OBS 4x4 nv3500 into NBS 4x4 Silverado

This is for anyone wanting to put a OBS 5 speed (newer internal slave cylinder style) into a NBS Silverado from my own experience.

The reason for this conversion was my desire for a 5 speed in my auto 99 Silverado 4x4 and the limited availability and higher price of the proper NBS nv3500 in my area.

This was a very budget friendly swap, I have seen a few write ups where the older nv3500 tranny (external slave, clutch fork style) was mated to a LS1 motor where an extended throw-out bearing was used to compensate for the difference in bell housing depths from the OBS to the NBS trannys. Without a NBS nv3500 to compare to, I found that the OBS tranny bell housing was roughly about 0.250in deeper. A few other very quick (rough) measurements showed that the difference in the input shaft are not really significant to the swap as far as the pilot bearing and clutch spines are concerned.

I used a 5 speed out and transfer case of a v6 97 Silverado (same tran mated to the 5.7 trucks) which had the internal slave cylinder in place of the original 4L60e in my truck. My truck is a 99 Silverado with the 4.8L motor (with a 5.3 motor sitting in my garage I am able to confidently confirm the crank shaft etc are the same with the auto 4.8 and 5.3 motors) so this swap would also work with the 5.3 version trucks as well.

I used a slave cylinder for the NBS 4.8 5 speed trucks. Reason being, the quick disconnect fittings on the clutch lines are located in different positions on the NBS vs the OBS trucks. The use of a NBS master cylinder was necessary do to the different (pedal to master cylinder) shaft lengths NBS vs OBS. The NBS shafts are longer and the quick disconnect fittings on the NBS hydraulic assemblies are found under the hood vs OBS which are down by the tranny. I had trouble finding the hydraulic line with the roll pin fitting on one side and quick disconnect fitting on the other for the master cylinder so I bought a steel braded line for a 2001 Camaro and it fit great (a little to long length wise but worked fine) with the same fittings as the trucks have.

A 4.8L 5 speed flywheel was used as well. A 5.7 fly wheel will not work on the NBS trucks. My clutch assembly is a early 90s style. I found that the older clutches are a little larger than the later 90s clutches and would allow more surface area of the clutch to the 4.8 flywheel. Id imagine a 4.8 clutch assembly would work but they are much more expensive (budget friendly swap).

The mounting of the pedal was a little tricky. After seeing where the mounting is supposed to be under the dash, I simply welded a few nuts to the bracket already present under the dash. It was a little awkward but worked fine for me. There maybe another way (use your imagination).

To compensate for the bell housing depth difference I just used two nuts as spacers behind the slave cylinder and bought longer bolts. these nuts (or in my case spacers) measured about 0.350in which turned out to be perfect. My clutch engages and disengages right in the middle of the travel of the clutch pedal.

The drive shaft from the OBS truck is also needed as well as the reverse light plug and speed sensor plug. The wires must be adapted to these plugs to regain your reverse lights and speedometer (I do not recall exactly which wires but it is not difficult to find out).

I used a pressure brake bleeder that I had from summit to bleed the clutch. I used an extra master cylinder reservoir cap and drilled a hole in the top to place a fitting in it to hook my pressure bleeder to. Bleeding the clutch was a little more tedious then I had expected but worked after I ran a couple quarts of dot3 fluid through it at 7-10psi on the bleeder.

I did not have the computer flashed for the swap but seems to be alright with the stock settings. Does idle high or any other problems that I expected to experience. The truck will not start until the yellow and purple wires found on the original gear position sensor plug are tied together tricking the truck to thing its in park so that it will start. These wires could also be tied into a clutch safety switch as well but I personally do not use those anyways (do to some tricky situations on steep hill start ups in the past wheeling in the woods in some of my other trucks).

here are some part numbers for anyone who would like to try this swap, the clutch came from auto zone about $120 I don't remember the exact diameter of it, 12in maybe? Also, the pedal came from my local auto parts dealer about $70.
Ill also include the bleeder I used, recommend it to anyone, it is a very useful tool I use mine all the time doing brake lines makes the job much quicker.

Hope this post helps ya out!


AUTO PARTS WAREHOUSE

Part #: W0133-1693892
Dorman Products
Dorman Products, Inc. is a leading supplier of automotive products and hardware to the automotive aftermarket. Clutch Slave Cylinder
Dorman
Qty: 1.00
Price: $ 79.95

Part #: S2NFW1050
SACHS FLYWHEEL, NEW -- A high quality flywheel; With 1-year Sach limited warranty. Flywheel
Sachs
Qty: 1.00
Price: $ 89.69

Part #: CE136.66013
CENTRIC CLUTCH MASTER CYLINDER -- 0.69 in. diameter, O-ring type port; Complete with reservoir, switch, and float; Offered in the original aluminum casting body design where applicable; Manufactured under the highest quality standards by OEM and OES manuf Clutch Master Cylinder
Centric
Qty: 1.00
Price: $ 41.43

Part #: TM302CC
TIMKEN ALTERNATOR PILOT BALL BEARING -- A high quality, direct fit OE replacement alternator pilot ball bearing. Pilot Bearing
Timken
Qty: 1.00
Price: $ 29.99


SUMMIT RACING

MCL-139212
Clutch Line, Hydraulic, Chevy, Camaro, Chevy, Small Block, LS1, Each
(Mfr. #: 139212)

MVP-0250
Power Brake Bleeder, 2 qt. Capacity, GM/Thread-On, Kit
(Mfr. #: 0250)

Good write up, so if I use the obs slave cylinder in the obs 96-98 nv3500 no spacers are needed behind the slave cylinder? Setup is going to be 2002 6.0l with 97 obs nv3500

The obs slave cylinder and the nbs slave are the same size and travel length so spacers will be needed due to the different dimensions of the obs bell housing. The travel on both slaves (compressed to depressed) are only about 1in. That being said, if the clutch pedal is all the way to the floor and the slave is at the end of it travel it will be about 0.25in short of pressing the pressure plate fingers to their full potential clutch disengagement potential. Doesn't sound like much but without that last 0.25in compared to the 1in travel of the slave it would be like you were only pushing your clutch pedal 3/4 of the way to the floor.
Basically, the obs tranny sits the slave and input shaft 0.25 further away from the motor than the nbs trannys do.
Hopefully that makes sense....

This was pretty much just a trial and error attempt which is why I just threw nuts in there for spacers. I plan to eventually have a more legit spacer cut out on the burn table at work now that I know what I need.

I have also seen flexplate spacers that some have used when mating a obs 4L60e to a LS motor to make up the differences in depth which could be an alternative to using spacers behind the slave to make up the difference in this application.

Like I said, this was a cheap and quick swap and wanted to use common (stock) parts I could get anywhere. Took a couple measurements, ordered the stuff I thought would work, and tossed it all together in a few hours. My biggest hold up was the master cylinder hydraulic line which I could not find anywhere which is why I tried the Camaro one.

If you where to use the obs slave you would need to use the obs hydraulic line all the way to the roll pin fitting at the master cylinder which will connect to the nbs master cylinder needed for the longer rod length. If I were to do it again I would do it this way if the obs lines would have been good but they were looking rough (quick disconnect was corroded and the roll pin fitting was leaking at the slave on my obs line)

Glad you wrote this up takes all the work and research out of it for me, all I need is to make a slave cylinder spacer. Thanks again, Chase