Lack Of Power To One Wheel

[theduck]

During my IVA the car was on the rollers in order to test the speedo. During this test the tester drives the car up to certain speeds to check the speedo accuracy. Now from what I understand they would normally put the car in 3rd or 4th to do this without having to work up through the gears because the rollers offer little to no resistance. When the tester tried this, the car would just cut out. So he then tried working his way up through the gears, but it still bogged down and died when changing to 3rd. I was stood on the offside of the car so at this point I cant say for certain what the nearside wheel was doing, but can assume based on what happened later it was acting as you would expect, however, the offisde wheel would slow very quickly when he changed gears, almost to an immediate stop.

 

We advised the tester of this and he, like us assumed a binding brake drum, so we tried moving each wheel by hand, and they span freely. So he tried again, only this time the nearside wheel span up fine, but the offside did not move at all, at which point we abandoned that part of the test assuming a knackered diff.

 

Later on during the test when I was required to drive the car, when changing from 1st to 2nd the car seemed to noticeably slow, again like a stuck on brake.

 

I have another known good diff sorted, so I can change it, but I was wondering if the great minds that are the rhocar membership had any other ideas on what else could have caused these symptoms?

[brumster]

Wonder if it's something on the input (prop) side of the diff...? So turning wheels by hand - I assume both wheels were free - would just rotate the diff and the input was held tight for whatever reason, so they would feel to spin freely.

 

Does the engine feel laboured at all, have you had a chance to even floor it in any gear? I wonder if the engine is out of tune and not making big numbers on wider throttle openings, so when it gets into 3rd it's not got the pull? Or maybe this is with a combination of some 'sticky' part of the transmission, but the gearing of 1st and 2nd makes it far less noticeable... maybe the gearbox or diff input bearing are a little 'toight' ?

 

You did put oil in them didn't you ;-)

 

Maybe drop the prop off the diff (just unbolt it) and have a twiddle, see if anything is stiff from the prop down into the gearbox/engine, and at least you rule that out and know it's the diff and not the box?

Edited May 8, 2015 by brumster

[cb750]

I agree with brumster. Can't really see how it's the diff unless it's the input bearing. Sound very much like something in the transmission line as you have ruled out the brakes.

[sj-bradley]

Did you install the brake pads the right way round? If one wheel is still spinning and the other stopped, the spinning wheel is going at twice the normal speed which may add to the load on the engine significantly feeling like a power loss.

 

It sounds like the pads are getting snatched up and causing excess drag. Did the drums feel hot at the time?

 

Simon.

[Guest mower man]

If the preload on the rollers is not balanced the diff will work as it supposed to [ as if one wheel is jacked up and spin ] mick

[Bob Tucker]

Put the car in neutral, jack up just one wheel, & try spinning it.

If it turns freely, the diff internals, the crown wheel & pinion, the input bearing

& the neutral cogs in the gearbox are all fine.

Drop that side, jack up the other side & try it again.

Post results & we'll look again...

[Guest 2b cruising]

Might be worth while jacking one rear wheel up , chocking the other three.

Run it up and see how it is.

Does it still stall out in third. Are there any noises coming through the drive line.

Then try the other side.

This might help determine where the fault lies.

If it still stalls out in third, it may not be a diff fault but gearbox. As already stated, if no resistance on rollers, the diff is acting as it should.

Cost you nothing to try this.

 

I will have to type faster.

Edited May 8, 2015 by 2b cruising

[Guest 2b cruising]

Though - IF its a dodgy diff and you are one wheel down relying on the diff to let it stay stationary with engine running - possible the car will move even with one off the ground?

 

Do you think 2b?

not if you start off at idle then work up slowly. That's why I said chock remaining wheel well.

It could even be done by lifting both wheels off the ground and lock one side brake out followed by the other.

If as already tested, both wheels turn freely, the diff will not jam up anyway.

I also should state the obvious, when cars are jacked up, the jack itself should not be relyed on. Use blocks or stands at all times when working on the car.

Edited May 8, 2015 by 2b cruising

[richyb66]

Stu, I think you should be looking at the prop. When I unbolted the prop plange from the diff, I couldn't turn the prop by hand, it was very stiff and I had to turn it with a big screwdriver through the joint. (though the car does seem to roll, it does take some pushing)

 

Also, the prop didn't slide easily in and out of the gearbox (again I had to use a big screwdriver to move it). Something isn't right?? As you can't see the front ent of the prop easily, I'd drop the diff out so you can check it runs freely and then have a look dow the tunnel at the prop and see why it's not moving freely in the box.

[Guest 2b cruising]

Stu, I think you should be looking at the prop. When I unbolted the prop plange from the diff, I couldn't turn the prop by hand, it was very stiff and I had to turn it with a big screwdriver through the joint. (though the car does seem to roll, it does take some pushing)

 

Also, the prop didn't slide easily in and out of the gearbox (again I had to use a big screwdriver to move it). Something isn't right?? As you can't see the front ent of the prop easily, I'd drop the diff out so you can check it runs freely and then have a look dow the tunnel at the prop and see why it's not moving freely in the box.

The prop itself is just a shaft with no working parts that would make it hard to turn. By turning the loose diff end and finding it very difficult to turn is pointing toward a gearbox fault.

However, as you have a new diff coming anyway, it might be worth while removing the diff back plate and inspecting the working of the diff part anyway.

I would still run it up first and listen for noises and see if it still stalls out in third.

Edited May 8, 2015 by 2b cruising

[richyb66]

If the diff isn't perfectly in line with the gearbox (which it won't be) then the spiders in the joints need to rotate as the prop turns.

 

Siezed or damaged rollers in the spider cups would make the prop harder to turn.

 

Consider everything, discount nothing as a possible cause.

[richardm6994]

We advised the tester of this and he, like us assumed a binding brake drum, so we tried moving each wheel by hand, and they span freely.

 

Thinking this through from what has been said.........you've already established that the wheels spin freely.....so it's not brakes or drive shafts.

 

Did you do anything to the nose of the diff when building the car?......It has a crush collar inside the nose and if you overtighten this it can cause problems / tightness.

 

If your diff spins freely....check your prop UJ's move freely....

 

If they are ok......could it be that your engine was out of tune.....ignition timing etc....causing it to bog down under load....and the wheel thing is just a bit of a red herring?

[theduck]

Engine tune is not right. Though revs fine out of gear. It is driveable enough for me to get it to Steve Walford for so could do that but if we can't get it running on the rollers when it's there...

 

I will see if I can replicate the issue with both wheels in the air and post a video.

 

Lots of ideas of things to check though so will work through them and post findings.

 

[Grim]

personally i'd keep it simple. Fix what you know to be wrong and then reassess.

 

Perhaps check your wheel bearings as it's not unknown for people to have problems with incorrect or over tightness there.

[HAWKNORTH]

If you are removing the prop shaft you could run the engine and work through the gears without any load in the drive chain.