5 Speed Identification and rebuild kit information

[Sam280Z]

The 5-speed in my daily driver has bad counter-shaft bearings. I have a couple of extra 5-speeds from various parts cars (all 280Zs). I pulled one out of storage to rebuild.

 

Since I didn't know which transmission it was, I counted the teeth on each gear and compared to the 1978 factory service manual. It was a perfect match for a 78 five speed. However, I thought it odd to figure out that the main-shaft nut was left-hand threaded when the service manual made no mention of that.

 

I worked on the assumption that it is a 5 speed from a 78 and called http://www.drivetrain.com to order a rebuild kit. I explained the situation to the salesman (Brian) who was very helpful and helped me figure out the best kit to get.

 

Believe it or not, it was a bearing kit with synchros for a 81-86 300ZX, part # BK104WS. Every bearing was a Nachi brand and fit in its respective place. The only difference was that the front counter-shaft bearing has a snap-ring groove (you can ignore it) and the kit has a small brass 5th gear synchro ring that you cannot use (the earlier 5-speeds and steel servo type synchros). The only needle bearings it has was for the input shaft. But the others usually do not need to be replaced. The total cost for the kit shipped was a hair over $160.

 

After I dismantled and cleaned up the internal parts, I noticed small "dents" in the internal bearing surface of the 5th gear that were apparently caused by the needle bearings. No problem, I'll just grab that other transmission on the shelf and use the best parts from each...

 

Well, I pulled that one down to find that the gears all "appear" to be that same (I haven't counted the teeth yet) but the main-shaft nut is right-hand thread and the thrust washer is located with a tiny ball bearing (the other had a small cylinder "pin"). I imagine that this transmission came form a 78.

 

My question is: what transmission has the same ratios as a 78 but a left-hand main-shaft nut?

 

If I get a good answer, I'll post what I found out about main-shaft nuts backing off, or at least my latest theory...

 

Thanks,

Sam

[cygnusx1]

The 200SX transmissions and the truck series were all internally similar if not identical to the Z transmissions.

[mom'sZ]

Roger at the Zbarn taught me how to identify the 5 speeds by looking at the tail shaft area. The early 5 speeds like those that came in a 280z have a steel collar around the end of the tail shaft (where the driveshaft comes out) The later 5 speeds like those that came in a 280ZX don't have the steel collar, that area is just plain cast aluminum. BTW he also told me the 79 ZX came with the earlier style and the later style wasn't available until 1980.

[technicalninja]

found this from an earlier post I did concerning the differences between 4 and 5 speeds "See, I didn't lie to you. The 4 speeds should be just as strong as the 5 speeds mainly because Nissan just used all of the basic 4 speed parts when they built the 5 speed. All of the bearings are the same, Shaft diameters are all identical. Only serious improvements that I can think of were in the 82-83 NA cars which has a left handed threaded main shaft lock nut which does not loosen up with use. This is an important feature to have for a high HP car as they tend to loosen up the right handed lock nuts quickly."

 

The left handed lock nut trannys are better IMO. Nissan first modified the final thrust washer for use with the roll pin locator (instead of a tiny ball bearing) about 1980 and further modifed to the left handed lock nut sometime in 1982. The left handed versions are the rarest IMO. I am not aware of an early (pre 82) tranny that used the left handed nut. The 82 tranny was factory installed with the 3.9 R200 and was the closest ratio trans installed in a Z in the US .It did not need a low first gear due to the rear end ratio.

 

In figuring gear ratios did you first figure the reduction between the main and countershaft? This is what most people consider the "4th" gear. In 4th the input shaft is basically locked directly to the output (main)shaft and the countershaft is taken out of the power delievery path. In all gears but 4th the power comes into the tranny via the input shaft, transfers to the countershaft via the gear built into the input shaft to the first gear in the countershaft, then from the countershaft back into the main shaft by the gear selected (other than 4th). The input shaft gear and the counter shaft gear have different number of teeth and thus have an effect on the overall gearing of all gears but 4th.

 

You should have the 82-83 gear ratios instead of the 77-79 ratios. IMO the later ratios are better. It might be possible that someone replaced the main shaft in an early 5 spd with a left handed replacement as the shafts are basically the same critter and as long as the last thrust washer, the retaining pin and the left handed lock nut are used it would work fine.

 

A real quick indentifier for the late tranny is massively long shifter ears. The shift lever pin hole is 1 1/4" below the top of the ears. These ears allow you to make a cheap shift lever ratio change by redrilling them and lengthening the bottom section of the shift lever. There is a long thread with the shifter mod info in the archives.

 

One last note.... It can be a real pain getting a replacement left handed lock nut from Nissan (especially if you tell them its a 78 tranny). Tell them its an 83 and hope that they get you the proper nut. It may take multiple attempts. It also may be better to order for 300 ZX as I expect all of them had left nuts. I am very very careful when I take the original ones off and can normally reuse the nut as they will usually tighten up more than the original stake area thus allowing restaking. I tighten the nuts as tight as I can get them with a BIG channel lock (I don't have the cool super deep socket that is needed), use blue locktight being careful to keep it out of the fifth gear assembly. Then restake the lock area of the nut. Only ones I every have further trouble with are the right handed versions and then only on high HP engines.

 

Hope this helps,

Rick

[Sam280Z]

Rick,

Thanks a lot. I think you are correct about the use of a later shaft. Here is the link to the thread that contains your original post: http://forums.hybridz.org/showthread.php?t=108856

 

I couldn't find it in when I was originally searching because it was in the turbo forum and I didn't think to look there.

 

To figure out the gears, I actually counted teeth on all gears and compared them to the 78 manual specifications. They are definitely 78 style gears. Someone must have gotten a later main-shaft and put it in.

 

I did re-use the nut with red loctite. I had to swap the 5th gear with one from a known 78 transmission. I also had to use the collar that goes under the needle bearings from the mystery transmission.

 

When I tightened the main-shaft nut, it would bind against the fifth gear making the transmission behave as if 5th was engaged. I found a post at zcar.com outlining a similar problem:

http://www.zcar.com/forums/read.php?f=1&i=678847&t=678847#reply_678847

 

However, my fifth was not separating from the synchro collar as his was. The collar under the needle bearings was too short relative to the fifth gear assembly. The thrust washer should take the torque before the gear. I assume that this was due to use of mismatched parts. To remedy, I turned down the face of the thrust washer to the diameter of the collar for a distance of about .005 inches. This provided clearance between the fifth gear assembly and the thrust washer.

 

I installed the transmission this weekend and, as of now, everything seems to be working fine.

 

Sam