telidor99

Question:
If I went from a 3SPD auto to a 4spd Auto what all would I need? Is there a certain year 4spd that would be better than others? What problems would I encounter down the road with a 4spd over a 3? Should I just remain with a 3spd and get it replaced/refurbed?

Parths I think I would need
Obviously a 4spd tranny
4Spd TT
New Shifter


What the Car is doing:
Car starts, but wont go into gear.

In the past the car would some times hesitate then grab when it shifted.
After taking the car home from the shop I hear a clank and a pop..then the car made a whining noise that sounded like a TT problem coming from the middle of the car. Noise sound seemed to change when it was shifted from D to R (etc)

my thoughts:
If I am going to have to spend a number of thousands on a 3spd..would it be better it get a better performing 4spd for a few thouusand more.


My Car
1981 Row 3Spd Auto

heinrich

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Vilhuer

Get '83-86 gearbox. Torque converter is smaller than in '87+ making it easier to install. S4 and GTS stuff needs body mods in rear seat area. '90+ PSD diff would be useless anyway without all electronics etc.

telidor99

Vilhuer:
How much of a acceleration gain will I get going from a 3spd to a 4spd?

Vilhuer

Impossible to say for certain as in both US and ROW models there were engine changes done at same time when 4sp auto was introduced. US got 4.7L S engine in '83 and ROW S jumped from 300 to 310 in '84. As ROW change was smaller it might be little better indication what effect gearbox had in it. Factory numbers are 7.2 and 6.7 second 0-100 kph (0-62 mph). About .5 second improvement is probably likely in almost all 3sp cases.

telidor99

hmm.. I had heard that the 3spd w/ my 4.7 engine was causing slow acceleration (3 speeds over 170mph) and that 4 spd had much faster take offs.
When a automatic 2 door truck was accelerating faster than I..felt my tail inbetween my legs.

Podguy

Here is the deal. If you are replacing the three speed with a US model four speed then you will be changing the differential final drive from about a 2.75 to a 2.20. In the end you will get better gas mileage, but at the expense of performance.

Most of the four speed transmissions start in second gear unless you really push them. You can get around this by tightening the kick down cable or by retrofitting a modulator valve.

The four speed tends to kick up to top gear as soon as you release the gas and has a coast mode in fourth gear. All this is to get better gas mileage to make the EPA happy.

Here is what you will need.

1. A transmission. An 83-84 is your best bet. Some of these were programmed to start in first - at least this is what I have been told, but do not hold me to it. An 85-86 will fit. If you can find a Euro trans then you can end up with the lower final drive ratio and have a nice set up and an improvement over the current 3 speed. Other than that you are looking at a compromise.

2. A torque tube. Three speed torque tubes are a dime a dozen - they never break. Four speed torque tubes break because they are pushing more horses. As a result you will pay a bit to find a four speed tube. Even broken ones are worth something for cores. Count in replacing the bearings - an easy and cheap job. The $25 dollars in bearings is well worth paying.

3. Flex plate for the front and maybe a new flywheel. Do not hold me to the flywheel but don't rule it out either.

4. Shift linkage. This comes out as one unit. Easy to change.

5. Kick down cable. Connecting one to the transmission will take almost as long as the complete conversion. You might have to modify the gas linkage to accomodiate the kick down cable. You may need to run a vacuum line for the modulator too,

6. Maybe a cross member. Again do not hold me to this, but there are some weirdnesses in cross members. I know the 78-79 five speed cross member has to go with the transmission or you come up short.

7. You will have to change some things on the wiring harness. The four speed uses a switch to postion for reverse and the starter lock out. If you get a switch and harness from an 85-86 and a tach with the lights then you can wire up the shifter lights on the dash. Takes a bit of work, but it is a nice touch.

Other than the above i cannot think of much else. I am sure you will find something. Of course for the effort and cost you could convert to a five speed and be done with the automatics completely.

Good luck

Dan the Pod Guy.

Vilhuer

AFAIK this is not needed. Only really different version is '80½-95 manual gearbox. '78-79 manual and all automatics use basically same version. There are different part numbers for different model years but they have more to do with exhaust mounting points than how gearbox itself is mounted.

TAREK

I've done it. Not sure if I would recommend it. If you're paying someone, my advice is DON'T...because they'll nickel and dime you to death for something not worth that much more in the big picture.

I did all the work myself. ANY 4 spd tranny will fit fine. Also you will not need to change the cross member. You will need the shifting cable and kick down cable too. There are compatibility issues with these cables so it would be perfect to have them donated from the same model car as the tranny, otherwise prepare for parts hunting you didn't plan on. You also need to wire up the tach to the tranny, which didn't work for me. Then again I didn't spend much time on it.

I did not feel a significant change in performance in my assometer, except for a more relaxed feel in highway cruising. My car was a '79 US. I also hadn't experienced nearly as many problems with 3 sp tranny as with 4sp trannies. May be the number of gears makes it more complex and less robust? or may be my data sample is not representative of the entire population of trannies out there.

Having been there done that, and despite my strong passion for "modifications and customization", I'd say stick with stock if you want to take the conservative approach. where are you located anyway?

....just my 2 cents.

TAREK

In my experience, no body mods were necessary when using '87 + trannies in a '79

TAREK

...also don't forget to flush the transmission lines and cooler very very VERY VERY well, otherwise you'd be introducing debris into your replacement transmission. Do a search. All kinds of opinions on how to do that. Repetitive pressure flushing using tranny fluid followed by mineral spirits followed by tranny fluid again and again worked well for me. Probably total of 15 flushes. May seem like overkill, but it isn't....and it's well worth it for insurance....that's unless you're willing to pay for all new lines and transmission cooler.

Vilhuer

This is interesting as another '79 definitelly needed mod between rear seats before S4 automatic fitted in. You are certain gearbox was original S4 and not S3 box coming from S4 car for example?

telidor99

tarek:
Atlanta GA (Woodstock GA really).

If my acceleration sucks could autotrans be the problem (over a stick?)
Could my 3spd have been worn and a referbed one have better performance?
Could my 4.7 engine have just wore and its not peforming like it did when new?
Could I have a fuel/something else issue?

When my car was running it would accelerate..then hit a hit 45 or so and really accelerate.


What all I have had done (that could be related to the problem of acceleration)
new sparkplugs/wires
new warm regulator (this acutally made a large diffrence in acceleration..was a boat before that)
new fuel distributor
Tun of vac hoses.
few new fuel injector hoses.
A engine leak down (near perfect according to the tech)
lot of seals.
New battery.

Jim bailey - 928 International

OK the gears for a 3 speed euro are first 2.306 second 1.460 third is 1-1 so times the final drive ratio of 2.75 that makes first a 6.34 second a 4.01 and 3rd is 2.75 .....the 83-84 USA 4 speed has a first of 3.67 second 2.41 third 1.44 forth is 2.20 the final drive ratio so first is an 8.07 second is 5.31 third is 3.17 with 4th a 2.20 ratio ..... So which should accelerate BETTER a 6.34 1st gear or a 8.07 1st gear ? and those are the real numbers. Where is Kibort when we need him ?

G Man

I had an 81' with the three speed and I liked it way more than I like the four speed in my 84'. It just seems like something is not right with it. It drives down the road fine and shifts fine but it just doesn't shift where I would like it to shift. With light throttle It is in fourth by 30mph. I have done the cable adjustment and serviced with fresh fluid and filter.It is still not to my liking. I may send the valve body to Steve C. for a check up. I would find someone with a four speed car you could drive or at least ride in before you go for it.