It seems the overdrive went up on my Doug Nash 4+3.

Have considered several options. The Silver Sport Perfect Fit TKO 600 is one of them. They want four grand, though.

Dad thinks we should do the cheapest option, with our rebuilding the overdrive. He noted many improvements have been developed over the years for this unit. Sure, the thing worked while it was working. Yet, really, it is an odd thing, and even though I was accustomed to it, it is far from a typical stick-shift driving experience. On top of that - I do not baby cars. I drive them. While this seems like a fragile, pesky system.

For cost considerations, I was looking to do a ZF6 swap. On the forum, it seems many of you have done it. Yet - one of the techs at Glen Burnie Transmissions, a well-regarded transmission shop here in Baltimore, said it was a bad swap. "You'd be lucky to get over 15mph," he said, which seemed very odd... yet apparently this has something to do with the computer in cars like my '86.

Where should I be looking? What should I be looking to do? What is the best option, versus the most cost-effective one? Many thanks in advance.

 

I have an 86 and it had a transmission swap done to it prior to my purchasing it, I can comment on that only. Mine started with a 4+3 and for whatever reason it has a Tremec TR3550 swapped in. I was under the car on a lift shortly after purchase and from what it appeared it looked to be a swap in. Things like the bellhousing, slave cylinder etc. all look to be original. The C Beam bolts right up to it. I don't know if the drive shaft length was modified or not, I cannot find any indication of that but I don't know. One mod that was done was a DakotaDigital converter was wired into the speedometer to apparently change the signal so it drives the speedometer. Tremec told me that though they don't currently (as in 4 years ago) make this tranny, it is available as a rebuilt unit.

Operationally I think that first gear is a little to low. I would not consider this the best transmission for those powershifting through the gears or drag racing. There's a little too much room in the 5th/reverse area of the shift pattern (5th and reverse are offset so there's more room in that area of the shift pattern) opening up the chance for a missed shift if you're not careful. For normal driving it's fine, just a little too much wiggle room for my taste if rapidly going through the gears. Overdrive works well

That's my recap of the Tremec TR3550 tranny. Hope it helps. Good luck.

PS Know that there are more than 1 type of slave cylinder depending on the age and model. Tranny's like yours and mine have an external slave on them. Tranny's like the ZF have one that fits onto the transmission input shaft so there are additional changes required there.

 

The ZF6 is a wonderful transmission. It's strong, shifts smooth, has great gear ratios and was designed for the C4 Corvette.

It's a bolt in. Your 86 has a 1 pc rear seal crankshaft, so it's very simple swap. You can use all the junkyard/doner car parts (FW, Clutch, Bellhousing, slave cyl ect) to do the swap. It uses a mechanical speedometer drive just like your 4+3. The ECM Computer doesn't control anything on the ZF6.
Will

 

Just curious. Do you know for certain it is an old TR3550 or did you just see that on the tag when you put it on the lift? If the swap was done with a new transmission any time in the last 10 years I would think it is a TKO as I believe Tremec quit making the old TR3550 back in the early 2000s.
My TKO 600 has a TR3550 tag because that is the part number of the case but it is accompanied by a TCET5009 which makes it a TKO 600.

 

When I was under the car I got every number and tag off it I could find and contacted Tremec. They were the ones that told me it was a Tr3550. They said based on the numbers it was made in 2008, I called them in 2013 IIRC. They said at that time you could not buy them new as there was a newer model available but you could get them rebuilt.

 

If it was manufactured in 2008 it is definitely a TKO 500/600 trans.

I was worried that the guy I bought my '84 from lied to me about the trans being a TKO 600 when I had to pull it to change the clutch a couple months ago. Like a stated before, my TKO 600 has a TR3550 tag on it. After I looked into it further I realized it is what the seller said it was.

 

Good to know, thanks. Regardless of which it is, it works well with my main interest being cruising. The main issue I still have is the extra space when shifting into 5th due to the extra space for reverse. I've always wondered if there was some way to make a plate to act as a shift gate, make it a little more positive going into 5th, that's my main complaint on it. That and I think the 1st gear ratio is a little too low.
Oh well, it will likely outlive me.