chevy v8 of the 70s thrust bearing load/time adequacy 1

[Tmoose]

A friend has a mostly original 1976 Corvette.
In a Motorcycle Safety Foundation course he took, their preference was when at a light stay in first gear and hold in the clutch.

I've seen a few cranks with deeply worn thrust faces of mixed makes.
The modern bearing manufacturers make a big deal about the improved profile they use today on thrust bearings to prevent wear.

Is he taking much of a chance of shortening the crank thrust bearing life (not the throw out bearings) holding depressing the clutch?

He will be replacing the original clutch with a centerforce unit in a few weeks, and I will lend them my dial indicator to check existing crank endplay, among other things.

 

[MikeHalloran]

Chebbies are not motorsickles.

The cyclist must be able to depart _immediately_ when the light changes, or when the car behind starts to move, for personal safety. The clutch reaction in a motorcycle is taken by bearings in the transmission, not engine bearings.

The Chevy driver probably wants to save his plain thrust bearing by leaving the box in neutral until the light changes. His incentives are different, since his personal safety is at less relative risk at a light.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I just watch for the cross traffic light to turn orange then select low gear. On more complex sequence lights I try to predict and see the last orange before I get a green. This might involve selecting and disengaging low a few times.

This not only saves crank end thrust bearings but also saves clutch face wear.

Regards
Pat
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[blacksmith37]

As pointed out, different engines have different characteristics ( chebbies vs various bike engines); (old guy story): When the Hydramatic trans factory burned down -in the 50's- GM put Buick Dynaflows in Cad and Olds. The Buick engines had closer tolerance on crankshaft end play than Cad and Olds; The greater crank end play (Cad and Olds) wore out the Dynaflow front pumps (as they got more mileage). Even the GM engineers hadn't anticipated that.

 

[Pancholin]

I believe that any automatic with a torque converter will put a forward thrust on the crank while the engine is running (front wheed drive excepted.) The oil pressure inside the converter is trying to push it off.

 

[MikeHalloran]

Yes, a converter will apply a thrust to the crank.
It may not be particularly large, amounting to the converter internal pressure times the area of the seal between converter and transmission nose.

Mike Halloran
Pembroke Pines, FL, USA

 

[Lou Scannon]

Blacksmith37, great vignette!
I am an early Hydramatic fan, Dynaflow, not so much, though it too is a very interesting engineering exercise. I recall a report that the Dynaflow equipped Old's had slightly better 0-60 acceleration than the Hydramatics, probably because they allowed the engine to rev a little higher on average during the accel. Fuel economy, fahgettit!

I forgot what I was going to say

 

[blacksmith37]

Ahh! the good old days. A friends' (father) had a 54 Buick , the engine would rev at full throttle and seemed like RPM didn't change even as speed got to 70 (about all you could do in Chicago and hope not to go to jail). I had Cad 348 flathead (very "torquee", 4.5 stroke/3,5 bore) and the real hydromatic would get rubber on the 1/2 and the 2/3 shifts ( and the 3/4 if you where someplace where you could go 80).
Of course you needed an anchor to stop the old Dynaflows- very little engine breaking. Brake shoes lasted about 6 mo /10,000; compared to hydro cars which could get a whole year/ 20,000 miles. Of course then you were past needing plugs and points and probably a fuel or water pump.I invented a fuel pump in nowhere Wyoming one afternoon (or I would still be there).
You kids today are spoiled with modern cars.

 

[Lou Scannon]

My modified 55 Olds would could be countd on to "bark" the tires at WOT on the 1-2 and 2-3 shifts (after I installed traction bars)!
Palpable engine braking as well as decel downshifts were certainly distinguishing features of the original Hydramatic.

I forgot what I was going to say

 

[benta]

Erm, I believe the OP is talking about a _manual_ transmission.

Benta.

 

[franzh]

In the 70's, I overhauled more than my share of small block Chevy's. Remember, that particular engine design dated from 1955 and lasted until the mid 2000's on heavier trucks. Thrust bearing wear was never an issue on the majority on those engines. On those engines that had abnormal thrust bearing wear, the driver may been a perpetual clutch rider and probably replaced clutches annually. I bet I didnt replace more than one or two cranks due to thrust bearing wear, and both of them were automatic transmissions in 4 door sedans in light driving duty.

Franz

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[izzmus]

It is not uncommon for the torque converter to apply excessive load on the thrust bearing and destroy in in a short period of time, usually right after transmission overhaul.

That said, aside from the excessive wear on the thrust bearing, throwout bearings aren't meant to handle the high duty cycle involved.

THAT said, it is also a safety concern. If rearended, the driver's foot can slip off of the clutch and the car can lurch into cross traffic.