drb5721 Posted February 19, 2018 Report Share Posted February 19, 2018 Bought my 84 720 under the impression it needed a clutch. Engine runs great and I felt the clutch could be the culprit when I had the engine running and could throw the trans in any gear without any issues without using the clutch. Checked fluid level and slave motion. All looked ok. Proceeded to remove trans in hopes of seeing a clutch fiber furball. To my surprise. No furball. Clutch disc looks relatively decent. So I grabbed the input shaft and the output shaft and could spin them independently of each other regardless of what gear it was in. Seems as if a shaft broke or a gear or something. Very noisy and no fluid came out when I pulled the driveshaft. My question pertains to a replacement. I have a spare S13 KA trans sitting in my storage truck. Bellhousing of course is identical. However, the shifter bolts in whereas the truck pops in and is held in via the mounting plate. Is there anything I can do with the KA trans? Parts? Simply swap it in and maybe trim the opening and use it? 1 Quote Link to comment
datzenmike Posted February 20, 2018 Report Share Posted February 20, 2018 Length is the problem. The S13 will be too long, but it is a superior transmission than the 720. See about changing the driveshaft length and for this cost you could use your spare 5 speed. Be sure to keep and use the 720 release bearing collar.... it's matched to the 720 clutch and should never be separated from it. The rear mount should be the same but check and the shifter location. Worth looking into. 1 Quote Link to comment
drb5721 Posted February 20, 2018 Author Report Share Posted February 20, 2018 I will be updating this as it seems to be the way to go at this point. I tore down the bad transmission this morning to find that the main drive gear is shot henceforth not turning anything regardless of what gear I shift to. So now, onto the install of the s13 trans. Yay! Somewhat of a relief. I guess i will go home, grab the driveshaft out of the truck and see how much sizing needs to be done. Somewhat happy this seems to be a possible solution. 1 Quote Link to comment
drb5721 Posted February 22, 2018 Author Report Share Posted February 22, 2018 So far so good on this. Cut a piece of metal out of the floor back to the center console and got it slid up in part way. Now I have to mount the pressure plate and clutch. Then we will see about the driveshaft and trans mounting. Quote Link to comment
drb5721 Posted February 23, 2018 Author Report Share Posted February 23, 2018 Trans is perched on the crossmember. Still have to bolt it to the block. Having a hard time getting it to seat into the clutch/pilot hole. Anxious to make this happen. 1 Quote Link to comment
Crashtd420 Posted February 23, 2018 Report Share Posted February 23, 2018 Trans is perched on the crossmember. Still have to bolt it to the block. Having a hard time getting it to seat into the clutch/pilot hole. Anxious to make this happen. Did you use an alignment tool when installing the clutch and pressure plate? 2 Quote Link to comment
drb5721 Posted February 23, 2018 Author Report Share Posted February 23, 2018 Oh absolutely. Haha. Just wasn't holding my tongue right last night. I was late, arms were tired. 1 Quote Link to comment
Crashtd420 Posted February 23, 2018 Report Share Posted February 23, 2018 Oh absolutely. Haha. Just wasn't holding my tongue right last night. I was late, arms were tired. That's good.... 1 Quote Link to comment
drb5721 Posted February 24, 2018 Author Report Share Posted February 24, 2018 Got it in, bellhousing bolted up. Had to slot the holes in the crossmember and trans mount but everything worked out pretty smooth. Not sure what the purpose of the shock that bolts to the trans and crossmember beyond rotational dampening. Didnt mount it back yet. If it's needed and recommended I will. Need a slave cylinder and to bolt up the starter then its on to the driveshaft 1 Quote Link to comment
datzenmike Posted February 24, 2018 Report Share Posted February 24, 2018 I think that may not be an S13 5 speed.The S13 transmissions are like 35" long and would not fit the 720 unless the drive shaft were shortened. You may have a 2wd D21 Hardbody KA 5 speed. 1 Quote Link to comment
drb5721 Posted February 25, 2018 Author Report Share Posted February 25, 2018 Definitely an s chassis trans. Driveshaft will certainly have to be shortened by a couple inches. Plus the shifter is a different setup between each of those. 1 Quote Link to comment
datzenmike Posted February 25, 2018 Report Share Posted February 25, 2018 Oh, OK thought you had it bolted together and running. 1 Quote Link to comment
