TRExp

Spitfire & GT6 Forum

3.33 Differential?

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
Not sure if I should post this in the SF or TR forum but I online purchased a differential with a "CG" prefix indicating it was a 3.63 from a 4 speed TR7. I wanted to swap the 3.89 differntial in my Spit for it. The unit arrived today and appears to be in great condition however.... the ring is 40 teeth and the pinion is 12 teeth thus providing a 3.33 ratio and not the 3.63 it was supposed to be. All my research indicates there was no such offering for the TR from the factory although the euro TR7 5 speed did have a 3.45 differential. Is this a ratio one of the forum members may have knowledge of?

Before I contact the seller I thought it wise to ask, would a 3.33 differential work well in a Spitfire with overdrive, maybe even better than a 3.63 or 3.67?



Edited 1 time(s). Last edit at 2018-05-14 06:24 PM by Taco.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
1147cc Avatar
1147cc Silver Member Douglas Hansen
Westminster, SC, USA   USA
NO and no
never made a 3.33 a 3.27 yes but you cant really run it in a Spitfire... trust me Ive tried it. unless you run a turbo
best ratio for a spit is the 3.89



Douglas Hansen
New Parts; Engine Rebuilds; Sheet Metal work and Advice.
http://www.1147cc.com

triumph74tr6 Avatar
triumph74tr6 Chad Jester
Tulsa, OK, USA   USA
1964 Triumph Sports 6 "Speed 6"
1968 Triumph TR250 "Gene"
1971 Triumph GT6 MkIII "Ken"
1974 MG MGB GT "MiGiBiGiT"    & more
Never heard of a 3.33 GT6's came with 3.27 on non-OD cars.

Chad in Tulsa

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Taco Richard Dalrymple
Hope Mills, NC, USA   USA
In reply to # 1533108 by 1147cc NO and no
never made a 3.33 a 3.27 yes but you cant really run it in a Spitfire... trust me Ive tried it. unless you run a turbo
best ratio for a spit is the 3.89

I have heard that too.. that a 3.27 differentisl and an overdrive is a bad combination but I've also previously read of people having that combination who like it.
At any rate I stand corrected, it is indeed a 3.63.



Edited 1 time(s). Last edit at 2018-05-14 07:05 PM by Taco.

spitlist Avatar
spitlist Joe Curry
Sahuarita, Sahuarita, AZ, USA   USA
Are you sure you didn't miscount the pinion teeth. 11 teeth on that shaft and 40 teeth on the crown gear would produce 3.63:1 ratio.

Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
I can attest, when I had my 3.27 diff with O/D I didn’t like it.....

I LOVED IT!

The only relevant mods to tha car were 30-over pistons, EI, no pollution equipment, and a well sorted ZS carb, so it was making 49 HP at the wheels. Was fabulous on the highway, and still a blast to Autocross.

I’d say for the average Spit with even only a mediocre engine the 3.63 would be the best, so congrats on your purchase.

If you have a solid engine and spend any time on the highway you may like the 3.27s.



Steve
http://stevew10.wix.com/spit16

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
Joe, it is a 3.63 and yes, dummy me miscounted.
Sounds good Steve, I've read other posts from Spitfire owners with the 3.63/OD in a 1500 Spit that really like the combo. Thus far my 1500 is stock internally with, ei, twin HS4'S and a 421 exhaust. I do plan a cam upgrade in the future and have a 9:1 head on hand for an afternoon swap.



Edited 1 time(s). Last edit at 2018-05-14 08:19 PM by Taco.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
clshore Carter Shore
Beverly Hills, FL, USA   USA
Note that the TR-7 diffs lack the 4 drillings on the nose of the case to attach the 'moustache bar' front mounting.
You can however use the mounting as a drill jig to drill & tap them yourself.

Wolfcreek Steve Steve P
Central, WI, USA   USA
Didn't TR7s have a live axle?

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
14GPDJENGINEERING Avatar
Silver Spring, MD, USA   USA
Yes, it is a live axle and to use in a Spit you will have to swap the Casing - Housing - Front Pinion.

https://rimmerbros.com/Item--i-GRID006128



Dennis smiling smiley

teeka56 Avatar
teeka56 mike leisner
Seattle, WA, USA   USA
Sure seems like a 3.63 would be a great alternative to the ever desireable OD. Simple swap, reasonable cost, and reduced rpm

Mike

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
The early (4-speed) TR7 came with a 3.63:1 diff, and the option with automatic transmission came with a 3.27:1 diff - in the UK at least.

Taco Richard Dalrymple
Hope Mills, NC, USA   USA
I attached a photo of what I actually purchased. I'm debating on whether to purchase a used case - housing or use the one on the car. I'm thinking I should get another housing as the 3.89 differntial on the car is a good one and should probably be left intact?


Attachments:
Pic_20180515_075315.jpeg    83.3 KB
Pic_20180515_075315.jpeg

billspit Bill Kea
Moore, Spartanburg, SC, USA   USA
I installed a 3.63:1 diff in my Mk I Spitfire and it was too much gear for 1147cc. I put in a 3.89:1 diff and it is happier. The other diff is going into a 9180 1500 that has been upgraded.

grumpicus Steve Jackson
Leicester, Leicestershire, UK   GBR
In reply to # 1533207 by Taco I attached a photo of what I actually purchased. I'm debating on whether to purchase a used case - housing or use the one on the car. I'm thinking I should get another housing as the 3.89 differntial on the car is a good one and should probably be left intact?

Well, that's the very late type diff assembly, fitted to TR7s after 1977 or 1978, and with the different front casing, fitted to Spits around the same time. It's identifiable by the flat machined surfaces on the diff carrier. It has the strongest differential carrier fitted to the Spitfire, and the stronger 'large teeth' sun and planet gears. The diff carrier will have the code RKC1983 cast into its surface - if the ident is RKC2802 it's the version with extra machining to take the 3.27:1 crownwheel and pinion, as used on the auto TR7 and the late 1500 Spit for Switzerland! If you find the RKC2802 number, you might just have a 3.27:1 ratio diff. Unfortunately, it will also have the fibre thrust washers behind the sun gears.....



Edited 1 time(s). Last edit at 2018-05-15 07:52 AM by grumpicus.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster





Join The Club

Sign in to ask questions, share photos, and access all website features

Your Cars

1974 Triumph TR6

Text Size

Larger Smaller
Reset Save

Sponsor Links