|T O P I C R E V I E W|
|Graminal95||Posted - 06 Oct 2015 : 03:29:16|
After killing my stock ring and pinion and talking with guys that have broken many of ring gear behind very hot V4 motors, I decided to try and do all that I can to make my 7:38 final drive last. I started with a cast iron ribbed case, added an oil spray bar to cool the ring and pinion after meshing along with the spraying onto the gears. I also added oil feeds to the shafts to take the place of the little oil catch troughs. This way I can keep the case from growing and opening up the gap between the pinion and ring gear. It also allows me to filter the oil which is never a bad thing.
I also wanted to get away from the deep groove ball bearings that hold the diff. carrier in place. There are substantial axial loads created at the ring and pinion interface and ball bearings do not take axial loading well, even with C3 clearance. So I was able to substitute some tapered roller bearings by machining 4mm off of the small bearing side of the carrier, and 1.75mm off of the spacer ring on the large bearing side. I am thinking about adding a girdle to join the two bearing caps together to minimize movement.
I'll let you guys know how it turns out. If things go well then I won't have to design and produce some uprated ring and pinions, but the 7:38's are getting hard to find.
I've also found alternatives to just about all the bearings in the transmission. I'll post the cross-reference sometime.
|15 L A T E S T R E P L I E S (Newest First)|
|lumpey||Posted - 08 Mar 2018 : 18:59:32|
Hi Graminal, I've emailed you back with regards to the gearset.
As far as the other queries are concerned, Unfortunately I sold the lsd straight after the conversion... In a road car it was truly horrible to drive....
|Graminal95||Posted - 08 Mar 2018 : 17:44:55|
Originally posted by Graminal95
Thanks Lumpey, I sent you an email about the gear set.
|Graminal95||Posted - 08 Mar 2018 : 17:40:43|
Thanks Lumpey, I send you an email about the gear set.
|Gavinc||Posted - 08 Mar 2018 : 00:11:47|
Dammit, wish I'd thought to ask first! Now I'm third in the queue :(
96V4 stage rally car
99 stage rally car.
|Chicago Turtle||Posted - 07 Mar 2018 : 15:31:11|
Do you still have the lsd as well? I'm also looking for a set of the spec 2 gears - but Graminal95 get's first right.
|lumpey||Posted - 07 Mar 2018 : 10:34:27|
I've recently fitted a refurbed cast iron case gearbox to my turbo'd 95. Its a road car so I got rid of the lsd, fitted a Sonett crown and pinion and put standard gearing in it (well Graham McDonald did). This means I have the original type 2 rally gears sat in my garage. I wasn't sure whether to keep them so that the box can be returned to its original state, but this isn't anything I'd consider doing tbf.
|Graminal95||Posted - 24 Feb 2018 : 02:13:34|
I can't believe it's been two years since I started the transmission mods. The plumbing on the back of the transmission did not fit and I decided to just run a spray bar and not modify the sheet metal that the trans mount mates too in order to have active oil feed to the shafts. So far I have only snapped an input shaft but the rest of the transmission is working fine. The car has been down while I have a bunch if head work done, but I'm hoping to be doing a couple stage rallies this coming summer. If anyone has some spare special 2 gear I could use some.
|Gavinc||Posted - 14 Feb 2018 : 23:42:56|
Ok, bit of a thread resurrection here, Graham, if you are still active on the forum could you give any update on how your box modifications worked out? Did the box fit at the rear bulkhead with the additional pipework? How has your taper bearing setup worked out?
96V4 stage rally car
99 stage rally car.
|Graminal95||Posted - 19 Jan 2016 : 01:17:06|
Hi rsimps, I didn't have an all steel speedo drive gear so I was unable to put one in. I do not believe this will be much of an issue but when I have time I can look at the change in stiffness of the gear in a loaded state.
"Also set the pinion to its most forward position within the gear tolerances, then take no notice of the factory manual and shim the crown wheel so you can only just feel the smallest amount of rock far less than the figure Saab give" Have you verified that this produces the best mesh pattern between the gears with this method? One of the reasons I went with tapered roller bearings was to keep the diff. carrier from moving away from the pinion causing a much greater gap and bad gear meshing. This should allow me to run normal lash without issue.
A tapered roller will easily take the radial load a the end of the pinion and I looked tirelessly to find one that would fit but was unable too. If you know of one that will fit please let me know.