drb5721 Posted February 25, 2018 Author Report Share Posted February 25, 2018 I wish. Gotta measure and call a driveshaft shop. 1 Quote Link to comment
Pyromancer Posted February 27, 2018 Report Share Posted February 27, 2018 I would love to see pictures and a write up on this. I have an 85 4x4, my trans failed catastrophically and I cant find a replacement within 100 mile to save my life. KA's for days though. 1 Quote Link to comment
drb5721 Posted February 28, 2018 Author Report Share Posted February 28, 2018 For future reference, from centerline of the front u-joint to the centerline of the rear for a s13 trans the driveshaft will measure 55" or 56.5" from front u-joint to diff flange. This is all in a king cab 1 Quote Link to comment
drb5721 Posted February 28, 2018 Author Report Share Posted February 28, 2018 The write up is actually pretty simple lol. I started by unbolting the driveshaft and removing it and the center support bearing bracket. Then I proceeded to unhook the speedometer cable and any harness connectors on the trans. Unbolted the slave cylinder. Disconnected shifter lever. Unbolted trans crossmember and mount. Unbolted bellhousing. Lowered trans to ground. The ka trans will HAVE to have the shifter removed. I cut the hole for the shifter open towards the rear and additional 6-8 inches and about an 1in total in width more than the already existing hole. I unbolted the pressure plate and dropped it and the clutch out. Then I proceeded to lifting the trans into place. Jacking up on the rear of the engine helped alot here. Once the trans is sitting on the main crossmember, I then installed the clutch and pilot tool and bolted in the pressure plate. Wiggle trans forward for bellhousing mating. Remove the speedo sleeve and install into KA trans. Reconnect the speedo cable and any wiring/sensors. Basically done at this point. The only thing to do here is to either fab a mount/crossmember or dremmel the holes SLIGHTLY farther back to make everything bolt up properly. Then you are onto the slave cylinder and driveshaft. The slave will have to be from an s chassis as the hose is mounted to the slave a little different and the 720 slave will hit the bellhousing stopping it from being able to bolt up. The driveshaft, in my case, 2wd KC, will need shortened roughly 4in. Shifter access is easily achieved after enlarging this hole in the tunnel so you can fill the trans once the driveshaft is in. Install shifter plate. I do not know how much of this can be used with a 4wd nor do I know if any measurements will be the same. Attempt at your own risk. 2 Quote Link to comment
Pyromancer Posted March 3, 2018 Report Share Posted March 3, 2018 I cut the hole for the shifter open towards the rear and additional 6-8 inches and about an 1in total in width more than the already existing hole. 4x4 means I have the T- case selector behind the shifter lever. I don't think I would have 6-8 inches to move the shifter back and still have things function. *sigh* :blush: Quote Link to comment
datzenmike Posted March 3, 2018 Report Share Posted March 3, 2018 You don't need an S13 or S14 transmission. Get the D21 Hardbody 2wd transmission it's almost the same length as your 720 5 speed. Quote Link to comment
drb5721 Posted March 4, 2018 Author Report Share Posted March 4, 2018 The shifter doesnt really move back all that far. The hole has to be opened up for the trans to have room to be maneuvered into place due the the tail housing being bigger. Datzenmike has a great suggestion. I had a spare trans and didnt wanna spend money i didnt have to. Plus the trucks are rare around me. Quote Link to comment
Pyromancer Posted March 4, 2018 Report Share Posted March 4, 2018 You don't need an S13 or S14 transmission. Get the D21 Hardbody 2wd transmission it's almost the same length as your 720 5 speed. I miss-read the post I saw KA Trans and though this was about the trans behind the KA engine in the D21 hard bodies. I have understood that they are longer then the 26" in the 720 4x4 and haven't been able to find anything about someone swapping one into a 720 or what is involved. Quote Link to comment
datzenmike Posted March 4, 2018 Report Share Posted March 4, 2018 Most 720s had the longer 31.5" 4 and 5 speeds although a 26" was used on some.. Quote Link to comment
Pyromancer Posted March 5, 2018 Report Share Posted March 5, 2018 I have an 85 26” that’s most of my struggle in finding one. Old one failed and punched a hole in the rear of the case so I can’t swap the tail either. Quote Link to comment
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