LSD Question

LSD Question 1993 Buick Roadmaster 88k Mi 5.7L RWD

Recently on acceleration, the right rear tire spins until I let
off the gas a little, but this car has a Limited Slip Differential
so that shouldn't happen. The RR tire is normal, like the rest,
and not slick.

It only happens occasionally, on medium to hard acceleration
from a stop. Not drag race acceleration, just entering-the-
freeway-from-a-stop acceleration.

I checked the differential and it is full to the fill hole, but I have
only had the car for 1 month and I don't know what lubricant
is in there.

Does this condition indicate a failing differential? If so,
what is failing, and what actions are possible to treat the
problem? New gears? New lubricant? New Rear End?
Other? What other checks can I make?

Thanks for any ideas.

Rodan.

Rodan wrote:
> LSD Question 1993 Buick Roadmaster 88k Mi 5.7L RWD
>
> Recently on acceleration, the right rear tire spins until I let
> off the gas a little, but this car has a Limited Slip Differential
> so that shouldn't happen. The RR tire is normal, like the rest,
> and not slick.
>
> It only happens occasionally, on medium to hard acceleration
> from a stop. Not drag race acceleration, just entering-the-
> freeway-from-a-stop acceleration.
>
> I checked the differential and it is full to the fill hole, but I have
> only had the car for 1 month and I don't know what lubricant
> is in there.
>
> Does this condition indicate a failing differential? If so,
> what is failing, and what actions are possible to treat the
> problem? New gears? New lubricant? New Rear End?
> Other? What other checks can I make?
>
> Thanks for any ideas.
>
> Rodan.

That sounds normal to me. All the GM limited slips I have owned would
allow the RR to spin up from a stop. If I was moving 3-5 mph instead
and floor it on gravel, I have two rooster tails.

One good test for a worn out locker or limited slip is to jack up both
rear wheels and hand spin one wheel. If the other side spins the same
way as the one you are hand turning, the limited slip is functioning.
If the wheel turns the opposite direction, the limited slip is worn out
or not there.

There is also an 'old' trick that is even in my Jeep owners manuals for
locking up both rear wheels from a start, no matter if you have an open
diff like I do or a limited slip.

When stuck on ice and having the RR and in my case LF tires spinning
away and going no place fast while my friends are gong for tow straps, I
can give the brake pedal a hard hit while giving the gas a pulse. This
loads up the free spinning tire so the torque needed to keep it spinning
against the brake pressure equals the torque needed to break the other
tire free from the ground, so both tires spin up. My owners manuals say
this can also be done by applying the emergency brake but I have much
better success with using the brake pedal. It takes practice, but it
works very well.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com

Rodan wrote: ( 1993 Buick Roadmaster 88k Mi 5.7L RWD)

<Question about RR tire spin when car has Limited Slip Differential>
__________________________________________________ _____

"Mike Romain" wrote:

That sounds normal to me. All the GM limited slips I have owned would
allow the RR to spin up from a stop. If I was moving 3-5 mph instead
and floor it on gravel, I have two rooster tails.

One good test for a worn out locker or limited slip is to jack up both
rear wheels and hand spin one wheel. If the other side spins the same
way as the one you are hand turning, the limited slip is functioning.
If the wheel turns the opposite direction, the limited slip is worn out
or not there.

There is also an 'old' trick that is even in my Jeep owners manuals for
locking up both rear wheels from a start, no matter if you have an open
diff like I do or a limited slip.

When stuck on ice and having the RR and in my case LF tires spinning
away and going no place fast while my friends are gong for tow straps, I
can give the brake pedal a hard hit while giving the gas a pulse. This
loads up the free spinning tire so the torque needed to keep it spinning
against the brake pressure equals the torque needed to break the other
tire free from the ground, so both tires spin up. My owners manuals say
this can also be done by applying the emergency brake but I have much
better success with using the brake pedal. It takes practice, but it
works very well.
__________________________________________________ ______

Ashton Crusher wrote:

I used to have a 95 Caprice which I think is pretty much the same car.
It had the 5.7L corvette engine but I don't recall if it has Limited
Slip. I do know that I often accelerated hard in it and never had a
problem with rear wheel spin. You say "recently" this happened, does
that mean it wasn't doing this before and nothing has changed (that
you know of) and now it's started doing it? I had an 88 Caprice that
would easily spin the RR, unlike my 95. About the only thing I can
think of is that your LSD went bad, you have a spring that cracked and
that corner of the car is no longer holding up it's share of the
weight, or the tire is worn out even though it might look ok or maybe
the colder whether has made the rubber harder and less sticky.
__________________________________________________ _

Thanks for the insights, Mike and Ashton. My experience with LSDs
is that they are there to prevent single wheelspin. I love Mike's ice
trick for non-LSD cars. I used it more than once years ago, but in my
current advanced age (71) my taste for adventure has faded and I
religiously avoid getting into icy situations.

Yes, the Roadmaster is almost exactly the Caprice under the sheet metal.
Buick openly calls the engine a Chevy. My use of the word "recently"
was misleading because I have only had the car one month, so everything
that happens happens "recently". It may have always had this condition.

This 93 Roadmaster has less features that my former 92 Roadmaster.
The 93 has mechanical seat adjustments, a manual outside mirror adjustment,
and slide-and-fan-speed temperature control instead of presettable climate
conrol. Looking up its specifications reveals that LSD was an extra cost
option. So my 93 may not have LSD at all, therefore it may be working
normally. Anyway, I will spin the rear tires next time I have it in the
air.

Thanks again for the comments.

Rodan.

Ashton Crusher wrote:
> On Sat, 29 Nov 2008 06:41:27 GMT, "Rodan" > wrote:
>
>> LSD Question 1993 Buick Roadmaster 88k Mi 5.7L RWD
>>
>> Recently on acceleration, the right rear tire spins until I let
>> off the gas a little, but this car has a Limited Slip Differential
>> so that shouldn't happen. The RR tire is normal, like the rest,
>> and not slick.
>>
>> It only happens occasionally, on medium to hard acceleration
>>from a stop. Not drag race acceleration, just entering-the-
>> freeway-from-a-stop acceleration.
>>
>> I checked the differential and it is full to the fill hole, but I have
>> only had the car for 1 month and I don't know what lubricant
>> is in there.
>>
>> Does this condition indicate a failing differential? If so,
>> what is failing, and what actions are possible to treat the
>> problem? New gears? New lubricant? New Rear End?
>> Other? What other checks can I make?
>>
>> Thanks for any ideas.
>>
>> Rodan.
>

Look on the option sticker for G80. That is the normal GM code for a
locking rear.
However the G80 does NOT operate like a standard LSD. It is a governor
controlled unit.
One tire has to spin at least 100rpm faster than the other AND you have
to be going slower than 20mph for it to work. They are also known as the
"grenade80" because they have a nasty habit of blowing up even when not
abused.

--
Steve W.
Near Cooperstown, New York