I had decided on adding a cooler after measuring the transmission case at the last rallycross even, and seeing over 180*F with out much driving. The rate of thermal expansion is much much greater for Aluminum than it is for iron and one of the reasons I chose to use the iron case.
No need to repeat yourself with the pinion nut coming loose, this is a known issue and one I understand. This was not the issue for the last box that I killed and for countless boxes that a friend of mine killed many years back when he was actively racing.
I would be happy to hear about any issues you have had or others you know have had with their boxes. The more information I have the better I can understand and try and fix if possible.
|rsimps||Posted - 29 Nov 2015 : 16:38:48|
The strong alloy casings were sand cast with an extra rib, the myth that the later alloy casings are stronger is that a myth. My White car has one of the sand cast batch with extra rib which I bought off Mr CP yers ago.
|rsimps||Posted - 29 Nov 2015 : 16:29:05|
I am fed up telling people this the nut on the pinion loosens because the pinion bearing has worn therefore the shaft has moved back and lost its pre-load and surprise the nut seems loose!!!!! You need to understand the fundamental problems before you start re-engineering a solution. If you just tighten this up the pinion will be in its backed off position although it will be better at taking shock loadings.
Like I said I took one look and saw the nylon speedo gear and thought newby error!
One thing I did is to drive with a freewheel on rallies, I recon I am the only person that did out of the crop of resent UK rally drivers and I only ever broke one gearbox and that was in locked drive in my early days and Mr P built that one. We never broke one either Dad or myself built using free wheel. We did rebuild them after about 6-8 events event even if they where all ok. Its easy to make a note of the crown to pinion clearance then take the box out after a season and compare the clearance and check the preload on the pinion nut. The reason that I used freewheel was it makes left foot braking so easy and it takes the backlash off the box on rough events and from the LSD.
|rsimps||Posted - 29 Nov 2015 : 16:10:25|
You need to use a 2 stroke steel speedo drive gear, the nylon one really does not help the positioning of the pinion. Also set the pinion to its most forward position within the gear tolerances, then take no notice of the factory manual and shim the crown wheel so you can only just feel the smallest amount of rock far less than the figure Saab give. The 7:38 is made of weaker material than the other gears, I believe it was made at a different supplier. There was a rally version made of stronger steel. The problem is that all the gears are old and have cracks in them, combined with a too smaller bearing taking axial load down the pinion shaft. If you could take the radial load you could have a taper roller at the pinion gear end of the shaft, but I recon you wont have enough radial load capacity.
I would try a transmission cooler in there somewhere as one of the problems is that the std alloy box expands faster than the shafts pulling the pinion back with it, put one in an oven at operating temp and see for yourself. The steel case expands less than alloy. The only gearbox case I have seen broken is a steel one that cracked between all three bearings at the diff housing end.
|Graminal95||Posted - 15 Oct 2015 : 20:13:57|
To my knowledge the only major differences in the later transmission is the change in countershaft diameter from 20-22mm? the loss of needle bearings on one of the gears for really late transmissions (>77?) and 6-10 roller freewheel.
The ribbed cases are stronger and there are two versions of the cast iron case, with and without ribs. IIRC the factory never used the iron cases in rally for weight reasons and used Al cases that were cast without the cavity behind the big diff. bearing.
The metal selector is made from as you say, stamped sheet and a rod with a hole in it. It would be very easy to make one.
|melle||Posted - 15 Oct 2015 : 16:48:42|
No, all my boxes are the V4 type, the majority later ones with the crappy 10 roller freewheel as well. It's said that apart from the freewheel they're stronger than the early boxes though?
Although the later plastic selectors are pretty hard wearing (I have a couple very good ones), I want to upgrade to metal anyway for the reason you mention. Two stroke selectors seem hard to come by though. Are they cast or welded? They can't be too hard to make from some cut off bar and flat. Casting and after machining shouldn't be too hard either provided a mill is at hand. I can make a pattern for sand casting.
|Graminal95||Posted - 15 Oct 2015 : 16:28:58|
Nope, it's from a old two-stroke box. The plastic ones are prone to breaking, and to help with overall reliability I sourced one from JVAB, and powder coated it.
Melle, do you have any 2-stroke boxes? I could really use a spare 7:38 ring and pinion.
Originally posted by melle
Is the freewheel selector home made by the way?