[Nitebird]

Is a pilot bearing or pilot bushing more likely to ruin a T10 4speed trans if the bellhousing is not properly dialed in for perfect alignment?

I will be using either of these two for my 1975 455 that will be going into my 79 Trans Am SE 4speed car

Pilot bearing - Timken #7109

or

Pilot Bushing - Dorman 690-023

[mgarblik]

I would tend to try my luck with a bearing rather than a bushing. Trans damage is not the main concern. The main thing that happens with slight mis-alignment is the car is very hard to get into reverse without grinding. Since reverse is not synchronized, if the input is not aligned properly, the shaft will "bite" into the bushing and continue to spin it when the clutch is disengaged. This is not much of an issue in the forward gears because they are synchronized, but can be a bitch to shift into reverse. That's why on some cars you have to go to a forward gear first and then quickly shift into reverse before the shaft starts turning again. That is a sure way to diagnose a pilot bearing issue. With a bearing you stand a better chance of the shaft stopping and not binding.

[geeteeohguy]

All due respect, my opinion is exactly the opposite. While I believe a bearing is superior to a bushing (I use them, just as the factory did), a bronze bushing will allow for some wear and slop to develop....which is just what you want if not 100% aligned. A bearing will not move, and cause more side load on the shaft and parts. The best solution it to get off set dowel pins and get it aligned dead on, IMO.

[Doug]

I seem to recall reading that the input shaft has something like a 0.0003 thousandths clearance fit into either the bearing or the bushing. I don't know how that translates into making allowance (if any) for a slight amount of bellhousing alignment.

UNLESS you have positive information that there is a bellhousing misalignment, I would assume that it is within tolerance of alignment and go ahead and put whichever (bearing or bushing) you prefer.

There is a ton of discussion debating which to use. It is basically agreed that Pontiac used bearings instead of bushings and that bearings seem to be favored.

I assume that the 455 is actually drilled for a bearing/bushing because it appears that SOME engines weren't drilled (may be confined to 66-67 automatics not drilled).

Having just gone through some difficulties with a 67 428 motor, I will offer some comments and observations.

First off, my engine was from an automatic car and was drilled. Using a (cheap) set of mechanical calipers, I measured the drilled hole as 1 3/8" diameter (1.375"). I bought the National #7109 bearing ($22) and tried to fit it in. It was far from a "slip fit" and I "drove" it in using a 6" long-9/16" (0.5625) diameter bolt, nut and large washer instead of a plastic pilot shaft or an old tranny input shaft). It was hard to drive in. When I got it installed, the inner bearing race could not be turned by hand. When I figured out how to turn it with the end of a flat file, it was hard to turn and it turned roughly.

After a great deal of difficulty I removed the bearing and the inner race turned somewhat freely but had a rough spot or two. I decided to do some research about the bearings and bushings.

Here is where it really gets interesting. I had measured the hole as 1 3/8" or 1.375" diameter. I assumed that Pontiac would not have drilled the hole at some "off" dimension say like 1.3755" but that assumption may be in error. ( I don't have precise inside diameter measuring tools.) I would be curious as to what exact diameter Pontiac drilled it to.

Looking mostly at what is offered on Ebay, I found that the measurement listed for the specifications of various brands of bearings and bushings varied somewhat. What is most disturbing is that the outside diameters were "inconsistent".

The National #7109 bearing ($22.00) lists outside diameter as 1.3781". This would apparently be 0.0031" larger than the 1.375" hole. Other common brands of the #7109 bearing were similarly sized.

Now when we get to bushings, the Dorman 690-023 (3.00) lists an outside diameter of 1.381" as does the Pioneer PB-75. Now, if the bearings are 0.003" oversize to the hole and the bushings are even larger at 0.006", the bushings for sure aren't going to fit.

A very interesting listing is a Center Force #43002 bearing listed at 1.375" O.D. which seems to be an ideal fit. It is listed by Summit Racing at a steep $76.44.

