S S0DEN

I own a 1988 Z51 and I hate the 4 plus 3 transmission on the highway, it needs another gear...

I have begun a 383 build, but when I make the engine swap, I am thinking about changing out the Doug Nash for a 6 speed.

Who here has done this and what can I expect for cost, other aspects of the swap that require customization of the car?

tunedport85inject

take everything from the donor car ,you need everything from the donor,the 4+3 has different bell housing and slave piston and other parts like the throw out bearing,imput shaft splines numbers...lots of minor things.a guy in my club has just completed the swap and he found lots of little issues becouse he was missing parts from the donor.just one advice take everything from the donor.

S S0DEN

I was afraid of that, I was hoping to just buy a trans on Ebay and adapt the slave...

tunedport85inject

For example he found a dual mass flywheel on ZF6 vs a single mass in the 4+3 consequently he had shorter bolts than needed,just a litle issue,then he said that the starter has a difrent lay out on a 4+3 bellhousing and he needed a new starter .Another issue was the oil line hose from the Master to the slave different thread ,he needed a new ZF6 oil hose.Another issue was the yoke on the driveshaft,he needed a new yoke to match the Zf 6,lots of little thinghs to deal with,pay attention to everythings or you may slow down the swap cuz you miss right parts.

vetteoz

The ZF6 swap bible

http://members.cisdi.com/~anesthes/zf6/

hcbph

I've read about issues with the ZF6 - like the DM Flywheel etc. Have you considered any other tranny? My 86 started with the 4+3 and a PO had replaced that with a Tremec 5 speed. From what I can tell, it has original master & slave, bellhousing, driveshaft etc. The shifter even fits in the original hole from what I can tell. Far as I can tell, looks like the one real issue was the need for a Dakota Digital converter for the speedometer.

All I'm suggesting is you consider all your alternatives, some may be a little better than others.

Paul

S S0DEN

I am looking for a 6 speed, the 4-3 already is a 5 speed.

tunedport85inject

i would definitively go with a black tag ZF6,it's doable .

hcbph

I wasn't suggesting that you put in a 5 speed. Rather that the tranny can be replaced without having to throw out everything to do it. Mine was already replaced with a 5 speed and in my situation it works out, just using that as an example.

Tremec sells a 6 speed. Richmond sells a 6 speed. Far as I know neither has the same issues with things like the unavailable Dual Mass Flywheel or if something else is used all the noise and clatter. Seems like there are a lot of negatives in using the ZF6 tranny, though it was sold by GM that aren't present in the aftermarket tranny's.

Just offering some thoughts.

FOURSPEEDVETTE

[QUOTE=S S0DEN;1586701896]I own a 1988 Z51 and I hate the 4 plus 3 transmission on the highway, it needs another gear...






The rpm's are really low at highway speeds with a 4+3 transmission. In overdrive, it's totally capable of going 150 mph and it downshifts and upshifts automatically if you kick the throttle down. Wow, how fast do you go?

S S0DEN

[QUOTE=FOURSPEEDVETTE;1586707815]I may have a set of gears, because at 70 MPH, and O/D on - I am over 3,000 RPM's, speed limit here is 75...

FOURSPEEDVETTE

[QUOTE=S S0DEN;1586708643] You must have something different than stock. I have a stock 3:07 Dana 44 rear end in my 85. My rpms are way lower than yours at 70 mph when I'm in overdrive. Previous owner on yours must have put different gears in for higher torque at low speeds. Although what the factory initially installed was a pretty good set up right out of the box to give you plenty of torque.

S S0DEN

[QUOTE=FOURSPEEDVETTE;1586711630]Yeah highway driving is annoying and expensive.

Slow86vette

Instead of doing a zf6 swap like they are saying, maybe you should look into a t56 swap out of a t56 lt1 car or an fbody. A t56 will e much cheaper to rebuild and will be easier to find parts for and just as strong with more shifter choices aswell. You have to use an lt1 t56 though, as the ls t56's have a different input shaft and it won't work. You can find an lt1 t56 for $800 pretty easily, then just need hydraulics and a clutch.

c4cruiser

[QUOTE=FOURSPEEDVETTE;1586711630] My '87 with the 4+3 and 3.07 gears runs at just over 1600 RPM at 70 MPH. Without the OD being engaged, the same MPH results in about 2700-2800 RPM.

Are you sure the OD is working? 4th gear and no OD is a 1:1 ratio. The OD ratio is something like .62 or .68 (depended on the year) and a ZF should be .50 in 6th gear. Even with the L98 cars and 6-speeds, the top speed of the car will be seen in 5th; 6th gear is for cruising only and stock L98's won't have the power to overcome aerodynamic drag to reach 150 or so.

You should check the diff gear ratio to see what you have.

project C4

that thing must have some 4.11's in it or something. if it does you will never get the rpms down where you want them to be at 80mph. I have the same problem around here. speed limit is 75 and everybody is actually going 85mph. I drive to work with 2.41 gears and no overdrive @ 85mph.
A buddy of mine at work likes the LT1 Trans-Am's. He has had a few them. His favorite combo is 2.73 gears with the 700 overdrive.

hooked073

have you though about changing your gears? It may be the cheapest way to go.

hcbph

If you're getting over 3K rpms at 70, either you're stuck in 2d (that's a joke) or you have had a gear change. My old Dodge with 4.10's, no overdrive ran over 3K at 70.

Quick check, jack the rear end up. Mark the driveshaft and with the trans in neutral, rotate a rear wheel. Count the rev's on the drive shaft and I suspect it will be 4+, confirming it's not the original gears in it.

My 86 with the Tremec runs somewhere in the 1600-1800 rpm range at 75 in OD, just for comparison against my 3.07's.

Rohn

Hurst driveline conversions is plug and play but for a cost. Keisler is about to come back out of bankruptcy and offer once again plug and play. Not sure if there is a third P+P option.

pezter22

I looked into swapping a ZF6 into my '84 because my 4+3 OD unit is dying. It looked like too much work. I also looked into rebuilding my 4+3, but that would cost nearly as much as a new Tremec.

So I am opting for a Tremec TKO600 from Hurst Drivelines. The price a bit hefty at $3800 with free shipping. But it's a complete kit, so no hefty customizing except for a slight trim in the trans tunnel for the shifter.

Their online calculator tells me that with my 3:07 gears and 17" tires I will be cruising 70mph at 1800rpm.

Hurst tells me my Tremec will be shipping this weekend.