The Mystery 5 Speed...and finding the correct fluid

[jc06vmax]

It's about time to give the transmission some attention, primarily to change out the fluid. The problem here is I am not 100% exactly sure what trans I have, making it difficult to decide on the right fluid.

My '89 has had it's guts changed out by a PO who was unable to tell me the fine details. Through my figuring, it has a early 90s 305 TBI, NV3500, and NP208...presumably all out of a K1500. The 305 and 208 are labled...the trans is the problem. Unfortunately it is not a NV4500.

Apparently late 80s and early 90s GM 5 speeds were not created equal. Between 87 and 93, there were 5 different 5 speeds visually similar to the NV3500. Some reccommend Synchromesh, some 80w gear oil...and I have even heard mention of 5w-? oil. The choice appears to be critical as the wrong fluid can wreck them allegedly.

How would I go about correctly identifying what trans I have without taking it apart? Apparently all of these are a mess to work on due to the changes and high prices for parts, so I'd like to stay a step ahead and keep mine running smoothly.

 

[Stomis]

All nv3500 or pre nv3500 variants will live a happy life on syncromesh.

 

[jc06vmax]

All nv3500 or pre nv3500 variants will live a happy life on syncromesh.

So regardless of the specific trans, Syncromesh is the go to fluid? Is there a justifiable difference in going with the GM fluid over the cheaper "equivalents"? The GM fluid seems a little pricey..

 

[jc06vmax]

...didn't think to include a few pics to help ID this trans. I also found these two numbers on the housing but didn't have much luck finding anything specific when I looked them up.







..and just one for what it's pushing

 

[Stomis]

The pennzoil stuff from advance auto works perfectly fine.

And yes thats definately a nv3500 variant. Figuring it out isnt really worth the time lol. Run it until it blows and if you liked it upgrade to a later unit with an internal throwout bearing.

 

[jc06vmax]

The pennzoil stuff from advance auto works perfectly fine.

And yes thats definately a nv3500 variant. Figuring it out isnt really worth the time lol. Run it until it blows and if you liked it upgrade to a later unit with an internal throwout bearing.

I gotcha. It serves me well for what I do. I'll probably pick up some of the Pennzoil and check it out.

Any idea what that hole is for in the second pic? Makes it easy to see the slave cyl working, but doesnt look like there should be a hole to let trash in there..

 

[kennyw]

I'm sure it should have a plug of some sort in that hole.

 

[USSkoval]

My '91 S10 came with that same trans, whatever it is. It held up well for over 200K punishing miles.

I don't understand why everyone thinks an internal slave is better. I don't want to pull a trans just because the slave failed. Also, an external slave is generally much easier to bleed.

 

[jc06vmax]

I'm sure it should have a plug of some sort in that hole.

It's threaded. Guess it would be worth it to hunt down or make a piece to plug it right?

My '91 S10 came with that same trans, whatever it is. It held up well for over 200K punishing miles.

I don't understand why everyone thinks an internal slave is better. I don't want to pull a trans just because the slave failed. Also, an external slave is generally much easier to bleed.

Mine works well. Sounds a little whiney when its in neutral...maybe just a little low on fluid...but runs pretty solid overall.

I had to replace the slave on mine a few months back. Was literally a 5 minute job minus the bleeding. I'd hate to have to drop a trans for a 15 dollar part and a 5 minute job. Did yours have that hole right there where the slave is like in that picture?

 

[USSkoval]

It's threaded. Guess it would be worth it to hunt down or make a piece to plug it right?



Mine works well. Sounds a little whiney when its in neutral...maybe just a little low on fluid...but runs pretty solid overall.

I had to replace the slave on mine a few months back. Was literally a 5 minute job minus the bleeding. I'd hate to have to drop a trans for a 15 dollar part and a 5 minute job. Did yours have that hole right there where the slave is like in that picture?

I seem to remember it having that hole. I still have the truck sitting around, curiosity my be strong enough to go take a look. I do remember there was a grease fitting for the fork pivot stud.

 

[Stomis]

My '91 S10 came with that same trans, whatever it is. It held up well for over 200K punishing miles.

I don't understand why everyone thinks an internal slave is better. I don't want to pull a trans just because the slave failed. Also, an external slave is generally much easier to bleed.

The internal slave really makes no difference in a 4wd application. Its way better for shifting fast in a go fast application though. The recommendation comes from the revisions to the transmission that made it stronger that came along with the internal slave.

 

[USSkoval]

The internal slave really makes no difference in a 4wd application. Its way better for shifting fast in a go fast application though. The recommendation comes from the revisions to the transmission that made it stronger that came along with the internal slave.

My truck is 2wd and that external slave had no problem banging through the gears. You had to be very precise with the shifter, but besides that, it went between the gears very quick. That truck got beat like a red-headed step-child on a daily basis for many years, it always begged for more. The trans even outlasted the 4.3 motor... I think my brother over-revved it. I know it was just a 2wd, but it was also a longbed and it was used for work that even a full size truck wouldn't like. The abuse that trans put up with was simply amazing.

That's my experience with it anyway. Maybe mine held together better than most, I dunno.

 

[jc06vmax]

My truck is 2wd and that external slave had no problem banging through the gears. You had to be very precise with the shifter, but besides that, it went between the gears very quick. That truck got beat like a red-headed step-child on a daily basis for many years, it always begged for more. The trans even outlasted the 4.3 motor... I think my brother over-revved it. I know it was just a 2wd, but it was also a longbed and it was used for work that even a full size truck wouldn't like. The abuse that trans put up with was simply amazing.

That's my experience with it anyway. Maybe mine held together better than most, I dunno.

That's encouraging to hear. Most of what I have read/heard sounds like the NV3500 family is just a waste of time, that they are unreliable and break easily.

