Rebuilding LSDs and fitting 115 LSDs to 101/105 Diffs - Alfa Romeo Bulletin Board & Forums
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post #1 of 55 (permalink) Old 01-19-2009, 10:42 AM Thread Starter
Richard Jemison
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Rebuilding LSDs and fitting 115 LSDs to 101/105 Diffs

This started in a non related thread and I am copying it here and expanding it for member interest.
The Earlier post from the "Lowering" thread is below, in blue. I will expand a bit for better explanation:
There is just no reason to spend big bucks for aftermarker LSDs when a PROPER set up 115 LSD unit will handle 300+ HP easily with stock 4 disk layout.
The layout of the normal 4 disk setup, is to separate the 2 disk on each side by floater plates. In this manner the locking ratio is in excess of 40%. This is a bit too much for street use, as in rain, the rear will be very hard to control. But hard driving, autocrossing, with a single disk on each side will often strip the internal teeth off of the clutch disk, as one disk is just not up to the task of drag racing, autocrossing or that type hard use. Particularly where there is some wheel speed differential involved. For such application the LSD unit can be assembled with 4 disk but with the 2 disk on each side placed together rather than separated as in the race set up. this continues to provide about 25% lockup as the factory built, but twice the amount of metal to drive the axles on each side.
The disk are very durable and a good cleaning and media blasting will bring them back to as new condition generally. If galled toss them. They are available in every 2 liter diff, and most Alfa parts supliers. The floater plates are made in several different thicknesses for setting up the units with the correct amount of freeplay. I set up a street LSD with about .015 total to keep it quiet, and a 4 disk racing unit with about .030-.040 total dry. Always build dry, you can measure, then when lubed it works correctly.

The units do get noisey when it is time to re-set up the shim pack but they don`t quit working until they get like the bottom picture.
For the competition side of the spectrum, the "road" racers use the units fairly hard but the 4 cyl cars really don`t stress the units much if set up correctly. Neither do the 6 cyl. cars in a road racing environment. These guys are quite gentle on equipment.
The problem is somewhere, someone started suggesting that the "racing" setup" was to "preload" the unit so that it was "loaded" before the ramps moved off of the bottom of the ramp. In reality all they were getting was the initial feeling of "lock" and not much more as the LSD unit could not do what it is designed to do. For it to work the plates must have a bit of room to allow the axles to move in the ramps and the plates compress the clutch disk. Then you start to have some of the design lock up.

The same 115 LSD can be machined to fit into a 105 (and 750 and 101) axle and the axles resplined to fit the 115 center. (see fitst 2 pics)

We have a local "Autocross" racer with a 3 liter Supercharged Milano, with 13 inch wide wheels and race tires who really only cares about winning. (Remember the "guts" of the 116 LSD is the same as the 115 Spider`s internally)
I originally set this up 3 years ago, and just this week had to "re-gut" it. (tossed out all the internals but could re-use his LSD housing so he just had to jerk out the ring gear and housing and UPS it to me. So it required no new pinion set up$$$)(see lower pics)

1st pic- LSD for 101/105 with 5.13 gears in backgroubd compared to stock 115 LSD in foreground.
2nd pic- LSD (modidied 115 in 101/105 Diff housing with 5.13 R&P
3rd -5th pics internals from LSD from 3.0 Supercharged AutoX Milano. Note no teeth in clutch plates! Still pushed the car since the stripped teeth from the clutch disk locked the drive drums, and the lower left part is a clutch disk friction welded to a floater plate???

Since racing Alfas since the `60s this is the first really "ruint" LSD I have had the misfortune to have to fix
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post #2 of 55 (permalink) Old 01-19-2009, 03:18 PM
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Richard,

The rebuilt LSD arrived today...thanks!

Wife went with me to the Delta Region Awards banquet--I never told her what it cost to get that lucite trophy and the magnetic decals for winning Street Modified for the 2008 Region Series....
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post #3 of 55 (permalink) Old 01-20-2009, 08:08 AM
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So, what is the main contributing factor to the destroyed LSD? Is it the nature of AutoX? All that SC power combined with the traction generated by the HUGE tires?

Would a road racing (where smooth is the name of the game) 116 with same or more naturally aspirated power, running 235 to 245 Hoosiers R6 face similar LSD issues? How many events/track time did it last?

Jes

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post #4 of 55 (permalink) Old 01-20-2009, 01:27 PM Thread Starter
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LSD Use.......

Road racing by most drivers won`t hurt these LSD units. If they are set up correctly. If they are set up with "preload" they will slip and overheat the clutch disk, burning a carbon coating on them, which reduces their lock up effectivness, increasing the problem ad nauseum...

Bill`s use, is like no other.
I have no idea how many runs were on this transaxle, but it is way more than expected! He will have to supply that info!

