1975 1500TC rear disc conversion - NOW ROAD TESTED!

[Carledo]

I was gonna say much the same thing, but Dave beat me to it above^^^^

I would think you need a TJ kit up front (if you don't have one already) either that or some sort of pressure limiter for those rear calipers, otherwise your front/rear bias will be all to cock!

I ran an unlimited Sprint rear setup on the Carledo briefly, it's propensity to change ends under heavy braking was disturbing, to put it mildly! A Cavalier pressure limiting valve fixed that until I could afford the TJs.

Steve

Yes that was my thought, why would a 1500 need rear disk brakes? The big drums on the Sprint need a valve to stop the brakes locking up and you're likely to need a similar system for this conversion, unless the fronts are upgraded as well.

To be honest I am not a fan of all disk setups on front engineed cars full stop. Most of the braking is done by the front brakes, so rear disks are pretty pointless. They just complicate the fitting of a handbrake, at least until electronic parking brakes were introduced. Drums are perfectly fine for rear brakes.

I can see the point, to a degree, and in this "special" case. With the car needing EVERYTHING including drums replacing, the bill would be fairly extensive (course I'D have looked for a pair of used drums) Then you have the poor quality of repro w/cyls and increasing difficulty now and in the future of getting the requisite bits. Add in the fact that a standard Dolomite handbrake is weedy at best and useless at worst and you ALMOST have a case for the disc conversion, just on the grounds of reliability and parts access. It's why i've avoided the "why bother?" comments here.

For myself, i'm happy with the drums, even on my much modified track used cars. But it'd be a boring old world if we all liked the same things. I salute the engineering, even though I feel no need to duplicate it!

Steve

[bazyerma]

I was gonna say much the same thing, but Dave beat me to it above^^^^

I would think you need a TJ kit up front (if you don't have one already) either that or some sort of pressure limiter for those rear calipers, otherwise your front/rear bias will be all to cock!

I ran an unlimited Sprint rear setup on the Carledo briefly, it's propensity to change ends under heavy braking was disturbing, to put it mildly! A Cavalier pressure limiting valve fixed that until I could afford the TJs.

Steve

Hi Steve

As below I am running MG TF 8 spoke wheels with 185/55/R15 tyres.

Up front I already have TJ brakes with ford Puma calipers (54mm) and 239mm discs. As to a bais valve, I plan re-routing the line to the rear brakes into the car, to the hydraulic hand brake with a brake bias valve in series to allow adjustment.

Regards

Barry

[bazyerma]

That looks very similar to the setup I ended up with during first lockdown.
I used a pair of new Renault Scenic calipers, bought a while ago from Ebay for about £35(!) after using an online brake bias calculator to work out a suitable piston diameter to avoid overbraking the rear.
Since I'm already running 6R4 4pot calipers on the front, these were fine.
The front will be getting Wilwood calipers soon anyway.

Main difference seems to be that I picked up on 5 of the 6 axle flange bolts.
This did mean that I was limited on where I could put the caliper, because the gap also has to avoid the grease nipple on the back.

Hi

Only the sprint axel has 6 flange bolts, mine is the 1500 axel so I only have 4 bolts to choose from!

As the rear drums are only held in place with a bit of tin, I think (hope) this will be strong enough.

Regards

Barry

[bazyerma]

I was gonna say much the same thing, but Dave beat me to it above^^^^

I would think you need a TJ kit up front (if you don't have one already) either that or some sort of pressure limiter for those rear calipers, otherwise your front/rear bias will be all to cock!

I ran an unlimited Sprint rear setup on the Carledo briefly, it's propensity to change ends under heavy braking was disturbing, to put it mildly! A Cavalier pressure limiting valve fixed that until I could afford the TJs.

Steve

Yes that was my thought, why would a 1500 need rear disk brakes? The big drums on the Sprint need a valve to stop the brakes locking up and you're likely to need a similar system for this conversion, unless the fronts are upgraded as well.

To be honest I am not a fan of all disk setups on front engineed cars full stop. Most of the braking is done by the front brakes, so rear disks are pretty pointless. They just complicate the fitting of a handbrake, at least until electronic parking brakes were introduced. Drums are perfectly fine for rear brakes.

Hi

As stated, I know they are functionally pointless , but thanks to Covid I have more time (no more commuting) and Money (all holidays refunded!) than I know what to do with, so I need projects.

To me, the joy of owning Johnny P (that's my triumphs name) / classic car is having fun and learning new skills. I really enjoyed making them up, fitting them, designing the brackets and writing it up on the forum.