Variations of bearing/bushing/brands vary I.D.'s from 0.590", 0,5906", 0.592", 0.593", 0.594".

Variations of bearing/bushing/brands vary widths from 0.350", 0,3543", 0.363", 0.437".

I found a listing for A FAFNIR 202K bearing with dimensions of I.D. 15mm (0.59375"); O.D. 35mm (1.375"); width 11.05mm (0.4375"). This bearing probably correlates with the "6202" which some people use but that requires drilling the hole about 2mm deeper.

I have read of home mechanics using a Dremel tool and stones "boring out" the crank hole. I don't favor that. I have read of some people having to machine down bushings (and maybe even bearings?).

I decided to use the Dorman 690-023 bushing which lists an O.D. of 1.381". I "machined" it down by putting it on a "homemade" axle where it could spin freely and using a Dremel with a small "barrel" sanding attachment lightly with the bushing spinning fast. I gradually removed enough material to make the bushing fit firmly but not excessively tight. I suppose a bearing could be similarly "machined.

Since the I.D. of the bushings/bearings are not close to standard dimension bolts or rods I was hard pressed to find a piece that would fit the bushing well enough to keep it from "wobbling" as it spun. As luck would have it, my junk bin had an axle shaft that I had taken out of a bicycle one of the neighborhood kids had me fix. The diameter of the body of the bearing races is almost exactly the same size as the bushing I.D.. By mounting the bushing on one race and putting the other race on backwards to hold it formed a nearly perfect spindle for the bushing to spin on. Holding the tool at aslight angle, although squarely across the bushing will ensure the bushing will spin and not get "flat spots" in it. The pics will explain.

Unless you have access to some precise measuring tools and machining services, and you are working on a budget as an "at home" mechanic, I suggest you use the bushing, spin-sand it to fit and put it in. IF you wanted to try to spin-sand it to fit, I suggest you cover the open side of it with masking tape to keep the bearing clean of grit.

I have concluded that the bushings advertised for Pontiacs are actually not for Pontiacs in that they seem to be too oversized.

Hopefully, some well experienced engine builders and such will contribute information that will explain/clarify some of these issues.

Good luck!

[Tom Vaught]

I have run a bushing for years with no issues.

I have also modded the Dorman 690-023 bushing several times (using a friend's lathe).

Always did a couple of them when I had access to the lathe as sometimes a friend needed one. About time to order and mod a few more as I am currently at zero on stock.

Tom V.

[455Darren]

Ran into this problem many years ago on my first Pontiac. Ended up doing the sanded down bushing deal. The next time around on a different car I pulled the old bearing out and the new bearing went in just right. I'll have to remember all this on my next engine which will be a stroker to have that bore checked for the bearing.

[Carl S]

I have seen a number of input shafts ruined by a bearing. I have never seen an input shaft ruined by a bushing.

[ANDYA]

Tens of thousands of Pontiacs were put together at the factory using a pilot bearing. That's what the factory engineers spec'd out and that is what I would use. If your 455 has not been align bored(other than the factory) and your using a stock bellhousing that is in good condition than you should be good to go. The test will be when you go to install the trans, if it slides right in then the input shaft will be aligned close enough with the bearing. If your block was align bored at the machine shop, you have an aftermarket bellhousing or your trans will not easily slide in then you MUST index the bellhousing to the block. If you force the trans in that's when you will get other problems such as hard shifting and worn out pilot bearings/input shafts. If everything is aligned correctly you should never get any unusual wear with a factory pilot bearing other than routine maintenance.

