Overdrive installation

 As many will agree the gearing on smaller British cars from the fifties era is woeful if you want to travel faster than about 50mph. Living in central west Queensland I am faced with fairly long distances to go anywhere. The two closest towns are Winton about 170 km west and Barcaldine 107 km east. A shopping trip would be to Emerald 400km east or Rockhampton a further 300 km. On the long straight roads it would be nice to be able to cruise at the 110 kph speed limit without the engine sounding so very busy doing it.

The alternative is getting lower revs at cruising speed  are either to fit taller rear end gears or a gearbox with overdrive gearing.

Fitting taller rear end gearing is an engineering exercise as there are no suitable gear sets to fit in the existing casing and updating to a later complete rear end would leave me with different wheel studs on the rear requiring I carry two spares. All the Mark cars having three stud wheels, the later Hillmans have 4 stud wheels  same pattern as Fords.

So a Japanese 5 speed or an overdrive seemed the best options. Not wanting to alter to much that is visible I also preferred to keep the original column shift so the Laycock overdrive seemed the best option. Having a bench front seat also created issues with using a modern gearbox with the gear lever set well back.

As there  just happened to be an overdrive gearbox from a Sunbeam Rapier in my shed (and Rapiers are just a Minx in a party dress  :-) ) it seemed like an easy low pain solution.  

The original Mark VII Gearbox;

As can be seen the gearbox is somewhat shorter than the later Minx offering and when used with column shift is laid on its side with the controls on the drivers (right) side. This gearbox was  similar to the unit used from 1939 in the side valve models, the only change being a longer primary shaft. Rootes used pretty much the same internals in the Series 1 Minx also but with a longer tail shaft with a slide in driveshaft rather than a mounting flange.

To quote from Rootes documentation on gearboxes  in the post war years up until the all synchro model in 1966 "All internals can be swapped as an ASSEMBLY". From this we can infer that the gear case remained the same but that at times improvements may have occurred to individual parts.
However I felt fairly confident that I could use the series 1 Rapier gearbox in place of the original.
My Rapier was a series 1 with column shift as were all Rapiers until series 2 was released, The internal selectors are identical to my car so the gearbox top (side) should bolt straight on.
After looking at the two cases it was decided to install the entire Rapier works into a spare Mark VIII case as this already had appropriate drain plugs and other drilled and threaded  holes needed to attach things to. One being the exhaust pipe which crosses from left to right under the gearbox. The OHV Mark VIII was an upgrade on the original side valve which had manifolds on the right side and the only exit for the exhaust was on the right side.

The Rapier gearbox  with a Mark VIII side cover already installed alongside the original from the car

I could not just use the Rapier gearbox sitting upright as it was in the original installation as there was insufficient room above in my car and the column change mechanism was incompatible.
As can be seen from the pictures the Mk VIII gearbox mount cannot be used because the overdrive is occupying the required real estate.

My first thought was the simple approach and use the Rapier mount as shown in the picture above. Unfortunately the clever Rootes people had a random number of mounting holes in the rear of the gearbox which no longer lined up when rotated 90 degrees and the result with two that did match was the gearbox would would have been on an odd angle.

So much head scratching and cardboard engineering to find a "simple" solution.
This is what transpired:

Much fiddling to get everything to fit around the overdrive and clear the exhaust pipe.
These pictures show the two hand fabricated mount brackets that attached to the car underbody in place of the original cross member, but before they were joined together to brace them the same as the original set up. More pictures which show evidence of several revisions to get it all together.    At this stage I was getting impatient to get it back on the road :-)

Suffice to say I was never totally happy with the mount. It did the required job but was very "Unpretty".
The picture shows it on the construction jig alongside an original Mk VIII item.

Enough of the old stuff. 

The overdrive seemed to work OK except after about 40 km run it would drop out of overdrive. If parked for a few hours it would work again for about the same distance.. The clever cross member made any servicing with the unit in place impossible and after removing it for the third time to have another look (removal requiring it come out with the engine) I decided to get serious about finding the problem. The combined wisdom of all my internet sources was most not helpful in this, The only specialist repair places were in the UK and there seemed to be nobody offering Laycock parts or advice in Australia. So long story short, I pulled it right down myself and think I have found the cause of the trouble. 

                Edit: Apparently I didn't find the problem at this time, details in the next page about repairs

Have replaced various parts in the hydraulic circuit and repaired wiring to the solenoid which probably was not causing any problem.
Confident enough That it will now work as intended to manufacture a better gearbox mount that will allow access to service parts from underneath if needed.

The new cross member

This first picture illustrates the basic issue with putting a later model gearbox into the Mark body.

Shows the  Series 1 Rapier mount and the modified mark mount lined up on the gearbox centre line.The Mark mount is the wider piece sitting higher with the series 1 in front of it.

