What are your views on this?

[West7se]

Hi all

 

I am just after some thoughts on the idea of a welded up open diff.

 

I know folks do it to `drift cars`, but has anyone ever done this on a live axle seven?

 

The reason for asking is that I have the live axle open MK2 Escort diff and it has huge amounts of backlash in it, now I have not stripped it yet so I am not sure what parts have worn, but you can spin the wheels between 12 o`clock to about 2 o`clock before the backlash is taken up. I can`t really afford an LSD to be honest and this wacky idea came into my head.

 

Your comments for and against welcome.

 

Cheers

[Ian7]

Not yet going in to the (any?) pros and (many) cons of a locked diff on the street, my first thought is that a backlash that gives 60 degrees of rotation may suggest a problem much greater than can be 'cured' by simply welding up the diff....

[slngsht]

I think the car will plow through corners with a locked diff, and parking spot maneuvers will just be painful.

[scannon]

Not good for street or track use. With both wheels locked together the car will resist turning, it wants to go straight. To make a turn it must slip one rear wheel, usually the inner one. You will squeal the tires on almost every turn you make.

 

I think you are better off with an open diff. The ring and pinion are the most likely suspect for the play you are experiencing. Try adjusting the backlash.

 

It also puts more stress on your front suspension.

 

I did this once in the 60's with a Corvette powered A-H 3000. It was miserable to drive and ate a lot of front wire wheels. I eventually replaced it with a Chevy posi-traction rear end when I was able to scrape up the money as I was a poor college student at the time.

[West7se]

Thanks folks, I did already know of the tyre scrub and possible understeer issues, perhaps as Ian7 says I need to look at the causes of the backlash first.

 

After paging through 600 odd pages of various ford and locost sites, the general views are that the backlash is caused by the pinion not mating with the crownwheel correctly. As I mentioned I have not yet stipped the unit down, but the adjustment is via a collapseable bush apparently.

 

The diff still operates ok apart from the cluck when taking up the backlash, it has an oil leak between the front and main cases, but thats just a gasket issue which I am not worried about at this stage, getting back to the locked diff thing, I did find a thread on the locost site asking the very same question as myself. As you have all said its not really an option for general use of the car, but there were a few posts actually questioning the need even for an LSD on such a light car, which I thought was interesting.

 

The thread is below.

http://www.locostbuilders.co.uk/viewthread.php?tid=24764

 

I also took the liberty of coping the text from a post that describes how to set the diff up for loads etc.

 

Copied text>

"I don't know the specifications for the diff you're using, but below should give you an idea of what your looking for. I'm a Technician at a Ford dealer and regularly work on diffs. Been doing it for 20 years or so. Apoligies if some of this is old hat for some, but for the benifit of anyone else who may be interested, here goes.

Normally if the gearset doesn't have too many miles or any abnormal noise I'd re-use them. If you're just replacing seals and bearings and no abnormal noises were present. I'd re-use the originally pinion depth shim. Pinion depth is how far the pinion engages into the ring gear. It remains the same with the original gear set and original case, but if anything is changed it needs to be re-set. A bit beyond this proceedure.

The amount of force that's required to rotate the pinion flange is the pinion preload. Its measured with a spring scale(like for wieghing fish) and a short bar and a bit of math or with a dial type torque wrench on the pinion nut. The pinion preload is generally between 8 inch pounds and 16 inch pounds. (2 ft lbs is way too much thats 24 inch pounds. a bit much for the small diffs we would use) It's measured with just the pinion, bearings, seal, flange and nut installed. Not the ring gear. All measurements are made with the bearings lubricated in new clean oil. If you need more preload tighten the pinion nut. If you go too far, pull it apart and get another collapsable spacer. They don't stetch or spring back, once they're crushed thats it. I always use a new collapsable spacer. They are only a few dollars so why risk ruining the cost of everything else you just done over a dollar or two. Some diffs use shims instead of a collapsable spacer, but the same thing applies, add or subtract shims until you get the correct preload.

To explain carrier bearing preload. A certain amount of shims will just eliminate any play. The specified preload is the extra amount or thickness of shim that will need to be added beyond that. If threaded adjusters are used then they are generally torqued to a certain amount- I recall something in the order of 60 foot pounds for larger diffs. Its not a bad idea to keep track of what was originally there as its usually not too far off.

Now the total gear back lash is adjusted by taking shims from one side and adding them to the other. Always keeping the same total thickness. The back lash is measured with a dial indicator on a ring gear tooth. Its gernerally in the range of 0.008 inch to 0.016 inch Larger gearsets are usually in the higher range smaller in the lower. You need this play or distance between the gears to allow for heat expansion and to give the gears a bit of room to move against each other. No need to get too picky yet as this may be re-adjusted in the next step. You just try to get it some where in the middle of the specs. Then a paste like marking compound is painted on the ring gear teeth. It can be anything that'll stick but can be wiped or rubbed of by the gear teeth. The real stuff is lead based so be careful. I've used chalk, blueing while its still wet, and crayon. It sometimes pays to be inventive here. Rotate the gears against each other and apply a bit of force. Your looking at the convex drive side of the ring gear. What gets wiped off is the point the gears are sliding against each other. The aim is to have the area of contact in the center of the gear and the back lash within the specified range. Dependant on the pattern it may be necesary to adjust the pinion depth. I usually aim to be in the low side of the specs to allow for wwear.The correct setting of pinion depth is quite a bit more involved as is reading the contact patterns and knowing what to adjust. It wouldn't be harmfull to make an adjustment the wrong way if things are done in small amounts. Just keep track of where you started in case you have to go the other way. Hope that helps."

[Kitcat]

My modestly powered open diff dedion seems to corner better at the track when it lifts the inside rear wheel a bit. The heavily loaded outside wheel has super grip and the inside, lightly loaded wheel very little so it spins slightly as it loses traction. The result is the car seems to pivot around the slightly spinning inside wheel in the desired direction around the turn.

 

If I had tons of power it might really light up the spinning wheel and subtract power from the outside one. But that doesn't seem to happen on my car. Again, it's all about balance.