on a conventional u-joint set-up. All of the angle should be in the CV joint.

I will get you a picture and some measurements. Don't have any handy.

No vibration. Should be noted that I installed a traction bar. So, I get no axle wrap or other changes in the pinion angle that could cause vibration under load.