I'm not too hard on mine as I just use it for a dd, but turning 35s can't be easy on it. You do have to be precise like you said...if not you'll jerk around some. If you hit it on the spot though, it's butter.

 

[Stomis]

My truck is 2wd and that external slave had no problem banging through the gears. You had to be very precise with the shifter, but besides that, it went between the gears very quick. That truck got beat like a red-headed step-child on a daily basis for many years, it always begged for more. The trans even outlasted the 4.3 motor... I think my brother over-revved it. I know it was just a 2wd, but it was also a longbed and it was used for work that even a full size truck wouldn't like. The abuse that trans put up with was simply amazing.

That's my experience with it anyway. Maybe mine held together better than most, I dunno.

I'm talking like 6000rpm speed shifts with a heavy clutch. Any stock situation really doesn't apply here.

That's encouraging to hear. Most of what I have read/heard sounds like the NV3500 family is just a waste of time, that they are unreliable and break easily.

I'm not too hard on mine as I just use it for a dd, but turning 35s can't be easy on it. You do have to be precise like you said...if not you'll jerk around some. If you hit it on the spot though, it's butter.

Its a common misconception based off the early units. The 96+ units were pretty damn strong and the 99+ units that were behind 4.8 LS motors are even better. Russell will also attest to it. They were upgraded during the internal slave revision without any rating change.

There's guys with Joe Gibs c1500 super charged 4.8s making 400+ wheel horsepower in a 5000lbs truck that have had long lasting performance from late model nv3500s.

 

[USSkoval]

I'm talking like 6000rpm speed shifts with a heavy clutch. Any stock situation really doesn't apply here.

I know what speed shifting is, did a lot of street racing in my stupid years. And not to sound like an ass, but we were talking about stock stuff. And even in most street driven modified cases, an external slave works just fine there too.

 

[Stomis]

I know what speed shifting is, did a lot of street racing in my stupid years. And not to sound like an ass, but we were talking about stock stuff. And even in most street driven modified cases, an external slave works just fine there too.

Tell that the the 100s of LS guys that do the same swap on t56s because they lag when they shift with the stock master and slave...

I'm aware that we are talking about stock stuff. My recommendation had nothing to do with the hydraulics themselves. I only pointed out the advantages of the internal slave because you pointed out the disadvantages. The recommendation of the internal slave is because its a simple and easy landmark to identify when the nv3500 got stonger...

 

[USSkoval]

I know we are a little off topic here, but it is a tech discussion...

Tell that the the 100s of LS guys that do the same swap on t56s because they lag when they shift with the stock master and slave...

LS cars come stock with an internal slave, what would they be swapping for? Debating about the differences is hard when there's also poor factory designs thrown into the mix.

For whatever it may be worth, I run an LT1 style T56 with the external slave and a fairly stiff clutch. Quick shifting is never a problem and the motor is very far from stock. It's been a while, but I seem to remember slightly modifying the hydraulics to improve flow... but that might have been my brother's LS car, honestly I can't remember anymore. But now that I think about it, that car is a good comparison. The modified LS car with internal slave shifted comparable to my car with external slave.

Again, not trying to argue, just having a discussion.

 

[Stomis]

I know we are a little off topic here, but it is a tech discussion...



LS cars come stock with an internal slave, what would they be swapping for? Debating about the differences is hard when there's also poor factory designs thrown into the mix.

For whatever it may be worth, I run an LT1 style T56 with the external slave and a fairly stiff clutch. Quick shifting is never a problem and the motor is very far from stock. It's been a while, but I seem to remember slightly modifying the hydraulics to improve flow... but that might have been my brother's LS car, honestly I can't remember anymore. But now that I think about it, that car is a good comparison. The modified LS car with internal slave shifted comparable to my car with external slave.

Again, not trying to argue, just having a discussion.

A 13/16ths to 7/8 bore master is a big upgrade in order to push the fluid in volume quick enough for a fast shift in an LS scenario when running a heavier clutch. I have seen plenty of guys running aftermarket and GMPP slave cylinders for the internal units. Maybe the necessity for the upgrade is actually due to the internals inherent flaws rather than improvement? Regardless master cylinder selection is pretty irrelevant in a discussions of pros and cons of the salve style, that I'll admit.

Ive also seen a fair share of retrofit guys usings universal internal slaves on 4 speeds, TKOs, richmonds 5 spds, etc. Im not saying the design of an external slave has anything wrong with it. From a personal standpoint I like the internal slave because I think the clutch has more feel to it (if you can even call it that) because theres no fork intermediate between the return on the clutch and the movement of the pedal.


That being said my recommendation of upgrading to an NV3500 with an internal slave really has nothing to do with the slave setup itself. Its because these years are notably stronger than the earlier counterparts and the internal slave just happened to be along for the ride with the upgrades which makes it an obvious way to pick them apart. Just like the early confusion with whats actually an nv3500 or a hm290 or that other POS oddball they had early on. They can be difficult to tell apart, but one thing thats easy in a yard is to go "O there internal slave bell, thats new enough to be stronger"

 

[USSkoval]

I think when retrofitting a trans, an internal slave can be a good option just because of packaging. Which I think is why the OEM's started using them to begin with.

And it didn't take me very long to realize you originally mentioned the internal slave because it's an easy way to identify an NV3500, but by that point, other thoughts were in my head. You can tell me I have A.D.D. and it won't offend me

 

[Stomis]

I think when retrofitting a trans, an internal slave can be a good option just because of packaging. Which I think is why the OEM's started using them to begin with.

And it didn't take me very long to realize you originally mentioned the internal slave because it's an easy way to identify an NV3500, but by that point, other thoughts were in my head. You can tell me I have A.D.D. and it won't offend me

O the header debacle is definitely a plus side to the internal.

its all good lol.