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Value of Pilot Bearing

B

Bill Blue

Platinum Level Sponsor
I am at a point where I should make a decision about the pilot bearing, as the installation will require a sleeve over the stock bearing. The transmission is a 70's Volvo unit that I am mating to a 1725. The transmission appears to be the roller (needle?) bearing type. I am not at all sure that I will be able to indicate the input shaft in relation to the crankshaft. If I cannot, should I install using a pilot bearing which may put a load on the transmission input bearing, or let the input shaft "float"? In reality, the only weight placed on the input shaft is the clutch disc, which is probably less than 5 lbs. The dynamic forces placed on the input shaft are totally unknown to me. I do know that not all transmissions even bother with a pilot bearing.
Bill
 
DanR

DanR

Diamond Level Sponsor
I think best to support the input shaft. centrifical force of the clutch disc will exert lots of pressure. And if the disc should be out of balance, it will add to greater force.
 
husky drvr

husky drvr

Platinum Level Sponsor
Bill Blue said:
The dynamic forces placed on the input shaft are totally unknown to me. I do know that not all transmissions even bother with a pilot bearing. Bill
Click to expand...

The only manual transmissions I am aware of that don't use a pilot bearing are front wheel drive. It was a surprise to me when I found out.

After I examined a couple of exploded diagrams of FWD trans, I think I have a theory about why just FWD and not RWD.

The input shaft in a FWD case is long enough the extend through the case and be supported by a bearing as large as the front bearing. Plenty of support to maintain shaft support, alignment, and clearances.

In the RWD trans, the input shaft is only supported by the one bearing at the case wall. The main shaft relies on support and alignment by the small bearing in the tail of the input shaft - not the other way around. That small bearing is so close to the front input bearing it has no leverage to support main shaft alignment unless the front of the pilot shaft is supported in the rear of the crank. With heavy torque loads, the lower gears are going to try and spread the gears apart and pivot the input shaft in the input bearing. The more spread the faster all the bearings will wear.

For best service, I think you need a pilot shaft bearing.

Of course I might be completely wrong concerning this theory, but it sounds logical.

Just a few thoughts,
 
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