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To the O.P. I unfortunately don't share such a glowing history with my 4+3. I think a lot of their reputation is due to some shoddy production from Doug Nash Engineering (IIRC the carrier (ball) bearings were assembled with too much lash to preload). Yes they shift/feel differently than the later ZF. I didn't mind the "old school" feel and button OD, but it just didn't hold up (rebuilt professionally back in "94, carrier bearing failure again in 2012).
My advice, drive it. If you don't mind the feel and it shifts, OD engages without hickups it maybe OK. Maintain it, drive it correctly. If it's starting to have issues, don't buy it. If you own it and it's starting to have issues get it rebuilt NOW (before it blows up and becomes unrepairable) or end up swapping to a T5 or T56.
Well, here's my experience with the 4+3: I bought my '85 back in 2013 and was willfully ignorant about the signs. The transmission was very difficult to get into gear and had pronounced gear whine but engaged/disengaged overdrive pretty smoothly and operated normally. The ATF in the overdrive unit which was burned and really nasty (along with the gear oil, explaining shifting resistance), suggesting that the crucial regular maintenance was neglected. I changed it along with the filter as soon as I started driving the car and did it a year after that as a precaution. Not long after, the transmission started grinding into reverse (this and gear whine are a sign of a bad carrier/thrust bearing, common especially on '84 and '85 cars). I drove it about 10,000 miles that way without any other additional problems until a clutch replacement.
A hundred miles or so after a clutch replacement (and everything that goes along with it, incl. hydraulics), the car began to slip in direct drive and overdrive. I naturally attributed this to the recent clutch replacement, and the slippage only became worse over time. I replaced the clutch with only about 500 miles and had everything thoroughly examined, coming up with nothing. The slippage persisted afterwards, only getting worse. The car is now all but undriveable and feels as if the clutch is just 50% engaged under load when warmed up; while OD still engages and disengages, I attribute the slippage to a failure in the overdrive which uses friction plates. However, I think that a complete rebuild is still in order because of the thrust bearing symptom. Sorry to thread hijack, but if anyone here has any experience with such a problem, I'd really appreciate any input.
In any event, I really like these transmissions. I now own another 4+3-equipped car that will be a project rather than a donor. It's a neat system that also works surprisingly well, and the Super T-10 section is pretty bullet proof. Rebuilt overdrive units and well-maintained '86+ units seem to do quite well in terms of reliability and it's a fun gearbox to use in my experience. These 4-speed manuals feel a bit dated but are great to row, and the ability to have the tall ratios on the highway is more than welcome. The fact that overdrive is available whenever you want and engages automatically is another neat aspect. Despite my experience, I wouldn't be deterred from a C4 by this transmission but would pay special attention to reverse engagement, overdrive engagement, slippage, and transmission noises. They really are fun to use and I won't be swapping mine despite that route being financially justifiable. As an added bonus, clutches and the 143 tooth flywheels ('84-'85) are inexpensive.
Last edited by C4+3=/=C7; Jan 22, 2017 at 07:48 PM.
As long as the car is stopped (not rolling) any difficulty with reverse engagement, particularly "grinding" is a clutch problem. NOT a transmission or overdrive problem. Reverse grinding can also be a pilot bearing problem.
If the transmission input shaft is turning because of a dragging clutch, or dragging pilot bearing, it WILL grind into reverse. These maladies also cause a difficult engagement into 1st, but it shouldn't grind because 1st is syncro'd. Reverse is not.
The clutch, FW, slave and master cylinders, fork, and slave pushrod were all replaced (clutch, FW, and slave pushrod twice when clutch was suspected as culprit of slippage). Grinding persisted; perhaps it was improperly bled, though fwd gear engagement was smooth enough. At this point the big issue is slippage and the clutch has been pretty well ruled out. Reverse mechanism in the shifter tower also seems to have broken, though these seem unrelated. I probably should've thrown some Sta-bil in the tank back when I parked it
Last edited by C4+3=/=C7; Jan 27, 2017 at 09:31 PM.
I'll have a video series posting to Youtube soon on a complete rebuild. The pics from the action center were from an article I did years ago. I rebuilt them for GM, did the specials for Callaway and the Challenge cars.
If I am correct, on my "1988" the OD engages automatically in 2-3-4 and shuts off either with the on/off button or fast acceleration. It will work in 1st (no need really), but it is not automatically engaged, you would need to use the OD button to put it on in 1st.
I always liked the DN 4+3, maybe cause it is basically an old style 4 speed and the OD was kind of cool in the 80's.! That said, a 5 or 6 speed would have also been fun too, which of course they changed to in "89".
Was fine for many many years, just had it completely serviced last year, now hopefully will be fine again for many more.! : )
Certain combinations of RPM/Speed will allow OD to remain on in 1st if you've been rowing the gears down without first disabling OD in a higher gear. It doesn't take much for it to disable.
Attached is the chart from the factory chip. If you're doing less than 12MPH all it takes is 1.95% TPS to disable the OD. I have yet to find anyone doing 100 MPH in 1st to test 50%.
If I am correct, on my "1988" the OD engages automatically in 2-3-4 and shuts off either with the on/off button or fast acceleration. It will work in 1st (no need really), but it is not automatically engaged, you would need to use the OD button to put it on in 1st.
Relations between RPM, TPS, and MPH all factor into when the OD will or will not engage. Oh and the pressure switch for the OD preventing you from running it w/o any fluid.
There actually is a "1st Gear Upshift" table in the ECM, but it's blanked out by default. I posted 1st Gear Downshift table from '87 in another post.
I'll have a video series posting to Youtube soon on a complete rebuild. The pics from the action center were from an article I did years ago. I rebuilt them for GM, did the specials for Callaway and the Challenge cars.
I understand that the push button DN OD transmission actuator sends a message to the computer to deactivate/activate the OD. Mine responded to the push-button about 90% of the time, but now does not at all. Upon looking at the connection under the bezel (I surmise it to be the connection), all seems to be fine. The switch that the rod pushes down seems to be fine as well. Does anyone know what might be keeping the push-button from working as it should?
Also, there is a small wrench-head looking linkage beside the gearshift, visible under the bezel that doesn't appear to be connected to anything. When I push the linkage, I hear a brushing sound behind the dash. I don't know what it is supposed to connect to or what its function might be. Any ideas?
Thanks, Jim
