BTR Hydratrack Diff Needed

[Adrian_J]

I have recently acquired a parts built Ace Brooklands fitted with a BTR Hydratrak with FD ratio 4.10:1. The correct FD ratio should be 3.23:1. Does anyone out there have experience of re-gearing a diff or know of a used unit for sale please? The car has covered 15k miles, the diff is in perfect condition and available for part exchange if needs be.

[Flyinghorse]

A lot of modern TVR had the Hydratrack. They often come up on Ebay and I had some details written down just in case ---
TVR breaker:
Bell Hill Garage. They may also have an R code on the alloy tag.
01373 834252

The final drive of the CRS  is 3.23:1  and I also assume the Brooklands Ace.  The TVR from memory are 3.46 or 3.73  but you may luck out with a secondhand one being right ratio.

As you say its built from parts-I would check what the Tremec T5 ratios are in your gearbox as its thats what matters when combining with the diff (fixed ratio).
5th in the Worldclass Tremec T5 in my CRS is .633 having calculated it (handbook says .68).

I would have thought that the 3.46 ratio would work ok with the standard AC fitted Tremec ratios but interesting to see what others think-as with lower ratios (3.46 or 3.73) you will get lower top speed but better acceleration, though the speedo drive on the Tremec may also have to be changed.

[Adrian_J]

Many thanks Flyinghorse! The guys that built my car referred to a lot of AC documentation for the Mk V Cobra and knowing that the CRS is the same ratio will certainly aid my search. It seems that none of the TVR's had 3.23:1 but the Chimaera and Cerbera both had 3.45:1; so that's a possibility. I've enquired with Neil Fisher and Steve Gray in the hope that someone has the correct ratio. I will meanwhile check the Tremec ratios and thanks again for the advice!

[Flyinghorse]

I have just rebuilt my Tremec WC T5--the installed (original) speedometer gear on the output shaft is yellow (colour defines the different ones).

Your box should have a alloy tag with the numbers like M-7003-Z  1352-249 (it could be different -I have a decoding sheet I can send if yopu pm/email me via forum.)
The  1352-249 defines the gear box as & with ratios     Ford Mustang All 5.0 V8 WC (see below)   U   2.76   2.95   1.94   1.34   1.00   0.63

The 2.76 ratio is reverse, followed by first thru to 5th(0.63).  The obvious problem is the speedometer gear is on the T5 output shaft so I don't know if its also suitable for the 3.45 TVR BTR diff--you would have to see what the TVR gearbox was running colour wise.  And if you had to change it it means at least taking of the tail housing of the T5. Tyre diameter would also have an impact.

Easiest route for me (assuming you cant get a 3.23 final drive diff) would be to uses the 3.45 and calibrate/correlate  speedo with a sat nav and live with it or ....