Richard Jemison
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post #5 of 55 (permalink) Old 01-20-2009, 04:42 PM
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Number of events

Probably about 60 events, with between 4 and 6 runs per event.

These days, with sticky tires, autocross in not smooth--it is violent. .8 Gs acceleration, .8 Gs braking, 1.25 Gs cornering (I have data acquisition). Very hard transitions that throw your head around if you aren't ready.

I'll likely need to send the LSD to Richard every 18 months or so to keep it in decent shape, and not let it get to the condition it was in this time.
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post #6 of 55 (permalink) Old 01-21-2009, 04:40 AM
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I agree; that's why it's so much fun. The goal is to link all of this violence into a good timed run; which, interestingly, can look smooth to a spectator. My favorite definition of autocross is "Controlled rage" (apologies for the slight thread highjack).

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....These days, with sticky tires, autocross in not smooth--it is violent. .8 Gs acceleration, .8 Gs braking, 1.25 Gs cornering (I have data acquisition). Very hard transitions that throw your head around if you aren't ready....


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post #7 of 55 (permalink) Old 01-22-2009, 11:19 PM
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Ok, so to pick up from the other thread... When I installed this rear end over the summer (for all of 24 hrs) before installation, I spun the axles and it was a bit on the loud side, kind of a rumbling noise. Once on the car and driven, it sounded like I had a splash guard rubbing some place (shrill squeaking noise) and the rumbling was really bad. Do these symptoms sound like bad wheel bearings plus dead LSD or just bad wheel bearings. There was no rubbing on the splash guards and I couldn't find anything else to make the noise. The axles do have some play in them but only in the in and out direction.

I'm trying to diagnose this because I don't have a work shop that I can pull this apart at leave it for a while, its got to come apart and go back together in a day or so.

Thanks,
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post #8 of 55 (permalink) Old 01-24-2009, 05:38 AM Thread Starter
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Diff Issues

Quote:
Do these symptoms sound like bad wheel bearings plus dead LSD or just bad wheel bearings. There was no rubbing on the splash guards and I couldn't find anything else to make the noise. The axles do have some play in them but only in the in and out direction
The in & out play are issues related to wear/ bearing size (OD of the outer race case) that is thinner than stock or wear. Common Problem. Solution is to use retaining "C" clips from later syncronisers as shims between bearing retaining plate and bearing in the housing. The "C" clip cab be opened and slip right over the axle and be clamped perfectly in the retainer housing, as if it were made to go there!
An RjR Special!
But you need to change the wheel bearings anyway to get rid of the noise. Heat them a bit they will come off easier.
I would suggest you run the diff then without the axles to listen to the R&P if it is quiet (no whining noise), then I would suggest pulling the LSD out and just tightening up the shim pack to get it back in order.
Usually the bearings are very durable inside unless abused. If so find another 3rd member and start over.

Richard Jemison
RJR Racing

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post #9 of 55 (permalink) Old 01-24-2009, 10:45 AM
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Excellent discussion. Teach me MORE!


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post #10 of 55 (permalink) Old 01-24-2009, 05:32 PM
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post #11 of 55 (permalink) Old 01-25-2009, 07:03 PM Thread Starter
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Subtle`s Carbon Fiber LSD Parts

I know Bob likes to have his "special" LSD pieces show up on the BB occasionally.
I built him a LSD for his 101 Spider Diff using Carbon Fiber LSD Clutch Disk, with resplined axles to fit the 115 modified LSD unit.
Only Street one in existance!
The CF ones are overlayed "normal" clutch disk in the pics
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post #12 of 55 (permalink) Old 01-25-2009, 07:18 PM
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Agghh! You KNOW you do this Richard just to make me crazy! Are you going to mention that there are no more?


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post #13 of 55 (permalink) Old 01-25-2009, 09:31 PM
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Gee..

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post #14 of 55 (permalink) Old 01-25-2009, 09:43 PM
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Soon we will talk about RJ's "grippage" and who has more any why. I like grippage!


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post #15 of 55 (permalink) Old 01-25-2009, 11:49 PM
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Quote:
Originally Posted by Alfar7 View Post
The in & out play are issues related to wear/ bearing size (OD of the outer race case) that is thinner than stock or wear. Common Problem. Solution is to use retaining "C" clips from later syncronisers as shims between bearing retaining plate and bearing in the housing. The "C" clip cab be opened and slip right over the axle and be clamped perfectly in the retainer housing, as if it were made to go there!
An RjR Special!
Richard,

Thank you for referring me to this tip in the other thread, and thank you also for the kind offer of further help during my LSD's R&R. I'll pass on this information to the guy who will be doing the (re)rebuilding, and let you know what's found when the case comes apart! I'll be in touch about those dropped spindles in due course (first priority is to sort out an gigantic quantity of parts I've just purchased).

Cheers,

Alex.
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