[rtanner]

i hone the inside of my bronze bushings slightly and grease w teflon lube

[Nitebird]

Originally Posted by ANDYA

Tens of thousands of Pontiacs were put together at the factory using a pilot bearing. That's what the factory engineers spec'd out and that is what I would use. If your 455 has not been align bored(other than the factory) and your using a stock bellhousing that is in good condition than you should be good to go. The test will be when you go to install the trans, if it slides right in then the input shaft will be aligned close enough with the bearing. If your block was align bored at the machine shop, you have an aftermarket bellhousing or your trans will not easily slide in then you MUST index the bellhousing to the block. If you force the trans in that's when you will get other problems such as hard shifting and worn out pilot bearings/input shafts. If everything is aligned correctly you should never get any unusual wear with a factory pilot bearing other than routine maintenance.

I have both the stock bellhousing and a Lakewood bell housing. I was planning on using the Lakewood just for safety reasons behind a 500 to 550HP Pontiac 455 that is going in.

[ANDYA]

Originally Posted by Nitebird

I have both the stock bellhousing and a Lakewood bell housing. I was planning on using the Lakewood just for safety reasons behind a 500 to 550HP Pontiac 455 that is going in.

If your motor is going to make 550hp then I would say the Lakewood bellhousing is mandatory for safety sake. Once you go that route then as part of the overall build-up you should index the bellhousing to the block. Think of it as part of the blueprint procedure when building a high HP engine. I have a 500 hp 428 in my firebird with an older Lakewood scattershield and Supercase Muncie. Good thing I indexed the bellhousing because I found it to be .017 out of spec. After that the trans went in very easy and the trans shifts like butter. I used the pilot bearing ,not a bushing. Like I said in my previous post, If you don't index a Lakewood bellhousing you can have all kinds of problems.

[Tom Vaught]

Originally Posted by Carl S

I have seen a number of input shafts ruined by a bearing. I have never seen an input shaft ruined by a bushing.

Agree, Due to the Bushing "Material Properties", it is extremely unlikely you would ever have an issue.

Originally Posted by ANDYA

Tens of thousands of Pontiacs were put together at the factory using a pilot bearing. That's what the factory engineers spec'd out and that is what I would use. If your 455 has not been align bored(other than the factory) and your using a stock bellhousing that is in good condition than you should be good to go. The test will be when you go to install the trans, if it slides right in then the input shaft will be aligned close enough with the bearing. If your block was align bored at the machine shop, you have an aftermarket bellhousing or your trans will not easily slide in then you MUST index the bellhousing to the block. If you force the trans in that's when you will get other problems such as hard shifting and worn out pilot bearings/input shafts. If everything is aligned correctly you should never get any unusual wear with a factory pilot bearing other than routine maintenance.

If the Input shaft is properly indexed, you can still have issues with a Pilot Bearing:
.
The Bearing is not self lubricating, therefore if the lubricant goes away the bearing goes away taking your input shaft with it occasionally.

The Bearing is designed to run smoothly, never seeing high impact loads.
That means "NO POWER SHIFTS" at extreme rpm points if you want maximum life out of the bearing. You flat spot the balls and the bearing will fail.

"That's what the factory engineers spec'd out and that is what I would use."

(This is not an challenge on your statement above)

That assumption is what will get you in trouble UNLESS you drive the car and shift the trans the way the Engineer ASSUMED the trans would be used (to get maximum life out of his parts).

"Power Shifting" is not in the GM Engineers "Design Requirements"

Now a Liberty Transmission Engineer might have a different idea on what to use.

Just saying, DO NOT ASSUME that the GM Engineer's Job was to protect your equipment from your "Forceful" driving style.

Tom V.

[fiedlerh]

I think a bushing would be more forgiving of misalignment.
Misalignment will make it more difficult to engage the clutch smoothly.
Misalignment will also cause faster wear on the front bearing retainer and probably the input bearing too.
Per the Borg Warner print the end of the input shaft is .5895 to .5900 diameter (14.9733 to 14.986 mm). A 7109 bearing has a 15 mm bore with a tolerance as much as -.008 mm) so worst case shaft and bearing you'll still have .0002" clearance.
As we know the input shaft is loose in the front bearing retainer to allow for some misalignment.