720World

Little Trucks, Big World

Hi guys, hopefully I can get a little insight as to what is going on with my transmission.

Here is the background.   I just had this transmission installed about two years ago when my original locked up when i tried to grab a downshift for an exit ramp.

This one was the only one I could locate and it was out in California, supposedly it was professionally rebuilt and I had it shipped to my installer.   

After the install I drove it for a couple months and then decided to rebuild my truck and give it a longer life so it was down for two years or so while I worked on it.   I live in a townhouse with a homeowners association that likes to get in peoples business so it was fun trying to hide all the work I was doing on it from head gasket to cutting out bad sections and welding in new ones and replacing the tank, bed, etc.

I finished it up and it looks great and drives really well also but for whatever reason, the other day when i was driving home (actually turning into the entrance for my development) I was cruising down the road in 5th gear and grabbed a downshift to 4th gear and when I went to go into 3rd the stick would not move.

When I let the clutch out it would still pull in 4th gear so I pulled into a parking lot to get out of traffic

and see what was going on.   If I pushed in the clutch it would roll backwards without any issue and if I let it out the truck would try to pull.   I checked the clutch reservoir and it is full, I also checked the slave cylinder and it is fine (and new) and the transmission has fluid.

I just took out the console to get a look but their really isn't anything to see and the small plate on the side is so hidden up in the tunnel I don't think anything of merit will be seen that way.   

I tried to pump the clutch and work the shifter and it just will not budge at all.

Have any of you had an issue like this?   If so, what did you do to fix it?

I am bouncing around what to do if this has to come out of the truck again, I would like to put in something much stronger and less prone to failure, it seems like our box is made out of toothpicks and rubber cement.

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Nevermind....did a little research and see it is from the Z31.

While it is an interesting proposition I think the overall cost would be higher and possibly more difficult to locate one plus the install would be involving.

I think I will just stay with the "C" for now.

Strange item of note though.   I found a company that sells high quality rebuild kits for the 5W71 trans. but no mention of the "b" just an "A" and "C" plus other variations of each.

Other than the few mods mentioned everything else bolts up. Make sure to keep the slave compressed. Every time I changed a trans and the piston came out of the slave it usually took a dump shortly afterwards.

Found a transmission from a 1990 D21 with 81k on the clock.   Hopefully it has no issues and will not need anything.  

The company i got it from said it was fully tested and worked great...we shall see.

I decided since I am already in this far I might as well also replace the oil pan gasket that has been leaking for a while now, that sounds like fun.   Wish they made a good rubber gasket instead of these damn cork ones, I have never had much luck with the cork ones.

Is their any other gaskets I need in the oil pan area while it is all apart?

There are a couple of weird gaskets next to the rear main seal. Don't pull on them, they break off. As long as you are in there change rear main seal. Use a torque wrench on the pan. Overtorquing them results in leaks. This isn't fun, but it is even less fun if they leak right after replacing trans. Good luck!
I was totally bummed when I found out that even with the front diff. out of the way, you still have to jack up the engine.

Also of note, the rear main seal was replaced when the last transmission was put in at less than 5k miles and about two years ago.

I was looking at Rock Auto for throw out bearings replacements and they have three different sizes and they all say they fit the D21 (C) transmission or the 720 (B).     The weird thing is that some are just bearings and others are complete "bearing assembly" units but their are two different bore sizes and one Timken says "optional" and it has a larger bore.

TIMKEN DNE01576C {#30501K0400, 30501K0401, 3050221000} 1.303 Bore Info
Standard
TIMKEN 01576 {#3050221000} 1.575 Bore; 0.788 Width Info
Optional
Any idea which one I should be ordering to put the "C" version Transmission in my truck?
Are you just replacing the TO bearing? I kind of thought nissan used the same one forever. Maybe the collar the bearing rides is different. Think I am still rolling b series collar on mine. Also last clutch kit came with new collar and bearing but since they were Chinese I ran the low milage Japanese bearing and collar I already had. Works fine.
Ok, that's what I was looking for.

My clutch is one of the last available OEM clutch kits and the throwout bearing was new, just needed to be sure it would work with the "C".

Just wanted to give a quick update on where it stands right now.

I got the "C" transmission and after cleaning it up real good I changed over my relatively new throwout bearing and boot, replaced the springs on the arm and bearing collar with new ones and made sure the nec essary items got lubrication.

I did the oil pan gasket, which was way more fun than any one man should have, those hidden bolts are a bitch but were made easier by reaching them through the passenger side wheel well and having a plethora of different wrenches to work with, only bad part was that even my smallest (1/4" drive) torque wrench would not fit so I had to tighten those four bolts by hand but I used the already torqued bolts as a measure as to how much force to apply.

I chose to not use the cork gasket and used "The Right Stuff" by Permatex instead. just have not put any oil in yet.

I managed to get the transmission in place today, not super easy to do by myself  in the driveway of my townhouse but by using a large hydraulic jack and a scissor style transmission jack. Crawl under the truck, make an adjustment, crawl back out and go to the front to make an adjustment from that side, crawl back under...it went on and on like that for quite some time.

I finally have it bolted in place but I still have to install the support and make an adapter plate for the mount and get the driveshaft shortened.

For now, things are going well and I couldn't ask for better weather at the moment to get this stuff done outside...68 with no chance of rain.   Only potential slow down is vacation out of town next week.   Got to keep moving though because Christmas and Winter are quickly approaching.

What did you use to cover the speedometer cable output?   My transmission has the threaded output still attached to the transmission.   I take it if I leave it alone it will leak fluid out? 

Also, you mentioned you had to have your driveshaft lengthened but mine is the opposite, I have to get it shortened by a couple inches and had to move my transmission support back to get it in position.

Yep it has been a while. Can't remember shorten or lengthen. Drove it today all good. Used a Mtn dew cap with some epoxy to seal the speedometer hole no issues. Bought a speed sensor when doing the ka swap and expecting to use the 2wd empty slot for the sensor but turns out not needed. Cap still sealed. Used to roll trans on chest and bench press into position. Had the truck nearly 30 years, can't do that anymore!

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