Jump to content
Guest Anonymous

Max lock for E21 LSD rebuild?

13 posts / 4710 viewsLast Reply

Recommended Posts

Guest Anonymous

Without getting into changing the ramp angles, what is the maximum lockup that can be achieved with an E21 LSD (168mm small case) by adding more friction discs? How many discs total can be used and what thickness would they be? The reason I ask is that I had a 25% E21 LSD rebuilt and shimmed to about 40% a number of years ago. (I did not measure the breakaway torque then, so I can't tell how much the slip-limiting has degraded with use.) I am having the LSD opened up for a ring & pinion swap and thought I might have the locking percentage increased if possible. I have read that E21 LSDs cannot be shimmed as high as the original 2002 LSDs--I assume it has to do with how many or how thick of discs can be added. Thanks.

Fred

'74 tii track car

Silver Spring, MD

Share this post


Link to post
Share on other sites

I'm fairly sure >50% is possible. Ireland Engineering can tell ya. Might be something on their website also.

Cheers,

Ray

Share this post


Link to post
Share on other sites
Guest Anonymous

Thank you. I have done extensive internet research on LSDs, but talking to someone who knows their stuff is always the best. I have not seen specific references to e21 LSD's with high lock ratios, such as 75-90%. At this performance level people get into ramp angle changes, quaifes and such. I am just looking for what can be easily done while we have this diff apart for the RP swap. The answer may be to wait until I have the money for a highly modified unit, but wanted to ask people's experience here.

Thanks,

Fred

Share this post


Link to post
Share on other sites

ramp changes is a pure myth. I dare you to find any reliable data on that.

in order to work (ramp) both wheels need to have traction. as soon as one wheel looses its grip, only the preload on the clutches will give you grip to the wheel/ground.

inspect ANY lsd where the ramp are. there is no wear above where the end of the cross sits. period.

with a e21 25% you only have two clutches set. increasing the sliping factor too much will lead to overheating of the clutches and very fast wear.

have a early one with 40% where you can easely modify it to add 2 more clutch set.

I successfuly modified a 25% to a 70% by adding two clutches set (one on each side), but it required machining and very specific tooling and black knowledge.

Share this post


Link to post
Share on other sites

Making it a 4 disc set up is the way!! I run one in my car for 4 years now. I built mine, but Metric Mechanic is set up to do them. Give them a call should not be a problem.

Share this post


Link to post
Share on other sites

50% is straightforward with the addition of a pair of clutches. Machining of the LSD housing and end cover required. The original 2002 40% units get their extra lock up from different ramp angles, so that is not a myth. To get more out of a E21 unit, you'd have to modify the ramp angles (and realistically also reharden the parts, so that the shafts don't wear through.)

A 50% 4 clutch E21 unit is plenty for most track use, IMHO. Plus it'll last longer and run cooler than the stock 25%

Share this post


Link to post
Share on other sites

I prefer a more simple approach. Fabricate a .020 to .022 shim and add it on to the stack with a set of new disks. I do this every three to four years for my race car. Works fine. How much additional lock up does it provide - don't know. But, it works fine!

Bob

Share this post


Link to post
Share on other sites
Guest Anonymous

Great! Many thanks for all the replies. This is exactly the kind of info I was looking for. Best, Fred

74tii track car

Share this post


Link to post
Share on other sites
50% is straightforward with the addition of a pair of clutches. Machining of the LSD housing and end cover required. The original 2002 40% units get their extra lock up from different ramp angles, so that is not a myth. To get more out of a E21 unit, you'd have to modify the ramp angles (and realistically also reharden the parts, so that the shafts don't wear through.)

A 50% 4 clutch E21 unit is plenty for most track use, IMHO. Plus it'll last longer and run cooler than the stock 25%

the static % friction factor is set by presure set on the clutches, by the spring washer or the overall thickness of the clutches, not the ramping.

Ramping will increase locking factor ONLY when both wheels get traction.

Ask metric mechanic what they does when they take a 25% and bring it up to 40%. No, they dont change the ramping.

And a 25% compared with a 40% are totaly different units. They are mechanicaly very different. I have both in my home basement and can show you how different they are, i wouldnt compare them ever.

I opened enough lsd's and played too much with them to stand correct with all i am saying.

And before assuming you realy require more % factor, try a bone stock 25%.

Share this post


Link to post
Share on other sites

I'd check in with Dave at Aardvarc for some adviace and or parts. He built mine (he rates it at 40%) and it works great. For me its not too much and not too little. Then there is always room for some adjustment using friction modifier.

Share this post


Link to post
Share on other sites
Guest Anonymous

PatAllen wrote:

Ask metric mechanic what they does when they take a 25% and bring it up to 40%. No, they dont change the ramping.

-----------

Thanks, a very interesting discussion. But now I'm a little confused about the value of ramp modifications. MM says their Variable Limited Slip varies from 20% to full lock-up, depending on side load and acceleration/deceleration. From their diff booklet, this is done by lowering the initial slip rate, changing the ramp angle, and increasing the number of clutch discs. According to MM (quote below), the changed ramp angle is important. Of course, here they are talking about a variable LSD, not just a straight increase in % lock from adding friction discs.

From the booklet:

http://www.metricmechanic.com/pdfs/metric-mechanic-differential-booklet.pdf

“Metric Mechanic’s Variable Limited Slip works by lowering the limited slip down to 20% from 25% and decreasing the ramp angle to 30° from 45°. These reductions make it easier for the spider gear pin to move up and down the ramp angle of the thrust plates allowing the thrust plates to push out and increase the load against the limited slip clutch discs.”

MM small case diff specs:

-------------------------

Stock 2-disc: initial lock 25%, breakaway torque 44 ft-lb, ramp angle 45°

MM 3-disc: initial lock 20%, breakaway torque 35 ft-lb, ramp angle 30°

MM 4-disc: initial lock 20%, breakaway torque 35 ft-lb, ramp angle 30°

It may be that my 40% LSD is just fine for my use. I have never had any inside wheel spin on the track in the dry. However, I am upgrading the engine significantly, and thought it might be worth increasing the diff's % lock at the same time if it is not too expensive.

Thanks, Fred

Share this post


Link to post
Share on other sites

I think the 40 number is easier to obtain without major work and I should state that my car does see use on the road so higher lockup would be a hinderance and create unneeded stress on the rear axle. I had run my 25% with red line friction modifier to check out the lock and see what I liked and the 40% unit from Dave was just about like I had been running the 25%. I drive hard and the car see's lots of hairpins and I almost never have any wheel spin.

I like Bob's approach.

Share this post


Link to post
Share on other sites

I have quite a few now that are 100% lockup.

heh.

t

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.