 

 

The Series 1 mount has two mount rubbers attached on each side with a much wider cross member (not in picture) under it. The biggest issue with this is that the exhaust pipe has to fit where the right side gearbox mount is attached.

The next picture from above shows where the later mount needs to be located which is not in the centre of the existing cross member. It is desirable to retain the original mounting points in the under body area so the fore and aft location of the cross member is not able to be altered.  The previous mount bolted into the cross member shown but used some Minx front engine mounts mounted at 90 degrees to the originals so it would fit between the overdrive and the gearbox. Access to the bolts attaching all this to the gearbox casing and to install the overdrive to the adapter was very difficult.

The lower mount in the picture is the original mount used which was a chopped about Mk VIII mount

So a full size drawing was created to see if we could utilise the Series 1 mount complete by just adding two simple adapters. This would require the least special fabrication.😊

I have the engine and gearbox sitting in a stand so the parts were attached to check clearances. The front section of the exhaust system was also put in place and as mentioned already it needed to be where the right side gearbox mount was located. This was the reason for the much tighter original set up  which allowed the exhaust pipe to fit.
The Series 1 mount also was for the gearbox mounted "upright" and was not directly compatible with the gearbox being laid on its side.

So I added many lines to the mount drawing, which rapidly began to resemble an old Disney cartoon about playing pool and trying to illustrate the different angles to put a ball in the left side pocket.

This is the Series 1 mount, the rubbers are about 2" high  but I had removed them at this point.

At this point a decision was made to first make a complete new bracket to fit on the gearbox then to create a suitable cross member to interface between this and the chassis.

Fast forward a little and here is the test piece from the Cardboard Engineering department  😃               A craft knife and hot glue is so much quicker to test a design than steel and welder.

I had a pair of mounts that looked suitable so I added these to the mix. They have metric threads so came off something "Foreign" :-) The wider spacing leaves room to access all the fastenings and the service points on the overdrive. Edit: Turned out they were BSF that someone previous had tried to fit the wrong nuts to. I cleaned up the threads and used some 5/16 BSF nuts, Didn't have any suitable 3/8 BSF bolts but noticed some 10mm fine metric bolts had the same 20 tpi. As 10mm is just slightly larger than 3/8" this allowed me to run a BSF die down the threads and create some bodgie BSF bolts😁 This trick would not work with the matching 10mm metric nuts.

This design with one very minor alteration has moved forward as the preferred option.

That pesky exhaust pipe, the mount clears this.

Slow progress over many days. Trying to create a mount that is strong enough and fits around all the conflicting parts that cannot be relocated.

As it happened I had just "stored" the original construction jig with other things that could be useful one day.
What I could not remember was how I had decided the adapter mount location and checking it showed that it was not aligned as well as I would like.
So I went back to the last good part and decided that I needed a mount plate simulating the gearbox casing attached to the cross member in my jig. Not trusting my previous work I decided to use the original Mk VIII parts to set that up. Then it would have to be right.

Now this was the gearbox I removed from my car with the original mounts still attached. I had just assumed these were the Rootes supplied items. So I removed the bracket and the mounts, leaving the aluminum gearbox cover in place as I had a complete gearbox and casing in a box. Found that something did not line up as this bracket would not attach to an original unmolested cross member. Turns out these are not Mk VIII gearbox mounts

As it happened I had a brand new set of standard Mk VIII gearbox mounts

The mount holes had been enlarged to suit the ring in replacements, but still would have needed some serious encouragement to fit the 5/16 bolts to attach to the cross member.
So I used the correct mounts  and attached the standard gearbox rear cover using the original gearbox mounts to the standard Mk VIII cross member.      A few pieces of scrap angle welded to the plate and the assembly jig rail.  and there was the mount exactly where it needed to be in relation to the cross member mountings and the rear of gearbox case correctly located.

Swap the Mk VIII cover for the overdrive adapter and there we are with my new bracket bolted up right where it needs to be in relation to the cross member. There was an unmentioned extra step where I removed the stock cross member and relocated it to the other end of the assembly jig to ensure the mount points remained in the correct alignment. This leaving me with the eight mount holes that the cross member bolted into the underbody also in the correct alignment

Some discussion took place on the various Hillman pages regarding rubber mounts.
Jim Withers sent me pictures of the correct Mk VIII mounts which were the spares I used to set up the assembly jig.

I had pretty much decided to use these ring in ones that have BSF threads and seemed an easier fit.

The next picture shows the overdrive adapter casting attached in the jig. The mount bracket is mounted on the front flange of this  bolted through into the cast iron gearbox case. Pretty much the same as the original Mk VIII bracket. The beginnings of the new cross member are attached to the jig along with the mounts I first thought of using. As it happened this arrangement was unworkable as it was not possible to remove the cross member once the overdrive unit was added to the mix.

The reason for the choice (apart from the fact that I had them at zero cost :-)  ) was that the mounting bolt was offset  which I thought would be easier to mount. They are shown in the last picture above sitting where they should go but reversed as I had not yet drilled the mount holes.