Also, most importantly they look awesome and cant wait to paint the front TJ brakes to suit, and start skidding about with my hydraulic handbrake!

Regards

Barry

[Carledo]

Looks like all you need now is some POWER!

Steve

[SprintV8]

I personally will be changing my Sprint to rear discs.
To match the front Jaguar XJS callipers and Renault vented discs.
I also have a Wilwood biased pedal box.

Purely for extra stopping Power Looks and ease of servicing.

[bazyerma]

Looks like all you need now is some POWER!

Steve

Hi Steve

I think that's the next plan, the rusty bits can wait. Not sure, missed out on an 2.2 omega for sale in abe, there is a guy selling a 1.8 cvh serria engine but not sure if it's worth the effort.

If I could get a cheap Nissan leaf, I am tempted to.go electric.

The dream would be a small block V8 with a 4 speed manual, but there so expensive!

Regards

Barry

[Carledo]

Looks like all you need now is some POWER!

Steve

Hi Steve

I think that's the next plan, the rusty bits can wait. Not sure, missed out on an 2.2 omega for sale in abe, there is a guy selling a 1.8 cvh serria engine but not sure if it's worth the effort.

If I could get a cheap Nissan leaf, I am tempted to.go electric.

The dream would be a small block V8 with a 4 speed manual, but there so expensive!

Regards

Barry

An iron smallblock would be too heavy in the front of a Dolomite, the alloy Rover V8 is bad enough. I too LOVE the sound of a V8, but the practicalities outweigh the advantages. And you can make the CVH fit, but at little over 100BHP it's not worth the effort. I quite fancy the 1.8 turbo Rover K series with a Ford T9 box if I was to stray from my Vauxhall roots. You can get a gearbox adaptor to make it fit. My other choice, going back to Vauxhall, is the Z20LET 2.0 Turbo with the obligatory Omega box. You can get a Z20LET fitted Zafira or Astra for not much more than £600 and drive it home. Or of course, that other favourite, the S13 Nissan turbo motor. And the well proven 2.0 Saab Turbo bolts up to an Omega gearbox! Considering how tight the working space is in a Dolomite, there are a fair few useful choices available and most are not terribly expensive.

Steve

[GrahamFountain]

I was told that, all up, the Rover 3.5L V8 was only about 20 lbs heavier than the TR7 engine. Not sure about the difference from the TR7 to the 1850 and Sprint versions of the slant 4, but I don't expect it's a lot.

Graham

[Carledo]

I was told that, all up, the Rover 3.5L V8 was only about 20 lbs heavier than the TR7 engine. Not sure about the difference from the TR7 to the 1850 and Sprint versions of the slant 4, but I don't expect it's a lot.

Graham

I can't give you an absolute figure for the Rover V8 engine, there was much talk at the time of the advent of the MGB V8 that the V8 was the same weight or slightly lighter than the all iron 4 cylinder it replaced. But this MAY have been hype or urban myth.

What I CAN be more precise about is that the Sprint engine/O/D gearbox combo is a ferociously heavy unit unit for a 4 cylinder, nearly 40kgs HEAVIER than the Vauxhall 8v/5 speed that I have in the Carledo. So probably not all that much difference between the V8 and the Sprint unit. Still I had a fascinating conversation with the guy that owns (and built) THIS V8 powered 2 door........



He told me that it took him nearly 6 years to get the car operational and he still found the roadholding disappointing, in his own words, it's too nose heavy to work well, partially from the weight of the V8, but also from the "natural" POSITION of that weight, further forward even than a Sprint's. The Carledo's lighter 4 banger also sits 4" further back than the Sprint engine, which only helps it become the point and squirt joy that it is to hammer round track or lanes. Weight is certainly important (to go faster, add lightness) but balance is even more crucial.

Steve

[SprintV8]

Triumph slant-4 290Lbs (also SAAB 99)
Triumph 2000 L6 403Lbs (Spitfire, 2.5 TRs)
Triumph Stag V8 446Lbs

Chevy small block V8 575Lbs (generic for 1960s-1970s motors)
Chevy small block V8 535Lbs (1959 Corvette 283 w/alum. intake)
Chevy small block LS1 460Lbs

Ford England Essex V6 379Lbs (3 liter)

Buick/Rover 215 V8 318Lbs


Vauxhall Calibra 245Lbs (75) 24v, 2.5L V6
Vauxhall Swindon 230Lbs (106) race motor, 2.0L
Vauxhall 16 valve 237Lbs (199)



TVR Cerbera 4.5: 121kg 265Lbs
Mazda 13B RX8 112 kg (247 lb)



https://www.gomog.com/allmorgan/engineweights.html

( The engine on project 13B Sprint is pushed back to the bulkhead.)

