Guys is the 42RH transmission a 904 series with 4 speed overdrive? Is is compatible with a 904 installation? Are they stronger than a 904 ie 5 band?
What is a 42RH Transmission?
- Thread starter 340inabbody
- Start date
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I don't think the work that needs to be done, is worth using a 42RH. Tail shaft is larger, (You may have to mod the floor pan) drive shaft is different length, I think the trans mount is different, no speedo cable hook-up. I'm sure there are other problems.
TT5.9mag
Two atmospheres are better than one
42RH is a hydraulically controlled 4 speed automatic overdrive based on a 904. Compatible, no, work has to be done to fit one in a Abody due to length and girth. They are typically behind 3.9 v6s and 318 v8 s so I’d say they are similar in strength to a 904. But can be built to handle a good amount of power.
Professor Fate
Push the button, Max...
Basically the A500/42RH is the OD version of the A904 family. Hydraulically controlled as opposed to the 42RE which is electronically controlled. They were used in V6 and 318 Dakotas, vans, and light duty pickups.
The big overdrive housing on the tail of the transmission necessitates substantial floor pan and transmission crossmember modification, as well as fabrication of a new transmission mount in order for it to work in an A body.
42RH still has a speedometer drive that is compatible with the gear and adapter housing from the 904; many used a drive that mounted a VSS, just remove that and install the standard speedo drive. You will most likely need a longer cable since it is located further to the rear on the 42RH.
The big overdrive housing on the tail of the transmission necessitates substantial floor pan and transmission crossmember modification, as well as fabrication of a new transmission mount in order for it to work in an A body.
42RH still has a speedometer drive that is compatible with the gear and adapter housing from the 904; many used a drive that mounted a VSS, just remove that and install the standard speedo drive. You will most likely need a longer cable since it is located further to the rear on the 42RH.
Got it thanks guys
No floor pan surgery necessary, at least not when I put one in my Duster. Torsion bars cross member needs to be skinnied up in the trans tunnel though. New trans mount cross member does need to be fabricated. I may have better pics at home.
Cley
Cley
67Dart273
Well-Known Member
There are (or were) 1 or 2 threads on here with photos on the crossmember mod. Most guys use a healthy piece of strap steel to form a hoop up under the floor to bolster the strength that was removed when cutting down the upper mount. I don't remember I think Greg, Trailbeast? posted one thread
So an unrelated question. Is there any way to determine if a transmission (904) has been “rebuilt” without opening it up?
May be some tell-tale signs of the trans. being removed, bolt head witness marks, trans. lines witness marks etc. but, I don't think there's a way of telling it was rebuilt unless the pan is dropped, at least.
There are several folks using the RH42 behind smallblocks here (including me). As stated above there is work needed to the torsion bar carrying frame member along with a serious heavy duty crossmember to take up the slack for what you cut out. That is most easily accomplished using a US Car Tool crossmember that they offer for an A516 in an A-body and modifying it. Yes you need a shorter driveshaft. There is only some mild massaging with a large hammer on the floorpan, that you will forget about once the carpet is in the car. No cutting and welding of the floor.
This trans is probably not the best for a very high horsepower motor, but for a mildly hotrodded 318, 340, 360 it is great. In addition to the serious overdrive 4th gear it has lower first and second gears than the old 904 and uses a lock up converter. I can cruise at 75 on the interstate at 1900 rpms.
This trans is probably not the best for a very high horsepower motor, but for a mildly hotrodded 318, 340, 360 it is great. In addition to the serious overdrive 4th gear it has lower first and second gears than the old 904 and uses a lock up converter. I can cruise at 75 on the interstate at 1900 rpms.
2.94s, but if I think I'm headed for 3.23. With the overdrive you could run 3.91s on the street and still cruise at 75 at 2400. I think Trailbeast is running 3.55s in his with that trans. When figuring it out don't forget the lower first and second gears compared to a 904.
here is the gear spread:
Trans 1st 2nd 3rd 4th
A904 2.45 1.45 1.00
RH42 2.74 1.54 1.00 0.67
here is the gear spread:
Trans 1st 2nd 3rd 4th
A904 2.45 1.45 1.00
RH42 2.74 1.54 1.00 0.67
slantsixdan
=..=
Particularly a pre-'67 A-body. Very detailed thread with pictures here.
JDMopar
Well-Known Member
That dude had some crazy good metal skills......then fell off the face of the earth and dropped the thread.
TrailBeast
AKA Mopars4us on Youtube
Yep, 42RH with a 3.55 sure grip in an original 73/74 8.25.
The Jeep Grand Cherokee gears fit with different carrier bearings and the disc brakes bolted right up.
Adding the disc requires longer wheel studs.
The Jeep Grand Cherokee gears fit with different carrier bearings and the disc brakes bolted right up.
Adding the disc requires longer wheel studs.
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