No I don’t actually lug the engine at 1700 RPM and 60 + MPH…but almost.
It will pull over the Cascade mountain passes in OD with the Cruise on but
really loses speed. At very low RPM’s such as I am running there is a
noticeable lack of reserve torque.It will run over the same route in D
without missing a beat.
After spending an hour at the swap meet talking to a 700R4 rebuilder about the
lockup issue, I glean the following, which is about the point Wes makes. The
700R4 raises a torque issue when towing or going up mountains in overdrive.
The problem is not with the engine or tranny per se, it is with where the torque
requirements are reflected. According to him, 70MPH on the flat requires very
little torque, so a .78 ratio works fine. However, when towing or going up
a hill, the torque required increases even though, initially, the engine speed
does not. Those who use more throttle to resolve the problem create tremendous
negative numbers which translates to heat in the tranny, particularly the torque
converter. According to him, the way the tranny is built, at low rpm-high torque
demands, it cannot cool the fluid effectively, and you ultimately ruin the gearbox.
Simply shifting the R4 to third, which is 1:1 [like 3rd in the TH350] imposes
no strain on the engine or tranny, and keeps fluid circulation and temperatures
where they belong. Normally, the radiator cooler is adequate. Under extreme
conditions, a tranny cooler is useful. Otherwise, he said, the 700R4, properly
rebuilt with heavier clutches, etc, is increasingly the racers’ choice. The
moral of his story is, “Downshift!”
Richard
Rear Ends: What car do the 3.31 rear ends come out of? How much does
one cost?
Russ
As I understand it various XJ6 Series II’s and XJS’s. As I understand it
either can be used in a Series III XJ6…provided you have the right
one. There are apparently two different standard (not limited slip) rear
ends. The difference is in the way in which the actual rear gear “pumpkin”
attaches to the rear axles. Replacement cost from Coventry West is
something on the order of $800 for a remanufactured unit. Jaguar does not
provide access to ring and pinon gears but there has to be a supplier
somewhere to support the remanufacturing process. I just haven’t found it
yet.
The tach readings you report parallel mine with essentially the same drive
line. My approach so far has been to just drive the vehicle in 3rd gear
instead of overdrive unless I am on the highway. The 700R4 handles that
fine…In fact GM recommends that procedure whenever it is used in towing
and I have done it for years while towing boats with my '84 Suburban.
If you find a source for either a less costly rear end replacement or the
appropriate parts to change the gearing in an existing unit let me know.
Wes,
Thanks for the toughts on the rear end. I have been pondering what you
said in the past concerning your rear end and transmission. Do you
actually lug your engine on the highway? And is this under normal use? I
do alot of highway driving and I would think that fewer RPM’s the better.
Obviously there is a limit to this logic
-Mark Dierker
Columbia, Missouri.
Mark
First, my components.
350 TPI, 700R4 Transmission, 2.88 Rear end, 215x65HR15 tires(same
Revolutions per mile as 205x70xVR15)
No I don’t actually lug the engine at 1700 RPM and 60 + MPH…but almost.
It will pull over the Cascade mountain passes in OD with the Cruise on but
really loses speed. At very low RPM’s such as I am running there is a
noticeable lack of reserve torque.It will run over the same route in D
without missing a beat.
The TPI engine will handle the the low RPM’s because of the computer
adjustment of timing and throttle is better than a normally aspirated
engine which relies on vacuum and centrifical force. Basically the 350
starts to “breathe” around 18-1900 RPM’s and runs strong through about
34-3500. Different Cams will change the range.
In terms of highway cruising at 60+ MPH the OD is fine and provides 20+
MPG. However, unless I am actually on the highway I use D to maintain the
RPM’s in the 2000-3000 range (2000=50MPH and 3000 gets tickets). This is
the same as your TH350 in D. My view of the 3.31 rear end gearing is tied
to having the 700R4 OD capability. It would raise cruise RPM’s somewhere
around 200 which should put me closer to the bottom of the power/torque
curves. I still wouldn’t be beyond 3000 RPM’s in OD until the 100 MPH
range. In D however RPM’s would be approaching 3500 at 75 MPH.
The short version is that the 3.31 will give you more “scat” but will cost
you for fuel on I-70 and running around the Ozark Mtns. Remember these are
4000 lb. luxury touring cars and they respond accordingly. My opinion
boils down to higher gearing (2.88) with the TH350 or 400 and lower gearing
(3.31) with the 700R4 to position the engine in its best operating range.
My experience after several hundred thousand 700R4 miles pulling 5,000 lb.
trailer with my Suburban in the fornt range of the Rockies says:
Make sure the torque converter lockup is functioning properly.
Add an external transmission cooler.
Service the transmission regularly at about 30,000 miles.
Use synthetic Transmission fluid.
Never ever use the OD when pulling a trailer and downshift to drive
based on RPM’s to maintain desired speed.
Wes (Just replaced the 700R4 in my cat last fall because the DPO didn’t do
1,2,or3)
700R4 raises a torque issue when towing or going up mountains in overdrive.
The problem is not with the engine or tranny per se, it is with where the
torque
requirements are reflected. According to him, 70MPH on the flat requires
very
little torque, so a .78 ratio works fine. However, when towing or going up
a hill, the torque required increases even though, initially, the engine
speed
does not. Those who use more throttle to resolve the problem create
tremendous
negative numbers which translates to heat in the tranny, particularly the
torque
converter. According to him, the way the tranny is built, at low rpm-high
torque
demands, it cannot cool the fluid effectively, and you ultimately ruin the
gearbox.
Simply shifting the R4 to third, which is 1:1 [like 3rd in the TH350]
imposes
no strain on the engine or tranny, and keeps fluid circulation and
temperatures
where they belong. Normally, the radiator cooler is adequate. Under extreme
conditions, a tranny cooler is useful. Otherwise, he said, the 700R4,
properly>rebuilt with heavier clutches, etc, is increasingly the racers’ choice. The
moral of his story is, “Downshift!”
Richard
What are my options?
Looks like I have a 2.88 and I am thinking 3.31 or something.
Who rebuilds, or can just anybody rebuild these?
Did they make a 3.31?–
charlesmajor
hallsville/TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from charlesmajor sent Mon 21 Nov 2011:
Mine is a 3.31 Posi. It is in a 77XJ12L. My limited understanding
is that it is a Dana 44. If you take it out yourself, you’re way
ahead of the game. I’m going with a 461 (454) and 700R4.–
Clyde
Canton, OH, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
In reply to a message from charlesmajor sent Mon 21 Nov 2011:
Jag used a 3.31 and also a 3.03 IIRC in addition to the 2.88. The
fly in the ointment is for some reason jag used an oddball
carrier/ring gear assembly with the 2.88 gear set that prevents you
from installing any other gears on the differential. The pre-81
cars is where you’ll find the lower ratios. It is possible to use
Dana 44 gears, but you’ll have to replace the differential with a
Dana unit and convert the driveshaft to a chevy-style yoke.–
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