8 replies to this topic

[matt_a20]

Hi, 

 

I've just put my engine/gearbox back in the car after reconditioning the gearbox (baulk rings / bearings etc). 

 

I wanted to test the new clutch, so sitting in the car I pushed the clutch down but struggled to move the car back and forth in 1st (pushing it) which didn't seem right to me. 

 

Cut a long story short the clutch is fine, I proved this by removing the flywheel and thereby taking the clutch out of the equation, so I am now just on gearbox resistance.  Bell housing is on and engine sitting in engine bay.  I am still having slight problem pushing it back and forth in gear and want to check if this is normal?, or am I inventing a problem that is not there..?

 

I can push the car with no resistance in neutral, as expected.  4th gear limited resistance, with each selected gear up to 1st making the car slightly more difficult to push.  In 1st I have to put some effort in to get the car to to move (same with reverse), but not hernia inducing.  There is however a discernible difference between 1st and 4th.

 

I can hear all the gears engaging with no sounds I would not expect to hear, although 1st and 2nd can be a little reluctant to engage until one has been gently persuaded, then fine. 

 

The box is currently dry.

 

Part of me thinks I should feel no difference whatever gear is selected (when disconnected from the engine), but I can also reason the shorter the gear this might be expected.

 

Any ideas if if is normal to feel a difference in resistance turning the gearbox in 4th as opposed to 1st?  And it's not correct any suggestion on what I've done wrong?  (it has a 2.9 diff in, A+ gearbox)

 

Thanks Matt

[nicklouse]

Yep that is what a gearbox does.

[TheFabMini]

The ratio of what you're turning is changing with the gear selected so there will be a difference in rolling resistance.

[matt_a20]

Thanks.  

 

Yep that is what a gearbox does.

 

The point I was trying to make is that I am slightly surprised that when the box is under no load you see quite such a difference in rolling resistance, but if that is how it is so be it.  

[sonscar]

Dyno engine horsepower 60 for example,wheel horsepower 45,drivetrains losses are typical(outputs totally fabricated for example),Steve..

[xrocketengineer]

The lower the gear the faster the engine spins under normal operation and at a given speed. When back driving (pushing the car) in fourth gear the differential pinion gear and the engine input gear are on a direct 1 to 1 ratio and is easier to push. In first gear, the input gear will have to spin faster than the differential pinion gear and because of the additional friction it will be harder to push. The additional resistance will depend on the gear ratio and any additional items that need to be rotated like idler gears that might increase the friction.     

[Gaz66]

This is why you leave the car in first or reverse instead of fourth on a hill when you have a dodgy handbrake. Lol

[Ethel]

Trust you lubed everything as you assembled it?

 

In neutral you'll be turning the mainshaft when you push it. When you select a gear you'll drive the 1st motion gear & transfer gears which will drive the primary gear around the crank nose. I'd have some potential concern about that, but if you checked all those bits ran freely as you fitted them it's less likely & turning the engine in neutral would be a better test.

 

New baulk rings can be a bit grabby so what's hopefully happening is the ones that aren't engaged are creating some extra drag for the one that is. Selecting any gear will have started the layshaft turning and so all the other gears against the synchro hubs too. There'll be loads more oomph to disengage them when it's running at full speed.

[mini13]

Even with the flywheel removed your having to turn the drop gears, and the one on the crank is especially draggy as it has bushes rather than bearings, so there's going to be significant friction once the gearbox bearings and baulk rings have been added to the equation.

 

In 4th, you'll there will be much less loss as the gears are "locked straight though so no actual force is going via the laygear, once 3rd is selected there will be the added friction of the laygear bearings, and a gear onto the laygar and back to the 1st motion shaft, as you go down this will be magnified by the ratio. so with a 1st gear ratio of 3.6:1 you can expect it to be probably 4 or more times harder to push in first over 4th.