The Triumph Dolomite Club - Discussion Forum

I have read in the SE section that a couple of people are considering doing this upgrade. I wrote an article for issue 131 of Dolly mixtures, November / December 2008, on doing this upgrade to a 1500HL and I believe that some members still find it a useful document but over the years I have become aware of some issues that I did not cover when I wrote that document because I was not aware of them at the time.

Starting at the front end of the gearbox. During the build runs of the 1300cc and the 1500cc gearboxes the design of the front oil seal was changed. The majority of gearboxes that are around rely on a scroll seal but the later gearboxes have a lip seal, Part number 132292. What can catch you out is that the two types of seal require different housings / covers that fit into the bell housing. Part number 122566 for the scroll seal and a part number UKC7926 for the lip seal and the gearbox input shafts are also different but difficult to tell apart. The scroll seal input shaft is a part number TKC1267 and the lip seal type is a part number TKC3259. This is machined to accommodate the lip seal. Quite often people purchase a gearbox and the J type Overdrive without the bell housing and fit the assembly to their existing bell housing without knowing about the different oil seal arrangements. Even if you purchase the complete arrangement I recommend you take the bell housing off to check that your parts are compatible. From looking at the Official Triumph Dolomite Range 1976 onwards parts catalogue it looks as if the 1850 gearbox was designed and built with a lip seal. If you know anything different please let me know. See attached photo’s that show the different types of housing / covers which cost about £40 each and the gearbox input shafts which cost about £115

Now considering the Over Drive. In my original document I identified that each overdrive has a tally plate which indicates what model of car it has been built for, as an example 22/61985/0013296. The “22” relates to the Overdrive ratio, the “61985” indicates it is built for a TR6 and finally the “0013296” that it is the 13296 unit to be built to that specification. For the Dolomite range a J type O/D identified by 25/115842 is for a Sprint, for a 1850cc it is identified by 25/11586, for an early 1500cc with a 3.89:1 rear axle by 25/115867, (You will find DM1 stamped on the rear axle) and a later 1500c with a 3.63:1 rear axle by 25/115868, (You will find WF1 stamped on the rear axle). If you find yours is stamped with DP1 I am afraid I am not certain as to the ratio. If you know please tell me. 1300cc as far as I can see these were never fitted with O/D at the factory.
Obviously as both the 1850 and the later 1500 have the same rear axles the speedo drives will be the same so my assumption is that the J type O/D units should be interchangeable as I have not been able to determine any other difference. If you know of any differences again do please tell me.
If you fit the wrong unit in a 1500cc Dolomite your speedo will read incorrectly and to correct this, I believe, it requires both the speedo drive gear and its associated pinion gear being changed. It is easy to change the pinion gear but what makes this difficult is that the drive gear is fitted on a shaft inside the O/D unit.

My recommendations are :
1. If you are considering going to implement this upgrade purchase a complete kit from someone who has removed all the bits for a scrap Dolomite because some of the bits are now becoming difficult to source separately. The full list of bits required can be found in my original document on fitting overdrive to a 1500cc but the items that are becoming difficult to source are:
Restrictor plate (Fit to bottom of rubber mount), part number 160268
Mounting bracket to connect O/D to rubber mount, part number UKC2797
Bracing plates (These secure the next item the cross member to the car body and can easily be fabricated) 2 in number required. (Part number 155304)
Bracket (Cross member), Part number 218519
Bracket (To clamp exhaust pipe to rear of Overdrive - Part number UKC4098
O/D gear lever UKC3283
Gear knob part number UKC7614 - (Note I believe there is a difference between a sprint and the 1500 gear knob caps in respect to the engraving as reverse gear is in a different location)

2. Get the Gearbox and O/D unit refurbished before you fit it. This will not be cheap but the gearboxes in particular suffer from layshaft bearing wear.

Perhaps I was lucky Richard but I just sourced the bits from your original article in issue 131, passed the lot to Willow triumph near Darlington and drove away in a "5 speed" 1500HL.
It's been fine for several years now, no leaks or anything and is probably the best thing I ever did to my Dolomite. Some cracks have appeared in the overdrive unit where it bolts to the car but these don't seem to be causing any problems. If I could find a fresh housing at a reasonable price I'd probably fix it but I don't think I'll find another - they just don't seem to come up for sale as spares.

I also had a lucky experience with my 1850HL. It was manufactured without overdrive and when I took it on in 2016-17 I wanted to change that, especially as the gearbox was jumping out of gear occasionally. Hunting on ebay one day I came across a gearbox and overdrive that said it was from an 1850 Dolomite and that it was in good working order. After contacting the vendor I took a chance and bought it.

It duly arrived on a pallet together with the correct gearbox mounting and the gear lever. I took the top cover off to have a look inside and it looked clean with no obvious wear marks on the bits I could see. I cleaned the overdrive filter and popped it in the car. I didn't even need to change the propshaft as the original could be compressed enough to fit.

It worked fine from the outset with good synchromesh and the O/D was fine, at first. Then I started to have problems with not coming out of O/D. That was cured with a new solenoid, and a relay for the puny switch. Since then I have had at least two years good motoring with it doing just what it should do.

It certainly makes a huge difference to the car at motorway speeds.

_________________
Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)