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Discussion in 'Project Progress' started by redriderjf87, Dec 14, 2017.
Ah good to know
That’s why I went with the bronze bushing instead of the needle bearing more tolerance.
i'm not sure that's how it works. it's load on the front transmission bearing not the pilot bearing/bushing. at that is my understanding. misalignment may also cause shift issues.
I too went with the Bronze. I read arguments for both but in the end went with the bronze because it was an easier option.
I believe shifting is effected by everything around the input shaft; pilot bushing/bearing, dial in of the bell and the type of bell.
I did do the dial in but I went with a quick time bell and NOT the OEM 621; I heard with the OEM you don't need to dial it in also if you are doing 5K pulls you don't need it so much.
I am doing 6200 and soon 6500+ pulls at the track.
It's been a looooong time since I posted anything on nasty Z or any other car site for that matter. I'd like to help you understand why it's important to use a needle bearing pilot bearing and get the housing within .005"when using a TKO or Magnum. Unlike the Muncie that has a ball bearing front bearing, the TKO has a tapered roller bearing with .000" to .004" end play, that when at operating temperature has a fairly significant load on it and it's very important not to induce a side load on it. The bronze bushing in time won't support the end of the input shaft and IF the bell housing is out of alignment will cause the input shaft to hog out the bushing making it a sloppy fit and can cause vibration and premature front bearing wear and eventually shifting issues. A properly aligned bell housing and the needle pilot bearing will last much longer and the transmission will shift much better. Believe me when I tell you a misaligned bell housing out more than .006" WILL pop out of gear on deceleration, even at low rpm. We were the first company to reproduce the GM 621 bell housing correctly and any housings that were out of spec were sent back to the foundry where they were to be destroyed but soon found there way to the aftermarket after our agreement for exclusivity deal expired. The .005" alignment spec isn't new! It was used for years and years by auto manufacturers but wasn't critical because of transmission design. When the big 3 and others introduced transmissions with the tapered front roller bearing configuration things changed.
Great reply. I am pretty sure I have my alignment correct but it was a real bear to do and I always have this tiny lingering doubt as I am not a pro at this. I would gladly swap bell housings for one that I knew was certified in spec when I got it and switch to the needle bearing. Not sure what company you represent but if you sell such a thing I am interested.
There is no such thing as a "bolt on" bell-housing because of stacked tolerances. Your bell-housing can be prefect, but that doesn't mean the engine block dowels are prefect or anything else.
IMHO, if a manufactures calls for a needle bearing, use a needle bearing. The transmission is designed a certain way and metals are treated with particular ways for designed used components. Don't understand why you would go against the manufacture based on preference on such a high dollar transmission. Too many internet experts scare people away from something that really isn't an issue.
I have ran nothing but bearings for the last 10 years, 6800RPM shift, road courses, Drag Strip...no issues. Failures are from improper installation. Bushings will erode away over time increasing tolerances allowing the input shaft to wiggle. This will cause damage to transmissions bearings. There is good reason NO modern car uses a bronze pilot bushing.
IF, you were able to buy a new 621 bell housing at your local GM dealer would you measure it when installing it on your never rebuilt engine? Nope, you would bolt it on and go. If you were to buy an aftermarket housing that was checked to be within the factory spec it's basically the same thing. What I'm trying to say is the bell housings we sold (Chevy and small block Chrysler) were checked very carefully with an expensive jig to be within factory specs. .005". Having said that IF your engine was rebuilt and has been line bored or if the dowels have been banged around or replaced (machine shops treat bare blocks pretty rough), or your building a new engine from a used or aftermarket block I would recommend checking the runout. I was one of the previous owners of Classic Motorsports Group (now Hurst Driveline) and was the vice president of product development and technical support and it was our company that developed this bell housing because good used 621 housings were getting very hard to find and dialing in an expensive scatter shield was a pain and other aftermarket 621 housings we tested were junk. Since I left Hurst two years ago I haven't kept up with their day to day operations and am NOT SURE they still check the housings the way we used to. I would give them a call and ask. I believe the housings were about $260.?? BTW I wrote instructions with a simple two step procedure to check runout and it should still be available on Hurst's site to make it easy. The biggest challenge is to configure your dial indicator and get it in the bell. After that it's a 5 minute job unless you need to change the dowels.
What badazz81z28 said about stacked tolerances is true but with a bell housing sitting on two dowels this isn't an issue. The needle bearing pilot bearing that replaced the oil lite bronze bushing for your little Chevy is the same one used on the 6.5 turbo diesel pick ups so it pretty tough. When properly aligned they last a very long time.
It's slowly getting there... other than trimming part of the floor to get access to a couple of the shifter bolts, everything is pretty much lining up...
The stick ended up just a hair farther back than the T10, which works well still and gives me plenty of room to the dash even with the tall handle and pistol grip
Working on getting my driveshaft done, speedo cable and reverse wire run, and cleaning up the sheet metal around the outer boot.
Looks sweet brother ... Maybe you can get'er done before the snow falls and test her out