Good Morning Everyone!!

I'm trying to rebuild my tach drive distributor and I was wondering if anyone has expierenced any of these problems.

I seem to have alot of clearance on the shaft of the distributor between the gear and housing, about .125 or so. I know they should be shimmed down to .015 or so, but is something else wrong that I have this much clearance to start with? I dissasembled the unit and the brass bushings looks good, I don't see any unsual wear anywhere. Its the orginal dist from the car.

Also, the gear on the shaft itself has been destroyed, I would assume most likely because of the excess clearance. I purchased a repro shaft, the special high perfomance unit, which I assume is for the L82, from one of the aftermarket suppliers. They weren't sure either. As far as I'm concerned it's a piece of junk. It is missing what I assume is an oiling groove the twists around the top section of the shaft, and the soldering/welding job on top is so lousy that I'll have to grind it down to make it work, and that's just the beginning. Any idea where I can get a good original shaft, or has anyone used a repo with good results? Any help and tips would be appreciated greatly!! Sorry for being so long winded!!

 

TonyZ,
I have done about 20 of these, and i`m sure Lars has done many more. I believe the "factory" clearance comes around .060 so your not that far off at .125. I am curious where your mainshaft came from as Alwyn just bought a cheap ($40) repro that was very high quality. If you have any side play between the shaft and the bushings they need to be changed. ...redvetracr

 

I have had good luck with the "set screw" kit which includes a drill guide for proper perpendicular alignment, and both my set scew and my gear end were polished to avoid galling. However, I used a 1/4-28 ss screw instead of a set screw, and a jam nut on the outside to retain the setting. The set crew would not stay put to my satisfaction.

 

Tom,
Out of curiosity what did you set the clearance to between the "bolt" and the drive gear?? I have a bare housing that has been drilled and tapped but has no bolt. ...redvetracr

 

It's been a long time since I set it, but I think it's (cross shaft gear end play) around .010.
The thickness of the washer on the opposite end affects your ability to make adjustments as well.
Basically, I tried to eliminate as much lateral movement as possible, and still allow for heat expansion.
I had one fail due to end play... the bushing and cross-gear were tight.... no wobble, no excessive shaft to bushing clearance. The endplay was excessive, and the gears failed.
I suspect the in/out movement of the cross gear set up some sort of "vibration" that caused the failure.

I also re-read the post above... and now I'm not sure which end clearance is in question-

The end clearance for the tach cross gear, or the clearance for the mainshaft drive gear?

Also, I stopped using the factory style bushings a long time ago... I use the needle bearing type now. Haven't had any problems.... yet.

 

Redvetracr,

Thank you for the info. I didn't realize that the clearance was supposed to be set at .060. I haven't done a whole lot of work with these distributors yet, so I just assumed it would be the same as a standard passenger car unit. I guess it would be a better idea to check the manual next time!!

As for the shaft, I bought my current one from Zip products, pn M2984 for $70.00. Maybe it's just me, and it could function fine, with some modifications but it just doesn't look no where near as good as the original. Do you happen to know where Alwyn got his new shaft? I would like to get the best peice I can for the car if possible.

As for the side play, the rest of the unit looked very good and it was tight getting the shaft out. I had to wipe it down with laquer thinner in order to remove the shaft from the body, but I will check it to make sure. The car has only about 60,000 miles on it and was cared for so most parts are in decent shape.

Tom454,

Thank you for the info on the set screw kit. I was wondering if anyone had used this and how well it worked. I am also interested to see what you had sent the clearance at so I may do the same.

 

Tom454,

I was orginally referring to the clearance between the body of the distributor and the mainshaft gear that runs off the cam. But following the posts I also wanted to get the clearance for the cross gear that turns the tach cable, which you had said you set to 0.10. I will do this and hopefully it will eliminate problems in the future. You had also menitoned needle bearings. I assume they are for the cross gear, but please clarify me if I'm wrong.

 

I set all of my GM distributors to about .008 to .012 on the main drive (cam) gear. I think Lars sets his in that ballpark as well.

The cross gear endplay is a subjective topic, as I am not aware of any GM specified end clearance value for the cross gear.... GM mechanical tach drive distributors are genarally not adjustable in this area.

I adjusted mine so that there was zero clearance and then backed it off to about .010 to allow for heat expansion and variance in production tolerance during the machining phase.

The needle bearing "bushing" or "coupler" is the part where the cross gear rides.
I believe it is still being manufactured by "Hi Tech Innovations", although it is marketed by several vendors.
They have both brass (or bronze) and stainless versions.

 

Tom454,

Thank you once again for your info. I'll work on getting another shaft and using your information I'm sure this will turn out good! I hope the rest of the car isn't this much trouble!!

 

TonyZ,
I didn`t say they were supposed to be set at .060 ,I just said that is how the new ones came according to the NOS parts gurus at the NCRS web site. Like Tom said .012 give or take. ...redvetracr

PS: Alwyn`s shaft came from TLD in (or around Atlanta) $40 and $20 for a side gear.

 

redvetracr,

I picked that up after I re-read your email a second time. I'm a little slow so sometimes it takes me a few tries before I get it all right!! I also talked to alwyn and he gave me the info about that shaft also. Thanks again for all the help and hopefully I'll have things together soon!! If I can ever help in any way, please feel free to ask!!

 

TonyZ,
Send $$$$ I want to build an ALL aluminum 434" small block. ...redvetracr

 

The check is in the mail!! LOL..............Let me know if you do build that motor and how it turns out, I'm interested, althought probably could never afford it!!

I'd just be happy with a running car again!! And by the way, that is one killer Vette you have!!