At this point I realised that the new wider mount bracket  would prevent the cross member being removed. So the first cut of the mount plates was made smaller to allow for this.  Some new holes would need to be drilled in the mount on the car but that seemed workable.

Taking a step back and a cool craft beer  to help my careful consideration I decided that A double check on fitting the intended cross member was required so I tacked a angle between the mount plates and crawled under the car to see what I could see. Note to self: getting too old for this need a car hoist :-).

Some fine adjustments were made to the hole spacing at this point. Happy that it would fit into the car I returned to the job in hand. 

After taking a good look at the fixed parts that needed to be avoided it was decided to use the stock gearbox mounts but mounted opposite way around. That is with the single stud outwards and the two 5/16 bolts on the mount bracket. The reason for this was to allow a suitable piece to join the two mount plates together. The original design cross member was a fairly strong part and  the mounting points under the car looked like they would require this to avoid breakage.

First picture the mounts in place. The bracket on the gearbox will require some minor alteration to facilitate the second mounting bolt.

Having got that in place a template was made to work out how to join the two sides together.              The easiest way to make this was to use a piece of 2" square steel  with the ends cut at the right angle and some shape to mimic the original cross member and provide clearance for the exhaust system.

 

Welded in place and providing bracing for the gearbox mount rubber mount point

The cut away on the lower side is the same as the original cross member so all under body items have room.

Here is the cross member with stock rubber mounts attached prior to extending the mount plate to pick up the original under body holes and to extend the mount plates to brace the cross tube. Included this picture as it shows clearly the slot cut in the cross tube to allow the mount bracket on the gearbox to retain sufficient depth and stiffness.

Some detail work to complete. A bracing on the rear of the mount point and perhaps a 3/4" extension to allow the original holes in the body to be used for mounting. This would now have better access for fitting or removing. 

                                                        The next picture showing the end result

 

                                                              From underneath after painting

         from front

 

Test fit of cross member showing exhaust system needs to be lowered 1"
This was the misalignment on the original mounting which had the engine sitting lower at the back causing clearance issues between the head and the firewall.
The Californian engine bay was designed with the little 1200cc sidevalve engine in mind and the larger OHV engine was a tight fit in some places.

 

After adjusting the exhaust pipe alignment lower this shows the clearance with the cross member properly attached. The overdrive unit has now been refitted to the gearbox.

 

                                      Side view of Cross member and exhaust system in place

 

The exhaust system from the left side. This is a Sunbeam Alpine dual outlet cast manifold fitted with more effective longer primary pipes  joined under the gearbox into the 2" system created previously

 

             The engine from the right hand side showing the cross member and exhaust headers.

             Note: This engine is from the 1966 Humber Vogue but to be used in this car it needed to use the Mk VIII sump which has a cut away on the front part to clear the steering cross rod. The bell housing is also different as the starter is mounted lower (below the bottom face of the block)  I think this was done because   the floor hump over this area was too low to allow the higher mount position used on the series 1 Minx. This also allowed the dipstick to be in the block where the later model starter was. The series 1 dipstick would have been blocked by the rear mounted fuel pump that was used because the series 1 fuel pump would have hit the steering box. The Hillman designers working through exactly the same problems any other person has when fitting a different engine in a car.

 

Another view of the primary exhaust tubing, these are about 900mm long. My preference would have been for a 4 - 2 - 1 extractor system but this was simpler, I had the manifold and performance probably very similar. It also has the benefit that under bonnet heat is greatly reduced, a consideration in our hot climate.

 

This has been as it happened post. Often people post the glossy pictures of what they finished up with.
Giving the impression that they decided what was needed and built it without making any reference to the dead ends and multiple "descriptive words" expended :-) .

When dealing with things in  three dimensions it is virtually impossible to predict what will clash with the existing parts so the design grows organically around the things you cannot change.

One of the aims of this Blog is to demonstrate that anyone with reasonable mechanical skills can do this work.
My engineering skills are far from "Expert".
I have only a reasonable home mechanic workshop.
The only really good items are a small lathe and the MIG I shouted myself as a retirement present. That has been the best tool I have bought in years :-)

Anyone can develop the skills needed to rebuild old cars, including the panel and paint tasks.
It just requires a little faith in yourself and being prepared to toss out the work and tell yourself "I can do that better ".

A Post Posting Postscript.

The overdrive had a catastrophic failure on the test run and destroyed the oil pump.
It has taken some considerable time to get to the point of having it together again.

I just had to much invested in the modifications to the drive line to take the easy way out and fit the Celica 5 speed. The time and cash invested in the new crossmember and getting a driveshaft made to suit would have been lost.
Much of the time was in finding who has suitable parts available and deciding if they were compatible with the series 1 overdrive.

Many thanks to John Harris for his help both in parts and knowledge.