[GrahamFountain]

So, 28 lbs between 1850 and Rover V8 - and whatever between bell housing and gear boxes.

But given that the bulkhead is closer to the dissy in the TR7 Sprint than the Doly Sprint, it seems odd the V8 in the Doly can't be further back, in relation, than the V8 in the TR8.

Graham

[Carledo]

So, 28 lbs between 1850 and Rover V8 - and whatever between bell housing and gear boxes.

But given that the bulkhead is closer to the dissy in the TR7 Sprint than the Doly Sprint, it seems odd the V8 in the Doly can't be further back, in relation, than the V8 in the TR8.

Graham

You're looking at an incorrect datum, the distance from motor to bulkhead is irrelevant when the position of the bulkhead related to the length of the car and the position of the front axle line is different.

In a TR7/8 the engine sits considerably further back (about 2 cylinder widths) relative to the front axle centreline than in a Dolomite, thus the bulk of the engine/transmission weight is carried within the confines of the wheelbase. In a Dolomite, the engine is carried higher and further forward because of a) the Dolomite's less favourable rack mount position behind the axle line and above the subframe and b) the Dolomites complex and obstructive 3 bar front subframe. This results in the Dolomite carrying around 50% of the engine's weight AHEAD of the front axle - never a good idea and the heavier the engine, the worse an idea it is! It's a basic design flaw that Audi, with billions in development, have yet to solve the consequences of!

But these 2 considerations, rack position and subframe shape, along with a small side order of gearbox length, govern where the Slant engine fits in a Dolomite shell which looks and, from a balance perspective, IS, too far forward. Don't forget, the shell was never originally designed to accept the slant motor, (or it's power) it had to be adapted to fit the space available, evidence of the bodges committed to make it fit are still clear today, like the Sprint's horizontal offside mount. The TR7, on the other hand, was designed from first principals to accept the slant motor (and probably the V8 too) and it shows!

Steve

As a personal project, I'd like to modify a front subframe to carry the rack ahead of the axle line and a little lower in the subframe, i'm just not sure what reversing the balljoints side to side would do to the Ackermann angles inherent in the balljoints to make it work. It's obviously something the factory (cash strapped as always) didn't consider worth doing to make the car work better. To be fair, at the time they'd already built one of the quickest saloon cars of it's day, they probably didn't see the need that I do with the benefit of 50 years worth of engineering advances.

[SprintV8]

Steve.

Rather than hijack this again I’ve sent you a PM.

[GrahamFountain]

Well I meant that I thought the V8 could be further back in the Dolomite than the TR8 in relation to where the slant-4 sits in the Dolomite and TR7. I take the point that it's still forward with respect to the lines of the front wheels, but that's not what I meant.

I think that the TR7 was probably intended for the Triumph 3L V8 more than the rover, had that not proved somewhat problematical an engine. Otherwise I don't think it would have taken till mid 1977 to get any TR8s into production.

And that was only the limited run of Fixed Head Coupes built during the changeover to the 1978 year model and needed for Homologation of the TR8/TR7V8 - granted on 1 April 1978. It's an interesting story how there were only about 150 built when it was approved and the other 250 or so were built after at Canley, which Neil Eason-Gibson (RAC homologation inspector and later their director of motorsport) gave me a bit of. Then they stopped with the FHCs, as soon as the FIA requirements were met, and only built convertible TR8s thereafter.

I still don't know why BL never told anyone about any of the homologation specials they built, when Ford, Vauxhall, Talbot, Lancia/Fiat, etc., made a song and dance about 'em. Maybe about lack of trust that the workforce wouldn't hold'em to ransom.

Don't give me short of money - BL had just started getting shedloads under Don Ryder's recovery plan in the Ryder Report. His guess was near to £3 billion to 1985 - inc. the paltry sum of £270 million of operating capital upfront -, but there's suggestions it were nearer £10 Billion by the time Edwardes had done with the government. So, for them programmes that made it through the bankruptcy of 1974, it should have been a happy time till 1 Nov 1977 - had it not been for the Castle Bromwich body builders, BL toolmakers, Lucas toolmakers, and Coventry axle workers. Did I miss anyone?

Graham