SPEEDOMETER PINIONS. LT77

j.johnson23 · Postby **j.johnson23** » 07 Apr 2013 19:14

Having converted my tr7 to v8 spec I was surprised to see that the speedo was reading 25 mph at a true 30.
I`d not driven it beforehand but the only difference was the mgf 15" alloys with 195-65/15 tyres instead of the standard alloys.
Now when I went to see which speedo drive pinion was in it I found a blue one which indicates a 3.45:1 final drive.Not had chance to check the final drive but thought all manual 2.0 tr7`s with a 5 speed box had 3.90:1 final drives?
Its a uk spec car so I wondered if anyone else had seen this before.

Beans · Postby **Beans** » 07 Apr 2013 19:53

No some US spec and the Solihull cars had the 3.45:1 back axle

<center>

1980 TR7 DHC (my first car, now restored and back on the road)
1981 TR7 FHC Sprint (better known as 't Kreng)
[url="http://www.tr7beans.blogspot.com/"]My full Weblog[/url]</center>

TR Tony · Postby **TR Tony** » 07 Apr 2013 21:15

If only the wheel/tyre size has changed then your 195-65/15 will give a +7.1% difference in the rolling circle of the tyre compared to a standard 185-70/13 tyre/wheel.

Because the rolling circle is bigger the wheel will rotate less times to cover a given distance, this will alter the overall gearing of the car.

To get the rolling circle back to close to the original, you need 195-55/15 tyres on a 15" rim, that will give +1% difference which should not be critical to your speedo reading.

Tony

1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow

FI Spyder · Postby **FI Spyder** » 07 Apr 2013 23:59

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Beans

No some US spec and the Solihull cars had the 3.45:1 back axle
<hr height="1" noshade id="quote"></blockquote id="quote">

Not all Solihull cars, mine is Solihull (July '80 build date) but has the 3.9 back end. I think '81 cars had 3.45 (September 80 and later build dates). Production at Solihull started around March '80 and slowly ramped up until Canley closed in July '80 which no doubt went a long way to better quality assembly as they had time to iron things out as they familiarized themselves with the car. I think it was optional before hand as Ron's (Orange rag) 30th Anniversary Edition (build date late '79 I think) had 3.45.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

trickyx12000 · Postby **trickyx12000** » 08 Apr 2013 00:21

efi spiders had 3.45:1 ...

jeffremj · Postby **jeffremj** » 08 Apr 2013 08:57

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Not all Solihull cars, mine is Solihull (July '80 build date) but has the 3.9 back end. I think '81 cars had 3.45 (September 80 and later build dates). Production at Solihull started around March '80 and slowly ramped up until Canley closed in July '80 which no doubt went a long way to better quality assembly as they had time to iron things out as they familiarized themselves with the car. I think it was optional before hand as Ron's (Orange rag) 30th Anniversary Edition (build date late '79 I think) had 3.45.<hr height="1" noshade id="quote"></blockquote id="quote">Interesting. They obviously had a transition problem. Back in the 80's a friend of mine was stopped by the Police for speeding even though his speedo read 70 mph. Basically, he had the 'new' axle but the 'old' gearbox!

FI Spyder · Postby **FI Spyder** » 08 Apr 2013 13:08

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by trickyx12000

efi spiders had 3.45:1 ...
<hr height="1" noshade id="quote"></blockquote id="quote">

Again not true. Mine is a EFI Spider and it doesn't have the 3.45 diff.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

j.johnson23 · Postby **j.johnson23** » 08 Apr 2013 15:09

I will have to see if the blue pinion was fitted to any other lt77 application-Rover,Ldv etc.

jbsjim · Postby **jbsjim** » 08 Apr 2013 17:58

My early 1980 efi Canley car has the 3.45 rear axle.

trickyx12000 · Postby **trickyx12000** » 08 Apr 2013 21:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by trickyx12000

efi spiders had 3.45:1 ...<hr height="1" noshade id="quote"></blockquote id="quote">

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by FI Spyder
Again not true. Mine is a EFI Spider and it doesn't have the 3.45 diff.<hr height="1" noshade id="quote"></blockquote id="quote">

ok... bit harsh...
well mine was a efi spider and but has a 3.08:1 and a v8 now and when I started sorting the speedo out this is what came out the box..exhibit A.. for a 3.45:1 I believe? [img][IMG]http://i1341.photobucket.com/albums/o759/trickyx12000/CIMG4158_zps850c4e33.jpg[/img] [/img] quote]
The diff ratio for the fuel-injected TR7 is 3.45:1 as against 3.90:1 for the manual carburettor 5-speed models.<hr height="1" noshade id="quote"></blockquote id="quote"> from Ken Boss's web page " a long came a spider"
http://littledoggarage.com/alongcamespider.html

hi look at that ... the cameras still on British summer time!

j.johnson23 · Postby **j.johnson23** » 09 Apr 2013 06:18

My car was registered in Aug 1981,but god knows when it was actually built.
I suspect that it was thrown together with what ever was available at the time,remember that disputes did cause supply difficulties.
I am amused by the fact that the headlight fuses are labeled incorrectly,the left hand labeled fuses control the right lamps on mine for instance!
I will have to see if I can find out where and when it was actually made.

FI Spyder · Postby **FI Spyder** » 09 Apr 2013 13:17

The build date will be on the trim/paint plate on the edge of the door unless the plate is missing.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

Anonymous

SPEEDOMETER PINIONS. LT77

SPEEDOMETER PINIONS. LT77

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