3 speed to 4 speed conversion......

[challenger71]

I currently have a 318 with a 3 speed in my 71 Challenger.  I want to convert over to a 4 speed and eventually a big block. I just purchased a a-833 4 speed that has the 2 mounts but the rear mount was never drilled, so it came out of a b-body car.  I also have a bellhousing that needs 1/10000 taken off the mounting area because it does not fit correctly.  My question is, how many of the 3 speed parts are interchangeable with the 4 speed?  Will the rods, bellhousing, clutch, flywheel, etc all swap over or do I have to purchase 4 speed parts?  I wouldn't normally ask this but the 3 speed is still in the car and I need the car to be movable, otherwise I would take it out. Thanks for your help.

[rottenfish]

I swapped from 3spd to 4spd in my Duster. If I recall, the two transmissions had different bolt patterns on the front, but my bellhousing (aluminum) was drilled for both setups. I don't know if all bellhousings were drilled both ways though. All the linkage was the same, as I used the same bell. If I recall, the year/types of 833's had 3 different size front bearing retainers, and if you have one with a large retainer (OD units were larger I *think*) it may not fit in your bellhousing if it has the smaller hole. I think the retainers can be swapped with minimal issues. The bearing retainer stuff is purely from memory, so double check! On the back end, I used the same driveshaft, but the yoke is larger on the 4spd than the 3spd. Get a yoke from a 727 equipped car, and swap it onto your old driveshaft... I think there is a different U joint required for this. I am not sure what you mean by having to take off 0.00001" off the bellhousing? Obviously the shifter will be different as well. This was all nearly 15 years ago that I did this, and it was an A body, but it might give you a start. I am sure someone else here can clarify any errors.

[Killer_Mopar]

Rottenfish did a good job summing it up. I did the 4-speed upgrade on my dad's car two years ago. The bellhousing is drilled for both trans, so that shouldn't be a problem. The driveshaft should slip in without a new yoke, at least it did for me. Everything on the clutch side can be used again as long as the spline count is the same. The retainer might need changing, they are readily available and pretty easy to install. Only problems I see it that you will need to get a new shifter assembly and find the correct e-body tailshaft for the trans. Good luck

[Chryco Psycho]

you may have an overdrive , the tailhousing not being drilled is typical for the truck OD unit this starts the problem with the brg retainer , there are 3 sizes , 4.35 diam , 4.8" diam  & 5.2 , the OD has 5.2 " , you can easily either swap to 4.8" as the bolt pattern is the same or have the retainer milled down to 4.8" , there is no swap to the 4.35 though as the bolt pattern is totally different so you will need a different belhousing , or you could have the belhousing milled out to 4.8"
You will need a shifter & shift rods 

[Aussie Challenger]

  As above, OD box is usually Aluminium, normal box is Cast Iron. Some A833 std boxes had the small 904 slip yoke, but most had the bigger 727.

[challenger71]

Well I took a closer look at the transmission and here is what I found.  The retainer is 5.2" according to my dial caliper and the case is made of aluminum. However, the tailshaft is made of cast. The bellhousing has 2 sets of mounting bolts and the hole for the trans measured in at 5.1".  This is my problem, I guess I need to mill down the bellhousing 0.1" correct.  I have never had to deal with this so I may be a bit confused.  One person said I do not need to buy all new rods and the other says I do, which do I need?  I know I will need a new shifter.  So the clutch and pressure plate will swap over?  I do need a new throw out bearing for the 3 speed anyways because it is starting to squeal when the clutch is not engaged.  Anyone now where I can get one of those?  How about the trans mount, does that frame piece need to be replaced or will mine work?  Thanks for all your help

[Chryco Psycho]

I would cut the front brg retainer instead of cutting the belhousing , the retainer is far easier to trim to match the hole in the bell
the 4 spd used 3 shift rods , the 3 spd used 2 so you weill need at least one rod for sure even if you can make the 3 spd rods work
I do not know what the flywheel & clutch system was that was used with a 3 spd but I bet it is a 130 tooth flywheel , a better clutch with 10.95 diameter woulkd be a better choice behind any big block though
the throw out brg is available at any parts store for around $30 unless you have the 18 spline trans which yours is not.
the trans mount / crossmember will be the same
the 5.2" brg retainer + alum case has to be a A833OD so the front shift lever will need to go on pointed down not up

[rottenfish]

Yes, chances are that this is an OD trans, so be prepared for that. Not necessarily a bad thing, but you don't want to be surprised if that isn't what you are looking for. When I swapped 3-4, I retained the same flywheel and 10.5" clutch, no problems. As for machining the retainer, have a look for the next size smaller retainer. They shouldn't be too hard to find used, and I believe somebody was reproducing them?

[Aussie Challenger]

  I am going to convert my Challenger from auto to 4spd, the bellhousing I have got has the smaller opening and the front bearing housing is the larger one with the wider spaced bolt holes. Also from memory the bracket that the clutch fork pivots on is fairly close to the hole. I have bought the correct fork and bracket for the E body. Got it from Brewers with most of the other parts needed.
   My car is being transported at the moment so from memory I think I may have to have both machined. I wasn't aware until after I had bought the 4spd that there was one with the bolts further out due to the larger front bearing. This may also be an issue with the above case on an O/D box???
  Any way I am going to have to wait about 5 more weeks until the car arrives to know exactly what I have to do. Hope this sheds some light on the subject.

  David

[Chryco Psycho]

the 5.2" OD  retainer can easily be cut down to 4.8", but if the belhousing has the 4.35 it has to be opened up to 4.8 or replaced to work with the large front brg tranny